Felix W. Wehrli - US grants

We propose to evaluate and further develop a novel technique based on magnetic resonance (MR) for quantitative assessment of the structure of trabecular bone in normals and patients with clinically established osteoporosis. We intend to determine whether this index of trabecular structure predicts the presence of fractures in patients with osteoporosis and to compare and correlate the findings of this new parameter with bone mineral density measurements. The new technique is based on a measurement of MR T2* which is related to the intrinsic inhomogeneity of the magnetic field in the intertrabecular space, caused by the presence of two phases of different diamagnetic susceptibility: bone and bone marrow. In support of this hypothesis, our preliminary data show that T2* increases in the lumbar vertebrae with age and is markedly increased in patients with clinically evident osteoporosis with fractures. Moreover, we have found that T2* predicts the degree of trabeculation of die distal femur with T2* following the order: diaphysis>metaphysis>epiphysis. Both findings corroborate the expected inverse relationship between trabecular plate density and T2*. A technique, denoted MR interferometry, developed in the investigators' laboratory, permits measurement of T2* from a series of gradient-who images acquired with an array of echo delays, using ROI analysis and curve fitting techniques. We intend to establish a normal baseline by measuring T2* as well as the apparent fat/water ratio (a by-product of the analysis) in 75 normal women. To assess the sensitivity and specificity of this technique in osteoporosis, we compare MR indices of trabecular structure with those obtained from bone mineral density measurements in 75 patients with osteoporosis with and without vertebral compression fractures. Finally, we intend to determine the relationship of the trabecular plate density as predicted by T2* and bone strength by evaluating the relationship among trabecular microstructure, as evaluated by MR microscopy, T2* and mechanical load-bearing capacity on cadaver specimens of human vertebrae.

The microarchitecture of trabecular bone is well known to be key to bone strength and thus resistance to fracture. The current methodology for micromorphometry involves the quantitative assessment of parameters such as bone fraction, trabecular thickness, star volume and intercept length on the basis of microphotographs of polished sections of bone by means of stereologic analysis. The hypothesis underlying the proposed work is that nuclear magnetic resonance imaging at microscopic dimensions ("NMR microscopy") is an alternative and potentially superior investigational tool for the derivation of morphometric parameters from the resulting digital images. The suitability of the technique is enhanced by the intrinsically high contrast between the trabeculae and the protons in the marrow spaces. Another unique feature of the technique is its ability to provide measurements in any arbitrary orientation from three-dimensional isotropic data sets by retrospective data rearrangement. The investigators' preliminary work provides evidence for the feasibility of NMR microscopy as a quantitative morphologic analysis method in vitro at 9.4T and in vivo at 1.5T. The principal aim of this project is to further develop and evaluate NMR microscopy for the study of trabecular architecture in vitro on cadaver specimens from the human patella and in vivo in normal subjects at the same anatomic location. For this purpose computer algorithms will be generated for the unbiased measurement of microarchitectural parameters including trabecular area and thickness, trabecular density, star volume and fabric tensor and to validate the resultant parameters against those derived from conventional stereology on anatomic sections. Another aim is to ascertain the statistical association of these parameters in cadaver specimens of human trabecular bone with Young's modulus. A final aim consists of exploring the feasibility of measuring these parameters in vivo on a suitably modified whole-body NMR scanner, the study of the age dependence of these parameters and their correlation with bone mineral density.

The chief clinical manifestation of osteoporosis is the occurrence of fractures. Most'osteoporotic fractures oc- cur at skeletal locations rich in trabecular bone. Prevailing among these are the vertebrae, wrist and proximal femur. There is now strong evidence that the loss of bone mass is accompanied by a decline in the trabecular bone network's structural integrity. The impaired mechanical competence secondary to gonadal steroid de- pletion is largely due to topological changes in the bone's architectural make-up, chatacterized by fenestra- tion of trabecular plates resulting in their conversion to rods, which eventually become disconnected. The in- vestigators have provided in vivo imaging evidence in previous cycles of this ongoing project in support of such an etiology. Complementing antiresorptive treatment, new therapies have recently become available to treat the devastating consequences of severe bone loss with bone-forming (i.e. anabolic) drugs. It is not clear, however, whether such therapies are, in fact, able to reverse the disintegration of the trabecular net- work, and to what extent the structural changes differ from those induced by antiresorptive treatment. In the new cycle of the project for which support is sought, we propose to significantly enhance our previously de- veloped MRI-based virtual bone biopsy technology to quantify the structural and mechanical consequences of two fundamentally different forms of drug treatment in patients with metabolic bone disease. We aim to apply this methodology to patients who are at high risk of fracture and who are treated either with recombinant 1-34 parathyroid hormone or alendronate. We advance the hypothesis that in vivo micro-MRI will be able to distin- guish the structural and mechanical manifestations of short-term treatment and that the method will provide new insight into the structural manifestations of trabecular bone exposed to antiresorptive and anabolic ther- apy. The project will consist of five specific aims involving the development, integration and evaluation of new methods involving data acquisition and reconstruction, motion correction, image processing and analy- sis, as well as image-based computational biomechanics.

Osteoporosis is a debilitating disease causing skeletal impairment resulting from loss of cancellous and cortical bone, eventually leading to fractures of the femur, vertebrae, wrist and humerus. Current methods for assessment of skeletal competence rely almost entirely on bone mineral density (BMD), which is widely considered the primary risk factor for the occurrence of fractures. However, the recognition that mass density is an unsatisfactory predictor of bone strength has, more recently, spurred the search for alternative modalities focusing on 'bone quality,' notably architecture. The P.I. and his co-workers have, during the prior phases of this project, shown theoretically and experimentally that the susceptibility-induced MR signal decay rate (R2') is related to the density and orientation of the trabeculae and that this parameter is able to predict the bone's elastic modulus in vitro. Further, clinical evidence was provided that decreased trabecular bone marrow R2' augments the probability for the occurrence of vertebral fractures and that BMD and R2' jointly improve fracture prediction. The central hypothesis to be tested is that, along with improved methodology and a new MR-based measurement of trabecular bone volume fraction (BVF), a single-modality examination that evaluates both R2' and BVF, better predicts fractures than bone densitometry. We shall examine the above hypothesis by pursuing the aims below; specifically, we shall 1. Further develop and validate improved methodology for acquiring and processing quantitative MR data for measuring R2', conceived during the current cycle of the project. 2. Evaluate a new MR method for measuring cancellous bone volume fraction and assess its relationship to R2' in cancellous bone models and specimens. 3. Measure both R2' and BVF in a cohort of peri- and postmenopausal normal, osteopenic and osteoporotic women and determine the association between the two independently measured parameters and DEXA BMD. 4. Determine the diagnostic accuracy of the techniques of Aims 1 and 2 relative to DEXA BMD z-scores as a means to assess fracture status in the spine in the subjects examined under Aim 3.

[unreadable] DESCRIPTION (provided by applicant): TRAINING IN QUANTITATIVE MAGNETIC RESONANCE IMAGING Magnetic resonance imaging (MRI) has, since its inception over two decades ago, been used mainly as a qualitative imaging technique practiced by radiologists utilizing predominantly qualitative criteria for establishing a diagnosis or excluding disease. This approach is fraught with problems, its main disadvantage being the subjective nature of the result, i.e., sensitivity to reader experience and judgment. Many problems in diagnostic medicine require a quantitative assessment. Among these are the sizing of vascular stenoses, the measurement of a perfusion deficit, or the evaluation of residual disease burden during regression of disease in response to therapeutic intervention in the treatment of tumors, white matter disease, etc. Moreover, for many diagnostic or staging problems, quantitation of an observation is not merely a better alternative to qualitative assessment, but the qualitative approach is entirely unsuited. Examples are non-focal systemic disorders such as osteoporosis where a quantitative measurement of some physiologic parameter, e.g., bone mineral density, has to be made. In diagnostic imaging in general, and MRI in particular, quantitative approaches require the tools of post-processing of arrays of images, typically performed off-line on workstations. This process is multidisciplinary, requiring close cooperation among physicians, MR physicists, and computer scientists, which is not possible without effective cross-training. Physicists, engineers and computer scientists usually lack an understanding of the medical problem and are often unable to translate abstract concepts to the physician. The problem is exacerbated by language barriers since the members of the exact sciences often have difficulties in effectively communicating with physicians, as their terminology is outside the scope of medicine. This project aims to train basic science students at the pre- and post-doctoral level in quantitative magnetic resonance methodology and, conversely, medical science trainees in the use of quantitative MR imaging tools for diagnosis and treatment monitoring. Training modalities involve a combination of colloquia, structured teaching and hands-on laboratory training, with particular emphasis on preceptor-directed research. The training faculty consists of both basic scientists and physicians who have a record of successful multidisciplinary research training. [unreadable] [unreadable]

DESCRIPTION (taken from the application): Funding is requested to cover the travel costs of the invited speakers for an International Society for Magnetic Resonance in Medicine Workshop on Magnetic Resonance of Connective Tissues and Biomaterials. This unique conference will address the diverse methodology and applications of magnetic resonance in the study of connective tissues and synthetic biomaterials used as tissue replacements. The materials to be covered include bone mineral and matrix, skin, cartilage, ceramics, polymers, and composites, in vivo and in vitro. The characterization of such materials is essential for the understanding of the structure, function, physiology, biology, chemistry and mechanics of these materials in human and animal systems. Magnetic resonance spectroscopy and imaging, because of their nondestructive and noninvasive character, are finding increased use in such studies. There has not previously been a conference focused specifically on the topic of magnetic resonance of connective tissues and biomaterials. Most conference presentations on this topic have been scattered over a variety of either materials science or generalized magnetic resonance meetings, resulting in isolated presentations. Thus, communication between the physicists, chemists, biologists, engineers and physicians working in this area has been sporadic and ineffective. This workshop will provide a much needed opportunity to share information among these workers and create awareness of MR's potential for characterizing biomaterials.

