This observer performance study assessed lesion detection in the computed tomography attenuation correction image, as would be produced for myocardial perfusion imaging over a tube current (mA) range. A static anthropomorphic chest phantom containing simulated pulmonary lesions was scanned using the four available mA values (1, 1.5, 2 and 2.5) on a GE Infinia Hawkeye 4. All other computed tomography acquisition parameters remained constant throughout. Twenty-seven cases showing zero to four lesions were produced for a free-response receiver-operating characteristic method. Image observations were completed using our novel web-based ROCView software under controlled conditions. The Jackknife alternative free-response receiver-operating characteristic (JAFROC) figure of merit was used for significance testing, wherein a difference in lesion detection performance was considered significant at P values less than 0.05. Twenty readers with varying computed tomography experience (0-24 years) evaluated 108 images using an ordinal scale to score confidence. The JAFROC analysis showed that there was no statistically significant difference in performance between mA values (P=0.439) for this sample of observers. In conclusion, no significant difference in lesion detection performance was seen between the mA values. This suggests that there is no value in using anything other than the lowest mA value for the investigation of incidental extracardiac findings.