Purpose: Magnetic resonance imaging (MRI)-guided focal laser ablation (FLA) is an emerging, minimally invasive treatment for prostate cancer, which involves the therapy and monitoring of localized regions to preserve critical structures and healthy tissues. Accurate needle delivery is pivotal to the therapeutic success of FLA. We present a mechatronic-assisted MRI-guided needle delivery system for prostate FLA allowing for in-bore needle positioning. This work aims to validate its free-space and in-bore needle positioning accuracy, and to demonstrate its utility in prostate phantoms.
Methods: A compact MRI-conditional mechatronic system was developed with non-ferromagnetic components with actuation controlled by piezoelectric motors and optical encoders. It enables four degrees-of-freedom for transperineal positioning and an adaptable needle-guide. The needle-guide is remotely actuated, and needles are manually inserted for FLA to retain clinician expertise during the workflow. Needle positioning accuracy over the range-of-motion was assessed via free-space and in-bore MRI experiments (GE Discovery MR750 3T MRI) to virtual targets and the needle tip error was quantified. Prostate phantom experiments were performed to a 10.0cm needle insertion depth and needle tip error and needle trajectory error were quantified. Needle tracks were manually segmented on gradient recalled-echo (GRE) 3T-MRI images.
Results: Free-space and in-bore needle positioning resulted in a mean needle tip error (SD) of 0.80±0.36mm (N=40) and 2.11±1.05mm (N=25), respectively. Preliminary phantom studies show a mean needle tip error and needle trajectory error of 2.61±0.62mm and 0.32±0.62° (N=10), respectively. This error enables an accurate FLA ablation radius of 3.02mm, within a 95% confidence interval and under the intended MRI acquisition parameters.
Conclusion: We demonstrated the utility of a mechatronics-assisted system for MRI-guided prostate FLA. Preliminary prostate phantom studies show potential for accurate and precise MRI-guided needle delivery to localized focal zones, while maintaining manual needle insertion to improve safety with haptic feedback and optimizing MRI-guided FLA workflow.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the Ontario Institute for Cancer Research (OICR) Imaging Program, the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Canadian Institutes of Health Research (CIHR).
Thermal Ablation, MRI, Image-guided Therapy