Evaluation of 3D image registration as applied to MR-guided thermal treatment of liver cancer

There are many potential applications of three-dimensional (3D) image regis tration in MR-guided radiofrequency (RF) thermal ablation of tumors. For ex ample, after registration of image volumes obtained before and after therma l ablation, a variety of quantitative and visual assessments of therapy wer e performed, For liver tumors, the accuracy of rigid body, manual registrat ion on 19 pairs of image volumes was evaluated, almost all of which were ob tained during thermal treatment sessions. Registration error was estimated as a distance between anatomical landmarks, including both internal vascula r structures as well as the surface of the Liver. Over all image pairs and throughout a large portion of the liver, the registration error was 3.1 mm (mean + I SD), From the bottom to the top of the liver, error increased on the order of 13%, probably because of liver motion and deformation resultin g from respiration, Although probably insufficient for blind guidance of th erapy, registration accuracy was undoubtedly sufficient for interesting app lications in the planning, assessment, and optimization of interventional M R-guided thermal treatment of liver tumors.