Fast 3D registration of multimodality tibial images with significant structural mismatch

ABSTRACT Recently, micro-magnetic resonance imaging ( P MRI) in conjunction with micro-finite element analysis has shown great potential in estimating mechanical properties – stiffness and elastic moduli – of bone in patients at risk of osteoporosis. Due to limited spatial resolution and signal-to-noise ratio achievable in vivo , the validity of estimated properties is often established by comparison to those derived from high-resolution micro-CT ( P CT) images of cadaveric specimens. For accurate comparison of mechanical parameters derived from P MR and P CT images, analyzed 3D volumes have to be closely matched. The alignment of the micro structure (and th e cortex) is often hampered by the fundamental differences of P MR and P CT images and variations in marrow content and corti cal bone thickness. Here we present an intensity cross-correlation based registration algorithm coupled with segmentation for registering 3D tibial specimen images acquired by µMRI and P CT in the context of finite-element modeling to assess the bone’s mechanical constants. The algorithm first generates three translational and three ro tational parameters required to align segmented µMR and P CT images from sub regions with high micro-structural similarities. These transformation parameters are then used to register the grayscale P MR and P CT images, which include both the cortex and trabecular bone. The intensity cross-correlation maximization based registration algorithm descri bed here is suitable for 3D rigid-body image registration applications where through-plane rotations are known to be relatively small. The close alignment of the resulting images is demonstrated quantitatively based on a voxel-overlap meas ure and qualitatively using visual inspection of the micro structure. Keywords: Multimodality registration, P MRI, P CT, Bone strength, Trabecular b one, Cortical bone, Biomechanics