Image protocol

MPS were performed using the 2-day protocol. In the resting phase, a dose of 20mCi ⁹⁹mTc-sestamibi was injected with acquisition of the images after 30 to 40 minutes, and in the stress phase a dose of 20mCi of ⁹⁹mTc-sestamibi was injected during the exercise test or pharmacological stress test, and image acquisition was performed after 15 to 30 minutes. The physical and pharmacological stress protocols were performed as described in a previous study.⁷ MPS images were acquired through the gated-SPECT technique in the Ventri gamma-camera, GE Healthcare.

The exams were classified as normal, or with reversible, fixed or mixed perfusion defects. The semi-quantitative visual analysis was independently performed by two cardiologists with extensive experience, through the standard 17-segment model, in which the quantification of radiotracer uptake was evaluated in each segment, graduated on a scale of 0 to 4, where 0 = normal uptake; 1 = slight reduction of uptake; 2 = moderate reduction of uptake, 3 = severe reduction of uptake; 4 = no uptake.⁸

The values attributed to each of the 17 segments were added in the stress phase, called summed stress score (SSS), and in the resting phase, called summed rest score (SRS). The difference between these two scores is called summed difference score (SDS), and represents the degree of transient reversibility. Abnormal MPS was defined by SSS > 3, and abnormal MPS with ischemia by SDS > 1. SSS and SDS were converted, respectively, into percent of total perfusion defect and ischemic defect by dividing the score by 68 (maximum value of the score) and then multiplying by 100. The ejection fraction (EF) and the left ventricular diastolic and systolic volumes were measured automatically using the software.