Gregoriou G K, Tsui B M, Gullberg G T
Department of Biomedical Engineering, The University of North Carolina at Chapel Hill, 27599, USA.
J Nucl Med. 1998 Jan;39(1):166-75.
For some camera systems used in cardiac SPECT, the limited field of view of fanbeam-collimated detectors produces truncation in the projection data. This truncation may generate artifacts and distortions in the transmission CT images and in the attenuation-corrected myocardial SPECT images (that use the transmission CT images as attenuation maps), thus affecting clinical diagnosis. Concern over this problem stimulated us to evaluate the effect of truncation with human observer performance studies.
A three-dimensional mathematical cardiac-torso phantom that realistically models the attenuation and 201Tl uptake distributions in different organs of the upper torso was used for the investigation. Five degrees of truncation (from 0% to 40% truncation) in the projection data were simulated by the use of five different detector sizes collimated by fanbeam collimators. The attenuation maps were obtained by reconstructing the truncated transmission data generated from these fanbeam geometries. The emission data obtained with the same fanbeam geometries were reconstructed by using the maximum likelihood-expectation maximization algorithm and were corrected for attenuation using the reconstructed attenuation maps. Two observer performance studies were performed. In Study 1, the images were reconstructed without using the body contour as support, whereas in Study 2, the exact body contour was used in reconstructing both the attenuation maps and the attenuation-corrected SPECT images.
The results of the receiver operating characteristics analysis indicate that there is very little difference between detection for the various degrees of truncation, and this difference only becomes noticeable for severe truncation of greater than 40%.
Using the acquisition and processing methods, we found the use of the body contour as support in reconstructing truncated transmission CT and SPECT data reduces the loss of defect detectability in attenuation-compensated myocardial SPECT images due to truncated data.
对于一些用于心脏单光子发射计算机断层扫描（SPECT）的摄像系统，扇形束准直探测器有限的视野会导致投影数据出现截断。这种截断可能会在透射计算机断层扫描（CT）图像以及衰减校正后的心肌SPECT图像（其使用透射CT图像作为衰减图）中产生伪影和畸变，从而影响临床诊断。对这一问题的关注促使我们通过人体观察者性能研究来评估截断的影响。
使用一个三维数学心脏 - 躯干模型，该模型逼真地模拟了上半身不同器官的衰减和201铊摄取分布进行研究。通过使用由扇形束准直器准直的五种不同探测器尺寸，模拟投影数据中的五种截断程度（从0%到40%截断）。通过重建从这些扇形束几何形状生成的截断透射数据来获得衰减图。使用最大似然期望最大化算法重建具有相同扇形束几何形状获得的发射数据，并使用重建的衰减图进行衰减校正。进行了两项观察者性能研究。在研究1中，不使用身体轮廓作为支撑来重建图像，而在研究2中，在重建衰减图和衰减校正后的SPECT图像时都使用了精确的身体轮廓。
接收器操作特性分析的结果表明，不同截断程度下的检测之间差异很小，只有当截断程度大于40%的严重截断时，这种差异才会变得明显。
通过使用采集和处理方法，我们发现使用身体轮廓作为支撑来重建截断的透射CT和SPECT数据，可减少由于截断数据导致的衰减补偿心肌SPECT图像中缺陷可检测性的损失。
