A System for MR-Ultrasound Guidance during Robot-Assisted Laparoscopic Radical Prostatectomy

We describe a new ultrasound and magnetic resonance image guidance system for robot assisted radical prostatectomy and its first use in patients. This system integrates previously developed and new components and presents to the surgeon preoperative magnetic resonance images (MRI) registered to real-time 2D ultrasound to inform the surgeon of anatomy and cancer location. At the start of surgery, a trans-rectal ultrasound (TRUS) is manually positioned for prostate imaging using a standard brachytherapy stepper. When the anterior prostate surface is exposed, the TRUS, which can be rotated under computer control, is registered to one of the da Vinci patient-side manipulators by recognizing the tip of the da Vinci instrument at multiple locations on the tissue surface. A 3D TRUS volume is then taken, which is segmented semi-automatically. A segmentation-based, biomechanically regularized deformable registration algorithm is used to register the 3D TRUS image to preoperatively acquired and annotated T2-weighted images, which are deformed to the patient. MRI and TRUS images can then be pointed at and examined by the surgeon at the da Vinci console. We outline the approaches used and present our experience with the system in the first two patients. While this work is preliminary, the feasibility of fused MRI and TRUS during radical prostatectomy has not been demonstrated before. Given the significant rates of positive surgical margins still reported in the literature, such a system has potentially significant clinical benefits.