MR compatibility, safety and accuracy of the redesigned UMC Utrecht single needle implant device

Purpose - The Utrecht single needle implant device was redesigned to increase needle insertion velocity. The purpose of this study is to evaluate the Magnetic Resonance compatibility, safety and accuracy of the implant device preparing its application in a patient study to investigate the feasibility of inserting a brachytherapy needle into the prostate to a defined tumour target point. Methods - Several experiments were performed to evaluate the mechanical and radiofrequency safety of the needle system, the magnetic field perturbation, the calibration of the implant device in the MR coordinate system, functioning of the implant device during imaging and accuracy of needle insertion. Results - Endurance experiments showed the mechanical safety of the needle system. Magnetic field perturbation was acceptable with induced image distortions smaller than 0.5 mm for clinical MR sequences. Calibration of the implant device in the MR coordinate system was reproducible with average error (mean±standard deviation) of 0.2±0.4 mm, 0.1±0.3 mm and 0.6 ±0.6 mm in the x, y- and z- direction, respectively. The RF safety measurement showed for clinical MR imaging sequences maximum temperature rises of 0.2 C at the entry and tip points of the needle. Simultaneous functioning of the implant device and imaging is possible albeit with some intensity band artefacts in the fast field echo images. Finally, phantom measurements showed deviations amounting 2.5-3.6 mm measured as target-to-needle distance at a depth of 12 cm. Conclusions - This preclinical evaluation showed that the MR compatibility, safety and accuracy of the redesigned UMC Utrecht single needle implant device allow its application in a patient study on the feasibility of inserting a brachytherapy needle into the prostate to a defined tumour target point.