Magnetic Resonance Imaging monitoring of histotripsy effects in agar phantom

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Abstract
Background: While the technical aspects of histotripsy have seen significant advancements, research on Magnetic Resonance Imaging (MRI) monitoring remains limited. Purpose: This preliminary study explored the use of conventional T2‐Weighted (T2‐W) Turbo Spin Echo (TSE) imaging to monitor histotripsy lesions in a pure agar gel, as a potential research tool for MRI‐guided histotripsy (MRgHt). Methods: Histotripsy experiments were conducted in a 3T MRI scanner using a 2% weight per volume agar solution in water. Pulsed Focused Ultrasound (FUS) was applied at a duty factor of 2%, with a pulse repetition period of 1s, delivering up to 2000 pulses. T2‐W TSE imaging was employed for intra‐procedural monitoring with 10s updates and post‐sonication assessment, with the first prioritizing rapid acquisition and the second focusing on resolution. Supplementary, MR thermometry tracked temperature variations throughout the procedure. Results: Dynamic T2‐W TSE imaging provided insights into the progress of phantom disruption. Mild thermal effects served as early signs of phantom response, as mechanical effects required more time to manifest. Typical histotripsy lesion characteristics were observed, including a hyperintense core with an elongated shape and a thin hypointense border. The developed temperatures remained well below hyperthermia levels, reaching a maximum of 34°C. Conclusions: The presented methodology, utilizing a pure agar gel within a simple, versatile setup alongside conventional T2‐W TSE imaging, holds promise for advancing MRgHt research.

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