随着前列腺特异性膜抗原（PSMA）PET / CT的引入，无论是原发性分期还是生化复发，前列腺癌转移的检测率都有了显著提高。EANM / SNMMI指南建议[68Ga] Ga-PSMA注射和采集之间有60分钟的时间间隔。本研究通过研究图像质量指标的动态变化，评估了缩短时间间隔的可能性。我们回顾性分析了10例连续的前列腺癌患者，他们接受了使用Siemens FlowMotion的75分钟全身[68Ga] Ga-PSMA-11 PET / CT。 PET图像是在注射1.5 MBq / kg [68Ga] Ga-PSMA-11后直接获取的。图像质量指标包括校正后的最大标准摄取值（SULmax）瘤周围与背景的比率（TBR）以及对比度噪声比（CNR）。使用PMOD（版本4.2），对动态PET图像质量进行定量分析。绘制区域包括不同类型的前列腺癌病变（原发肿瘤，淋巴结，骨转移），器官组织（肝脏，脾脏，泪腺，下颌下腺，腮腺，尿膀胱，肾脏血池[上行主动脉]，左心室），骨组织（第4腰椎体[L4]）和肌肉组织（臀大肌）。为了进一步研究图像质量，我们制作了四个带有临床参数的10分钟多帧重建，时间分别为15、30、45和60分钟。核医学医师对不同前列腺癌病变的这些多帧重建进行了盲目的病变检测评估。发现7名患有前列腺原位癌的患者中的6个原发性前列腺肿瘤，6名患者中的13个淋巴结转移以及3名患者中多达12个骨转移。所有不同类型的前列腺病变（淋巴结转移，骨转移和原发前列腺癌）在扫描期间随时间都显示出平均SULmax，TBR和CNR的增加。在注射后15、30和45分钟扫描的组合前列腺病变的归一化平均SULmax，TBR和CNR都明显低于60分钟[68Ga] Ga-PSMA-11 PET / CT（分别为9.5 ± 4.5，12.7 ± 6.2和41.8 ± 24.5）。在患者层面上，与参考扫描（注射后60分钟）相比，读者对所有<60分钟注射后的[68Ga] Ga-PSMA-11 PET / CT的原发前列腺癌复发，淋巴结转移和/或骨转移的存在/不存在得出了相同的结论。在病变级别上，在参考扫描中看到的所有骨转移也在所有<60分钟注射后的[68Ga] Ga-PSMA-11 PET / CT中看到，但是有一些淋巴结（n = 2）转移在15、30和45分同时注射后的扫描中被遗漏。在15和30分钟注射后的[68Ga] Ga-PSMA-11 PET / CT中错过了一个淋巴结转移灶，在45分钟注射后的[68Ga] Ga-PSMA-11 PET / CT中错过了一个淋巴结转移灶。与建议的注射后60分钟相比，缩短的注射后时间（15、30和45分钟）不是最佳选择。然而，对于图像质量（SULmax，TBR和CNR）和病变检测来说，45分钟而不是60分钟的缩短时间间隔的影响虽然显著，但相对较小。

With the introduction of prostate specific membrane antigen (PSMA) PET/CT, the detection rate of prostate cancer metastases has improved significantly, both for primary staging and for biochemical recurrence. EANM/SNMMI guidelines recommend a 60 min time interval between [68 Ga]Ga-PSMA administration and acquisition.This study evaluates the possibility of a shorter time interval by investigating the dynamic change in image quality measures.We retrospectively analyzed 10 consecutive prostate cancer patients who underwent a dynamic whole body [68 Ga]Ga-PSMA-11 PET/CT of 75 min from skull vertex to mid-thigh using Siemens FlowMotion. PET images were acquired directly after injection of 1.5 MBq/kg [68 Ga]Ga-PSMA-11. Image quality measures included lesion maximum standardized uptake value corrected for lean body mass (SULmax ), tumor-to-background ratio (TBR), and contrast-to-noise ratio (CNR). Quantitative analysis of image quality in dynamic PET was performed using PMOD (version 4.2). Regions of interest (ROIs), drawn included different types of prostate lesions (primary tumor, lymph nodes, and bone metastasis), organ tissue (liver, spleen, lacrimal gland, submandibular gland, parotid gland, urinary bladder, kidneys blood pool [ascending aorta], left ventricle), bone tissue (4th lumbar vertebral body [L4]) and muscle tissue (gluteus maximus). To further investigate image quality four 10 min multi-frame reconstructions with clinical parameters were made at different post-injection times (15, 30, 45, and 60 min). A nuclear medicine physician performed a blinded lesion detectability evaluation on these multi-frame reconstructions for different prostate cancer lesions.Six primary prostate tumors in seven patients with prostate in situ, 13 lymph node metastases in six patients and up to 12 bone metastases in three patients were found. The different prostate lesion types (lymph nodes metastases, bone metastases, and primary prostate tumor) all show an increase in average SULmax , TBR, and CNR over time during the scan. The normalized average SULmax , TBR, and CNR of the combined prostate lesions at 15, 30, and 45 min post-injection scans were all significant p < 0.05 lower from the 60 min post-injection [68 Ga]Ga-PSMA-11 PET/CT (9.5 ± 4.5, 12.7 ± 6.2, and 41.8 ± 24.5, respectively). At patient level, the reader concluded the same regarding the presence/absence of primary prostate cancer recurrence, lymph node metastases, and/or bone metastases on all <60 min post-injection [68 Ga]Ga-PSMA-11 PET/CT's in comparison to the reference scan (60 min post-injection). At lesion level, all bone metastases seen on the reference scan were also seen on all <60 min post-injection [68 Ga]Ga-PSMA-11 PET/CT's but there were some lymph nodes (n = 2) metastases missed on the 15, 30, and 45 min post-injection scans. One lymph node metastasis on both the 15 and 30 min post-injection [68 Ga]Ga-PSMA-11 PET/CT's was missed and one lymph node metastasis was missed, only on the 45 min post-injection [68 Ga]Ga-PSMA-11 PET/CT.Shorter post-injection times (15, 30, and 45 min) compared to the recommended post-injection time of 60 min are not optimal. However, the impact of a shorter time interval of 45 min instead of 60 min between [68 Ga]Ga-PSMA-11 administration and the start of PET/CT acquisition on both image quality (SULmax , TBR, and CNR) and lesion detection, while significant, is small.© 2023 The Authors. Medical Physics published by Wiley Periodicals LLC on behalf of American Association of Physicists in Medicine.