Transcranial MRI-guided Histotripsy Targeting Using MR-thermometry and MR-ARFI

Objective: Transcranial magnetic resonance imaging (MRI)-guided histotripsy has been demonstrated to treat various locations in in vivo swine brain through a human skull. To ensure that the histotripsy treatment is delivered to the intended target location, accurate pre-treatment targeting is necessary. In this work, we investigate the feasibility of MR-thermometry and MR-acoustic radiation force imaging (MR-ARFI) to perform pre-treatment targeting of histotripsy in ex vivo bovine brain through a human skull. Methods: A 700 kHz, 128-element MR-compatible histotripsy array was used to generate histotripsy and toneburst sonications. The array's electronic drivers were modified to also generate low-amplitude tone-burst sonications to perform MR-thermometry and MR-ARFI-based targeting. Twelve ex vivo bovine brains were treated with histotripsy at 35 MPa, 75 MPa and through a skull at 36 MPa. Before treating the tissue, both MR-ARFI and MRthermometry were used to estimate the lesion location. Finally, the location of the histotripsy lesion was compared with the focus estimated by MR-thermometry and MR-ARFI. Results: MR-thermometry and MR-ARFI were able to successfully perform pre-treatment targeting of histotripsy using the modified histotripsy array driver. Histotripsy focus was estimated with mean absolute errors along the transverse/longitudinal axis of 2.06/2.95 mm and 2.13/2.51 mm for MR-ARFI and MR-thermometry, respectively. The presence of the human skull reduced the pressure at the focal region, but it did not compromise the targeting accuracy of either of the two methods with a mean absolute error of 1.10/2.91 mm and 1.29/2.91 mm for MR-ARFI and MR-thermometry, respectively. Conclusion: This study demonstrated that transcranial histotripsy pre-treatment targeting is feasible with MR-thermometry and MR-ARFI.