Characterization of Image-based Refocusing for Transcranial Therapies

Transcranial focused ultrasound (tFUS) has the potential to provide precision ultrasonic targeting of brain circuits in the treatment neurological disorders. However, this potential is severely limited by FUS beam distortions through the skull. We have previously demonstrated the feasibility of using dual-mode ultrasound array (DMUA) capabilities to perform refocusing based on target identification on DMUA imaging. Furthermore, we have demonstrated improved refocusing when the target echoes are sufficiently coherent, as measured using a focusing data matrix (FDM) evaluated from raw channel data. The objective of this study is to characterize this geometric refocusing-aberration correction method and extend its use. Specifically, refocusing off of coherent echoes in the vicinity of the intended target as identified on DMUA imaging. In vitro transskull experiments were performed with sample skulls placed in the path of DMUA focused beams. Beam distortions were characterized using 2D hydrophone scans in planes orthogonal to the FUS beam axis before and after refocusing. The results provide experimental verification of the improved focusing gain achieved when refocusing at the target or points in its vicinity. The improvement was in the range of 3 7 dB for a variety of target locations with respect to the skull−suture lines.