Calcium homeostasis is governed by the interplay of intestinal calcium absorption, renal excretion and skeletal exchange of calcium. In the adult skeleton, bone formation and resorption are closely coupled. Supraphysiological levels of corticosteroids can interfere with calcium metabolism through various pathways, resulting in decreased bone formation and enhanced bone resorption, and thus leading to accelerated osteopenia. The resulting fractures typically occur at sites rich in trabecular bone, though cortical thinning is known to occur as well. Further, the architectural changes paralleling the reduction in mass density are different from those in involutional osteoporosis and there are indications that steroid-induced osteopenia compromises skeletal strength at higher mass density. The present project seeks to investigate the effects of corticosteroids on trabecular morphology and the biomechanical consequences of these architectural changes by means of magnetic resonance (MR) micro-imaging and dual-energy X-ray absorptiometry (DEXA) in vivo and in vitro in a rabbit model. The rabbit is particularly suited as model; in its mature skeleton remodeling prevails over modeling and significant bone loss occurs upon exposure to corticosteroids in comparatively short times. Most prior work has been done post mortem by means of densitometric and histomorphometric techniques. Using new ultrahigh-resolution magnetic resonance (MR) imaging and computer-based image analysis we propose to evaluate the steroid-induced skeletal changes serially in vivo. Specifically, we propose to test the following hypotheses: (1) The reduction in bone mass results in changes of the trabecular microstructure, which can be characterized quantitatively by in vivo 3D MR imaging and image processing. (2) The time course of the changes in trabecular bone mass and architecture, in response to administration of dexamethasone, can be evaluated by serial quantitative MRI measurements in vivo in a rabbit model. (3) Discontinuation of corticosteroid administration leads to partial re-establishment of skeletal integrity and mechanical competence. (4) Supplementation of corticosteroid treatment with gonadal steroids alleviates bone loss. (5) The corticosteroid-induced changes in trabecular microarchitecture are accompanied by a predictable reduction in the bone's elastic modulus.

Calcium homeostasis is governed by the interplay of intestinal calcium absorption, renal excretion and skeletal exchange of calcium. In the adult skeleton, bone formation and resorption are closely coupled. Supraphysiological levels of corticosteroids can interfere with calcium metabolism through various pathways, resulting in decreased bone formation and enhanced bone resorption, and thus leading to accelerated osteopenia. The resulting fractures typically occur at sites rich in trabecular bone, though cortical thinning is known to occur as well. Further, the architectural changes paralleling the reduction in mass density are different from those in involutional osteoporosis and there are indications that steroid-induced osteopenia compromises skeletal strength at higher mass density. The present project seeks to investigate the effects of corticosteroids on trabecular morphology and the biomechanical consequences of these architectural changes by means of magnetic resonance (MR) micro-imaging and dual-energy X-ray absorptiometry (DEXA) in vivo and in vitro in a rabbit model. The rabbit is particularly suited as model; in its mature skeleton remodeling prevails over modeling and significant bone loss occurs upon exposure to corticosteroids in comparatively short times. Most prior work has been done post mortem by means of densitometric and histomorphometric techniques. Using new ultrahigh-resolution magnetic resonance (MR) imaging and computer-based image analysis we propose to evaluate the steroid-induced skeletal changes serially in vivo. Specifically, we propose to test the following hypotheses: (1) The reduction in bone mass results in changes of the trabecular microstructure, which can be characterized quantitatively by in vivo 3D MR imaging and image processing. (2) The time course of the changes in trabecular bone mass and architecture, in response to administration of dexamethasone, can be evaluated by serial quantitative MRI measurements in vivo in a rabbit model. (3) Discontinuation of corticosteroid administration leads to partial re-establishment of skeletal integrity and mechanical competence. (4) Supplementation of corticosteroid treatment with gonadal steroids alleviates bone loss. (5) The corticosteroid-induced changes in trabecular microarchitecture are accompanied by a predictable reduction in the bone's elastic modulus.

DESCRIPTION (Taken from the application): Renal osteodystrophy (ROD) is a multifactorial disorder of bone remodeling, resulting in skeletal deformities and fractures. The histologic spectrum of ROD ranges from markedly increased bone turnover to absent bone turnover. High-turnover disease [osteitis fibrosa (OF)] is caused by secondary hyperparathyroidism, and was once a universal complication of renal failure. OF is characterized by trabecular bone sclerosis and severe cortical thinning. However, the incidence of low-turnover disease [adynamic bone disease (AD)] is now rapidly approaching that of OF. AD is characterized by decreased bone formation and trabecular thinning. The emergence of AD may be due to therapies aimed at preventing OF, such as calcium-containing phosphate binders and active vitamin D sterols. Current studies are focusing on the development of new strategies to prevent OF without suppressing normal bone remodeling. Knowledge of the underlying bone structural abnormalities is essential for developing, selecting and monitoring therapeutic regimens. To date, bone biopsy is the only available tool for characterizing ROD. However, the invasive nature of the procedure has limited its use in clinical care. In addition, bone biopsy is subject to sampling error and provides little information regarding cortical structure and bone's mechanical competence. Non-invasive measures of bone turnover have been disappointing. There is significant overlap in serum PTH levels among patients with AD, OF and normal bone tumover states. Bone densitometric techniques are rarely informative because the projected bone mass represents the integrated sum of the cortical and trabecular components. We hypothesize that a 'virtual bone biopsy' (VBB) based on micro magnetic resonance imaging (u-MRI), in conjunction with image processing, will provide a non-invasive technique to simultaneously assess trabecular structure and cortical thinning. VBB is inherently three-dimensional, is less subject to sampling error, and can be performed repeatedly in longitudinal studies. This pilot project proposes (1) to design and construct a u-MRI coils to assess trabecular structure in the distal tibia; (2) to develop MR-based measures of cortical thickness and cross-sectional area in the tibial diaphysis; and (3) to perform these measures VBB in healthy controls, and in dialysis patients with clinical evidence of extreme high-turnover or low-turnover bone disease. The development of a noninvasive technique to assess cortical and trabecular structure in ROD will facilitate studies of the prevention, treatment and assessment of the biomechanical implications of this prevalent disease.

During recent years transgenic animal models have become important research tools for studying the genetic causes of human disease. Micro- imaging in vivo provides a powerful tool to monitor animals longitudinally to assess the response to various forms of intervention and to quantify genotypic variations of development during growth. Micro- imaging further plays an increasingly important role for the study of tissue structure and function. Unlike histomorphometry, 3D microimaging is non-destructive and provides detailed information on the three-dimensional architecture of mineralized tissue, as well as the location and density of calcification. In this application, a broad range of investigators seeks funding for the acquisition of a novel microcomputed tomography (mu-CT) system for 3D microscopic imaging. The requested instrument is unique in that it is capable of imaging 1-inch specimens at an isotropic resolution of 25mu m as well as small rodents in vivo at 50/mu m resolution. The instrument is designed around a rotating gantry involving cone-beam scanning and reconstruction. The mu-CT scanner complements magnetic resonance micro-imaging widely used at the investigators' institution and provides new capabilities not currently available. Targeted applications of the proposed equipment include quantification of the micro-architecture and local mineral density of calcified tissues, in particular trabecular and cortical bone from human cadavers and bone biopsies, calcified heart valves and atherosclerotic plaques. The in vivo applications are aimed at the study of gene expression in genetically altered mice. Specific projects enhanced by the requested equipment involve the serial evaluation of metastatic cancer, the assessment of arterial wall calcification in marine models of atherosclerosis and the assessment of the response to therapy. Other funded projects benefitting from the requested instrument include the study of osteogenesis in mice lacking the AKL. bone morphogenetic protein receptor, the evaluation of the mechanism of regulation of apoptosis in endochondral bone formation, the quantification of craniofacial structure in mouse models of sleep apnea, and the study of tissue engineering of the intervertebral disc.

DESCRIPTION (provided by applicant): Stroke is the third leading cause of mortality and the leading cause of disability in the United States. It is estimated that a significant fraction of all ischemic strokes are caused by carotid atherosclerotic disease. Often stroke is preceded by neurologic symptoms and may therefore be preventable with timely intervention. While the degree of arterial stenosis is a major risk factor, there are strong indications that factors unrelated to the size of the vascular construction play a role in causing neurologic symptoms. These include the extent of collateralization and the morphology and composition of the atheroscleotic plaque itself. Further, since most strokes are believed to be embolic in nature, reduced perfusion prevents clearance of microemboli forming distal to an unstable lesion. We hypothesize that in addition to plaque composition, hypoperfusion is an independent predictor of symptoms. In order to evaluate the above hypothesis the following specific aims will be pursued: 1. We will further develop and perfect the methodology developed in preliminary work for acquiring, processing and analyzing high-resolution MR images to measure plaque volume and architecture in vivo. 2. We shall implement and evaluate a multi-slice arterial spin labeling perfusion imaging technique for measuring perfusion in a single vascular distribution to unambiguously assess the implications of carotid stenosis on blood flow to the affected hemisphere. 3. Utilizing the methods developed in Aims 1 and 2 we shall, in a pilot study of symptomatic and asymptomatic patients (N=50 each) with clinically significant carotid stenosis (>70 percent), who will subsequently undergo carotid endarterectomy (CEA), determine the prevalence of hypoperfusion in each hemisphere in relation to luminal narrowing, plaque volume and composition. We shall then re-examine these patients post CEA with perfusion MRI to determine the extent of restoration of blood flow and evaluate the hypothesis that the perfusion deficit established prior to endarterectomy was related to carotid disease. We shall examine the CEA specimens by 13C NMR spectroscopy, micro-MRI and micro computed tomography to establish plaque's lipid profile and calcium content as a means to characterize the lesion and evaluate the association between plaque characteristics and patients' symptomatology.

