The aim of our study was to evaluate the effect of stepwise-reduced doses on objective and subjective image parameters and on oncologic readings in whole-body ¹⁸F-FDG PET/MRI. Methods: We retrospectively simulated the stepwise reduction of ¹⁸F-FDG doses of 19 patients (mean age ± SD, 50.9 ± 11.7 y; mean body mass index ± SD, 22.8 ± 3.2 kg/m²) who received a whole-body PET/MRI examination from 3 to 0.5 MBq/kg of body weight (kgBW) in intervals of 0.25. Objective imaging parameters were assessed by measuring the SUV and coefficient of variation in different regions (aorta, liver, spleen, kidney, small bowel, lumbar vertebra, psoas muscle, urinary bladder) as well as the noise-equivalent counting rates in each bed position. Subjective image quality was evaluated with a masked reading of each simulated PET compared with the dose of 2 MBq/kgBW. Oncologic reading was performed first according to PERCIST in each dose and second by defining malignant lesions in doses of 2 MBq/kgBW and the maximum dose image (gold standard). The diagnostic confidence of each lesion was measured using a Likert scale. Results: With decreasing doses, regions in the mid abdomen showed a stronger decrease of SUV_mean and noise-equivalent counting rates than regions in the upper abdomen (SUV_mean, −45% and −15% on average in the small bowel and the liver, respectively). The coefficient of variation showed a nonlinear increase, pronounced below 1.5 MBq/kgBW. Subjective image quality was stable over a range between 1.25 and 2.75 MBq/kgBW compared with 2 MBq/kgBW. However, large photopenic areas in the mid abdomen were observed in 2 patients. In the PERCIST reading, target lesions were above the liver threshold with a stable SUV_peak in all cases down to 2 MBq/kgBW. Eighty-six of 90 lesions were identified correctly with a dose of 2 MBq/kgBW; Likert scores did not differ significantly. Conclusion: A reduction of doses in ¹⁸F-FDG PET/MRI might be possible down to 2 MBq/kgBW in oncologic whole-body examinations. The image quality in the mid abdomen seems to be more affected by lower doses than in the upper abdomen, and in single cases large photopenic areas can occur. Therefore, we do not recommend reducing doses below 3 MBq/kgBW in adults at this time.

我们研究的目的是评估逐步降低剂量对全身¹⁸ F-FDG PET / MRI的客观和主观图像参数以及肿瘤学读数的影响。方法：我们回顾性模拟了19例患者的¹⁸ F-FDG剂量的逐步降低（平均年龄±SD，50.9±11.7 y；平均体重指数±SD，22.8±3.2 kg / m ^2）），每3到0.5 MBq / kg体重（kgBW）进行一次全身PET / MRI检查，间隔为0.25。通过测量SUV和不同区域（主动脉，肝脏，脾脏，肾脏，小肠，腰椎，腰大肌，膀胱）的SUV和每个床位的等效噪声计数率来评估客观成像参数。主观图像质量是通过将每个模拟PET的掩盖读数与2 MBq / kgBW的剂量进行比较来评估的。首先按照PERCIST在每个剂量下进行肿瘤学阅读，然后通过以2 MBq / kgBW的剂量定义恶性病变和最大剂量图像（金标准）来进行肿瘤学阅读。使用李克特量表测量每个病变的诊断置信度。结果：随着剂量的减少，中腹部区域的SUV_平均计数和噪声等效计数率比上腹部区域更强（小肠和肝脏的SUV_{平均分别为}-45％和-15％ ）。变异系数显示出非线性增加，明显低于1.5 MBq / kgBW。与2 MBq / kgBW相比，主观图像质量在1.25至2.75 MBq / kgBW的范围内稳定。但是，有2例患者在腹部中部有较大的光笔吸收区域。在PERCIST读数中，在所有情况下目标皮损均高于肝脏阈值，并具有稳定的SUV_峰值，降至2 MBq / kgBW。以2 MBq / kgBW的剂量正确识别了90个病灶中的86个。李克特分数差异不显着。结论：在肿瘤全身检查中，可以将¹⁸ F-FDG PET / MRI的剂量降低至2 MBq / kgBW。与上腹部相比，较低剂量的剂量似乎对中腹部的图像质量影响更大，在个别情况下，可能会出现较大的光笔区域。因此，我们不建议此时将剂量降低至3 MBq / kgBW以下。