MRI of the prostate: potential role of robots

Every year, 220,000 new cases of prostate cancer are detected. Approximately 18% of these cases will be treated with brachytherapy [1,2]. Over 1.2 million prostate needle biopsies are carried out every year in the USA. Systematic transrectal ultrasound (TRUS)-guided biopsy is the most frequently used technique for detecting prostate cancer and is the most commonly used method for guiding brachytherapy. Several robotic systems have been proposed for TRUS-guided brachytherapy [3–7]. However, TRUS-guided biopsy has only a 32–43% detection rate [8,9], and needle deflection and seed misplacement may go unnoticed during the biopsy. Presently, with prostate cancer being detected at an earlier stage, most prostate cancers tend to be isoechoic to the surrounding healthy prostatic tissue imaging. MRI provides more detailed anatomical images of the prostate compared with TRUS imaging [10]. Therefore, for the purpose of intervention in the prostate gland, diagnostic or therapeutic, MRI guidance offers the possibility of more precise targeting that may be crucial to the success of prostate interventions. However, access within the scanner is limited for manual instrument handling and the magnetic resonance (MR) environment is the most demanding among all imaging equipment with respect to the instrumentation used. A solution to this problem is the use of MR-compatible robots, specifically designed to operate within the constrained space and environmental restrictions of the MR scanner, enabling real-time interventions. Building an MR-compatible robot is a very challenging engineering task, because, in addition to the material restrictions that MR instruments have, the robot requires actuators and sensors that have limited interference with the magnetic field of the MR scanner. Several important design problems must be overcome before a successful MR-compatible robot application can be built. A number of MR-compatible robots, ranging from simple manipulators to a fully automated system, have been developed proposing various solutions to the design challenge. Several systems have already been tested clinically for prostate biopsy and brachytherapy. As technology matures, precise image guidance for prostate interventions performed or assisted by specialized MR-compatible robotic devices may provide a uniquely accurate solution for guiding the intervention directly based on MR findings and feedback. Such an instrument would become a valuable clinical tool for biopsies directly targeting imaged tumor foci and delivering tumor-centered focal therapy. Prostate cancer is the most frequently diagnosed malignancy in the male population. Transrectal ultrasoundguided biopsy is still the imaging modality of choice in detecting prostate cancer. However, with prostate cancer being detected at an earlier stage, most prostate cancers tend to be isoechoic to the surrounding healthy prostatic tissue and, therefore invisible, resulting in transrectal ultrasound-guided biopsy having a positive predictive value of only 15.2%. MRI of the prostate has a superior soft-tissue contrast resolution, high spatial resolution and multiplanar capability. The ability to localize prostate cancer with MRI provides an opportunity to utilize magnetic resonance (MR) guidance for prostate biopsy. A number of MR-compatible robots, ranging from a simple manipulator to a fully automated system, have been developed to biopsy suspicious prostate cancer areas. When combining MRI with fast imaging sequences, it is possible to track the needle or organ deformation in real time. As technology matures, precise image guidance for prostate interventions performed or assisted by specialized MR-compatible robotic devices may provide a uniquely accurate solution for guiding the intervention, directly based on MR findings and feedback. Such an instrument would become a valuable clinical tool for biopsies directly targeting imaged tumor foci and for delivering tumor-centered focal therapy.