摘要目的 探讨基于特定重建算法及校正方法的SPECT/CT绝对定量方法及其影响因素.方法 分别对Jaszczak圆柱模型、国际电工委员会(IEC)体模进行SPECT/CT显像.根据圆柱模型重建图像获得系统容积感兴趣区(VOI)灵敏度(SVOI),对IEC体模内已知活度的不同大小热区进行绝对定量计算,并计算其定量精确性.比较三维(3D)-有序子集最大期望值迭代法(OSEM)和二维(2D)-OSEM重建算法、CT衰减校正(AC)和无衰减校正(NOAC)、散射校正(SC)和无散射校正(NOSC)及有无部分容积效应(PVE)校正对定量精确性的影响.采用两样本t检验、单因素方差分析和Pearson相关分析处理数据.结果 使用3D-OSEM+PVE校正+CTAC+SC时,6个不同容积热区球体绝对定量值与真实值(374 kBq/ml)的平均差异为-2.49％,其定量误差与球体容积无明显相关性(r=-0.795,P＞0.05).无PVE校正时,各球体定量误差随球体容积减小而增大(r=-0.852,P＜0.05).不同重建方法的不同容积球体的定量值与真实值间的平均差异有统计学意义(F=826.631,P＜0.05),其中3D-OSEM+CTAC+NOSC重建图像小于2D-OSEM+CTAC+NOSC[(52.83± 13.79)和(61.33±15.00) kBq/ml],3D-OSEM+CTAC+SC小于3D-OSEM+CTAC+NOSC[(9.33±5.47)和(52.83±13.79) kBq/ml],3D-OSEM+CTAC+NOSC小于3D-OSEM+NOAC+NOSC[(52.83± 13.79)和(307.66±9.24) kBq/ml;均P＜0.05].结论 基于3D-OSEM重建算法、CTAC、SC、PVE校正的SPECT/CT绝对定量可获得精确的定量结果.

abstractsObjective To investigate the methodology for absolute quantification with SPECT/CT using specified reconstruction algorithms and correction methods,and to determine the influence factors for quantitative accuracy.Methods The routine SPECT/CT imaging were performed with Jaszczak cylindrical phantom and International Electrotechnical Conmission (IEC) body phantom using a given acquisition and reconstruction parameter.The system volume sensitivities(SvoI)were acquired from the reconstructed images of Jaszczak phantom study.The absolute radioactivity of the hot spheres from IEC phantom study was calculated,and then the quantitative accuracies were checked.Differences of absolute quantitative value on quantitative accuracy were compared between 3 dimensional (3D)-ordered-subsets expectation maximization (OSEM) and 2 dimensional (2D)-OSEM,CT attenuation correction (AC) and no attenuation correction (NOAC),scatter correction (SC) and no scatter correction (NOSC),partial volume effect (PVE) correction and no PVE correction.Two-sample t test,one-way analysis of variance and Pearson correlation analysis were used.Results When 3D-OSEM,CTAC,SC and PVE correction were used,the average difference between absolute quantitative value and true value (374 kBq/ml) was-2.49％ in 6 hot spheres,and there was no obvious correlation between the quantitative error and the spheres volume (r=-0.795,P＞0.05).In the absence of PVE correction,the quantitative error of each sphere increased with the decrease of sphere volume (r=-0.852,P＜0.05).Differences of the quantitative value and the true value for 6 hot spheres among different reconstruction/correction methods were statistically significant (F =826.631,P＜0.05).The difference was smaller in 3D-OSEM+CTAC+NOSC than that in 2D-OSEM+CTAC+NOSC:(52.83±13.79) vs (61.33 ± 15.00) k Bq/ml (P＜0.05).The similar results were found when comparing differences between 3DOSEM+CTAC+SC and 3D-OSEM+CTAC+NOSC,also between 3D-OSEM+CTAC+NOSC and 3D-OSEM+ NOAC+NOSC:(9.33±5.47) vs (52.83±13.79) kBq/ml,(52.83±13.79) vs (307.66±9.24) kBq/ml (both P＜0.05).Conclusions An accurate absolute quantitative value could be obtained with 3D-OSEM reconstruction algorithm,CTAC,SC and PVE correction in SPECT/CT imaging.