MRI for the Assessment of Histotripsy Ablation in a Canine Osteosarcoma Comparative Oncology Model.

Abstract

OBJECTIVE: To explore the use of MRI for evaluation of mechanical focused ultrasound (histotripsy) ablation in spontaneous canine osteosarcoma (OS) as a comparative oncology model of human OS. METHODS: A retrospective analysis was conducted on MR images from a veterinary clinical trial, with the purpose of using canine OS as a preclinical model in which to study human OS. Eight dogs received histotripsy treatment to a portion of their tumor, with pre- and post-treatment MRI (pre- and post-contrast T1- and T2-weighted). Dogs then received standard-of-care surgical resection. Qualitative assessments included characterization of ablation on MRI, gross anatomy, and histopathology. Quantitative assessments included measurements of ablation on MRI and gross anatomy, as well as scoring tumor bone production in untreated tumor on MRI and histopathology to compare tumor composition assessments across modalities. RESULTS: Contrast-enhanced sequences with and without subtraction reliably visualized histotripsy ablation. For all dogs, the ablation zone was visible as a nonenhancing, hypointense region. There was a significant decrease in normalized mean signal intensity of the targeted tumor region from pre- to post-histotripsy. No significant differences were found between MRI and gross measurements of ablation dimensions and volume. Histopathology confirmed ablation in the targeted regions as identified grossly and on MRI, and tumor bone composition assessments on MRI and histopathology had a significant positive correlation. CONCLUSIONS: MRI is a valuable tool for the assessment of histotripsy ablation in OS and builds upon the potential of histotripsy as a non-invasive therapy for bone tumors in dogs and humans.