DESCRIPTION (provided by applicant): The mechanical competence of bone is determined by the amount of bone per unit volume (also referred to as apparent density), its structural arrangement and its chemical make-up. Age and osteoporosis-related deterioration of the bone has typically been attributed to a net loss of bone mass and architectural impairment but it has been widely assumed that the bone's intrinsic material properties remain invariant. This notion is in conflict with a substantial body of literature indicating significant decreases in the degree of mineralization of bone (DMB) following ovariectomy and increased DMB in response to antiresorptive treatment. Such a behavior is plausible since the bone turnover rate determines the average age of the bone and younger bone is known to be hypomineralized. Paralleling changes in DMB are the bone's biomechanical properties in that decreased DMB is associated with decreased static strength and Young's modulus. The extent to which mechanical failure in the form of fractures is related to changes in the bone's mineral content is not known. Unfortunately, DMB cannot currently be measured noninvasively. However, since DMB is related to the bone's osteoid water content, information on mineral density can be obtained indirectly. There is evidence that during mineralization some of the matrix water is displaced and its space taken by mineral in such a manner that osteoid volume remains constant. In this proposal we advance the hypothesis that there is an inverse relationship between osteoid water and bone mineral volume and that a measure of DMB can be obtained indirectly by quantitative proton magnetic resonance of solid bone. We provide evidence in preliminary work that decreased mineralization is associated with higher water content and that the matrix water can be imaged with appropriate imaging techniques in intact bone. In two disease models in which DMB is expected to be altered (rabbit osteomalacia and rat ovariectomy) we test the hypothesis using proton and 31P NMR that changes in DMB occur at the expense of a commensurate change in bone water and further that increased bone water decreases static strength and elastic modulus. The long-term goal of this project is to provide a noninvasive method for probing the intrinsic properties of bone in laboratory animals and ultimately in humans.

ABSTRACT NOT PROVIDED

DESCRIPTION (provided by applicant): MRI has proven its potential for noninvasive assessment of tissue architecture. However, the achievable spatial resolution is ultimately determined by the modality's limited detection sensitivity in terms of signal-to-noise ratio (SNR). An alternative approach toward characterizing the microarchitecture of structured materials and tissues is q-space imaging. Analogous to k-space and image space representing spatial frequency and its Fourier transform -- the spectrum of spin density -- the Fourier transform of the NMR q-space signal is the spectrum of displacements. In the white matter of the spinal cord an array of axons provides a quasi-regular array of parallel cylindrical structures separated from the extracellular medium by a semi-permeable myelin sheaths which imposes barriers to diffusion. Q-space NMR currently has several limitations. The first is the amplitude of the diffusion sensitizing gradients, since qmaxdetermines the resolution in the displacement domain. For example, for a propagator resolution of 1 mu/m and a gradient duration delta=1ms Gmax= 2,200 G/cm would be required, which is more than one order of magnitude greater than gradient strengths typically available. Access to such gradient capabilities further will allow probing of very small-scale diffusion restrictions. Second, while simulations of the q-space behavior have the potential to provide physical and biological insight and enable systematic planning of experiments, such approaches demand more elaborate models than those hitherto available. The investigators have, in preliminary work, explored the above issues and propose to further develop and apply q-space methodology for the non-destructive analysis of tissue microstructure and function, focusing on the axonal structure of the rat spinal cord. The overall hypothesis underlying this proposal is that ultra high-resolution displacement imaging in conjunction with simulations of diffusion diffraction from histologic images will provide new insight into tissue architecture. The following specific aims will be pursued: 1. Complete construction and evaluate the performance of a single-axis gradient system allowing amplitudes of up to 4,000 G/cm for performing q-space imaging of small specimens at 400 MHz. 2. Simulate q-space behavior on the basis of a previously developed finite difference model for (a) synthetic models of axons as a function of distribution of axon size and membrane permeability, (b) histologic images of rat spinal cord for different white matter regions. 3. Perform high-q 3D q-space imaging in excised rat spinal cord with the objective of quantifying axonal architecture and compare the results with histology.

DESCRIPTION (provided by applicant): The chief manifestation of osteoporosis is the occurrence of fractures. Most osteoporotic fractures occur at skeletal locations rich in trabecular bone. Prevailing among these are the vertebrae, wrist and proximal femur. Hip fractures are the most debilitating among osteoporotic fractures in terms of morbidity and mortality. There is now strong evidence that the loss of bone mass is accompanied by a decline in the trabecular bone net- work's structural integrity. The impaired mechanical competence secondary to gonadal steroid depletion is caused by topological changes in the bone's architectural make-up, chief among which is fenestration of tra becular plates resulting in their conversion to rods and the latter's eventual disruption. Complementing antire- sorptive treatment, new therapies have recently become available to treat the devastating consequences of severe bone loss with bone-forming (i.e. anabolic) drugs. It is not clear, however, whether such therapies are, in fact, able to reverse the disintegration of the trabecular network, and to what extent the structural changes differ from those induced by antiresorptive treatment. In this project we propose to develop novel micro-MRI-based technology suitable to quantify the structural and mechanical consequences of various forms of treatment of patients with metabolic bone disease. We aim to apply this methodology to patients who are at high risk of fracture and who are treated either with 1-34 parathyroid hormone or alendronate. The overall hypothesis is that the new methodology will provide detailed insight into the structural manifestations of trabecular bone subjected to short-term drug treatment. The project will consist of six specific aims involving the development, integration and evaluation of new methods involving data acquisition and reconstruction, motion correction, cryogenic RF coil technology, image processing and analysis, as well as image-based finite-element modeling of bone mechanical competence. We plan to address these goals in partnership with two external collaborators through subcontracts (Dr. Jarek Wosik, Department of Electrical Engineering, Texas Center for Superconductivity, University of Houston, and Dr. Edward Quo, Department of Biomedical Engineering, Columbia University). Already established Penn-internal partnerships with Dr. Charles Epstein (Department of Mathematics) and Dr. Peter Snyder (Department of Medicine, Division of Endocrinology) will be further expanded and strengthened.

DESCRIPTION (provided by applicant): The mechanical behavior and functional properties of all tissues are intimately associated with their micro-structural organization. Bone - a composite biomaterial - has evolved so as to provide the compressive and tensile strength needed for weight-bearing and locomotion. Trabecular bone (TB) - the bone most prone to fracture - consists of a meshwork of interconnected plates and struts that confer the tissue its unique mechanical properties. In recent years it has become evident that besides apparent density - the metric used clinically to assess fracture risk - the bone's structural arrangement as well as its intrinsic material properties, loosely termed "bone quality", are essential in determining static and dynamic strength. Advances in imaging technology (notably MRI) now allow imaging of selected anatomic sites at a resolution enabling analysis of the trabecular network. However, these methods, although promising, are only applicable to peripheral skeletal sites where sufficient SNR can be achieved but not at the most common fracture sites. In this pilot study, we wish to evaluate the potential of intermolecular double-quantum coherences (iDQC), as a means to obtain structural information without the need to actually resolve individual trabeculae. The signal derived from CRAZED-type pulse sequences is known to be sensitive to the correlation distance, the wavelength of the magnetization helix created by two RF pulses in the presence of a correlation gradient. The presence of quasi-periodic structures such as those pertaining to TB lattices causes a modulation of the signal when the correlation distance approaches the spatial wavelength of the structure. We have demonstrated the feasibility of this approach in preliminary work. However, the functional relationship between the CRAZED signal and architecture at the present is not understood. Here we propose to investigate the potential of the method by simulation in model lattices and micro-CT images of animal and human TB and compare the results with data obtained with a new volume-selective CRAZED-type pulse sequence. The hypothesis to be evaluated is that spatially-resolved iDQC MRI can provide quantitative information on TB spacing and structural anisotropy, both key parameters determining the mechanical competence of trabecular bone.

DESCRIPTION (provided by applicant): The chief manifestation of osteoporosis is the occurrence of fractures. Most osteoporotic fractures occur at skeletal locations rich in trabecular bone. Prevailing among these are the vertebrae, wrist and proximal femur. Hip fractures are the most debilitating among osteoporotic fractures in terms of morbidity and mortality. There is now strong evidence that the loss of bone mass is accompanied by a decline in the trabecular bone net- work's structural integrity. The impaired mechanical competence secondary to gonadal steroid depletion is caused by topological changes in the bone's architectural make-up, chief among which is fenestration of tra becular plates resulting in their conversion to rods and the latter's eventual disruption. Complementing antire- sorptive treatment, new therapies have recently become available to treat the devastating consequences of severe bone loss with bone-forming (i.e. anabolic) drugs. It is not clear, however, whether such therapies are, in fact, able to reverse the disintegration of the trabecular network, and to what extent the structural changes differ from those induced by antiresorptive treatment. In this project we propose to develop novel micro-MRI-based technology suitable to quantify the structural and mechanical consequences of various forms of treatment of patients with metabolic bone disease. We aim to apply this methodology to patients who are at high risk of fracture and who are treated either with 1-34 parathyroid hormone or alendronate. The overall hypothesis is that the new methodology will provide detailed insight into the structural manifestations of trabecular bone subjected to short-term drug treatment. The project will consist of six specific aims involving the development, integration and evaluation of new methods involving data acquisition and reconstruction, motion correction, cryogenic RF coil technology, image processing and analysis, as well as image-based finite-element modeling of bone mechanical competence. We plan to address these goals in partnership with two external collaborators through subcontracts (Dr. Jarek Wosik, Department of Electrical Engineering, Texas Center for Superconductivity, University of Houston, and Dr. Edward Quo, Department of Biomedical Engineering, Columbia University). Already established Penn-internal partnerships with Dr. Charles Epstein (Department of Mathematics) and Dr. Peter Snyder (Department of Medicine, Division of Endocrinology) will be further expanded and strengthened.

