HoloLens augmented reality system for transperineal free-hand prostate procedures

Purpose: An augmented reality (AR) system was developed to facilitate free-hand real-time needle guidance for transperineal prostate (TP) procedures and to overcome the limitations of a traditional guidance grid.

Approach: The HoloLens AR system enables the superimposition of annotated anatomy derived from preprocedural volumetric images onto a patient and addresses the most challenging part of free-hand TP procedures by providing real-time needle tip localization and needle depth visualization during insertion. The AR system accuracy, or the image overlay accuracy ( $n=56$ ), and needle targeting accuracy ( $n=24$ ) were evaluated within a 3D-printed phantom. Three operators each used a planned-path guidance method ( $n=4$ ) and free-hand guidance ( $n=4$ ) to guide needles into targets in a gel phantom. Placement error was recorded. The feasibility of the system was further evaluated by delivering soft tissue markers into tumors of an anthropomorphic pelvic phantom via the perineum.

Results: The image overlay error was $1.29\pm 0.57\mathrm{mm}$ , and needle targeting error was $2.13\pm 0.52\mathrm{mm}$ . The planned-path guidance placements showed similar error compared to the free-hand guidance ( $4.14\pm 1.08\mathrm{mm}$ versus $4.20\pm 1.08\mathrm{mm}$ , $p=0.90$ ). The markers were successfully implanted either into or in close proximity to the target lesion.

Conclusions: The HoloLens AR system can provide accurate needle guidance for TP interventions. AR support for free-hand lesion targeting is feasible and may provide more flexibility than grid-based methods, due to the real-time 3D and immersive experience during free-hand TP procedures.