MRI-Guided Prostate Motion Tracking using Multislice-to-Volume Registration

MRI-guided prostate needle biopsy requires compensation for organ motion between target planning and needle placement. Two questions are studied and answered in this work: is rigid registration sufficient in tracking the targets with a maximum error of 3 mm (smaller than average prostate tumor size) and how many intra-operative slices are required to obtain this accuracy? We developed rigid and deformable multisliceto-volume registration algorithms for tracking the biopsy targets within the prostate. Three orthogonal plus additional transverse intra-operative slices were acquired in the approximate center of the prostate and registered with a high-resolution target planning volume. Simulated intra-operative data, phantom data, and MRI-guided robotic prostate biopsy data were used to assess tracking accuracy. Registration tests on simulated intra-operative data with 3, 4, and 5 slices were performed to evaluate the effect on registration error and time. Results: Using three orthogonal slices provides sufficient accuracy. Convergence test results on phantom images demonstrated 100% success rate for initial misalignment of 5mm. Average registration errors for the patient data were 2.55mm and 2.05mm for the rigid and deformable algorithms, respectively. The algorithm was able to capture rigid biopsy target displacements of maximum 8mm and non-rigid displacements of maximum 1.5mm. Rigid tracking appears to be promising. Deformable registration does not seem warranted. i