Mr-guided biopsy of the prostate: an overview of techniques and a systematic review

Mr-guided biopsy of the prostate: an overview of techniques and a systematic review - Next to digital rectal examination and PSA level, biopsy of the prostate is an essential procedure for determining optimal treatment. Systematic TRUSBx is the gold standard, but it fails to detect numerous tumors. This systematic approach is characterized by low sensitivity (39-52%) and high specificity (81-82%).

The role of magnetic resonance (MR) imaging in the detection of prostate cancer is increasing but profoundly debated. Anatomical T2-weighted MR imaging has been disappointing in detecting and localizing prostate cancer, with an estimated sensitivity of 60% to 96%. Various MR imaging techniques, such as proton MR spectroscopy and dynamic contrast-enhanced MR imaging, have been applied for more accurate detection, localization, and staging of prostate cancer. Also diffusion-weighted MR imaging is increasingly used, which may lead to increased prostate cancer detection rates.

Using diagnostic MR images during an MR-directed biopsy procedure improves quality of the biopsy. In open MR scanners, the prebiopsy MR images often must be registered to the real-time biopsy images because open MR scanners do not provide optimal tissue contrast; thus, the patient must first be examined in a closed MR scanner and then biopsied in an open scanner. The advantage of open MR over closed MR is that the physician has easy patient access.

Closed MR scanners can be used for the prebiopsy scan as well as for the biopsy procedure. Because operating room is limited within the closed MR scanner, robots are used to perform the biopsy. These robots may not interfere with the images obtained using the MR scanner. For this reason, ferromagnetic and electronic devices cannot be used inside the magnet. These challenges exclude manual and traditional electromechanical robot handling of the biopsy needle. Therefore, numerous new methods and devices have been developed including real-time, in-scanner guidance methods to operate the devices. Most robots studied in this review have a manual positioning system, which means that the patient has to be removed from the scanner in order to correct the position. The mechanically powered robots can be adjusted from outside the scanner. Needle insertion has to be executed manually in all investigated robots.

Unfortunately, little is known about the accuracy of the robots. The MR detection rates after one negative biopsy round using MR-guided biopsy ranged between 38% and 55.5%.

The clinical value of MR-guided prostate biopsy lies in the fact that a high percentage of prostate cancers can be depicted using an targeted biopsy technique, eliminating unnecessary systematic prostate biopsies for patients with elevated PSA levels and repeated tumor-negative TRUSBx.

Extensive clinical studies are still essential to review the value of MR compatible robots. One of the largest challenges in taking biopsies of the prostate is the correction for movements of the prostate tissue during the biopsy procedure. Research is needed to design and evaluate techniques for determining and reducing these motions.

In conclusion the combination of a diagnostic MR examination and MR-guided biopsy is a promising tool and may be used in patients with previous negative TRUSBx.

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