Internal Three Dimensional Strains in Human Intervertebral Discs Under Axial Compression Quantified Noninvasively by Magnetic Resonance Imaging and Image Registration

Abstract

Study objectives were to develop, validate, and apply a method to measure threedimensional (3D) internal strains in intact human discs under axial compression. A custombuilt loading device applied compression and permitted loadrelaxation outside of the magnet while also maintaining compression and hydration during imaging. Strain was measured through registration of 300 خ¼m isotropic resolution images. Excellent registration accuracy was achieved, with 94% and 65% overlap of disc volume and lamellae compared to manual segmentation, and an average Hausdorff, a measure of distance error, of 0.03 and 0.12 mm for disc volume and lamellae boundaries, respectively. Strain maps enabled qualitative visualization and quantitative regional annulus fibrosus (AF) strain analysis. Axial and circumferential strains were highest in the lateral AF and lowest in the anterior and posterior AF. Radial strains were lowest in the lateral AF, but highly variable. Overall, this study provided new methods that will be valuable in the design and evaluation surgical procedures and therapeutic interventions.