Reversibility bull's-eye: A new polar bull's-eye map to quantify reversibility of stress-induced SPECT thallium-201 myocardial perfusion defects

Myocardial ischemia is currently interpreted from SPECT thallium-201 (²⁰¹Tl) tomograms by the subjective visual finding of stress-induced perfusion defects which 'normalize ' or 'reverse' by 4 hr. Thus, we have developed a computer method to quantify and display the three-dimensional distribution of reversible segments. Circumferential profiles generated from the short axis slices are normalized to the reference area in the stress study. The stress is subtracted from the normalized delayed data, and then displayed as a polar bull's-eye plot so that positive values show areas that have 'reversed' or 'improved.' Patient profiles are compared to means and standard deviations of reversibility for all pixels determined from the Emory normal male files. Criteria for reversibility were developed from studies of 42 male patients found to have 48 defects, as determined by the consensus of five blinded expert observers. There was computer agreement with the experts on 25 of 31 relatively fixed and 14 of 17 reversible defects. Our preliminary results indicate that this new method promises to aid observers to more consistently identify and quantify the reversibility of SPECT ²⁰¹Tl myocardial perfusion defects.