Umeda Takuro, Miwa Kenta, Murata Taisuke, Miyaji Noriaki, Wagatsuma Kei, Motegi Kazuki, Terauchi Takashi, Koizumi Mitsuru
Department of Nuclear Medicine, Cancer Institute Hospital of Japanese Foundation for Cancer Research, 3-8-31 Ariake, Koto-ku, Tokyo, 135-8550, Japan.
Department of Radiological Sciences, School of Health Sciences, International University of Health and Welfare, 2600-1 Kitakanemaru, Ohtawara, Tochigi, 324-8501, Japan.
Australas Phys Eng Sci Med. 2017 Dec;40(4):861-868. doi: 10.1007/s13246-017-0596-5. Epub 2017 Nov 2.
The present study aimed to qualitatively and quantitatively evaluate PET images as a function of acquisition time for various leg sizes, and to optimize a shorter variable-acquisition time protocol for legs to achieve better qualitative and quantitative accuracy of true whole-body PET/CT images. The diameters of legs to be modeled as phantoms were defined based on data derived from 53 patients. This study analyzed PET images of a NEMA phantom and three plastic bottle phantoms (diameter, 5.68, 8.54 and 10.7 cm) that simulated the human body and legs, respectively. The phantoms comprised two spheres (diameters, 10 and 17 mm) containing fluorine-18 fluorodeoxyglucose solution with sphere-to-background ratios of 4 at a background radioactivity level of 2.65 kBq/mL. All PET data were reconstructed with acquisition times ranging from 10 to 180, and 1200 s. We visually evaluated image quality and determined the coefficient of variance (CV) of the background, contrast and the quantitative %error of the hot spheres, and then determined two shorter variable-acquisition protocols for legs. Lesion detectability and quantitative accuracy determined based on maximum standardized uptake values (SUV) in PET images of a patient using the proposed protocols were also evaluated. A larger phantom and a shorter acquisition time resulted in increased background noise on images and decreased the contrast in hot spheres. A visual score of ≥ 1.5 was obtained when the acquisition time was ≥ 30 s for three leg phantoms, and ≥ 120 s for the NEMA phantom. The quantitative %errors of the 10- and 17-mm spheres in the leg phantoms were ± 15 and ± 10%, respectively, in PET images with a high CV (scan < 30 s). The mean SUV of three lesions using the current fixed-acquisition and two proposed variable-acquisition time protocols in the clinical study were 3.1, 3.1 and 3.2, respectively, which did not significantly differ. Leg acquisition time per bed position of even 30-90 s allows axial equalization, uniform image noise and a maximum ± 15% quantitative accuracy for the smallest lesion. The overall acquisition time was reduced by 23-42% using the proposed shorter variable than the current fixed-acquisition time for imaging legs, indicating that this is a useful and practical protocol for routine qualitative and quantitative PET/CT assessment in the clinical setting.
本研究旨在定性和定量评估正电子发射断层扫描（PET）图像随采集时间的变化情况，该变化针对不同腿围大小，同时优化一种针对腿部的更短可变采集时间方案，以实现真正的全身PET/CT图像更好的定性和定量准确性。将作为体模的腿部直径根据来自53例患者的数据来定义。本研究分析了一个美国国家电气制造商协会（NEMA）体模以及三个分别模拟人体和腿部的塑料瓶体模（直径分别为5.68、8.54和10.7厘米）的PET图像。这些体模包含两个球体（直径分别为10和17毫米），装有氟 - 18氟脱氧葡萄糖溶液，在背景放射性水平为2.65千贝克勒尔/毫升时，球体与背景的比率为4。所有PET数据在采集时间范围从10到180以及1200秒的情况下进行重建。我们直观地评估图像质量，并确定背景、对比度的变异系数（CV）以及热球体的定量百分比误差，然后确定两种针对腿部的更短可变采集方案。还评估了使用所提出方案在患者PET图像中基于最大标准化摄取值（SUV）确定的病变可检测性和定量准确性。更大的体模和更短的采集时间导致图像上背景噪声增加以及热球体对比度降低。对于三个腿部体模，当采集时间≥30秒时，视觉评分为≥1.5，对于NEMA体模，采集时间≥120秒时视觉评分为≥1.5。在高CV（扫描<30秒）的PET图像中，腿部体模中10毫米和17毫米球体的定量百分比误差分别为±15%和±10%。在临床研究中，使用当前固定采集方案和两种所提出的可变采集时间方案时，三个病变的平均SUV分别为3.1、3.1和3.2，差异无统计学意义。即使每个床位位置的腿部采集时间为30 - 90秒，也能实现轴向均匀化、图像噪声均匀，并且对于最小病变的定量准确性最大为±15%。与当前用于腿部成像的固定采集时间相比，使用所提出的更短可变采集时间，总体采集时间减少了23 - 42%，这表明这是一种在临床环境中用于常规定性和定量PET/CT评估的有用且实用的方案。
