Chen Ming-Kai, Menard David H, Cheng David W
Radiology and Biomedical Imaging, Yale University School of Medicine, New Haven, Connecticut.
Yale-New Haven Hospital, New Haven, Connecticut; and.
J Nucl Med Technol. 2016 Mar;44(1):26-30. doi: 10.2967/jnmt.115.165258. Epub 2016 Jan 14.
In pursuit of as-low-as-reasonably-achievable (ALARA) doses, this study investigated the minimal required radioactivity and corresponding imaging time for reliable semiquantification in PET/CT imaging.
Using a phantom containing spheres of various diameters (3.4, 2.1, 1.5, 1.2, and 1.0 cm) filled with a fixed (18)F-FDG concentration of 165 kBq/mL and a background concentration of 23.3 kBq/mL, we performed PET/CT at multiple time points over 20 h of radioactive decay. The images were acquired for 10 min at a single bed position for each of 10 half-lives of decay using 3-dimensional list mode and were reconstructed into 1-, 2-, 3-, 4-, 5-, and 10-min acquisitions per bed position using an ordered-subsets expectation maximum algorithm with 24 subsets and 2 iterations and a gaussian 2-mm filter. SUVmax and SUVavg were measured for each sphere.
The minimal required activity (±10%) for precise SUVmax semiquantification in the spheres was 1.8 kBq/mL for an acquisition of 10 min, 3.7 kBq/mL for 3-5 min, 7.9 kBq/mL for 2 min, and 17.4 kBq/mL for 1 min. The minimal required activity concentration-acquisition time product per bed position was 10-15 kBq/mL⋅min for reproducible SUV measurements within the spheres without overestimation. Using the total radioactivity and counting rate from the entire phantom, we found that the minimal required total activity-time product was 17 MBq⋅min and the minimal required counting rate-time product was 100 kcps⋅min.
Our phantom study determined a threshold for minimal radioactivity and acquisition time for precise semiquantification in (18)F-FDG PET imaging that can serve as a guide in pursuit of achieving ALARA doses.
为了追求尽可能低合理可达到（ALARA）剂量，本研究调查了PET/CT成像中可靠半定量所需的最小放射性及相应成像时间。
使用一个包含不同直径（3.4、2.1、1.5、1.2和1.0厘米）球体的体模，球体填充有固定浓度（18）F-FDG，浓度为165 kBq/mL，背景浓度为23.3 kBq/mL，我们在放射性衰变的20小时内的多个时间点进行PET/CT检查。在每个衰变半衰期的10个时间点，在单个床位位置采集图像10分钟，使用三维列表模式，并使用具有24个子集和2次迭代以及高斯2毫米滤波器的有序子集期望最大化算法，将每个床位位置重建为1、2、3、4、5和10分钟的采集图像。测量每个球体的SUVmax和SUVavg。
对于10分钟采集，球体中精确SUVmax半定量所需的最小活性（±10%）为1.8 kBq/mL，3 - 5分钟为3.7 kBq/mL，2分钟为7.9 kBq/mL，1分钟为17.4 kBq/mL。每个床位位置可重复测量球体SUV且不高估所需的最小活性浓度 - 采集时间乘积为10 - 15 kBq/mL·min。使用整个体模的总放射性和计数率，我们发现所需的最小总活性 - 时间乘积为17 MBq·min，所需的最小计数率 - 时间乘积为100 kcps·min。
我们的体模研究确定了（18）F-FDG PET成像中精确半定量所需的最小放射性和采集时间阈值，可作为追求实现ALARA剂量的指导。
