Magnetic Resonance Imaging Guidance Method of Low‐Intensity Transcranial Focused Ultrasound for Deep Brain Neuromodulation

ABSTRACT Low‐Intensity Transcranial Focused Ultrasound (LITFU) is a highly anticipated non‐invasive neuromodulation technique in terms of targeting accuracy, spatial resolution, stimulation depth, and reversibility. However, LITFU still faces challenges, most notably is and the reduced precision in deep tissue targeting and limited stimulation depth due to the distortion of the acoustic field by the skull. This study proposes a method for using a rectangular concave ultrasonic transducer to achieve deep brain stimulation with LITFU under Magnetic Resonance Imaging Acoustic Radiation Force Imaging guidance. First, k‐Wave simulation modeling is performed by the skull magnetic resonance imaging (MRI) with ultrashort echo time (UTE) sequence to calculate the acoustic pressure distribution and the maximum value within the tissue. Then, the time required for maximum tissue displacement is calculated using a biological tissue elastic deformation model. Based on the displacement and time, the motion encoding gradient is optimized to obtain a more distinct phase contrast. We validated the feasibility of this method on water‐filled balloons and ex vivo porcine brains, provided the optimized ultrasonic delay time coefficient, and achieved precise LITFU focusing on the amygdala located deep within the human volunteers. The results demonstrate that the rectangular transducer achieves a maximum stimulation depth of 80 mm with a maximum peak acoustic pressure of 3 MPa. The simulated and ARFI measured acoustic fields were compared and their consistency and differences were demonstrated. The improved EPI‐ARFI significantly enhances measurement sensitivity and reduces scanning time to 24 s and three‐dimensional imaging can be achieved. This work provides a localization and verification method for LITFU guided by MRI, deep brain stimulation of LITFU in future clinical applications.