部分容积效应对SPECT/CT定量计算结果的影响

Impact of Partial Volume Effect on Quantitative Results in SPECT/CT

目的部分容积效应是影响核医学显像图像质量和定量精确性的主要因素。本文探讨部分容积效应对SPECT/CT定量计算结果的影响。资料与方法分别对Jaszczak圆筒模型以及IEC体模进行SPECT/CT断层显像,并进行CT衰减校正和散射校正以及三维有序子集最大期望值法(3D-OSEM)图像重建。根据Jaszczak圆筒模型重建图像获得特定采集及重建条件下的系统容积灵敏度(cpm/k Bq),计算IEC体模内不同大小热区的绝对放射性活度(k Bq/ml),并与真实活度值进行比较,验算其定量精确性。比较特定采集及重建条件下不同大小热区定量精确性的差异,以及不同大小容积感兴趣区(VOI)、热区/本底比值(TBR)以及采集时间显像对定量精确性的影响。结果使用3D-OSEM重建算法、CT衰减校正、散射校正时,各球体的绝对放射性活度与真实活度值的差异与球体大小显著相关(r=-0.844,P<0.05),各球体平均定量误差随球体容积的增加而明显减小。不同VOI范围显著影响球体定量精确性。对于1.15~11.49 ml球体,其边缘的定量精确性明显低于中心,且各球体定量误差随VOI的减小而减小(r=0.999、0.992、0.994、0.767,P<0.05)。对于26.52 ml和0.52 ml球体,其定量误差与VOI大小无明显相关性(r=0.348、0.478,P>0.05)。不同TBR及采集时间显像中,高TBR显像各球体的平均定量误差(-44.19%)小于低TBR显像(-46.18%),20 s/帧采集显像(-44.33%)小于10 s/帧采集显像(-46.04%)。结论部分容积效应可显著影响SPECT/CT定量精确性,尤其对小病灶以及病灶的边缘部分更为显著。

Purpose The partial volume effect is a main factor to impact the image quality and the accuracy of the quantitative analysis of nuclear medicine image. The aim of this study is to evaluate the effects of partial volume effect on quantitative result in SPECT/CT. Materials and Methods A Jaszczak cylindrical phantom and IEC body phantom were performed with routine SPECT/CT imaging using CT attenuation correction, scatter correction and three-dimensional ordered subset expectation maximization（3 D-OSEM） reconstruct image. The system volume sensitivity（cpm/k Bq） were acquired from the reconstructed image of Jaszczak phantom study. The absolute activity concentration（k Bq/ml） of the hot sphere was calculated according to the IEC phantom study that the intensity of radioactivity had been measured in the dose calibrator, then checking computations the quantitative accuracy of all. The difference of quantitative accuracies from the different volume hot sphere was compared tusing a given acquisition and reconstruction parameter. The effects of volume of interest（VOI）, target-to-background ratio（TBR） and acquisition time on quantitative accuracy were evaluated. Results CT attenuation correction and scatter correction, the difference of absolute activity and true activity value was obviously correlation with the sphere size by using 3 D-OSEM. The quantitative errors were decreased along with the increased of sphere size（r=-0.844, P〈0.05）. The quantitative accuracy were significantly affected by the VOI size in the 1.15-11.49 ml sphere. It was obviously lower in the limbic of sphere than that in the center of sphere. And the quantitative errors were decreased along with the decreased of VOI size（r=0.999, 0.992, 0.994 and 0.767, P〈0.05）. However, the quantitative error was no obviously correlation with the VOI size（r=0.348, 0.478, P〉0.05） in the 26.52 ml and 0.52 ml sphere. The average quantitative error was lower in high TBR imaging（-44.19%） than that in low TBR imaging（-46.18%）, and it was lower in 20 s/frame imaging（-44.33%） than that in 10 s/frame imaging（-46.04%）. Conclusion The quantitative accurate could be obviously affected by the partial volume effect in SPECT/CT imaging, exceptionally in the small lesions and the limbic of lesions.