Department of Diagnostic and Interventional Radiology, Leipzig University Hospital, Leipzig, Germany.
Magn Reson Imaging. 2012 Apr;30(3):371-81. doi: 10.1016/j.mri.2011.10.006. Epub 2012 Jan 13.
To determine whether a greatly reduced spatial resolution of fully reconstructed projection MR images can be used for the simultaneous 3D localization of multiple MR-visible markers and to assess the feasibility of a subsecond position tracking for clinical purposes.
Miniature, inductively coupled RF coils were imaged in three orthogonal planes with a balanced steady-state free precession (SSFP) sequence and automatically localized using a two-dimensional template fitting and a subsequent three-dimensional (3D) matching of the coordinates. Precision, accuracy, speed and robustness of 3D localization were assessed for decreasing in-plane resolutions (0.6-4.7 mm). The feasibility of marker tracking was evaluated at the lowest resolution by following a robotically driven needle on a complex 3D trajectory.
Average 3D precision and accuracy, sensitivity and specificity of localization ranged between 0.1 and 0.4 mm, 0.5 and 1.0 mm, 100% and 95%, and 100% and 96%, respectively. At the lowest resolution, imaging and localization took ≈350 ms and provided an accuracy of ≈1.0 mm. In the tracking experiment, the needle was clearly depicted on the oblique scan planes defined by the markers.
Image-based marker localization at a greatly reduced spatial resolution is considered a feasible approach to monitor reference points or rigid instruments at subsecond update rates.
确定完全重建投影磁共振图像的空间分辨率大大降低是否可用于同时定位多个磁共振可见标记物，并评估亚秒级位置跟踪用于临床目的的可行性。
使用平衡稳态自由进动（SSFP）序列对三个正交平面中的微型感应耦合射频线圈进行成像，并使用二维模板拟合和随后的三维（3D）坐标匹配自动定位。对于降低的平面分辨率（0.6-4.7 毫米），评估了 3D 定位的精度、准确性、速度和鲁棒性。在最低分辨率下，通过跟踪机器人驱动的针在复杂的 3D 轨迹上，评估了标记跟踪的可行性。
定位的平均 3D 精度和准确性、灵敏度和特异性范围分别为 0.1-0.4 毫米、0.5-1.0 毫米、100%-95%和 100%-96%。在最低分辨率下，成像和定位需要约 350 毫秒，提供的准确性约为 1.0 毫米。在跟踪实验中，标记定义的斜扫描平面上可以清晰地显示针。
基于图像的标记物在大大降低的空间分辨率下的定位被认为是一种可行的方法，可以以亚秒级的更新速率监测参考点或刚性器械。
