Gould Sarah-May, Mackewn Jane, Chicklore Sugama, Cook Gary J R, Mallia Andrew, Pike Lucy
King's College London & Guy's and St Thomas' PET Centre, School of Biomedical Engineering and Imaging Sciences, King's College London, St Thomas' Hospital, Westminster Bridge Road, London, SE1 7EH, UK.
EJNMMI Phys. 2021 Jul 31;8(1):58. doi: 10.1186/s40658-021-00404-4.
A significant proportion of the radiation dose from a PET-CT examination is dependent on the CT protocol, which should be optimised for clinical purposes. Matching protocols on different scanners within an imaging centre is important for the consistency of image quality and dose. This paper describes our experience translating low-dose CT protocols between scanner models utilising different automatic exposure control (AEC) methods and reconstruction algorithms.
The scanners investigated were a newly installed Siemens Biograph mCT PET with 64-slice SOMATOM Definition AS CT using sinogram affirmed iterative reconstruction (SAFIRE) and two GE Discovery 710 PET scanners with 128-slice Optima 660 CT using adaptive statistical reconstruction (ASiR). Following exploratory phantom work, 33 adult patients of various sizes were scanned using the Siemens scanner and matched to patients scanned using our established GE protocol to give 33 patient pairs. A comparison of volumetric CT dose index (CTDI) and image noise within these patient pairs informed optimisation, specifically for obese patients. Another matched patient study containing 27 patient pairs was used to confirm protocol matching. Size-specific dose estimates (SSDEs) were calculated for patients in the second cohort. With the acquisition protocol for the Siemens scanner determined, clinicians visually graded the images to identify optimal reconstruction parameters.
In the first matched patient study, the mean percentage difference in CTDI for Siemens compared to GE was - 10.7% (range - 41.7 to 50.1%), and the mean percentage difference in noise measured in the patients' liver was 7.6% (range - 31.0 to 76.8%). In the second matched patient study, the mean percentage difference in CTDI for Siemens compared to GE was - 20.5% (range - 43.1 to 1.9%), and the mean percentage difference in noise was 19.8% (range - 27.0 to 146.8%). For these patients, the mean SSDEs for patients scanned on the Siemens and GE scanners were 3.27 (range 2.83 to 4.22) mGy and 4.09 (range 2.81 to 4.82) mGy, respectively. The analysis of the visual grading study indicated no preference for any of the SAFIRE strengths.
Given the different implementations of acquisition parameters and reconstruction algorithms between vendors, careful consideration is required to ensure optimisation and standardisation of protocols.
正电子发射断层显像-计算机断层扫描（PET-CT）检查的很大一部分辐射剂量取决于CT协议，应针对临床目的对其进行优化。在成像中心内不同扫描仪上匹配协议对于图像质量和剂量的一致性很重要。本文描述了我们在使用不同自动曝光控制（AEC）方法和重建算法的扫描仪型号之间转换低剂量CT协议的经验。
所研究的扫描仪包括一台新安装的西门子Biograph mCT PET，其CT部分为64层SOMATOM Definition AS CT，采用正弦图确认迭代重建（SAFIRE）；以及两台GE Discovery 710 PET扫描仪，其CT部分为128层Optima 660 CT，采用自适应统计重建（ASiR）。在进行探索性模体研究后，33名不同体型的成年患者使用西门子扫描仪进行扫描，并与使用我们既定的GE协议扫描的患者进行匹配，形成33对患者。对这些患者对中的容积CT剂量指数（CTDI）和图像噪声进行比较以指导优化，特别是针对肥胖患者。另一项包含27对患者的匹配患者研究用于确认协议匹配。计算了第二组患者的体型特异性剂量估计值（SSDEs）。在确定了西门子扫描仪的采集协议后，临床医生对图像进行视觉分级以确定最佳重建参数。
在第一项匹配患者研究中，西门子与GE相比CTDI的平均百分比差异为-10.7%（范围为-41.7%至50.1%），患者肝脏中测量的噪声平均百分比差异为7.6%（范围为-31.0%至76.8%）。在第二项匹配患者研究中，西门子与GE相比CTDI的平均百分比差异为-20.5%（范围为-43.1%至1.9%），噪声平均百分比差异为19.8%（范围为-27.0%至146.8%）。对于这些患者，在西门子和GE扫描仪上扫描的患者的平均SSDEs分别为3.27（范围为2.83至4.22）mGy和4.09（范围为2.81至4.82）mGy。视觉分级研究分析表明对任何SAFIRE强度均无偏好。
鉴于不同供应商之间采集参数和重建算法的不同实现方式，需要仔细考虑以确保协议的优化和标准化。