[unreadable] DESCRIPTION (provided by applicant): New powerful drugs for treatment and prevention of osteoporosis are already available or are currently under development. The primary endpoint for these studies continues to be fracture incidence, the secondary endpoint typically is bone mineral density (BMD), both of which are fraught with problems. The former requires a very large number of study subjects as fractures are relatively rare events and require long observation periods, therefore resulting in excessive costs and long development cycles. BMD has been an unreliable indicator of treatment efficacy showing often disproportionately small increases relative to the extent of fracture reduction caused by the drug, in contrast to the much larger architectural changes that occur in the trabecular bone (TB) network. Progress in 3D high-resolution MRI ([unreadable]-MRI) now allows acquisition of images from which the topology of the TB network can be established. Nevertheless, in spite of these advances, structure plays only a surrogate role and it is not known which parameters and combinations thereof are optimal in terms of responding to treatment, and which are most representative of strength. Advances in micromechanical modeling now permit micro finite-element ([unreadable]-FE) computations of TB mechanical competence, potentially providing insight into the mechanical implications of disease progression and regression. We have, in preliminary work, examined the feasibility of quantifying the effect of antiresorptive treatment in a small cohort of patients and demonstrated significant improvement in the elastic moduli after computing the full stiffness matrix on the basis of MR images acquired in the distal tibia. While encouraging, the feasibility of deriving mechanical parameters from in vivo images as possible end points in clinical trials demands further scrutiny. In this project we advance the hypothesis that the treatment-induced changes in the bone's mechanical parameters, estimated from [unreadable]-FE calculations on the basis of in vivo [unreadable]-MRI, represent a quantitative measure of treatment response. The proposed research, involving four specific aims, seeks to (1) further develop algorithms for processing in vivo [unreadable]-MRI data with improved motion correction and serial registration capabilities; (2) evaluate the effect of resolution and noise on the derived mechanical indices in images of intact specimen under conditions of in vivo [unreadable]-MRI as well as by simulation previously or currently in progress to determine the effect of treatment and comparing the mechanical with of specimen [unreadable]-CT images; (4) apply [unreadable]-FE analysis to three longitudinal [unreadable]-MRI studies performed structural indices. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Age and disease-related remodeling changes with a negative bone balance involve both trabecular and cortical bone. The micro and ultrastructural changes that affect cortical bone, however, are less well understood than those involving trabecular bone and are far more difficult to quantify. Although age-related thinning of the cortex is partially offset by periosteal expansion, this process is accompanied by increased porosity. It is well known that increased porosity, a hallmark of enhanced bone turnover, significantly contributes to the decline of cortical bone strength and thus increased fracture susceptibility in postmenopausal osteoporosis and, particularly, in renal osteodystrophy. While increased porosity results in decreased volumetric bone mineral density, the pores are below the resolution limits achievable in vivo with any imaging modality. However, the spaces of the haversian and lacuno-canalicular system making up total pore volume are fluid-filled, while a minor fraction of exchangeable water is bound to collagen of the osteoid. We have, in preliminary work in support of this competing renewal application, developed a MRI-based technique for quantification of bone water (BW) and thus, by inference, porosity, in humans and shown the differences in this parameter between subject groups to far exceed those of volumetric bone density. In this project we advance the hypothesis that BW, measured noninvasively by solid-state proton imaging of cortical bone, provides a new metric of cortical bone quality that is more sensitive than either areal or volumetric bone density and, further, that the technique is able to detect changes in response to intervention. In four specific aims we propose the further development of the methodology, its technical and clinical validation, and to apply the method in pilot studies of two groups of human subjects. The first group comprises healthy men and women covering the age range from 30 to 80 years. The second group involves 30 patients with end-stage renal disease who are part of an independently NIH- funded project. These subjects will be evaluated with the new technology at transplantation, compared with age and gender-matched controls, and re-evaluated one year later. The expected outcome of the proposed research is the emergence of a robust clinically practical procedure that provides a parameter of bone quality not previously amenable in vivo. PUBLIC HEALTH REVELANCE: Cortical bone porosity is a hallmark of rapid bone turnover and thus is a ubiquitous manifestation of most metabolic bone disorders including gonadal steroid deficiency and parathyroidism. Porosity, however, cannot be quantified with current imaging modalities. The proposed approach, based on quantification of bone water with a new magnetic resonance imaging technique provides noninvasive surrogate measurement of cortical bone porosity as a new metric of bone quality.

DESCRIPTION (provided by applicant): Changes in blood oxygen saturation are of pivotal importance in a multitude of clinical conditions, including peripheral vascular disease, congenital cardiac abnormalities, diabetes, hypoxemias such as in chronic obstructive pulmonary disease, and ischemic disease of various organs. Current noninvasive methods are based on near infrared spectroscopy (NIRS) which can measure tissue oxygen saturation. These methods, however, are hampered by poor resolution. Further, the relative opacity of mammalian tissue to optical radiation precludes measurements of deep-lying tissues, and the method is unable to target specific arteries and veins. Quantitative MRI resting on a measurement of blood T2 has proven useful but the method requires extensive calibration and its implementation is involved. In this project we propose the development, implementation and validation of a new method for measuring blood oxygen saturation that involves virtually no calibration, allows for rapid and reliable measurement of hemoglobin saturation in arteries and veins at high spatial resolution. The method's principle is based on a measurement of the bulk magnetic susceptibility of blood, which is a function of the blood's hemoglobin oxygen saturation. In a vessel that can be modeled as a cylinder whose diameter is much less than its length, the demagnetizing field has a simple closed-form solution. From the intra-to-extravascular induced magnetic field difference obtained by phase mapping, the blood's volume susceptibility can be computed and thus hemoglobin saturation obtained. We show in preliminary work the method's feasibility and demonstrate its ability to quantify the response to a physiologic stimulus in the peripheral circulation. In four specific aims we propose to further develop and evaluate the image acquisition and processing methodology and quantify potential sources of error, both computationally and experimentally. We plan to validate the method in human subjects in models of peripheral limb ischemia and compare the baseline and post-occlusion hyperemic response with those of blood gas analysis as well as with tissue oxygen saturation measured by NIRS. PUBLIC HEALTH RELEVANCE: Venous and arterial oxygen saturation are among the most important physiological parameters. Currently, there exist no robust noninvasive techniques for measuring hemoglobin saturation in individual deep-lying vessels. Magnetic resonance susceptometry has substantial promise to fill this gap.

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DESCRIPTION (provided by applicant): Peripheral arterial disease (PAD) affects about 8 million Americans. The disease is typically caused by atherosclerosis and thus is systemic in nature. PAD's clinical manifestations are caused by stenosing of the major arteries supplying the lower extremities (iliac, femoral and popliteal arteries). The condition has further been recognized as an independent risk factor for future cardiovascular events, in particular myocardial infarction and stroke. The initial test for diagnosing PAD is measurement of the ankle-brachial index (ABI), a simple inexpensive test typically performed in a physician's office. However, while being highly specific, the test's sensitivity is low. Thus, while low ABI is a strong indicator of elevated cardiovascular risk, a normal ABI does not rule out high risk due to the test's high false negative rate. The ABI is therefore of limited utility as a screening tool for the general population. It is well known that more subtle functional deficits precede the build-up of atherosclerotic lesions (which at a later stage cause obstructions or vulnerable plaques that can trigger a vascular event). It would therefore be particularly beneficial, both to the patient and also from a healthcare cost containment point of view, if the onset of the disease could be determined well before it becomes symptomatic, so as to allow for lifestyle changes or preventive drug intervention. Among the early manifestations of PAD is decreased vascular compliance and impaired microvascular reactivity, which has been suggested to provide better prognostic assessment in the general population. Microvascular reactivity is typically evaluated on the basis of a measurement of reactive hyperemic indices by ultrasound, performed in the brachial artery, which, however, is not a common site of PAD. Compliance is often inferred from a measurement of pulse wave velocity (PWV), which is proportional to vessel wall stiffness, and thus is inversely related to compliance. PWV is usually quantified from the time lag of the systolic pressure wave between a location in the carotid artery and a point in the femoral artery using tonometry, an approach that is problematic since the path length the blood travels can only be estimated. Thus, the current approaches have limitations and there is no single modality that allows noninvasive quantification of the various physiological parameters that may predispose a subject to develop PAD and, by association, augment a person's cardiovascular risk in general. We have, in preliminary work in support of this proposal, conceived and reduced to practice, new MRI- based techniques for measuring multiple parameters as part of a single examination, including (1) a measurement of microvascular reactivity based on monitoring the temporal changes in venous oxygen saturation serving as an endogenous label in the femoral artery and vein during reactive hyperemia, (2) a high- speed, ungated, projection-based technique for measuring time-resolved arterial blood flow, (3) a method for deriving aortic pulse-wave velocity and compliance (which accounts for 60-70% of systemic arterial compliance), by combining #2 with an image-based measurement of aortic path length. We hypothesize that the measured parameters vary characteristically with age and degree of peripheral vascular disease. We will evaluate the above hypotheses by addressing the following specific aims: 1. Fully implement, and evaluate, a high-speed projection technique for measurement of time-resolved aortic blood flow in a single heart beat simultaneously in the ascending and descending aorta for quantifying pulse-wave velocity and compliance. 2. Integrate the method of aim #1 with the previously developed oximetric technique for quantifying microvascular reactivity into a single protocol. 3. Apply the protocol of aim #2 to subjects, ages 25-65 years, without significant cardiovascular risk factors, characterized further by ABIe0.9, and subjects in the age range of 46-65 years who have PAD based on ABI<0.9 to address the question whether in healthy subjects (i) the metrics derived with the protocol of aim #2 vary in an age-dependent manner including the hypothesized decrease in overall systemic compliance and decreased microvascular reactivity;(ii) subjects with PAD, age-matched to healthy controls, have lower systemic compliance and microvascular reactivity than their healthy peers. Public Health Relevance: The expected outcome of this research is that the results will provide new insight into the early manifestations of PAD and the age-related changes in micro- and macrovascular competence of the arterial system through an entirely noninvasive procedure. Since the methodology to be used in the proposed project is largely in place the investigators have confidence that the project can be completed within the allotted time frame. Lastly, the project ensures retention of personnel in compliance with the stimulus initiative. There is currently no sensitive noninvasive for diagnosing preclinical peripheral arterial disease (PAD), which affects 8 million Americans. In this project we propose to implement and evaluate a new noninvasive MRI-based method in healthy subjects and patients with PAD to address the hypothesis that the measured parameters vary characteristically with age and degree of peripheral vascular disease.

