Medical Physics in Radiology (E020), German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120, Heidelberg, Germany.
MAGMA. 2012 Feb;25(1):15-22. doi: 10.1007/s10334-011-0245-z. Epub 2011 Mar 4.
Proton resonance frequency shift thermometry is sensitive to breathing motion that leads to incorrect phase differences. In this work, a novel velocity-sensitive navigator technique for triggering MR thermometry image acquisition is presented.
A segmented echo planar imaging pulse sequence was modified for velocity-triggered temperature mapping. Trigger events were generated when the estimated velocity value was less than 0.2 cm/s during the slowdown phase in parallel to the velocity-encoding direction. To remove remaining high-frequency spikes from pulsation in real time, a Kalman filter was applied to the velocity navigator data. A phantom experiment with heating and an initial volunteer experiment without heating were performed to show the applicability of this technique. Additionally, a breath-hold experiment was conducted for comparison.
A temperature rise of ΔT = +37.3°C was seen in the phantom experiment, and a root mean square error (RMSE) outside the heated region of 2.3°C could be obtained for periodic motion. In the volunteer experiment, a RMSE of 2.7°C/2.9°C (triggered vs. breath hold) was measured.
A novel velocity navigator with Kalman filter postprocessing in real time significantly improves the temperature accuracy over non-triggered acquisitions and suggests being comparable to a breath-held acquisition. The proposed technique might be clinically applied for monitoring of thermal ablations in abdominal organs.
质子共振频率移动测温对导致相位差错误的呼吸运动敏感。在这项工作中，提出了一种新的用于触发磁共振测温图像采集的速度敏感导航技术。
对分段回波平面成像脉冲序列进行了修改，以便进行速度触发的温度测绘。当在与速度编码方向平行的减速阶段中估计的速度值小于 0.2 cm/s 时，生成触发事件。为了实时去除来自脉动的剩余高频尖峰，对速度导航器数据应用了卡尔曼滤波器。进行了加热的体模实验和没有加热的初始志愿者实验，以展示该技术的适用性。此外，还进行了一次屏气实验进行比较。
在体模实验中观察到 ΔT = +37.3°C 的温升，并且对于周期性运动，可以获得加热区域外的均方根误差 (RMSE) 为 2.3°C。在志愿者实验中，测量到的 RMSE 为 2.7°C/2.9°C（触发与屏气）。
具有实时卡尔曼滤波器后处理的新型速度导航器显著提高了触发采集相对于非触发采集的温度准确性，并表明与屏气采集相当。该技术可能在腹部器官热消融的监测中具有临床应用价值。
