QUANTIFICATION OF TECHNETIUM 99M-LABELED SESTAMIBI SINGLE-PHOTON EMISSION COMPUTED-TOMOGRAPHY BASED ON MEAN COUNTS IMPROVES ACCURACY FOR ASSESSMENT OF RELATIVE REGIONAL MYOCARDIAL BLOOD-FLOW - EXPERIMENTAL VALIDATION IN A CANINE MODEL

Background. Quantification of single-photon emission computed tomograp hic (SPECT) images is generally based on determination of maximal coun ts on radial sectors of short-axis slices. We hypothesized that analys is of mean counts may reduce estimation error. Methods and Results. We compared quantitative Tc-99m-labeled sestamibi (MIBI) SPECT based on maximal myocardial counts with that based on mean myocardial counts fo r accuracy of quantifying relative regional myocardial perfusion in a canine model of permanent left anterior descending coronary artery occ lusion. MIBI and radiolabeled microspheres were injected during left a nterior descending coronary artery occlusion. Relative microsphere myo cardial blood flow was expressed as a percentage of normal (left circu mflex coronary artery territory) blood flow. SPECT imaging was perform ed in vivo and ex vivo. Relative MIBI uptake on SPECT short-axis slice s was quantified with normalized circumferential profiles based on max imal and mean counts. In vivo and ex vivo SPECT relative myocardial co unt density was compared to relative myocardial blood how in six dogs. In the comparisons, percent errors in estimating the relative blood f low and relative flow deficit with MIBI SPECT imaging were calculated. There was an excellent correlation between absolute myocardial tissue MIBI activity and regional myocardial blood flow for each of the six dogs (r = 0.90 to 0.98). The correlations between relative myocardial count density on SPECT and relative blood flow for individual sectors were similar for maximal and mean count profiles (maximal, 0.79 to 0.8 3; mean, 0.77 to 0.82). Comparing the nadirs of in vivo and ex vivo ci rcumferential count profiles, the correlations were slightly better (m aximal, 0.82 to 0.91; mean, 0.87 to 0.91). Average percent errors in a ssessing relative blood flow and relative flow deficit were decreased significantly by use of mean count profiles (p < 0.05). Conclusions. R elative SPECT count density with either maximal or mean count profiles correlated well with relative myocardial blood how Compared with maxi mal count profiles, quantification with mean count profiles improved e stimation of relative flow.