Osteoporosis is associated with bone loss, both cortical and trabecular, eventually resulting in structural failure. Most fractures occur at sites of a high degree of trabecular bone (vertebral proximal femur, distal radius, etc.). For this reason, the focus of osteoporosis has been on density of trabecular bone, as measured by bone mineral densitometry. The unsatisfactory outcome prediction of bone density prompted the investigators to search for alternative approaches relying on an assessment of structure rather than material density. The hypotheses underlying this project proposal are based on the spatially nonuniform magnetic field induced by the different magnetic permeability of bone and bone marrow, with the amplitude and direction of the induced field being a function of trabecular morphology and thus trabecular bone strength. The relative magnetic field inhomogeneity has been shown to be quantifiable in terms ofR2', the contribution from the induced inhomogeneous field to the total rate of decay of the transverse magnetization R. The principal aim of this proposal is to apply substantially improved methods to both the proximal femur and lumbar spine, in vitro in human cadaver specimens and in vivo in osteoporosis patients and their controls. The hip is a major osteoporotic fracture site. It is biomechanically more complex because of the multidirectional nature of the stresses to which it is subjected. Besides incorporation of new measurement methods providing higher precision, algorithms will be implemented for an exact measurement of the fat volume fraction as a means to correct the R2* data for the different magnetic susceptibility of fat and water relative to bone. It is expected that these steps will lead to improved diagnostic accuracy. As a gold standard for the presence or absence of osteoporosis objective criteria of vertebral deformity will be applied. By extending the technique to the hip, it is intended to demonstrate the more general validity of the investigators' previous results which proved a relationship between the induced magnetic field and trabecular structural parameters including number density, orientation and thickness; and the bone's modulus of elasticity and thus strength of the lumbar vertebrae. Specifically, it is proposed to assess in vitro whether Young's modulus for axial loading scales with R2', and whether in vivo the changes in bone remodeling occurring during aging and osteoporosis parallel those in the spine. Finally, the diagnostic accuracy of the method will be compared to conventional bone densitometry.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR040671-06
Application #
2413972
Study Section
Diagnostic Radiology Study Section (RNM)
Project Start
1991-07-01
Project End
1998-07-31
Budget Start
1997-05-01
Budget End
1998-07-31
Support Year
6
Fiscal Year
1997
Total Cost
Indirect Cost
Name
University of Pennsylvania
Department
Radiation-Diagnostic/Oncology
Type
Schools of Medicine
DUNS #
042250712
City
Philadelphia
State
PA
Country
United States
Zip Code
19104
Wehrli, Felix W; Song, Hee Kwon; Saha, Punam K et al. (2006) Quantitative MRI for the assessment of bone structure and function. NMR Biomed 19:731-64
Gomberg, Bryon R; Saha, Punam K; Wehrli, Felix W (2005) Method for cortical bone structural analysis from magnetic resonance images. Acad Radiol 12:1320-32
Wehrli, F W; Hwang, S N; Ma, J et al. (1998) Cancellous bone volume and structure in the forearm: noninvasive assessment with MR microimaging and image processing. Radiology 206:347-57
Song, H K; Wehrli, F W; Ma, J (1997) Field strength and angle dependence of trabecular bone marrow transverse relaxation in the calcaneus. J Magn Reson Imaging 7:382-8
Ma, J; Wehrli, F W; Song, H K et al. (1997) A single-scan imaging technique for measurement of the relative concentrations of fat and water protons and their transverse relaxation times. J Magn Reson 125:92-101
Ma, J; Wehrli, F W; Song, H K (1996) Fast 3D large-angle spin-echo imaging (3D FLASE). Magn Reson Med 35:903-10
Ma, J; Wehrli, F W (1996) Method for image-based measurement of the reversible and irreversible contribution to the transverse-relaxation rate. J Magn Reson B 111:61-9
Wehrli, F W; Ford, J C; Haddad, J G (1995) Osteoporosis: clinical assessment with quantitative MR imaging in diagnosis. Radiology 196:631-41
Wehrli, F W; Ford, J C; Chung, H W et al. (1993) Potential role of nuclear magnetic resonance for the evaluation of trabecular bone quality. Calcif Tissue Int 53 Suppl 1:S162-9
Chung, H; Wehrli, F W; Williams, J L et al. (1993) Relationship between NMR transverse relaxation, trabecular bone architecture, and strength. Proc Natl Acad Sci U S A 90:10250-4

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