DESCRIPTION (provided by applicant): Recent advances in high-resolution imaging have permitted the development of new tools, notably micro- magnetic resonance (5MR) imaging and high-resolution peripheral quantitative computed tomography (HR- pQCT), that promise to provide a better profile of overall bone strength beyond areal bone mineral density (aBMD) by dual-energy x-ray absorptiometry (DXA). In this application, we seek to determine whether image- based microstructural and 5FE analyses can distinguish between individuals who have vertebral fractures from their counterparts without vertebral fractures. In the proposed project we advance the following hypotheses: 1. Morphological measurements and 5FE predictions of stiffness and failure load of the distal tibia and radius from ex vivo 5MRI and HR-pQCT correlate highly with those from 5CT and direct mechanical testing, and, furthermore, that parameters from the two peripheral sites parallel those in the vertebrae. 2. 5FE-derived estimates of elastic stiffness and failure load from in vivo 5MR and HR-pQCT images can differentiate between individuals with vertebral fractures from those without vertebral fractures better than microstructural measures derived by the two imaging modalities alone or aBMD by DXA. We plan to address the above hypotheses with the following specific aims: Specific Aim 1a: Perform 5MRI and HR-pQCT scans of the distal tibia and radius ex vivo under signal-to-noise and resolution conditions achievable in vivo, and compare trabecular and cortical bone microstructural measurements obtained in this manner with those from high-resolution 5CT. Specific Aim 1b: Compare the stiffness and failure load of whole bone segments of the distal tibia and radius as predicted by HR-pQCT and 5MR image-based nonlinear 5FE analyses to those predicted by 5CT image- based 5FE analysis and direct mechanical testing. Specific Aim 2a: Perform 5CT scans of lumbar vertebrae from the same subjects as the distal tibia and radius used in Aims 1a and 1b Specific Aim 2b: Compare trabecular and cortical bone microstructural measurements and 5FE predictions based on the imaging data obtained by HR-pQCT and 5MRI in Aims 1a and 1b with the 5CT measurements and direct mechanical testing of the corresponding vertebrae in Aim 2a. Specific Aim 3a: Apply the microstructural and 5FE techniques validated in Aims 1 and 2 to in vivo 5MRI and HR-pQCT scans from healthy women and compare these measurements between the two imaging modalities. Specific Aim 3b: Apply the microstructural and 5FE techniques validated in Aims 1 and 2 to the two peripheral imaging modalities and determine the effectiveness of methods in distinguishing between vertebral fracture subjects and their non-fractured peers using data from two imaging studies previously performed or currently in progress in the investigators' laboratories. PUBLIC HEALTH RELEVANCE: High-resolution peripheral quantitative computed tomography (HR-pQCT) and micro magnetic resonance imaging (5MRI), which are state-of-the-art clinical high-resolution imaging modalities for the skeleton, will be validated for the determination of mechanical competence and prediction of vertebral fractures. This research will test the feasibility and establish the standard of high-resolution skeletal imaging in assessing bone health beyond the areal bone mineral density measurements obtained by dual-energy x-ray absorptiometry (DXA).

DESCRIPTION (provided by applicant): The cerebral metabolic rate of oxygen consumption (CMRO2) is one of the most important physiologic parameters and indicators of tissue viability. In the healthy organism CMRO2 is generally tightly regulated, varying little as a function of blood flow or environmental conditions. However, in a large number of disorders the neurometabolic-neurovascular coupling is disrupted, a condition that, if sustained leads to ischemia and irreversible damage. Positron emission tomography (PET) has been at the forefront of quantifying CMRO2. However, PET is expensive, requires administration of radiolabeled tracers, is complex in the technical set-up, and provides relatively low temporal resolution. Other methods for quantifying CMRO2 rely on measuring venous oxygen saturation levels by jugular vein oximetry and flow via optical measurements or Doppler ultrasound. In this project we propose the further development and implementation of a new method conceived in preliminary work for quantifying CMRO2, based on an integrated measurement of arterio-venous oxygen difference (AVO2D) via MRI susceptometry and simultaneous quantification of total cerebral blood flow via ungated phase contrast MRI. Target applications in view of subsequent translation to the clinic involve evaluation of patients who are at risk of systemic hypoxic injury to the brain as a result of either underoxygenation of the arterial supply or mutations of the hemoglobin gene as in sickle cell anemia. Specific Aims are: 1. Further develop an integrated magnetic resonance technique for simultaneous measurement of venous oxygen saturation and cerebral blood flow for quantification of CMRO2. 2. Test the hypothesis that the method is able to quantify the changes in CMRO2 in response to a stimulus in healthy test subjects in whom normal neurovascular and neurometabolic coupling is expected. 3. Perform two exploratory studies to assess clinical feasibility in two groups of patients in close collaboration with Pediatric Neurology at the Children's Hospital of Philadelphia. The longer-term potential and societal benefit of the proposed method is to provide a clinically practical, noninvasive, image-based means to evaluate patients with a variety of systemic conditions affecting brain metabolism, pre- and post-treatment, ranging from neurodegenerative to developmental disorders at a cost far below that of competing imaging modalities. PUBLIC HEALTH RELEVANCE: The cerebral metabolic rate of oxygen consumption (CMRO2) is one of the most fundamental physiologic parameters. Although tightly regulated in the healthy body there are numerous disorders where this regulation breaks down. The proposed MRI-based method allows rapid and reliable measurement of CMRO2 entirely noninvasively and thus could provide an effective new means for evaluating patients with impaired brain oxygen metabolism.

DESCRIPTION (provided by applicant): The disconnect between bone density and fracture susceptibility has spurred the search for other risk factors that cause compromised skeletal strength. The applicants of this proposal previously developed methods, based on quantitative MRI for assessing multiple measures of bone quality, including trabecular bone microstructure via a procedure referred to as virtual bone biopsy (VBB). The potential of this technology has been demonstrated in translational research studies showing that structural measures of bone quality are more strongly associated with osteoporotic fractures than areal BMD and that these structural measures are sensitive indicators of drug intervention efficacy in patients with impaired structural integrity. The critical missing link is the association between measures of structure and measures of strength such as stiffness and failure load. There are very few studies that have attempted to relate in vivo bone- structure derived mechanical estimates from micro-finite element (?FE) analysis, with actual fracture data. Whereas both, high-resolution CT and MRI, are suited for this purpose, MRI has substantial advantages over CT, besides being free of ionizing radiation, in that it has superior bone-to-marrow contrast; and most importantly, an installed base of over 10,000 units in the United States alone. In this project we advance the following hypotheses: 1) that FE-estimated parameters (whole-section stiffness and ultimate strength, and sub-volume trabecular bone elastic and shear moduli) derived from in vivo ?MR images at the distal tibia and radius, are associated with structural parameters expressing scale, topology and orientation at the measurement sites, with structural measures jointly explaining as much as 90% of the variation in the mechanical parameters; 2) that these associations are stronger than those involving bone volume fraction or BMD alone; 3) that the mechanical and structural parameters at the surrogate sites are correlated with vertebral structural and mechanical parameters evaluated ex vivo and vertebral deformity status in vivo. We propose to evaluate the above hypotheses by addressing the following specific aims: 1. We will validate the proposed method in specimens of the distal tibia and radius by performing mechanical testing and comparing the data with ?FE-derived estimates of elastic moduli derived from micro-CT and ?MR images as well as with those from vertebral bone of the same donors. 2. We will evaluate a cohort of postmenopausal women with a protocol consisting of acquisition of high- resolution 3D ?MRI of the distal tibia and radius, 3D BMD by pQCT at matching anatomic locations, MRI of the spine for vertebral deformity assessment, and DXA aBMD at the spine and hip. 3. We will derive structural and mechanical parameters at the two peripheral sites to test the above hypotheses by comparing ?FE-estimated parameters with measures of structure and BMD, and with vertebral deformity status. The proposed in vivo MRI study will provide new insight into the microstructural and mechanical implications of osteoporosis, thereby providing the basis for translation of the methodology to the clinic, which is the long-term objective underlying the project.

DESCRIPTION (provided by applicant): Digital imaging techniques for assessing the precise location and extent of disease burden in overt atherosclerotic CVD include computed tomography and magnetic resonance (MR) for directly imaging of atherosclerotic plaques and determining structure and biochemical make-up of the lesions. However, the tools available for detecting the earliest presymptomatic changes, brought about by endothelial dysfunction (EDF), are unsatisfactory. This gap is of particular concern as a reproducible, accurate, noninvasive technique for quantifying measures of these earliest stages of pathogenesis would allow preventive intervention well before the onset of symptoms, thus reducing morbidity and mortality, and curbing healthcare costs. A key hallmark of EDF is impaired vascular reactivity in response to increased shear stress or increased demand for oxygen delivery. All current methods for assessing vascular reactivity, typically based on ultrasound, have significant limitations in both precision and sensitivity. The objective of the proposed research is to develop, implement and evaluate a new MRI-based approach for quantifying vascular reactivity to detect early signs of functional deficits. Toward such a goal the investigators have, in preliminary work, conceived and implemented an integrated quantitative MRI protocol for noninvasively assessing endothelial function, as part of a single one-hour examination. Key elements of the protocol comprise high-speed projection mapping of time-resolved femoral artery velocity at baseline and during hyperemia, simultaneously with a method for quantifying the dynamics of venous blood oxygen resaturation during hyperemia, and a technique for efficient quantification of arterial pulse wave velocity from central to peripheral conduit arteries. We conjecture that, individually and collectively, the MRI-derived parameters vary both in an age- and lifestyle-dependent manner across two age groups of subjects, each partitioned into smokers and non- smokers, who will be evaluated at baseline and two years thereafter. We hypothesize that each time-point, (i) older subjects will have lower vascular performance than their younger peers, (ii) a similar relationship holds for smokers relative to their nonsmoking peers, and (iii) the decline in the physiologic parameters will be greater in smokers in either age group at the end of a two-year observation period, and (iv) the MRI parameters measured parallel those obtained by ultrasound but that, collectively, they are stronger group differentiators and are more sensitive to expected longitudinal changes. These hypotheses will be addressed in three specific aims designed to further develop, integrate and evaluate the performance of the method and apply it in an observational pilot study to a cohort of healthy men. The integration, evaluation and translation to the clinic of the proposed methodology is likely to yield more effective tools for noninvasive evaluation of subjects at risk of developing cardiovascular disease and to provide a basis for future large-scale intervention trials. PUBLIC HEALTH RELEVANCE: Cardiovascular disease (CVD) is the main cause of death and morbidity in the industrialized world. While significant advances have been made in diagnosis and treatment of CVD, patients diagnosed are often at a late stage of disease progression. This project proposes to develop and translate to the clinic novel imaging methodology that enable diagnosis of the earliest stages of disease thereby allowing for lifestyle changes and early intervention in subjects at risk.

