Impact of attenuation correction by simultaneous emission/transmission tomography on visual assessment of Tl-201 myocardial perfusion

It has been shown in clinical studies that for subjects with a low likeliho od of coronary artery disease (CAD), attenuation correction (AC) improves t he specificity of defect detection in the inferior wall (right coronary art ery [RCA] region). The aim of this study was to investigate the effect of A C on the visual interpretation of the RCA and anteroseptal (corresponding t o the left anterior descending artery [LAD]) regions in CAD patients. Metho ds: Fifty-six patients with suspected CAD underwent Tl-201 stress/4 h-delay ed imaging SPECT using a simultaneous Tl-201 emission/Tc-99m transmission i maging protocol. Images were reconstructed using the maximum likelihood-exp ectation maximum algorithm without and with AC. The stress/4 h-delayed imag es were interpreted blindly for reversible or fixed defects in the RCA and LAD regions by three experienced physicians. Coronary angiography, electroc ardiography and enzyme findings were used to establish diagnoses of ischemi a or infarction, and receiver operating characteristic (ROC) analyses were performed. Results: Statistical testing of ROC curve areas showed that defe ct detection performance improved with AC when compared with performance wi thout AC in the RCA region. This was mainly the result of a systematic incr ease in specificity of 12% or more (for any observer and any type of defect ) for a similar sensitivity (no definite change in sensitivity values). How ever, defect detection performance significantly decreased in the LAD terri tory with AC images (P < 0.05) because of a systematic decrease in sensitiv ity of 20% or more, with no consistent change in specificity. Similar trend s were observed when reversible and fixed defects were considered separatel y. Conclusion: AC significantly affects the visual interpretation of Tl-201 stress/4 h-delayed SPECT images. This study confirmed the increase in spec ificity obtained with AC in the RCA territory. However, in the population c onsidered, the studied AC was deleterious for the LAD territory assessment.