Zucchetta Pietro, Branchini Marco, Zorz Alessandra, Bodanza Valentina, Cecchin Diego, Paiusco Marta, Bui Franco
1 Nuclear Medicine Unit, Department of Medicine DIMED, University-Hospital of Padova , Padova , Italy.
2 Medical Physics Department, Veneto Institute of Oncology IOV-IRCCS , Padova , Italy.
Br J Radiol. 2019 Mar;92(1095):20180438. doi: 10.1259/bjr.20180438. Epub 2019 Jan 23.
: The study performs a comprehensive analysis of image metrics to objectively support the reduction of injected activity in pediatric oncology F-FDG PET/MR (F-fludeoxyglucose PET/MR) examinations. Contrast-to-Noise Ratio (CNR), Normalized Noise (NN), tumor burden, and standardized uptake value (SUV) parameters stability were investigated to robustly define the acceptable reduced activity level that preserves the clinical utility of images, considering different PET applications.
: 21 PET/MRI examinations performed on a 3-Tesla Biograph mMR scanner were analyzed. Tracer activity reduction was stimulated by decreasing the count statistics of the original list-mode data (3 MBq kg). In addition to the already studied SUV metrics and subjective scoring on lesion detectability, a thorough analysis of CNR, NN, Metabolic Tumor Volume (MTV), and Total Lesion Glycolysis (TLG) was performed.
: SUVmax and SUVmean increased more than 5% only in 0.6 MBq kg reconstructed images (+10% and +9%, respectively), while SUVpeak was almost unaffected (average variations < 2%). The quantified CNR, NN, MTV, and TLG behavior with the decrease of the injected activity clearly defines 1.5 MBq kg as a threshold of activity after which the quality of the image degrades. Subjective and objective analyses yielded consistent results. All 56 lesions were detected until activity of 1.2 MBq kg, whereas five lesions were missed on the 0.6 MBq kg image. Perceived image quality (IQ) decreased in Lower Tracer Activity (LTA) images but remained acceptable until 1.5 MBq kg.
: Results about the stability of image metrics beyond the semi-quantitative SUV parameters and subjective analysis, rigorously proves the feasibility of the reduction of injected activity to 1.5 MBqkg for pediatric patients aged between 7 and 17 years.
: This is the first report on the quantitative evaluation of the effect of activity reduction on image quality in pediatric PET/MR. The findings offer objective corroboration to the feasibility of a significant dose reduction without consequences on clinical image reading and tumor burden metrics.
本研究对图像指标进行全面分析，以客观支持降低儿科肿瘤学氟代脱氧葡萄糖正电子发射断层显像/磁共振成像（F-FDG PET/MR）检查中的注射活度。研究了对比噪声比（CNR）、归一化噪声（NN）、肿瘤负荷和标准化摄取值（SUV）参数的稳定性，以稳健地确定在保留图像临床效用的前提下可接受的降低活度水平，同时考虑不同的PET应用。
分析了在3特斯拉Biograph mMR扫描仪上进行的21次PET/MRI检查。通过降低原始列表模式数据（3 MBq/kg）的计数统计来模拟示踪剂活度降低。除了已经研究过的SUV指标和对病变可检测性的主观评分外，还对CNR、NN、代谢肿瘤体积（MTV）和总病变糖酵解（TLG）进行了全面分析。
仅在0.6 MBq/kg重建图像中，SUVmax和SUVmean增加超过5%（分别为+10%和+9%），而SUVpeak几乎未受影响（平均变化<2%）。随着注射活度降低，量化的CNR、NN、MTV和TLG行为清楚地将1.5 MBq/kg定义为活度阈值，超过该阈值图像质量会下降。主观和客观分析得出一致结果。在活度为1.2 MBq/kg之前，所有56个病变均被检测到，而在0.6 MBq/kg图像上有5个病变未被检测到。较低示踪剂活度（LTA）图像中的感知图像质量（IQ）下降，但在活度为1.5 MBq/kg之前仍可接受。
关于图像指标稳定性的结果超出了半定量SUV参数和主观分析，严格证明了将7至17岁儿科患者的注射活度降低至1.5 MBq/kg的可行性。
这是关于降低活度对儿科PET/MR图像质量影响的定量评估的首份报告。这些发现为大幅降低剂量而不影响临床图像解读和肿瘤负荷指标的可行性提供了客观佐证。