Imaging is a critically important technology for clinical, translational, cadaveric, and in vivo studies of animal and human disease. Whether the ability to characterize tissue structure or visualize molecular markers in a non-invasive manner, advanced imaging methods have proven to be powerful tools specifically for musculoskeletal applications. Research employing imaging that addresses problems in musculoskeletal injury and repair in humans has a long track record. Further, imaging is recognized to be vital as new evaluation and treatment modalities are developed and used for some of the major degenerative disorders such as osteoporosis and osteoarthritis or traumatic injuries such as fractures. The University of Pennsylvania has one of the most comprehensive imaging facilities in the nation, comprised of a complete range of imaging modalities dedicated to basic and translational research in animals and humans. Moreover, it is staffed by some of the leading scientists in the various imaging modalities. A key objective of the Penn Center for Musculoskeletal Disorders therefore is to provide an on-campus Imaging Core (IC) to musculoskeletal researchers for imaging of both humans and large and small animals. The overall objective of the IC is to develop and utilize a wide range of imaging techniques directed toward problems of musculoskeletal tissue injury and repair. The Specific Aims are: Aim 1: To provide guidance and expertise on the use of imaging for musculoskeletal research through educational enrichment programs and one-on one interactions. Aim 2: To provide a range of imaging resources for the study of structure, function and physiology of the musculoskeletal system in laboratory animals and humans. Aim 3: To provide pilot funding for development of new projects and collaborations and for investigators to generate preliminary data.

DESCRIPTION (provided by applicant): Osteoporosis and low bone mass are currently estimated to be a major public health threat for almost 44 million U.S. women and men aged 50 and older. While the disorder affects both genders, approximately 80% of those having the condition are women. After menopause and the concomitant decline in estrogen levels, bone undergoes structural changes and reduction in tissue volume density resulting in reduced strength and increased fracture susceptibility. Even though effective treatment is available, the high cost and numerous side effects of antiresorptive and anabolic drugs have spurred the search for alternative therapies. Equally important, however, is that pharmacologic intervention is generally not indicated until subjects have progressed to a level of bone density commensurate with the diagnosis of osteoporosis. It has recently been shown that low-magnitude mechanical stimulation (LMMS) at frequencies of tens of Hertz is osteogenic, presumably via downregulation of the nuclear hormone receptor, PPAR, resulting in preferential differentiation of marrow stromal cells toward the osteoblastic instead of the adipocytic lineage. This competing renewal project seeks to further develop methods for image-based micro-finite-element modeling for quantifying various properties of skeletal mechanical competence, along with improved methods for high-resolution structural magnetic resonance (MR) imaging of cortical and trabecular bone, and measurement of bone marrow composition by MR spectroscopic imaging. The resulting protocol will be applied in a subsequent randomized, double-blinded, translational patient study to evaluate the hypothesis that early postmenopausal women, subjected to a daily 10-minute treatment of LMMS for one year, will show an improvement in trabecular and cortical stiffness and failure strength at the tibia, along with a reduction in vertebral marrow adiposity relative to their placebo-treated peers. The successful completion of the project will provide new insight into the potential for image-based computational biomechanics for monitoring prophylactic intervention.

DESCRIPTION (provided by applicant): Myelin, accounting for 14% of white matter, is predominantly composed of a dielectric lipid-protein bilayer that is paramount to efficient neural current transport. Defects in myelin integrity are associated with numerous common neurologic abnormalities. Although demyelinating diseases first come to mind, myelin abnormalities have also been implicated in Alzheimer's disease, schizophrenia, traumatic brain injury, addiction, and dementias. Thus, improved myelin imaging may have profound impact on characterization of many CNS diseases. Virtually all current, noninvasive, methods for evaluating the integrity of the myelin sheath rely on indirect measures, principally magnetization transfer and myelin water fraction. Both measures have been shown to correlate to varying degrees with optical density in stained histological sections but both have shortcomings. Importantly, the biophysical mechanisms of these surrogates are not completely understood, thereby complicating data interpretation. They further require a number of conditions to be satisfied that may not apply across a range of myelin abnormalities, and achievement of absolute quantification is questionable at best. Here, we hypothesize that direct detection and quantification of myelin is practical. Building on preliminary work characterizing the proton and 31P signal from the liquid-crystalline matrix of the myelin lipid bilayer, and showing its detectability by ultra-short echo-time (UTE) imaging on a 9.4T laboratory micro- imaging system, we delineate a path toward image-based myelin quantification on a clinical imaging system. Central to this proposal is the development and evaluation of 3D zero-echo-time (ZTE) quantitative MRI acquisition and analysis methods involving tissue water suppression and compressed sensing reconstruction, with subsequent translation to a 3T clinical imager. Initial results on reconstituted myelin and intact neural tissue performed by UTE and ZTE methods demonstrate the proposed method's feasibility. The work's longer- term goal is translation to the clinic as an alternative and possily superior technique for regional myelin quantification in patients with myelin abnormalities and for providing means to evaluate treatment effectiveness.

DESCRIPTION (provided by applicant): Recent advances in high-resolution imaging have permitted the development of new tools, notably micro- magnetic resonance (5MR) imaging and high-resolution peripheral quantitative computed tomography (HR- pQCT), that promise to provide a better profile of overall bone strength beyond areal bone mineral density (aBMD) by dual-energy x-ray absorptiometry (DXA). In this application, we seek to determine whether image- based microstructural and 5FE analyses can distinguish between individuals who have vertebral fractures from their counterparts without vertebral fractures. In the proposed project we advance the following hypotheses: 1. Morphological measurements and 5FE predictions of stiffness and failure load of the distal tibia and radius from ex vivo 5MRI and HR-pQCT correlate highly with those from 5CT and direct mechanical testing, and, furthermore, that parameters from the two peripheral sites parallel those in the vertebrae. 2. 5FE-derived estimates of elastic stiffness and failure load from in vivo 5MR and HR-pQCT images can differentiate between individuals with vertebral fractures from those without vertebral fractures better than microstructural measures derived by the two imaging modalities alone or aBMD by DXA. We plan to address the above hypotheses with the following specific aims: Specific Aim 1a: Perform 5MRI and HR-pQCT scans of the distal tibia and radius ex vivo under signal-to-noise and resolution conditions achievable in vivo, and compare trabecular and cortical bone microstructural measurements obtained in this manner with those from high-resolution 5CT. Specific Aim 1b: Compare the stiffness and failure load of whole bone segments of the distal tibia and radius as predicted by HR-pQCT and 5MR image-based nonlinear 5FE analyses to those predicted by 5CT image- based 5FE analysis and direct mechanical testing. Specific Aim 2a: Perform 5CT scans of lumbar vertebrae from the same subjects as the distal tibia and radius used in Aims 1a and 1b Specific Aim 2b: Compare trabecular and cortical bone microstructural measurements and 5FE predictions based on the imaging data obtained by HR-pQCT and 5MRI in Aims 1a and 1b with the 5CT measurements and direct mechanical testing of the corresponding vertebrae in Aim 2a. Specific Aim 3a: Apply the microstructural and 5FE techniques validated in Aims 1 and 2 to in vivo 5MRI and HR-pQCT scans from healthy women and compare these measurements between the two imaging modalities. Specific Aim 3b: Apply the microstructural and 5FE techniques validated in Aims 1 and 2 to the two peripheral imaging modalities and determine the effectiveness of methods in distinguishing between vertebral fracture subjects and their non-fractured peers using data from two imaging studies previously performed or currently in progress in the investigators' laboratories.

