Structure, biomechanical competence, and incremental NMR line broadening (R') of water in the intertrabecular spaces of cancellous bone were examined on 22 cylindrical specimens from the lumbar vertebral bodies 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 R' for a wide range of values corresponding to cancellous bone of very different morphologic composition. NMR line broadening is caused by the inhomogeneity of the magnetic field induced as a consequence of the coexistence of two adjacent phases of different diamagnetic susceptibility-i.e., mineralized bone and water in the marrow spaces. Structural analyses performed by means of NMR microscopy and digital image processing indicated that the variation in R' is closely related to the trabecular microstructure. Mean trabecular plate density measured along the direction of the magnetic field was found to play a major role in predicting Rj (r = 0.74; P < 0.0001). This behavior was confirmed when the plate density was varied in individual specimens, which was achieved by rotating the specimen, making use of the bone's structural anisotropy. It is concluded that the NMR transverse relaxation rate in human cancellous bone of the spine is significantly determined by trabecular structural parameters relevant to biomechanical strength. The results further underscore the important role played by the transverse trabeculae in contributing to cancellous bone strength. The work has implications on possible in vivo use of quantitative magnetic resonance for the assessment of fracture risk in osteoporotic patients.It is widely accepted that the mechanical strength of the skeleton in vertebrates is largely determined by the material density of trabecular bone, generally referred to as bone mineral density (BMD). Osteopenia, characterized by a loss in bone mass, leads to impaired bone strength, which, in turn, has been associated with atraumatic vertebral fractures suffered by patients with osteoporosis (1). The association between bone strength and BMD has been suggested by a large number of studies, with bone strength statistically showing a quadratic dependence on density (2). However, in vivo BMD measurements by either quantitative computed tomography or dual-energy x-ray absorptiometry do not very well predict fracture risk in osteoporotic patients (3).More recently, the search for a better predictor of bone strength, and thus fracture risk, has shifted toward trabecular bone morphology (4-8). Kleerekoper (5) found in a study in which postmenopausal women with vertebral fractures were compared to age-matched normal women of equal mean BMD that osteoporotics had significantly lower trabecular plate density and, as a corollary, higher trabecular plate thickness. The data were interpreted as suggesting that anThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accorda...

Two conceptually related variable-flip-angle 3D spin-echo pulse sequences were designed for imaging at voxel sizes of 2-5 x 10(-3) mm3 corresponding to pixel areas of less than 100 x 100 microns2 and section thicknesses on the order of 300-400 microns on a conventional 1.5 T MR imaging system equipped with 1 G/cm imaging field gradients, providing 12 sections in 10 min imaging time. The pulse sequences make use of the concept of restoring longitudinal magnetization inverted by the 180 degrees phase reversal pulse and are derivatives of pulse sequences previously dubbed "FATE" and "RASEE." It is shown that even in the small-voxel regime (< 10(-2) mm3 voxel size) and at echo times on the order of 10 ms, gradient echo images are sensitive to intrinsic fields causing artifactual boundary effects, including signal loss from intravoxel phase scrambling and spatial mismapping. At this resolution the variable flip-angle spin-echo pulse sequences are demonstrated to be better suited for imaging magnetically heterogeneous systems such as trabecular bone microstructure in vivo. These pulse sequences are found to be substantially less sensitive to distortions from magnetic dipole fields occurring at the boundaries of two phases of different magnetic permeability.

A magnetostatic model consisting of a tetragonal lattice of struts of diamagnetic material, mimicking vertebral trabecular bone, was developed. The model allows estimation of the magnetic field histogram within the lattice's unit cell as a function of geometric parameters. The field was computed analytically from the induced magnetic surface charge density on the faces of the struts. The contribution from the induced magnetic field to the effective transverse relaxation rate, R2', was obtained as the mean decay rate of the Fourier transformed histograms, for both fixed and randomly oriented lattices. The model predicts the field distribution to increase with both strut thickness and density, paralleling material density. Finally, significant changes in R2' are predicted at constant material density, in that the field distribution widens with simultaneously increasing strut number density and decreasing strut thickness.

The evolution time of ADC is faster for TI than for WI. This difference, which likely originates from the different pathophysiologic and hemodynamic features of the two infarction types, might account for the relatively large range of ADC values reported for the time course of ischemic strokes.

The LWR had a positive correlation with the age, while the lipid LW had a positive correlation with BMD, even after controlling the age factor. The bone marrow lipid water content and metabolism acted as important roles in the internal environment of bone and influenced bone mineralization.