Room: Exhibit Hall
Purpose: Histotripsy is a form of therapeutic ultrasound that liquefies tissue mechanically via the formation of bubble clouds, and is being developed for the treatment of prostate pathologies, deep vein thrombosis, liver cancer, and fetal septal defects. The action of bubble clouds can be visualized in real time using diagnostic ultrasound imaging, whereas changes in tissue structure are most readily visualized with magnetic resonance (MR) imaging. In this study, MR and diagnostic ultrasound imaging were combined to assess histotripsy treatment progress in a tissue-mimicking phantom.
Methods: Porcine red blood cell layers were embedded in an agar phantom. For each layer, a 1-MHz focused source was utilized to apply histotripsy pulses of 5 cycle duration and peak negative pressures between 13 and 24 MPa. During the therapeutic excitation, acoustic emissions generated by the bubble cloud were tracked with passive cavitation images, and the grayscale value recorded with plane wave B-mode imaging. Following the excitation, histotripsy liquefaction zones were visualized with T1, T2, and diffusion weighted imaging in a 3T MR scanner. The phantom was then sectioned and liquefaction zones were registered with the diagnostic ultrasound and MR images.
Results: The spatial location of diagnostic ultrasound and MR imaging signatures correlated well with gross observation of phantom liquefaction. However, the spatial location of intense bubble cloud activity did not correlate with the largest changes in MR imaging intensity. The structure of the liquefaction zone as visualized with T2-weighted MR imaging was observed to change as the peak negative pressure increased beyond 21 MPa, indicating a shift in the resultant bubble cloud dynamics.
Conclusion: These results indicate that diagnostic ultrasound and MR imaging provide complimentary sets of information about histotripsy-generated liquefaction, and may provide improved assessment of the treatment zone.
Not Applicable / None Entered.