Effect of scattering correction on SPECT/CT myocardial perfusion imaging

Objectives: To investigate the effects of scattering correction on the image quality and semi-quantitative results of SPECT/CT myocardial perfusion imaging.

Methods: A retrospective analysis was made of 60 patients with reversible myocardial ischemia who underwent ⁹⁹Tc^m -methoxyisobutyl isonitrile (⁹⁹Tc^m -MIBI) exercise stress and rest myocardial perfusion imaging, both CT attenuation correction (CTAC) and dual-energy window scattering correction (SC) were performed. The CTAC, SC, CTAC+SC and no correction(NC) images were reconstructed respectively. The percentage of radioactivity counts of left ventricular wall segments and the semi-quantitative perfusion defect scores of exercise and rest image were obtained by myocardical Bulls-eye under different correction conditions. The differences of image quality and semi-quantitative results of ischemic myocardium under different correction conditions were compared. Data were analyzed by one-way ANOVA and x² test.

Results: The percentages of radioactivity counts in apex, inferior, septal and lateral wall of left ventricle in exercise imaging were significantly different among different correction methods (F = 12.772, 32.174, 3.344, 3.441, all P< 0.05). There were significant differences in exercise total perfusion deficit(TPD), summed stress score(SSS) and summed difference score (SDS) between different correction methods (F = 6.619, 8.681, 18.347, all P < 0.05), it was significantly higher in SC than in NOC images (t = 2.102, 2.204, 2.424, all P < 0.05), and significantly higher in CTAC + SC than in CTAC images (t = 3.152, 8.008, 9.091, all P < 0.01). There was no significant difference in rest TPD and summed rest score(SRS) between different correction methods (F = 1.072, 2.325, all P > 0.05). Visual comparison of ischemic myocardial images under different correction conditions showed that the degree of perfusion defect in SC images was significantly higher than that in NOC images, and CTAC + SC images were significantly higher than that in CTAC images. Among all the correction methods, CTAC + SC images show the ischemic myocardium most clearly. Radioactive distribution scores of ischemic myocardium were also significantly different under different correction conditions. The proportion of 3 score in SC images was significantly higher than that in NOC images [21.74% (20/92) and 9.78% (9/92), x² = 4.953, P = 0.026],and in CTAC + SC images was significantly higher than that in CTAC images [34.8% (32/92) and 17.39% (16/92), x² = 7.216, P = 0.007].

Conclusions: The image quality and semi-quantitative results of left ventricular ischemic myocardium under different correction conditions are significantly different. SC can significantly improve the display of ischemic myocardium, especially in CTAC images.