1 Department of Radiology, Division of Nuclear Medicine, NYU Langone Medical Center, 660 First Ave, 3rd Fl, New York, NY 10016.
AJR Am J Roentgenol. 2013 Nov;201(5):1120-3. doi: 10.2214/AJR.13.11305.
The purpose of this study was to compare the accuracy of the spatial registration of conventional PET/CT with that of hybrid PET/MRI of patients with FDG-avid metastatic lesions.
Thirteen patients with known metastatic lesions underwent FDG PET/CT followed by PET/MRI with a hybrid whole-body system. The inclusion criterion for tumor analysis was spherical or oval FDG-avid tumor clearly identified with both CT and MRI. The spatial coordinates (x, y, z) of the visually estimated centers of the lesions were determined for PET/CT (PET and CT independently) and PET/MRI (PET, T1-weighted gradient-echo sequence with radial stack-of-stars trajectory, T2-weighted sequence), and the b0 images of an echo-planar imaging (EPI) diffusion-weighted imaging (DWI) acquisition. All MRI sequences were performed in the axial plane with free breathing. The spatial coordinates of the estimated centers of the lesions were determined for PET and CT and PET and MRI sequences. Distance between the isocenter of the lesion on PET images and on the images obtained with the anatomic modalities was measured, and misregistration (in millimeters) was calculated. The degree of misregistration was compared between PET/CT and PET/MRI with a paired Student t test.
Nineteen lesions were evaluated. On PET/CT images, the average of the total misregistration in all planes of CT compared with PET was 4.13 ± 4.24 mm. On PET/MR images, lesion misregistration between PET and T1-weighted gradient-echo images had a shift of 2.41 ± 1.38 mm and between PET and b0 DW images was 5.97 ± 2.83 mm. Similar results were calculated for 11 lesions on T2-weighted images. The shift on T2-weighted images compared with PET images was 2.24 ± 1.12 mm. Paired Student t test calculations for PET/CT compared with PET/MRI T1-weighted gradient-echo images with a radial stack-of-stars trajectory, b0 DW images, and T2-weighted images showed significant differences (p < 0.05). Similar results were seen in the analysis of six lung lesions.
PET/MRI T1-weighted gradient-echo images with a radial stack-of-stars trajectory and T2-weighted images had more accurate spatial registration than PET/CT images. This may be because that the whole-body PET/MRI system used can perform simultaneous acquisition, whereas the PET/CT system acquires data sequentially. However, the EPI-based b0 DWI datasets were significantly misregistered compared with the PET/CT datasets, especially in the thorax. Radiologists reading PET/MR images should be aware of the potential for misregistration on images obtained with EPI-based DWI sequences because of inherent spatial distortion associated with this type of MRI acquisition.
本研究旨在比较常规 PET/CT 与 FDG 摄取转移病灶的杂交 PET/MRI 的空间配准准确性。
13 例已知转移病灶的患者接受了 FDG PET/CT 检查，随后使用全身混合系统进行了 PET/MRI。肿瘤分析的纳入标准为 CT 和 MRI 均清晰显示出球形或椭圆形 FDG 摄取病灶。为 PET/CT（PET 和 CT 分别）和 PET/MRI（PET、具有径向星堆轨迹的 T1 加权梯度回波序列、T2 加权序列）以及扩散加权成像（DWI）采集的 EPI b0 图像确定视觉估计病灶中心的空间坐标（x、y、z）。所有 MRI 序列均在自由呼吸的轴位进行。确定了 PET 和 CT 以及 PET 和 MRI 序列中估计病灶中心的空间坐标。测量了 PET 图像和解剖学模态图像上病灶等中心点之间的距离，并计算了配准误差（以毫米为单位）。使用配对学生 t 检验比较 PET/CT 和 PET/MRI 之间的配准误差程度。
评估了 19 个病灶。在 PET/CT 图像上，与 PET 相比，所有 CT 平面的总配准误差的平均值为 4.13 ± 4.24 mm。在 PET/MR 图像上，PET 与 T1 加权梯度回波图像之间的病灶配准偏差为 2.41 ± 1.38 mm，而 PET 与 b0 DW 图像之间的偏差为 5.97 ± 2.83 mm。在 T2 加权图像上也计算了 11 个病灶的类似结果。与 PET 图像相比，T2 加权图像的偏差为 2.24 ± 1.12 mm。与 PET/MRI T1 加权梯度回波图像（具有径向星堆轨迹）、b0 DW 图像和 T2 加权图像相比，配对学生 t 检验计算表明差异具有统计学意义（p < 0.05）。在对 6 个肺部病变的分析中也观察到了类似的结果。
与 PET/CT 图像相比，具有径向星堆轨迹的 PET/MRI T1 加权梯度回波图像和 T2 加权图像具有更准确的空间配准。这可能是因为所使用的全身 PET/MRI 系统可以进行同时采集，而 PET/CT 系统则进行顺序采集。然而，基于 EPI 的 b0 DWI 数据集与 PET/CT 数据集相比明显配准错误，尤其是在胸部。阅读 PET/MR 图像的放射科医生应该意识到，由于与这种类型的 MRI 采集相关的固有空间失真，基于 EPI 的 DWI 序列获得的图像可能存在配准错误的潜在风险。
