Osteoporosis is a disease characterized by bone volume loss and architectural deterioration. The majority ofwork aimed at evaluating the structural implications of the disease has been performed based on stereologicanalysis of histomorphometric sections. Only recently noninvasive imaging methods have emerged thatprovide sufficient resolution to resolve individual trabeculae. In this article, we apply digital topologicalanalysis (DTA) to magnetic resonance microimages (m-MRI) of the radius obtained at 137×137×350 mm³ voxel size in a cohort of 79 women of widely varying bone mineral density (BMD) and vertebral deformitystatus. DTA is a new method that allows unambiguous determination of the three-dimensional (3D) topologyof each voxel in a trabecular bone network. The analysis involves generation of a bone volume fraction map,which is subjected to subvoxel processing to alleviate partial volume blurring, followed by thresholding andskeletonization. The skeletonized images contain only surfaces, profiles, curves, and their mutual junctions asthe remnants of trabecular plates and rods after skeletonization. DTA parameters were compared withintegral BMD in the lumbar spine and femur as well as MR-derived bone volume fraction (BV/TV). Vertebraldeformities were determined based on sagittal MRIs of the spine with a semiautomatic method and thenumber of deformities counted after threshold setting. DTA structural indices were found the strongestdiscriminators of subjects with deformities from those without deformities. Subjects with deformities (n=29) had lower topological surface (SURF) density (p<0.0005) and surface-to-curve ratio (SCR; a measure of theratio of platelike to rodlike trabeculae; p<0.0005) than those without. Profile interior (PI) density, a measureof intact trabecular rods, was also lower in the deformity group (p<0.0001). These data provide the first invivo evidence for the structural implications inherent in postmenopausal osteoporosis accompanying bone loss,that is, the conversion of trabecular plates to rods and disruption of rods due to repeated osteoclasticresorption.
Keywords: trabecular bone; structure; topological analysis; magnetic resonance imaging; vertebral deformities