George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Micromachined Sensors and Transducers Group, Atlanta, Georgia, USA.
National Institutes of Health, National Heart Lung and Blood Institute, Bethesda, Maryland, USA.
Magn Reson Med. 2021 May;85(5):2904-2914. doi: 10.1002/mrm.28625. Epub 2020 Dec 21.
This work aims to demonstrate the use of an "active" acousto-optic marker with enhanced visibility and reduced radiofrequency (RF) -induced heating for interventional MRI.
The acousto-optic marker was fabricated using bulk piezoelectric crystal and π-phase shifted fiber Bragg grating (FBGs) and coupled to a distal receiver coil on an 8F catheter. The received MR signal is transmitted over an optical fiber to mitigate RF-induced heating. A photodetector converts the optical signal into electrical signal, which is used as the input signal to the MRI receiver plug. Acousto-optic markers were characterized in phantom studies. RF-induced heating risk was evaluated according to ASTM 2182 standard. In vivo real-time tracking capability was tested in an animal model under a 0.55T scanner.
Signal-to-noise ratio (SNR) levels suitable for real-time tracking were obtained by using high sensitivity FBG and piezoelectric transducer with resonance matched to Larmor frequency. Single and multiple marker coils integrated to 8F catheters were readout for position and orientation tracking by a single acousto-optic sensor. RF-induced heating was significantly reduced compared to a coax cable connected reference marker. Real-time distal tip tracking of an active device was demonstrated in an animal model with a standard real-time cardiac MR sequence.
Acousto-optic markers provide sufficient SNR with a simple structure for real-time device tracking. RF-induced heating is significantly reduced compared to conventional active markers. Also, multiple RF receiver coils connected on an acousto-optic modulator can be used on a single catheter for determining catheter orientation and shape.
本工作旨在展示一种具有增强可视性和降低射频（RF）诱导加热的“主动”声光标记物，用于介入 MRI。
声光标记物使用体压电晶体和π相移光纤布拉格光栅（FBG）制造，并与 8F 导管上的远端接收线圈耦合。接收到的磁共振信号通过光纤传输以减轻 RF 诱导加热。光电探测器将光信号转换为电信号，该电信号用作 MRI 接收器插件的输入信号。在体模研究中对声光标记物进行了表征。根据 ASTM 2182 标准评估了 RF 诱导加热风险。在 0.55T 扫描仪下的动物模型中测试了实时实时跟踪能力。
通过使用高灵敏度 FBG 和与拉莫尔频率匹配的压电换能器，获得了适合实时跟踪的信噪比（SNR）水平。单个和多个标记物线圈集成到 8F 导管上，通过单个声光传感器进行位置和方向跟踪读取。与连接参考标记的同轴电缆相比，RF 诱导加热显著降低。在动物模型中使用标准实时心脏磁共振序列演示了主动装置的实时远端尖端跟踪。
声光标记物具有简单的结构，可提供足够的 SNR，用于实时设备跟踪。与传统的主动标记物相比，RF 诱导加热显著降低。此外，连接在声光调制器上的多个 RF 接收线圈可用于单个导管上，以确定导管的方向和形状。
