Watanabe Yoichi, Lee Chung K, Gerbi Bruce J
Department of Therapeutic Radiology, University of Minnesota, Minneapolis, Minnesota, USA.
J Neurosurg. 2006 Dec;105 Suppl:190-3. doi: 10.3171/sup.2006.105.7.190.
The authors sought to evaluate and improve the geometrical accuracy of a 3-tesla magnetic resonance (MR) imaging unit used for Gamma Knife surgery (GKS).
To evaluate the geometrical accuracy of a Siemens Magnetom Trio 3-tesla MR imaging unit, two phantoms were used. Both phantoms were imaged with computed tomography (CT), a 1.5-tesla MR imaging unit (Siemens Avanto), and the 3-tesla MR imaging unit. A pair of orthogonal films was obtained with a radiotherapy simulator to validate the spatial coordinates of the marker positions determined with CT. The coordinates of the markers were measured using the GammaPlan treatment planning software. Magnetic resonance imaing was performed using three-dimensional (3D) magnetization-prepared rapid acquisition gradient echo (MPRAGE) and fast low-angle shot sequence (FLASH) pulse sequences. The voxel size was 1 x 1 x 1 mm3.
The root-mean-square error of MR images was 2 +/- 0.73 mm for 3D MPRAGE. The error was reduced to 1.5 +/- 0.64 mm for FLASH. The errors were decreased further by applying an image distortion correction method (the field-of-view filter) to the images acquired with FLASH. The mean errors were 1.3 +/- 0.39 mm and 1.5 +/- 0.77 mm for the two phantoms. The errors increased from 1 mm to 3.1 mm as the measurement points approached the caudal edge of the head coil (larger z value). Proper selection of a pulse sequence together with a geometrical distortion correction improved the geometrical accuracy of MR images. However, further study is needed to increase the geometrical accuracy of 3-tesla MR imaging units for radiosurgical applications.
作者旨在评估并提高用于伽玛刀手术（GKS）的3特斯拉磁共振（MR）成像设备的几何精度。
为评估西门子Magnetom Trio 3特斯拉MR成像设备的几何精度，使用了两个体模。两个体模均采用计算机断层扫描（CT）、1.5特斯拉MR成像设备（西门子Avanto）以及3特斯拉MR成像设备进行成像。使用放射治疗模拟器获得一对正交胶片，以验证通过CT确定的标记位置的空间坐标。使用伽玛刀治疗计划软件测量标记的坐标。采用三维（3D）磁化准备快速采集梯度回波（MPRAGE）和快速低角度激发序列（FLASH）脉冲序列进行磁共振成像。体素大小为1×1×1立方毫米。
对于3D MPRAGE，MR图像的均方根误差为2±0.73毫米。对于FLASH，该误差降至1.5±0.64毫米。通过对FLASH采集的图像应用图像失真校正方法（视野滤波器），误差进一步降低。两个体模的平均误差分别为1.3±0.39毫米和1.5±0.77毫米。随着测量点靠近头部线圈的尾缘（z值较大），误差从1毫米增加到3.1毫米。正确选择脉冲序列并结合几何失真校正可提高MR图像的几何精度。然而，对于放射外科应用，还需要进一步研究以提高3特斯拉MR成像设备的几何精度。
