Etezadi-Amoli Maryam, Stang Pascal, Kerr Adam, Pauly John, Scott Greig
Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA.
Magn Reson Med. 2015 Mar;73(3):1315-27. doi: 10.1002/mrm.25187. Epub 2014 Apr 1.
The development of catheters and guidewires that are safe from radiofrequency (RF) -induced heating and clearly visible against background tissue is a major challenge in interventional MRI. An interventional imaging approach using a toroidal transmit-receive (transceive) coil is presented. This toroidal transceiver allows controlled, low levels of RF current to flow in the catheter/guidewire for visualization, and can be used with conductive interventional devices that have a localized low-impedance tip contact.
Toroidal transceivers were built, and phantom experiments were performed to quantify transmit power levels required for device visibility and to detect heating hazards. Imaging experiments in a pig cadaver tested the extendibility to higher field strength and nonphantom settings. A photonically powered optically coupled toroidal current sensor for monitoring induced RF currents was built, calibrated, and tested using an independent image-based current estimation method.
Results indicate that high signal-to-noise ratio visualization is achievable using milliwatts of transmit power-power levels orders of magnitude lower than levels that induce measurable heating in phantom tests. Agreement between image-based current estimates and RF current sensor measurements validates sensor accuracy.
The toroidal transceiver, integrated with power and current sensing, could offer a promising platform for safe and effective interventional device visualization.
开发在介入式磁共振成像（MRI）中能避免因射频（RF）感应发热且在背景组织中清晰可见的导管和导丝是一项重大挑战。本文提出一种使用环形发射 - 接收（收发）线圈的介入成像方法。这种环形收发器能使受控的低水平射频电流在导管/导丝中流动以实现可视化，并且可与具有局部低阻抗尖端接触的导电介入设备配合使用。
构建了环形收发器，并进行了体模实验，以量化设备可见性所需的发射功率水平并检测发热风险。在猪尸体上进行的成像实验测试了该方法在更高场强和非体模环境下的可扩展性。构建了一个用于监测感应射频电流的光供电光耦合环形电流传感器，使用基于独立图像的电流估计方法进行校准和测试。
结果表明，使用毫瓦级的发射功率即可实现高信噪比的可视化，该功率水平比在体模测试中引起可测量发热的水平低几个数量级。基于图像的电流估计与射频电流传感器测量结果之间的一致性验证了传感器的准确性。
集成了功率和电流传感功能的环形收发器可为安全有效的介入设备可视化提供一个有前景的平台。
