MRI Method Developments for Stand-Alone MRI and CT Fiducial-Based Registration

Warren Foltz¹, Vickie Kong¹, Siddharta Baxi¹, Varadarajan Kumar¹, Peter Chung¹, David Jaffray¹, Cynthia Mnard¹

MRI and CT fiducial-based registration for prostate radiation therapy requires MR images which clearly display both implanted gold fiducial markers and the prostate boundary. However, stand-alone acquisitions of standard diagnostic techniques do no accomplish both of these tasks reliably at 1.5 Tesla. Consequently, fiducial-sensitive images and anatomical images for contouring are acquired in separate acquisitions, which increases protocol duration and compromises the registration process to prostate motion. This abstract introduces strategies which provide T2 or T2-like contrast for contouring, yet provide a moderate amplification of gold fiducial markers, utilizing the frequency response of ssfp and the off-resonance blur function of spiral imaging. A preliminary experiment validated an inconsistent visualization of gold 'seeds' in standard diagnostic T2-weighted images via retrospective review. A second experiment demonstrated that spiral and ssfp strategies provide consistent fiducial visibility with an adequate contrast for contouring.