Trabecular structure assessment in lumbar vertebrae specimens using quantitative magnetic resonance imaging and relationship with mechanical competence.

Abstract

The purpose of this study was to use quantitative magnetic resonance imaging (MRI; high-resolution [HR] and relaxometry) to assess trabecular bone structure in lumbar vertebrae specimens and to compare these techniques with bone mineral density (BMD) in predicting stress values obtained from mechanical tests. Fourteen vertebral midsagittal sections from lumbar vertebrae L3 were obtained from cadavers (aged 22-76 years). HR images with a slice thickness of 300 microm and an in-plane spatial resolution of 117 microm2 x 117 microm2 were obtained. Transverse relaxation time T2' distribution was measured by using an asymmetric spin-echo (ASE) sequence. Traditional morphometric measures of bone structure such as apparent trabecular bone fraction (app. BV/TV), apparent trabecular bone number (app. Tb.N), apparent trabecular bone separation (app. Tb.Sp), and apparent trabecular bone thickness (app. Tb.Th) as well as the directional mean intercept length (MIL) were calculated. Additionally, BMD measurements of these sections were obtained by dual-energy X-ray absorptiometry (DXA) and biomechanical properties such as directional stress values (to fracture) were determined on adjacent specimens. With the exception of T2', all morphological parameters correlated very well with age, BMD, and stress values (R between 0.79 and 0.92). However, in the direction perpendicular to the magnetic field, T2' values enhanced the adjusted R2 correlation value with horizontal (M/L) stress values in addition to BMD from 0.70 to 0.91 (p < 0.05).