Evaluation of a perineal access device for MRI-guided prostate interventions

Abstract

This paper describes a perineal access tool for MRI-guided prostate interventions and evaluates it using a phantom study. The development of this device has been driven by the clinical need and a close collaboration effort. The device seamlessly fits into the workflow of MRI-guided prostate procedures such as cryoablation and biopsies. It promises a significant cut in the procedure time, accurate needle placement, lower number of insertions, and a potential for better patient outcomes. The current embodiment includes a frame which is placed next to the perineum and incorporates both visual and MRI-visible markers. These markers are automatically detected both in MRI and by a pair of stereo cameras (optical head) allowing for automatic optical registration. The optical head illuminates the procedure area and can track instruments and ultrasound probes. The frame has a window to access the perineum. Multiple swappable grids may be placed in this window depending on the application. It is also possible to entirely remove the grid for freehand procedures. All the components are designed to be used inside the MRI suite. To test this system, we built a custom phantom with MRI visible targets and planned 21 needle insertions with three grid types using the SCENERGY software. With an average insertion depth of about 85 mm, the average error of needle tip placement was 2.74 mm. We estimated the error by manually segmenting the needle tip in post-insertion MRIs of the phantom and comparing that to the plan.