New architectural parameters derived from micro-MRI for the prediction of trabecular bone strength

This article reviews recent progress in magnetic resonance microimaging of cancellous bone in vitro and in vivo from the perspective of the authors' laboratory. It is shown that in particular in vivo the key technical prerequisites to satisfy are: (i) achieving sufficient signal-to-noise ratio (SNR) to allow for adequate spatial resolution; (ii) the image processing algorithms have to be robust enough to provide accurate structural information in the limited spatial resolution regime, i.e., in the presence of inevitable partial volume blurring and noise. The practical lower limit of voxel size in vivo was found to be about 6 x 10^-3 mm³ in the radius, and about 10^-4 mm³ for small specimens in vitro with state-of-the-art equipment and scan times of 10 and 30 minutes, resp., and SNR ~ 10. Finally, data are presented highlighting the potential of these methods for predicting the bone's elastic modulus in vitro and fracture risk in vivo.