Germano G, Chua T, Kiat H, Areeda J S, Berman D S
Department of Imaging, Cedars-Sinai Research Institute, Cedars-Sinai Medical Center, Los Angeles, CA 90048.
J Nucl Med. 1994 Feb;35(2):356-9.
We have observed that filtered backprojection may cause artifactual decreased myocardial wall uptake in the reconstructed images if the hepatic-to-cardiac activity ratio (HCR) in 99mTc clinical myocardial SPECT studies is sufficiently high (> 1).
To quantitatively relate hepatic uptake to this phenomenon, a commercial chest and heart phantom was modified with the addition of a customized liver insert, which was filled with various concentrations of 99mTc to simulate HCRs of 0:1, 1:1 and 2:1. The phantom was imaged with a high-sensitivity, three-detector camera, low-energy, high-resolution (LEHR) collimation and 180 degrees noncircular orbits.
Quantitative circumferential profile analysis of the reoriented SPECT images demonstrated artifactual inferior/inferoseptal maximal activity decreases of 17.8% and 46.2% for the 1:1 and 2:1 HCRs, compared to the 0:1 HCR. Hepatic scatter probably partly mitigates the decrease. Smoothing the projection data before reconstruction worsened the artifacts' severity. Using Butterworth filters of order 5 and cutoff frequencies of 0.1, 0.2 and 0.215 Nyquist (clinical standard) resulted in artifactual inferior wall activity decreases of 5%, 8% and 16%, compared to using the same filter with a cutoff of 0.3 for an HCR of 2:1.
These data indicate that if count statistics are good and liver uptake is high, higher frequency cutoffs in pre-reconstruction filters may improve specificity in 99mTc-labeled myocardial perfusion SPECT studies.
我们观察到，在99mTc临床心肌单光子发射计算机断层扫描（SPECT）研究中，如果肝脏与心脏放射性活度比（HCR）足够高（>1），滤波反投影可能会在重建图像中导致心肌壁摄取出现伪性降低。
为了定量关联肝脏摄取与这一现象，对一个商用胸部和心脏体模进行了改进，添加了一个定制的肝脏插入物，该插入物填充有不同浓度的99mTc，以模拟0:1、1:1和2:1的HCR。使用高灵敏度三探测器相机、低能高分辨率（LEHR）准直和180度非圆形轨道对体模进行成像。
对重新定向的SPECT图像进行定量圆周轮廓分析表明，与0:1的HCR相比，对于1:1和2:1的HCR，伪性下壁/下间隔最大活性分别降低了17.8%和46.2%。肝脏散射可能部分减轻了这种降低。在重建前对投影数据进行平滑处理会使伪影严重程度恶化。对于2:1的HCR，与使用截止频率为0.3的相同滤波器相比，使用阶数为5、截止频率为0.1、0.2和0.215奈奎斯特频率（临床标准）的巴特沃斯滤波器会导致下壁活性伪性降低5%、8%和16%。
这些数据表明，如果计数统计良好且肝脏摄取较高，重建前滤波器中较高的频率截止可能会提高99mTc标记的心肌灌注SPECT研究的特异性。
