Mohammadjavadi Morteza, Ash Ryan T, Glover Gary H, Pauly Kim Butts
Department of Radiology, Stanford University, Stanford, California, USA.
Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, California, USA.
Magn Reson Med. 2025 May 6. doi: 10.1002/mrm.30539.
MR acoustic radiation force imaging (MR-ARFI) is an exceptionally promising technique to non-invasively confirm targeting accuracy and estimate exposure of low-intensity transcranial focused ultrasound applications. Implementing MR-ARFI in the human brain has been hindered by (1) sensitivity to subject motion, and (2) insufficient SNR at low (<1.0 MPa) ultrasound pressures. The purpose of this study was to optimize human MR-ARFI to allow reduced ultrasound exposure while at the same time being robust to bulk and physiological motion.
We developed a novel timeseries approach to MR-ARFI with a single-shot spiral-out MRI sequence and correction for respiratory and cardiac motion artifacts. An MR-compatible four-element 500 kHz focused ultrasound transducer was coupled to the head and targeted to 60 mm depth in five participants. During spiral scans, two 6 ms focused ultrasound pulses (0.5-0.9 MPa in situ) were delivered in on-off blocks of 25 time frames.
Our method generates ARFI maps that with correction are largely immune to bulk and pulsatile brain motion with reduced scan time (80 s per acquisition). Robust ARFI signals were observed at the expected target in four human participants, using low intensity ultrasound that does not produce significant tissue heating, confirmed both by simulation and MR thermometry.
Single shot spiral MR-ARFI is motion robust in human applications, provides reduction in ultrasound exposure, and reduced scan time, enabling iteration for image-guided targeting. This provide persuasive proof-of-principle that MR-ARFI can be used as a tool to guide ultrasound-based precision neural circuit therapeutics.
磁共振声辐射力成像（MR-ARFI）是一种极具前景的技术，可用于非侵入性地确认靶向准确性，并估计低强度经颅聚焦超声应用的暴露情况。在人类大脑中实施MR-ARFI受到以下两个因素的阻碍：（1）对受试者运动敏感；（2）在低（<1.0 MPa）超声压力下信噪比不足。本研究的目的是优化人类MR-ARFI，以减少超声暴露，同时对整体和生理运动具有鲁棒性。
我们开发了一种新颖的MR-ARFI时间序列方法，采用单次螺旋出射MRI序列，并对呼吸和心脏运动伪影进行校正。将一个与MR兼容的四元件500 kHz聚焦超声换能器与头部耦合，并在五名参与者中靶向60 mm深度。在螺旋扫描期间，在25个时间帧的开关块中发送两个6 ms的聚焦超声脉冲（原位0.5-0.9 MPa）。
我们的方法生成的ARFI图经过校正后，在很大程度上不受大脑整体和搏动运动的影响，且扫描时间缩短（每次采集80秒）。在四名人类参与者的预期目标处观察到了鲁棒的ARFI信号，使用的低强度超声不会产生明显的组织加热，这通过模拟和MR测温法得到了证实。
单次螺旋MR-ARFI在人体应用中对运动具有鲁棒性，可减少超声暴露并缩短扫描时间，从而实现图像引导靶向的迭代。这提供了有说服力的原理证明，即MR-ARFI可用作指导基于超声的精确神经回路治疗的工具。
