A histotripsy targeting approach using a mobile C-arm

Abstract

Histotripsy is an emerging noninvasive, nonthermal, and nonionizing tumor treatment, which uses focused ultrasound to mechanically destroy tissue. Currently, targeting is performed using ultrasound imaging, which can be operator dependent. Additionally, many tumors cannot be seen or are poorly visualized on ultrasound due to obstructions, patient size, location, or echogenicity. In these cases, energy delivery for histotripsy treatment may still be possible if alternative targeting techniques are available. In this study, a mobile C-arm based targeting approach is presented, where a tumor can be selected on a 3D cone beam CT (CBCT) and automatically targeted using a histotripsy system with a robotic arm. To this end, a hand-eye calibration technique between a mobile C-arm and robotic arm was developed, where a CBCT and eight 2D x-ray acquisitions of a calibration phantom in different poses were acquired. The phantom poses in the CBCT coordinate system were estimated using a 2D/3D pose estimation approach and the corresponding robot end effector poses in the robot coordinate system were determined from the joint angles. A dual quaternion approach was then used to determine the relationship between C-arm and robot. During treatment, the histotripsy transducer can be aligned on a target using the calibrated robotic arm. Nine dual-modality soft-tissue mimicking phantoms were treated, and the resulting treatment zones were manually segmented from post-treatment CBCTs as reference. The average Euclidean distance between planned and actual treatment centers was 0.81 ± 0.45mm. This approach could considerably increase the number of patients that could benefit from histotripsy treatment, reduce operator dependency, and facilitate clinical translation of histotripsy.