Robust registration and phantom validation of mechatronics-assisted MRI-guided needle delivery for prostate focal laser ablation therapy

Magnetic resonance imaging (MRI)-guided prostate focal laser ablation (FLA) therapy shows potential as a minimally invasive treatment method for localized prostate cancer, which minimizes overtreatment of surrounding structures, thereby improving quality of life. We previously developed an MRI-compatible mechatronic guidance system capable of needle positioning within an open-air and in-bore MRI environment. In comparison to open-air testing, an increased error was reported from in-bore experiments, suggesting the effects of image distortion, fiducial localization, and registration error may impact its accuracy. In this paper, we describe the design of an improved registration multi-fiducial for the robust registration of the mechatronic system to MRI, and comparison and validation of MRI-guided needle delivery to virtual targets (simulating localized focal zones) in tissue-mimicking prostate phantoms. The multi-fiducial structure is composed of thirty-six MR-spheres arranged across an extensive volume. Mechatronics-assisted MRI-guided needle delivery (N = 10) to virtual targets were evaluated with tissue-mimicking phantoms. 3T MRI images were acquired for registration, the mechatronic system was remotely actuated and needle insertion was performed, then verification images were acquired. The needle tip and needle trajectory error were quantified between the planned and actual trajectories. Our preliminary results show significant improvements in needle targeting with the improved registration fiducial with an FLA ablation region radius of 2.0 mm within 95% confidence. Improvements in robust registration show potential to enable accurate mechatronics-assisted MRI-guided needle delivery for FLA therapy.