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The purpose of this study was to demonstrate the use of a transrectal system that enables precise magnetic resonance (MR) image guidance and monitoring of prostate interventions. The system used a closed-bore 1.5-T MR imaging unit and enables one to take advantage of the higher signalto-noise ratio achieved with traditional magnet designs, which is crucial for accurate targeting and monitoring of prostate interventions. In the first of the four canine studies, reliable needle placement, with all needles placed within 2 mm of the desired target site, was achieved. In two other studies, MR imaging was used to monitor distribution of injected contrast agent solution (gadopentetate dimeglumine mixed with trypan blue dye) in and around the prostate, thereby confirming that solution had been delivered to the desired tissue and also detecting faulty injections. In the final study, accurate placement and MR imaging of brachytherapy seeds in the prostate were demonstrated. The described system provides a flexible platform for a variety of minimally invasive MR image-guided therapeutic and diagnostic prostate interventions. Index termsMagnetic resonance (MR), experimental studies; Magnetic resonance (MR), guidance; Prostate neoplasms, MR; Prostate neoplasms, therapeutic radiology Prostate carcinoma is the most commonly diagnosed life-threatening cancer in men in the United States. In 2002, the estimated incidence of this disease in male patients in the United States was 189,000 (1). As the incidence of prostate cancer is known to increase with age, this cancer will become more common as the U.S. population ages (2). Moreover, due to the widespread acceptance of prostate-specific antigen screening, routine rectal examination, and transrectal ultrasono-graphic (US) image-guided prostate biopsy, there has been a great increase in the early detection of prostate cancer (3). © RSNA, 2003Address correspondence to E.A. (eatalar@mri.jhu.edu). Author contributions:Guarantors of integrity of entire study, R.C.S., A.K., G.F., E.A.; study concepts, R.C.S., A.K., L.L.W., G.F., E.A.; study design, all authors; literature research, R.C.S.; experimental studies, R.C.S., A.K., A.T., G.F., E.A.; data acquisition, R.C.S., A.K., A.T., G.F., E.A.; data analysis/interpretation, R.C.S., A.K.; manuscript preparation, R.C.S.; manuscript definition of intellectual content, R.C.S., A.K., L.L.W., G.F., E.A.; manuscript editing, R.C.S.; manuscript revision/review, R.C.S., J.A.D., G. Currently, the two most accepted methods for treatment of localized prostate cancer are radical prostatectomy and radiation therapy (10). Although both of these approaches are associated with a good chance of a cure, they are also associated with a substantial risk of morbidity, including incontinence, rectal toxicity, and erectile dysfunction (11). Owing to these conflicting factors, there have been increased efforts to develop focal minimally invasive treatment modalities that can be used to target cancerous tissue while reducing morbidity and treatment duration...

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We present the proof-of-concept prototype of a prostate biopsy robot to be used inside a conventional high-field MRI scanner. A three degree-offreedom (DOF) mechanical device translates and rotates inside the rectum and enters a needle into the body, and steers the needle to a target point pre-selected by the user. The device is guided by real-time images from the scanner. Networked computers process the medical images and enable the clinician to control the motion of the mechanical device that is operated remotely from outside the imager. The system is also applicable to localized prostate therapy and also demonstrates potential in other intra-cavitary procedures.