CT-based attenuation correction in lung perfusion SPECT-CT improves quantitative lesion contrast in patients with pulmonary embolism

2007 Objectives Analysis of the impact of CT-based attenuation correction on visualization of pulmonary embolism (PE) in lung perfusion SPECT-CT. Methods Lung perfusion SPECT-CT (Symbia T2, Siemens) studies of 45 patients with confirmed PE were analyzed. Comparative quantitative analysis of perfusion defect contrast was performed in attenuation corrected (AC) and non-attenuation corrected (NAC) SPECT data. The lesion-to-background ratio (LBR) of each PE lesion was calculated using the ratio of its average pixel counts to that of adjacent normal lung, each from AC and NAC data (LBRAC and LBRNAC). The AC benefit ratio (ACBR) was defined as the ratio of LBRNAC/LBRAC. The results of each lesion were correlated with the degree of SPECT-CT misalignment (Euclidian distance of misalignment in 3 dimensions, EDM) and with the lesion depth (distance-to-body surface, DBS). Results In total, 94 PE lesions were analyzed. The mean LBR of all lesions was higher for the NAC (0.31 ±0.17) than for the AC images (0.27 ±0.15), p 20 mm) was not lower than that of the remaining lesions (1.24± 0.27 vs. 1.23± 0.37, p=0.929). Conclusions This first systematic set of data on contribution of CT-derived attenuation correction to PE lesion contrast indicates that AC is associated with a better lesion-to-background ratio than NAC. This seems largely independent from the degree of misalignment between SPECT and CT acquisition or the distance-to-body surface.