Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA, United States of America. UCSF Physics Research Laboratory, 185 Berry Street, Suite 350, San Francisco, CA 94143-0946, United States of America. Author to whom any correspondence should be addressed.
Phys Med Biol. 2018 Sep 10;63(18):185002. doi: 10.1088/1361-6560/aada26.
Respiratory motion causes misalignments between positron emission tomography (PET) and magnetic resonance (MR)-derived attenuation maps (µ-maps) in addition to artifacts on both PET and MR images in simultaneous PET/MRI for organs such as liver that can experience motion of several centimeters. To address this problem, we developed an efficient MR-based attenuation correction (MRAC) method to generate phase-matched µ-maps for quiescent period PET (PET) in abdominal PET/MRI. MRAC data was acquired with CIRcular Cartesian UnderSampling (CIRCUS) sampling during 100 s in free-breathing as an accelerated data acquisition strategy for phase-matched MRAC (MRAC). For comparison, MRAC data with raster (Default) k-space sampling was also acquired during 100 s in free-breathing (MRAC), and used to evaluate MRAC as well as un-matched MRAC (MRAC) that was un-gated. We purposefully oversampled the MRAC data to ensure we had enough information to capture all respiratory phases to make this comparison as robust as possible. The proposed MRAC was evaluated in 17 patients with Ga-DOTA-TOC PET/MRI exams, suspected of having neuroendocrine tumors or liver metastases. Effects of CIRCUS sampling for accelerating a data acquisition were evaluated by simulating the data acquisition time retrospectively in increments of 5 s. Effects of MRAC on PET were evaluated using uptake differences in the liver lesions (n = 35), compared to PET with MRAC and MRAC. A Wilcoxon signed-rank test was performed to compare lesion uptakes between the MRAC methods. MRAC showed higher image quality compared to MRAC for the same acquisition times, demonstrating that a data acquisition time of 30 s was reasonable to achieve phase-matched µ-maps. Lesion update differences between MRAC (30 s) versus MRAC (reference, 100 s) were 0.1% ± 1.4% (range of -2.7% to 3.2%) and not significant (P > .05); while, the differences between MRAC versus MRAC were 0.6% ± 11.4% with a large variation (range of -37% to 20%) and significant (P < .05). In conclusion, we demonstrated that a data acquisition of 30 s achieved phase-matched µ-maps when using specialized CIRCUS data sampling and phase-matched µ-maps improved PET quantification significantly.
呼吸运动导致正电子发射断层扫描 (PET) 和磁共振 (MR) 衍生衰减图 (µ-图) 之间的不匹配，此外，在用于肝脏等可经历几厘米运动的器官的同时 PET/MR 中，PET 和 MR 图像上也会出现伪影。为了解决这个问题，我们开发了一种高效的基于磁共振的衰减校正 (MRAC) 方法，为腹部 PET/MR 中的静止期 PET (PET) 生成相匹配的 µ-图。MRAC 数据是在自由呼吸期间使用圆周笛卡尔欠采样 (CIRCUS) 采集的，作为相匹配 MRAC (MRAC) 的加速数据采集策略。作为比较，在自由呼吸期间也使用光栅 (默认) k-空间采样采集了 MRAC 数据 (MRAC)，并用于评估 MRAC 以及未门控的未匹配 MRAC (MRAC)。我们有意地对 MRAC 数据进行过采样，以确保我们有足够的信息来捕获所有呼吸相，从而使这种比较尽可能稳健。在 17 名疑似神经内分泌肿瘤或肝转移的 Ga-DOTA-TOC PET/MRI 检查患者中评估了拟议的 MRAC。通过以 5 s 的增量回顾性模拟数据采集时间，评估 CIRCUS 采样对加速数据采集的影响。通过比较肝脏病变的摄取差异 (n = 35)，与具有 MRAC 和 MRAC 的 PET 一起，评估 MRAC 对 PET 的影响。对 MRAC 方法之间的病变摄取进行了 Wilcoxon 符号秩检验。与 MRAC 相比，MRAC 在相同的采集时间内显示出更高的图像质量，表明 30 s 的数据采集时间可以实现相匹配的 µ-图。与 MRAC (30 s) 相比，MRAC (参考，100 s) 的病变更新差异为 0.1% ± 1.4% (范围为 -2.7% 至 3.2%)，无显著差异 (P >.05)；而，MRAC 与 MRAC 之间的差异为 0.6% ± 11.4%，差异较大 (范围为 -37% 至 20%)，具有显著差异 (P <.05)。总之，我们证明了当使用专门的 CIRCUS 数据采样和相匹配的 µ-图时，30 s 的数据采集可以实现相匹配的 µ-图，并且相匹配的 µ-图可以显著提高 PET 定量的准确性。
