Department of Radiology and Biomedical Imaging, University of California, San Francisco, 505 Parnassus Avenue, San Francisco, CA, 94143-0628, USA.
Department of Radiology, Stanford University School of Medicine, Stanford, CA, USA.
Abdom Radiol (NY). 2018 Mar;43(3):593-599. doi: 10.1007/s00261-017-1252-y.
To evaluate acquisition time and clinical image quality of a variable refocusing flip angle (vrf) single-shot fast spin echo (SSFSE) sequence in comparison with a conventional SSFSE sequence for imaging of liver lesions in patients undergoing whole-body PET/MRI for oncologic staging.
A vrfSSFSE sequence was acquired in 43 patients with known pancreatic neuroendocrine tumors undergoing Ga-DOTA-TOC PET on a simultaneous time-of-flight 3.0T PET/MRI. Liver lesions ≥1.5 cm with radionucleotide uptake were analyzed. Contrast-to-noise ratios (CNRs) were measured, and four blinded radiologists assessed overall image quality. Differences in repetition time and CNR were assessed using a paired Student's t test with p < 0.05 considered statistically significant. Inter-reader variability was assessed with Fleiss' kappa statistic.
53 eligible lesions in 27 patients were included for analysis. vrfSSFSE demonstrated higher mean lesion CNR compared to SSFSE (9.9 ± 4.1 vs. 6.7 ± 4.1, p < 0.001). Mean repetition time (TR) was 679 ± 97 ms for the vrfSSFSE sequence compared to 1139 ± 106 ms for SSFSE (p < 0.0001), corresponding to a 1.7-fold decrease in acquisition time. Overall quality of liver lesion and common bile duct images with the vrfSSFSE sequence was graded as superior than or equivalent to the SSFSE sequence for 59% and 67% of patients, respectively.
Compared to conventional SSFSE, vrfSSFSE resulted in improved lesion contrast on simultaneous PET/MRI in patients with liver metastases. Due to decreased SAR demands, vrfSSFSE significantly decreased TR, allowing coverage of the entire liver in a single twenty-second breath hold. This may have important clinical implications in the setting of PET/MRI, where scan time is limited by the necessity of whole-body image acquisition in addition to bed specific imaging.
在对接受全身正电子发射断层扫描磁共振成像（PET/MRI）用于肿瘤分期的患者进行肝脏病变成像时，评估可变重聚焦翻转角（vrf）单次激发快速自旋回波（SSFSE）序列与常规 SSFSE 序列的采集时间和临床图像质量。
在 43 例已知胰腺神经内分泌肿瘤并进行 Ga-DOTA-TOC PET 的患者中采集 vrfSSFSE 序列。分析放射性核素摄取的直径≥1.5cm 的肝脏病变。测量对比噪声比（CNR），并由四位盲法放射科医生评估整体图像质量。使用配对学生 t 检验评估重复时间和 CNR 的差异，p＜0.05 认为具有统计学意义。使用 Fleiss'kappa 统计评估读者间的变异性。
对 27 例患者的 53 个符合条件的病变进行了分析。vrfSSFSE 与 SSFSE 相比，病变的平均 CNR 更高（9.9±4.1 对 6.7±4.1，p＜0.001）。vrfSSFSE 序列的平均重复时间（TR）为 679±97ms，而 SSFSE 序列为 1139±106ms（p＜0.0001），采集时间减少了 1.7 倍。对于 59%和 67%的患者，vrfSSFSE 序列的肝脏病变和胆总管图像整体质量分别被评为优于或等同于 SSFSE 序列。
与常规 SSFSE 相比，vrfSSFSE 可在接受同时进行的 PET/MRI 的肝转移患者中改善病变对比度。由于 SAR 要求降低，vrfSSFSE 显著降低了 TR，可在单次二十秒屏气中覆盖整个肝脏。这在 PET/MRI 中具有重要的临床意义，因为扫描时间受到全身图像采集的限制，除了特定床位成像外，还需要采集全身图像。
