Abstract No. 52 Mobile C-Arm–Guided Histotripsy: Assessment of Image Quality in an In Vivo Porcine Model

Abstract

Histotripsy is an emerging focal tumor therapy that mechanically destroys tissue through focused ultrasound (US). To date, histotripsy has been guided by diagnostic US, which may limit visualization of tumors if obstructed by bone or gas. An alternative guiding approach has been successfully demonstrated using a fixed C-arm which provides sufficient image quality to accurately target tumors and assess histotripsy treatment zones. This study evaluates the feasibility of visualizing histotripsy treatment zones using an iso-centric, flat-panel based mobile C-arm, a more accessible and affordable imaging device. Histotripsy treatments (∼2 cm diameter) were performed in the liver and kidney of two ∼50kg swine with a 700 kHz multi-element therapy transducer and system (HistoSonics) guided by a mobile C-arm (CIOS, Siemens Healthineers). Post-treatment 3D cone-beam CT (CBCT) images were acquired with intravenous contrast with the mobile and a fixed C-arm system (Artis zee, Siemens) with and without a 12-14 L coupling water bath (WB). Image pairs from the fixed and mobile C-arms were registered using manually selected landmarks. Contrast and contrast-to-noise ratios (CNR) were measured using similar regions of interest in the treatment zone and background tissue. To compare treatment zone size and shapes, these were segmented and—to avoid registration errors—aligned about their centroids. The overlap between mobile/fixed C-arm pairs was quantified using the Dice Coefficient (DC, perfect overlap = 1). All treatments were visible in both mobile and fixed C-arm acquisitions. The corresponding CNRs with WB ranged from 2.0 to 7.2 for the mobile and from 1.7 to 3.8 for the fixed C-arm (Table 1). On average, CNRs observed for the kidney (4.1 ± 2.2) were higher than for the liver (2.3 ± 0.62). The lowest grayscale contrast was observed in the liver with WB, which was 44.5 and 79.2 AU for the mobile and fixed C-arm respectively. Comparing treatment overlap resulted in a DC of 0.91 ± 0.05 (range, 0.82 to 0.95). A mobile C-arm demonstrated sufficient image quality to distinguish histotripsy treatment zones from surrounding tissue, even with the attenuating WB present. Treatments in mobile and fixed C-arm images were similar in size/shape. This study supports further investigation of the clinical feasibility of histotripsy guidance with a mobile C-arm.