Potential role of nuclear magnetic resonance for the evaluation of trabecular bone quality

This paper discusses two novel applications of nuclear magnetic resonance (NMR) as an investigational tool for the assessment of cancellous bone microarchitecture. It further outlines extensions of the method for in vivo clinical evaluation of bone strength in patients with skeletal disorders such as osteoporosis. The first method relies on the hypothesis that the presence of two phases of different magnetic permeability, i.e., bone and bone marrow, causes a spatial nonuniformity of the magnetic field across the measurement volume. The resulting spread in resonance frequency shortens the decay time constant (T2*) of the time domain proton signal in bone marrow or its substitute (water). Increased trabecular spacing, such as it occurs in osteoporosis, reduces the spatial field inhomogeneity and thus prolongs T2*, which has been shown both in vitro and in vivo. Subjects with osteoporosis, characterized by either low bone mineral density and/or spine compression fractures, have T2* values that are significantly prolonged. The second method focuses on a direct measurement of micromorphometric parameters of cancellous bone, using the principles of proton NMR microscopy in conjunction with computer processing of the resulting digital images. Image contrast between the trabeculae and the intertrabecular space is based on the marrow protons providing a signal, as opposed to bone, which appears with background intensity. Once tissues have been classified (into bone and marrow), for example, by means of a histogram-based segmentation algorithm, bone area fraction, mean trabecular plate density (MTPD), and mean trabecular plate thickness (MTPT) can be computed without the need for further operator intervention.(ABSTRACT TRUNCATED AT 250 WORDS)