DESCRIPTION (provided by applicant): Obstructive sleep apnea (OSA) is a disorder resulting from failure of the upper airway to maintain patency during sleep. OSA is associated with extensive comorbidities, including hypertension, cardiovascular disease and stroke, as well as with significant cognitive dysfunction. The cardio- and neurovascular consequences of the disease are believed to result from periodic nocturnal hypoxia-reoxygenation cycles. While the normal physiologic response to volitional apnea (breath-holding) maintains cerebral oxygen delivery via reduced cardiac output, peripheral vasoconstriction, and central vasodilation, this response becomes blunted in OSA secondary to chronic intermittent hypoxia experienced during repeated nocturnal apneic events. Building on our recent work in developing techniques for quantifying the cerebral metabolic rate of oxygen consumption (CMRO2) to investigate brain oxygen metabolism, we propose to further develop and apply a new MRI method to study the neurometabolic-neurovascular consequences of OSA. Key to the method is the quantification of venous blood oxygen saturation from a measurement of magnetic susceptibility, which scales with deoxyhemoglobin concentration and which, along with cerebral blood flow, yields CMRO2. Since apnea represents a mixed hypercapnic/hypoxic stimulus for which no steady-state is reached, capturing the physiologic response requires high temporal resolution. Responding to this need, the investigators have developed a vastly accelerated CMRO2 measurement technique and shown its ability to resolve dynamic changes in CMRO2 in response to volitional apnea in healthy subjects at 3T and demonstrated its feasibility in OSA patients on a wide-bore 1.5T system. We posit that the breath-hold paradigm is a suitable model to evaluate the neurovascular response in OSA as it reflects the intermittent hypoxia experienced by apneics during sleep. In this project we hypothesize that the neurometabolic profiles in patients with OSA are impaired, including lower CMRO2 at baseline and blunted neurometabolic response to a breath-hold challenge. Further, we hypothesize that continuous positive airway pressure (CPAP) treatment will alleviate this abnormal response. These hypotheses will be addressed in four specific aims, comprising: (1) further development and validation of the method; (2) application to a cohort of OSA patients and their controls; (3) evaluation of the effect of CPAP in the cohort of Aim 2; and (4) an exploratory sleep study in a subset of patients to compare the neurometabolic effects of wakeful volitional and spontaneous nocturnal apnea. The proposed neurometabolic MRI measures could ultimately serve to identify patients at greatest risk of the neurocognitive and neurovascular sequelae from OSA, and to predict the efficacy of CPAP therapy. Further, the method could allow triaging of OSA patients to more invasive treatment approaches and provide an improved means for risk assessment in those affected by this increasingly prevalent disorder.

? DESCRIPTION (provided by applicant): Since its inception four decades ago, magnetic resonance imaging (MRI) has continued to evolve and is far from having reached its ultimate potential. MRI is unquestionably the most complex but also the richest and most versatile imaging method therefore requiring systematic training. Although inherently quantitative, MRI has been used largely as a qualitative imaging technique practiced by radiologists utilizing predominantly qualitative criteria for establishing a diagnosis or excluding disease. This approach is fraught with problems, its main limitation being the subjective nature of the result, i.e. sensitivity to reader experience and judgment. An increasing number of problems in medicine require a quantitative assessment of tissue structure, physiology and function. Moreover, for many diagnostic or staging problems quantification of an observation is not merely a better option but the qualitative approach is entirely unsuited. Examples are measurement of tissue perfusion, quantification of metabolite concentration by spectroscopic imaging, the assessment of non-focal systemic disorders such as degenerative neurologic or metabolic bone disease where a quantitative measurement of some structural or functional parameter has to be made. Over the years the modality has become ever more complex with the ongoing emergence of new methodologies, providing increasingly detailed insight into tissue function. Many of these new methods are conceived and reduced to practice years before being implemented by equipment manufacturers. Successful participation in these developments demands in-depth, modality-specific training to enable future scientists to effectively deploy the myriad of mathematical tools for pulse sequence design and data reconstruction. Translation of new methods from the bench to the clinic is equally important and highlighted as one of NIH's key priorities. The training process therefore needs to be multidisciplinary, requiring close cooperation among MR physicists, engineers, computer scientists and physicians in the various subspecialties. Basic science trainees often understand the medical problem incompletely and typically have difficulties in translating abstract technical concepts to the practicing physician. The proposed Training program builds on the director's earlier program and its record in terms of achieved training outcome, showing the large majority of former trainees having attained academic faculty or senior research positions in industry. The new program builds on this successful formula by proposing to train predoctoral and postdoctoral candidates in MRI physics and engineering, with particular focus on structural, physiologic and functional applications, for period of two years. Training modalities involve a combination of colloquia, structured teaching and hands-on laboratory training, and emphasis on preceptor-directed research. The training faculty consists of MR imaging and physician scientists with a record of successful multidisciplinary research training as well as basic and translational research excellence.

Project Summary/Abstract for µCT Imaging Core The development of high-resolution micro-CT (µCT) during the past two decades has revolutionized the quantitative assessment of calcified and X-ray dense tissue morphology. With the capability of non-destructive, three-dimensional (3D) visualization of tissue structure, µCT has largely supplanted traditional histomorphometry and become a gold standard for calcified tissue density and microstructure evaluation for many measures. Due to the low intrinsic X-ray contrast of non-mineralized tissues, traditional applications of µCT in musculoskeletal research have been limited to mineralized tissue. However, the development of contrast-enhanced imaging methods has greatly broadened applications of µCT to include musculoskeletal soft tissues as well. These cutting-edge image-based quantification methods not only enable characterization of soft-tissue morphology, but some also yield insight into tissue composition, such as glycosaminoglycan (GAG) density, which is associated with soft-tissue function and mechanics. Another important advance in the past decade is in vivo µCT imaging of living small animals. Research of musculoskeletal tissue injury and repair has been progressively utilizing animal models of human disease. Unlike many assays that require sacrificing the animal to extract tissues for analysis, in vivo µCT enables longitudinal evaluation of changes in a particular animal non-invasively over time. This new imaging strategy minimizes the number of animals required while enhancing statistical power. With these developments, µCT can now provide a deep and quantitative understanding of the genetic influences on the skeleton, as well as remodeling events in hard and soft tissues during repair, treatment, and with altered loading scenarios. Further, a µCT modality for clinical imaging of calcified tissue microstructure, called high-resolution peripheral quantitative CT (HR-pQCT), has recently been developed. This technology inaugurated a new era of non-invasive quantitative skeletal imaging, and has become a powerful tool for clinical research of musculoskeletal disorders. The overall objective of the µCTIC is to offer a wide range of µCT imaging approaches to evaluate musculoskeletal tissue injury and repair, and to provide training and consultation for new projects and collaborations utilizing these assays. The Specific Aims for the µCTIC are: 1) To provide guidance and expertise on the use of µCT imaging for musculoskeletal research through educational enrichment programs and one-on-one interactions, 2) To provide a range of µCT imaging resources, expertise, and services for the study of the structure, function and physiology of the musculoskeletal system in laboratory animals and humans, 3) To develop new µCT imaging-based techniques that will be applicable to musculoskeletal research, and 4) To provide funding for the development of new projects and collaborations and to develop preliminary and/or feasibility data for investigators.

Summary The popularity of electronic cigarettes (e-cigs) has grown at a startling rate since their introduction to the US market 10 years ago, with sales expected to outpace tobacco products within a decade. E-cigs are often per- ceived as a safer alternative to tobacco-based cigarettes, which is unsettling given the limited science on its chemistry and paucity of knowledge on long-term health effects of aerosol inhalation. Particularly alarming is marketing directed extensively toward adolescents, which indicates that young people are the key target mar- ket of e-cig companies. Further, there is no evidence among cigarette smokers that alternative e-cig use leads to smoking cessation. In fact, recent data suggests e-cig users who have never smoked conventional ciga- rettes are more likely to take up tobacco cigarette smoking within six months. E-cigs yield mainstream aerosols with particle concentrations similar or even higher than those in conventional cigarettes. Indeed, e-cig ?vapers? repeatedly inhale high concentrations of volatile organic compounds and, importantly, ultrafine particles and free radicals. The latter are then taken up by the alveoli where they translocate into the vascular space leading to endothelial dysfunction (EDF), the prime promoter of atherosclerotic cardiovascular disease. The current tools available for detecting the earliest presymptomatic vascular changes, brought about by EDF, are relatively limited. Building on recent work in the investigators' laboratory in which we quantified multiple functional and mechanical surrogate measures of EDF in tobacco cigarette smokers we propose to examine the effects of aerosol inhalation by quantitative MRI (qMRI) and compare the resulting biomarkers with pharmacologic measures. We hypothesize that the oxidative stress exerted by e-cig aerosol causes EDF comparable to that from cigarette smoke exposure and that MRI-derived biomarkers parallel inflammatory indi- ces measured in serum. We will examine both acute and longer-term effects by assessing microvascular reac- tivity via dynamic femoral oximetry, arterial hyperemia, femoral artery flow-mediated dilation, central pulse- wave velocity and neurovascular reactivity, all as part of a single integrated MRI protocol. The outcome of the proposed project will provide new insight into the acute and chronic effects of e-cig aerosol inhalation in terms of surrogate markers of EDF and aid toward establishment of future public health advisories, particularly in juvenile e-cig consumers.

Project Summary In general, the cerebral metabolic rate of oxygen (CMRO2) closely parallels blood flow. However, regional un- coupling of this relationship is well known to occur in many instances. Soon after its discovery, the blood oxy- gen level dependent (BOLD) contrast had become the main pillar of functional magnetic resonance (fMRI). However, the BOLD effect -- a change in gradient-echo signal in response to neural stimulation -- is a compli- cated function of cerebral blood flow (CBF), deoxyhemoglobin (dHb) concentration and capillary blood volume. Typically, the BOLD effect is positive since accumulation of dHb due to a local increase in CMRO2 is far ex- ceeded by the effect of increased blood flow, thereby more than offsetting the signal loss that would be ex- pected from increased oxygen extraction alone. In recent years there has been growing interest in measuring the change in response to functional tasks or vasoactive stimulants by dissecting the BOLD signal into its components to yield DCMRO2, the task- induced change in CMRO2. Two approaches have emerged, referred to as quantitative BOLD (qBOLD) and calibrated BOLD (cBOLD). Both models exploit the paramagnetism of dHb by eliciting a disturbance of the magnetic field in the intra- and extravascular space. QBOLD yields baseline CMRO2 in physiologic units but may not be suited for quantifying dynamic changes. In contrast, cBOLD provides typically provides the frac- tional change DCMRO2/CMRO2. The crux of cBOLD is the voxelwise determination of the calibration constant M that relates the measured change in the BOLD signal to a function of the fractional CMRO2 and CBF chang- es based on a hypercapnia challenge. Once M is known regional CMRO2 changes in response to neural stimu- lation can be determined with relatively high temporal resolution. However, the approach is limited by relying on questionable assumptions and suffering from sensitivity to measurement errors. Here, we propose the de- velopment, validation, and application in a pilot study, of a new cBOLD pulse sequence and analysis approach. The method, referred to as OxBOLD, building on our prior work in whole-brain oximetry, consists of an inter- leaved pulse sequence that measures the change in CBF and oxygen saturation in response to a well- tolerated hyperoxia challenge. We show in preliminary work that the new method yields calibration constants of superior quality. The four specific aims comprise (1) implementation, (2) technical performance evaluation, (3) testing in response to well-established neural stimuli to derive their effect on CMRO2 in comparison to BOLD, and (4) application of the method in a translational pilot study. The latter involves a subset of patients with ob- structive sleep apnea, currently studied under R01 HL122754, to evaluate the hypothesis that in these patients the CMRO2 response to volitional apnea, used as a model for spontaneous apneas, is blunted in an anatomic region-specific manner, thereby providing insight into the neurometabolic consequences of the disease and the cognitive impairment known to affect these patients.

