T1-weighted MRI as a substitute to CT for skull aberration correction in transcranial focused ultrasound: in vivo feasibility and in vitro comparison on human calvaria

CT scans have been used to refocus ultrasoundfor clinical transcranial MRI-guided focused ultrasound(TcMRgFUS). The refocusing of the ultrasoundarrays is a crucial step in TcMRgFUS therapy because skulls distort sound beams due to the ununiformed shape and composition of the bone. CT scan based algorithms have been developed to estimate the phase shifts induced by the bone. The corresponding phase conjugatedsignals are then emitted by ultrasoundarrays to be refocused on brain targets through the skull. However, CT scans elongate the TcMRgFUS treatment process and expose patients to ionizing radiation. This study tested three different MRI pulse sequences(T1, T2, and proton density) against CT to determine if MRI data could be a viable alternative to CT for planning ultrasoundrefocusing in TcMRgFUS.