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目的通过检测MRI的空间几何失真程度大小,研究其直接用于放疗计划设计的可行性。方法自制油脂管按每15°间隔辐射状排列置于泡沫模体内,制成模体1;自制油脂管按2.7cm间距网格状排列置于泡沫模体内,制成模体2。以Marconi1.5T超导型磁共振仪采用头部FSET2WI序列,分别对2个模体行平行于辐射状和网格状油脂管冠位面扫描和垂直于上述各面的横断位扫描,然后进行冠状面DRR重建。将获得的图像分为不同大小的5个视窗范围,测量直接扫描图像和DRR图像的边界绝对位置误差并计算其几何畸变率。结果对直接扫描的MRI,在11cm×11cm的视窗范围内,其边界最大位置误差基本为零;在22cm×22cm视窗内,其边界最大位置误差仅为1.1mm;在27.5cm×27.5cm的视窗范围内,其边界最大位置误差为1.4mm。对冠状面DRR重建图像,在16.5cm×16.5cm的视窗范围内,其边界最大位置误差<1.0mm;在22cm×22cm视窗范围内,其边界最大位置误差为1.4mm;在27.5cm×27.5cm的视窗范围内,其边界最大位置误差为2.0mm。结论对高场强的磁共振仪,在假定组织为均匀密度的前提下,MRI可以直接用于颅内肿瘤的放疗计划设计。
Objective To investigate the feasibility of direct planning for radiotherapy by detecting the degree of spatial geometric distortion in MRI. Methods Self-made grease tubes were arranged radially in the foam mold body at every 15 ° intervals to form a mold body 1. Self-made grease tubes were arranged in a foam mold body at grid spacing of 2.7 cm to form a mold body 2. The Marconi1.5T superconducting magnetic resonance instrument using the head FSET2WI sequence, respectively, on the two phantom parallel to radial and grid-shaped oil tube coronal plane scan and perpendicular to the above-mentioned transverse scan plane, and then Coronal DRR reconstruction. The obtained image is divided into 5 window ranges of different sizes, and the absolute position error of the direct scan image and the DRR image is measured and its geometric distortion rate is calculated. Results For the direct scanning MRI, the maximum position error of the boundary was almost zero in the window of 11cm × 11cm. The maximum position error of the boundary in the 22cm × 22cm window was only 1.1mm. In the 27.5cm × 27.5cm window Within the range, the maximum position error of its boundary is 1.4mm. For the coronal DRR reconstruction images, the maximum position error of the boundary is less than 1.0mm within the window of 16.5cm × 16.5cm; the maximum position error of the boundary is 1.4mm within the window of 22cm × 22cm; Of the window, the maximum position of the boundary error of 2.0mm. CONCLUSIONS For high-field magnetic resonance imaging, MRI can be directly applied to the planning of radiotherapy for intracranial tumors on the premise that the tissue is uniform density.