Project Summary Given that many of the most common fracture sites, such as those of the distal radius and vertebrae, are predominantly trabecular, the prevailing view is that osteoporotic fractures primarily result from decreased density and impaired structural integrity of trabecular bone. However, 80% of the skeleton consists of cortical bone and some of the most devastating fractures, such as those of the femoral neck, occur at a location where the stresses are shared by the two types of bone. Hormonal loss following menopause causes enhanced cortical remodeling leading to increased pore volume fraction caused by expansion of Haversian and Volkman canals and formation of composite osteons. Paralleling these processes is a decrease in mineralization, referred to as degree of mineralization of bone (DMB), due to the bone's failure of undergoing secondary mineralization. Both effects have previously been shown to be modifiable and partially reversible by treatment with antiresorptive drugs as assessed with measurements in iliac bone biopsy specimens. In preliminary studies leading up to this project, we conceived new quantitative solid-state 1H and 31P MRI methods based on zero-echo-time (ZTE) PETRA encoding and new non-iterative reconstruction techniques for evaluating measures of cortical porosity and mineral density, thereby delineating a path toward noninvasive assessment of cortical bone ultrastructure and chemistry. The approach chosen makes use of T2-selective suppression pulses providing pore and collagen-bound water. The latter is shown to represent a surrogate for bone tissue matrix density yielding, along with 31P density, DMB. In this competing renewal application we propose to reduce to practice, validate, and translate these methods to patient studies. Our primary hypothesis is that postmenopausal women with osteoporosis (OP) have greater cortical porosity as assessed by 1H MRI surrogate markers than their healthy peers; and further that porosity in these patients decreases upon antiresorptive treatment. Our secondary hypothesis is that OP subjects have lower DMB as measured by 31P MRI surrogate markers, and that antiresorptive treatment increases DMB. We propose to evaluate these hypotheses with an integrated MRI protocol in a cohort of OP women in comparison to matched healthy controls, both at baseline and after 12 and 24 months of alendronate treatment. We expect the outcome to show that the proposed technology can quantify and distinguish inter-group differences of the parameters measured, both at baseline and in response to intervention. The proposed comprehensive quantitative MR imaging protocol, which can readily be implemented on standard clinical MRI equipment, should yield new insight into microstructure and mineral properties of cortical bone, and provide new ways to evaluate the response to antiresorptive treatment in patients.

Abstract Computed tomography (CT) has been the standard imaging modality for pre- and postsurgical evaluation of pediatric patients with craniofacial skeletal pathologies. The large difference in attenuation coefficients between bone and soft tissue allows for straightforward segmentation, enabling creation of 3D models at high spatial reso- lution. However, there is growing concern about potential adverse effects of repeated exposure to ionizing radia- tion during infancy and childhood. In fact, the FDA has issued warnings cautioning against unnecessarily expos- ing children to X-rays, stating that even though the risk is deemed relatively small, it could, nonetheless, contrib- ute to increased risk of cancer later in life. As a result, non-radiative alternatives to CT would be particularly valu- able to identify and manage these patients, who require multiple examinations over the course of their lifetime. Unfortunately, conventional MR is not suited for imaging bone, which appears with near background intensity due to very short T2 relaxation times and relatively low proton density, and thus is difficult to distinguish from air. The premise underlying this proposal is that a new solid-state (SS) subtraction imaging technique, making use of bone signal attenuation during and following excitation, collected in an interleaved fashion with an acquisition yielding maximal bone signal retention, allows for superior bone-selective imaging. Along with a new k-space data sharing approach and compressed sensing reconstruction, achieved by exploiting signal sparsity in the difference image domain, it is hypothesized that the method will achieve high-resolution whole-skull coverage, yielding 3D render- ings comparable to their CT analogs in less than three minutes of scan time. This hypothesis will be rigorously evaluated in three specific Aims, starting with full implementation of image data acquisition, reconstruction and processing (Aim 1). Subsequently, the methodology is tested in human cadaver skulls to compare its performance based on craniometric accuracy and agreement with the gold-standard CT data. The latter is quantified in terms of the SØrenson-Dice (SD) coefficient of the binarized 3D-rendered images, and craniometric accuracy in the form of the concordance correlation coefficient (Aim 2). Finally, the SS-MRI method is evaluated in 30 children and ad- olescents who are clinically indicated for craniofacial surgery guided by high-resolution CT (Aim 3). We posit that the new method is superior to a competing gradient-echo imaging method that is unable to distinguish between bone and background (e.g. air in the sinuses) ? therefore denoted black-bone (BB) MRI. The specific hypothesis to be tested is that the SS MRI method is more accurate than its BB counterpart with respect to the reference CT- based renderings. Successful execution of this project should result in a clinically effective, radiation-free alterna- tive to CT for the pre- and post-surgical evaluation of pediatric patients with craniofacial abnormalities. Beyond the scope of the proposed pilot project, the rigorously evaluated method will provide a gateway toward establishment of a database of craniofacial anatomy during growth and development enabling recognition of abnormal pheno- types.

Project Summary A significant fraction of the US population suffers from various degrees of insomnia, conditions particularly prevalent in the elderly. Fractured sleep has adverse effects on cognitive function and memory, and may contribute to age-related cognitive decline. The brain is a highly metabolic organ, but during slow-wave sleep, cerebral glucose and oxygen metabolism decline. This reduction in brain metabolism may be critical for long-term homeostasis, while an inability to adequately lower brain energy expenditure during sleep may lead to oxidative injury. Prior work examining alterations in brain metabolism during slow-wave sleep relied on invasive methods. We have, in preliminary work, developed a noninvasive MRI-based method, termed OxFlow, to noninvasively quantify the cerebral metabolic rate of oxygen consumption (CMRO2) at a tem- poral resolution of seconds, along with concurrent, in-scanner EEG monitoring. OxFlow quantifies CMRO2 via Fick's principle using concurrent measurement of venous O2 saturation and total brain cerebral blood flow (tCBF). The approach's feasibility has been demonstrated in test subjects in whom neurometabolic pa- rameters were measured during wakefulness and sleep. In Aim 1 of this project we propose to further de- velop the OxFlow method for use in sleep research. Specifically, we will modify the gradient structure to at- tenuate acoustic noise so as to facilitate subjects' ability to initiate and maintain sleep. We will also optimize EEG filtering procedures to minimize interference of MRI gradient-induced electronic noise to reliably allow simultaneous EEG recordings needed as a means to establish the subject's stage of consciousness. In Aim 2 we will test the hypothesis that in older subjects, slow-wave sleep is associated with a reduced awake-to- sleep decrement in CMRO2 as compared to younger subjects. We will address this hypothesis by subjecting 12 young and 12 older subjects (25-40 vs. 60-80 years) to a combined MRI/EEG sleep protocol. This study will provide new noninvasive methods for measuring sleep dependent brain energy regulation and begin to demonstrate its utility in research on brain aging and dementia.

PROJECT SUMMARY/ABSTRACT Since its inception nearly five decades ago, magnetic resonance imaging (MRI) has continued to evolve and is far from having reached its ultimate potential. MRI is unquestionably the most complex but also the richest and most versatile imaging method, therefore requiring systematic training. Although inherently quantitative, MRI has been used largely as a qualitative imaging technique practiced by radiologists utilizing predominantly qualitative criteria for establishing a diagnosis or excluding disease. This approach is fraught with problems, its main limi- tation being the subjective nature of the result, i.e. sensitivity to reader experience and judgment. An increasing number of problems in medicine require a quantitative assessment of tissue structure, physiology and function. Moreover, for many diagnostic or staging problems quantification of an observation is not merely a better option but the qualitative approach is entirely unsuited. Examples are measurement of blood flow and perfusion, quan- tification of metabolite concentration by spectroscopic imaging and chemical exchange saturation transfer (CEST), the assessment of non-focal systemic disorders such as degenerative neurologic or metabolic bone disease where a quantitative measurement of some structural or functional parameter has to be made. Over the years the modality has become ever more complex with the ongoing emergence of new methodologies, providing increasingly detailed insight into tissue function and metabolism. Recent years saw the development and inte- gration of advanced machine learning approaches for a variety of tasks including segmentation and computer assisted diagnosis. Successful participation in these developments demands in-depth, modality-specific training to enable future scientists to effectively deploy the myriad of mathematical tools for pulse sequence design and data reconstruction. Translation of new methods from the bench to the clinic is equally important and highlighted as one of NIH?s key priorities. The training process therefore needs to be multidisciplinary, requiring close coop- eration among MR physicists, engineers, computer scientists and physicians in the various subspecialties. Basic science trainees often understand the medical problem incompletely and typically have difficulties in translating abstract technical concepts to the practicing physician. The proposed training program builds on the director?s earlier program and its record in terms of achieved training outcome, showing the large majority of former train- ees having attained academic faculty or senior research positions in industry. The new program builds on this successful formula by proposing to train four predoctoral candidates in MRI physics and engineering, with par- ticular focus on structural, physiologic and functional applications, for a period of two years. Training modalities involve a combination of colloquia, structured teaching and hands-on laboratory training, and emphasis on pre- ceptor-directed research. The training faculty covers a broad spectrum of expertise in multidisciplinary research training as well as basic and translational research excellence.