RELATIONSHIP BETWEEN NMR TRANSVERSE RELAXATION, TRABECULAR BONE ARCHITECTURE, AND STRENGTH

Structure, biomechanical competence, and incremental NMR line broadeni ng (R2') of water in the inter-trabecular spaces of cancellous bone we re examined on 22 cylindrical specimens from the lumbar vertebral bodi es of 16 human subjects 24-86 years old (mean, 60 years old). A strong association (r = 0.91; P < 0.0001) was found between Young's modulus of elasticity and R2' for a wide range of values corresponding to canc ellous bone of very different morphologic composition. NMR line broade ning is caused by the inhomogeneity of the magnetic field induced as a consequence of the coexistence of two adjacent phases of different di amagnetic susceptibility-i.e., mineralized bone and water in the marro w spaces. Structural analyses performed by means of NMR microscopy and digital image processing indicated that the variation in R2' is close ly related to the trabecular microstructure. Mean trabecular plate den sity measured along the direction of the magnetic field was found to p lay a major role in predicting R2' (r = 0.74; P < 0.0001). This behavi or was confirmed when the plate density was varied in individual speci mens, which was achieved by rotating the specimen, making use of the b one's structural anisotropy. It is concluded that the NMR transverse r elaxation rate in human cancellous bone of the spine is significantly determined by trabecular structural parameters relevant to biomechanic al strength. The results further underscore the important role played by the transverse trabeculae in contributing to cancellous bone streng th. The work has implications on possible in vivo use of quantitative magnetic resonance for the assessment of fracture risk in osteoporotic patients.