Sagiyama Koji, Watanabe Yuji, Kamei Ryotaro, Shinyama Daiki, Baba Shingo, Honda Hiroshi
Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
Department of Molecular Imaging and Diagnosis, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
Magn Reson Imaging. 2016 Apr;34(3):345-52. doi: 10.1016/j.mri.2015.10.037. Epub 2015 Dec 2.
The aim of this study was to investigate the effects of MR parameters on tissue segmentation and determine the optimal MR sequence for attenuation correction in PET/MR hybrid imaging. Eight healthy volunteers were examined using a PET/MR hybrid scanner with six three-dimensional turbo-field-echo sequences for attenuation correction by modifying the echo time, k-space trajectory in the phase-encoding direction, and image contrast. MR images for attenuation correction were obtained from six MR sequences in each session; each volunteer underwent four sessions. Two radiologists assessed the attenuation correction maps generated from the MR images with respect to segmentation errors and ghost artifacts on a five-point scale, and the scores were decided by consensus. Segmentation accuracy and reproducibility were compared. Multiple regression analysis was performed to determine the effects of each MR parameter. The two three-dimensional turbo-field-echo sequences with an in-phase echo time and radial k-space sampling showed the highest total scores for segmentation accuracy, with a high reproducibility. In multiple regression analysis, the score with the shortest echo time (-3.44, P<0.0001) and Cartesian sampling in the anterior/posterior phase-encoding direction (-2.72, P=0.002) was significantly lower than that with in-phase echo time and Cartesian sampling in the right/left phase-encoding direction. Radial k-space sampling provided a significantly higher score (+5.08, P<0.0001) compared with Cartesian sampling. Furthermore, radial sampling improved intrasubject variations in the segmentation score (-8.28%, P=0.002). Image contrast had no significant effect on the total score or reproducibility. These results suggest that three-dimensional turbo-field-echo MR sequences with an in-phase echo time and radial k-space sampling provide improved MR-based attenuation correction maps.
本研究的目的是探讨磁共振（MR）参数对组织分割的影响，并确定PET/MR混合成像中衰减校正的最佳MR序列。使用PET/MR混合扫描仪对8名健康志愿者进行检查，采用六个三维涡轮场回波序列，通过改变回波时间、相位编码方向的k空间轨迹和图像对比度来进行衰减校正。在每个检查环节从六个MR序列中获取用于衰减校正的MR图像；每位志愿者接受四个检查环节。两名放射科医生以五点量表评估由MR图像生成的衰减校正图的分割误差和鬼影伪影，并通过协商确定分数。比较分割准确性和可重复性。进行多元回归分析以确定每个MR参数的影响。具有同相回波时间和径向k空间采样的两个三维涡轮场回波序列在分割准确性方面显示出最高总分，且具有高可重复性。在多元回归分析中，具有最短回波时间（-3.44，P<0.0001）以及在前后相位编码方向上的笛卡尔采样（-2.72，P=0.002）的分数显著低于具有同相回波时间以及在左右相位编码方向上的笛卡尔采样的分数。与笛卡尔采样相比，径向k空间采样的分数显著更高（+5.08，P<0.0001）。此外，径向采样改善了分割分数的受试者内变异（-8.28%，P=0.002）。图像对比度对总分或可重复性没有显著影响。这些结果表明，具有同相回波时间和径向k空间采样的三维涡轮场回波MR序列可提供改进的基于MR的衰减校正图。
