Pre-treatment MR-guided Stereotactic Histotripsy

Stereotactic MRI Histotripsy System

Objective: Histotripsy uses B-mode imaging as real-time guidance to monitor therapy. However, tumors are often indistinguishable with ultrasound, thus reducing histotripsy accuracy for tumor ablation. We tested a stereotactic system that uses pre-treatment MR for treatment planning. This system leverages the tumor imaging capability of MRI and deep tissue targeting of histotripsy.

Methods: A stereotactic fusion system for small-animal histotripsy treatment (Figure 1A) was designed to have: 1) a stereotactic frame with two MRI fiducial markers to co-register MR images and two screws on the frame to rigidly secure the subject, and 2) a treatment bed that fixes the frame and co-registers the histotripsy transducer. Custom treatment planning software allowed users to outline the treatment zone on pre-treatment MRI scans and create treatment focus grids. This system was tested on 7 red blood cell (RBC) clot phantoms. A single point lesion was created in the clots. Post-treatment MR images were used to compare the ablated to prescribed point targets to determine the accuracy.

Result: Differences between the centers of prescribed and ablation point targets (figure 1B) were 0.53±0.43mm in lateral direction and less than 0.1mm in axial direction.

Conclusion: The stereotactic MRI system displayed mm accuracy on phantoms. We plan to investigate the effectiveness of this system in vivo Glioblastoma mice models and later address the impact of breathing motion on targeting when ablating abdominal regions.

Figure 1: System Features (1A) and MR-guided histotripsy result on RBC phantom (1B). Blue dot indicates the prescribed point (left) which is the center of the clot, and the red asterisk (right) indicates the ablated point.