Heller E N, DeMan P, Liu Y H, Dione D P, Zubal I G, Wackers F J, Sinusas A J
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520-8042, USA.
J Nucl Med. 1997 Dec;38(12):1882-90.
Increased extracardiac activity confounds conventional cardiac SPECT image reconstruction using a filtered backprojection method. Others have proposed that simultaneously acquired transmission-emission (STE) images that are reconstructed with a maximum likelihood (ML) method incorporating a nonuniform attenuation correction would less likely be affected by the presence of extracardiac activity. However, this approach corrects only for decreased myocardial counts from attenuation and not for increased myocardial counts from extracardiac activity. Therefore, STE with nonuniform attenuation correction may also result in reconstruction artifacts when extracardiac activity is present.
Acquisitions of phantoms with nonuniform and uniform attenuation were performed using STE and conventional approaches, in the absence and presence of extracardiac activity. All acquisitions used a triple-headed SPECT camera. STE acquisitions used fanbeam collimation and a 153Gd transmission source. STE images were reconstructed using ML, with and without nonuniform attenuation correction. Reconstructed short-axis images were quantitated, and percentage variability for each count profile was calculated.
In a nonuniform phantom configuration, STE reconstruction with nonuniform attenuation correction significantly improved image uniformity. This improvement in image uniformity was diminished with the addition of increasing extracardiac activity. In a uniform phantom, STE reconstruction with nonuniform attenuation correction significantly improved uniformity only in the presence of extracardiac activity.
The addition of attenuation correction in the presence of extracardiac activity can have complex effects on ML reconstruction with nonuniform attenuation correction, which depends on the amount of extracardiac activity and pattern of attenuation.
心脏外活动增加会干扰使用滤波反投影法的传统心脏单光子发射计算机断层显像（SPECT）图像重建。其他人提出，使用结合非均匀衰减校正的最大似然（ML）方法重建的同时采集的透射-发射（STE）图像受心脏外活动影响的可能性较小。然而，这种方法仅校正因衰减导致的心肌计数减少，而不校正因心脏外活动导致的心肌计数增加。因此，当存在心脏外活动时，具有非均匀衰减校正的STE也可能导致重建伪影。
在不存在和存在心脏外活动的情况下，使用STE和传统方法对具有非均匀和均匀衰减的体模进行采集。所有采集均使用三头SPECT相机。STE采集使用扇形束准直和153Gd透射源。STE图像使用ML进行重建，有无非均匀衰减校正。对重建的短轴图像进行定量，并计算每个计数轮廓的百分比变异性。
在非均匀体模配置中，具有非均匀衰减校正的STE重建显著改善了图像均匀性。随着心脏外活动的增加，这种图像均匀性的改善减弱。在均匀体模中，具有非均匀衰减校正的STE重建仅在存在心脏外活动时显著改善了均匀性。
在存在心脏外活动的情况下添加衰减校正对具有非均匀衰减校正的ML重建可能有复杂影响，这取决于心脏外活动的量和衰减模式。
