Spreter Felix, Fischer Johannes, Özen Ali Caglar, Maier Alexander, Bock Michael, Reiss Simon
Division of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
Department of Cardiology and Angiology, University Heart Center Freiburg-Bad Krozingen, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
Magn Reson Med. 2025 Oct;94(4):1663-1671. doi: 10.1002/mrm.30589. Epub 2025 Jun 4.
Intra-arterial spin labeling (iASL) applies a labeling pulse from a transmit coil at the tip of the catheter for regional myocardial perfusion measurements during MR-guided catheterizations. This study investigates the labeling efficiency of catheter-mounted coils under varying conditions to enable robust iASL measurements.
The labeling efficiency was assessed by analytical calculations, numerical simulations, and in vitro measurements at 3 T. Analytical solutions were provided for various simplified field distributions, and a numerical simulation was used to calculate for different catheter coil designs using the Biot-Savart Law. Using these fields, the RF excitation of the blood magnetization flowing around the catheter was calculated using the Bloch equation. Finally, in vitro measurements were performed in a flow phantom using loop and solenoid catheter coils.
fields produced by the catheter coils result in a saturation of the mean magnetization when the applied pulse exceeds a threshold power. This threshold power varies between 1 and 25 mW for different coil designs, flow velocities, and geometric parameters.
iASL creates a saturation that is robust against variations in flow and coil positioning. The simulations could determine the threshold pulse power for robust iASL excitation, which needs to be adapted to applications in different vessels. Thus, iASL may provide an efficient alternative to perfusion measurements with exogenous contrast agents during MR-guided interventions.
动脉内自旋标记（iASL）在磁共振引导下的导管插入术中，通过位于导管尖端的发射线圈施加标记脉冲，以测量局部心肌灌注。本研究调查了在不同条件下导管安装线圈的标记效率，以实现可靠的iASL测量。
通过分析计算、数值模拟和3T场强下的体外测量来评估标记效率。针对各种简化的场分布提供了解析解，并使用毕奥-萨伐尔定律对不同导管线圈设计进行数值模拟计算。利用这些场，使用布洛赫方程计算导管周围流动血液磁化的射频激发。最后，在流动模型中使用环形和螺线管导管线圈进行体外测量。
当施加的脉冲超过阈值功率时，导管线圈产生的场会导致平均磁化饱和。对于不同的线圈设计、流速和几何参数，该阈值功率在1至25毫瓦之间变化。
iASL产生的饱和对血流和线圈位置的变化具有鲁棒性。模拟可以确定可靠的iASL激发的阈值脉冲功率，这需要根据不同血管的应用进行调整。因此，iASL可能为磁共振引导介入期间使用外源性造影剂进行灌注测量提供一种有效的替代方法。
