EVALUATION OF AN ATTENUATION CORRECTION METHOD FOR TL-201 MYOCARDIAL PERFUSION TOMOGRAPHIC IMAGING OF PATIENTS WITH LOW LIKELIHOOD OF CORONARY-ARTERY DISEASE

Background. Image artifacts caused by nonuniform photon attenuation ar e a source off error in interpretation of images during myocardial per fusion single photon emission computed tomography (SPECT), A newly int roduced attenuation correction method was evaluated for improvement in image homogeneity during Tl-201 SPECT. The method was assessed with a cardiac phantom and in examinations of 42 patients (29 men) with a lo w likelihood of coronary disease. Methods and Results, Simultaneous tr ansmission-emission SPECT was performed with a moving collimated Gd-15 3 line source synchronized with a moving electronic acquisition window for transmission imaging and a novel variable-width electronic exclus ion window for emission imaging designed to avoid transmission-to-emis sion cross talk. The resulting uncorrected and corrected polar maps we re analyzed visually and divided into 31 segments for quantitative ana lysis. Visual analysis of the color-coded mean polar maps showed clear improvement in homogeneity after correction among the phantom, male p atients, female patients, and 42 patients combined at stress and redis tribution. The male and female mean polar maps showed very little diff erences in regional count distribution after correction. Quantitative analysis of the mean polar maps showed the following mean segmental co unts (% SD) before and after attenuation correction: phantom 88 (9) to 90 (7.5), P = .00005; men at stress 83 (10) to 88 (6), P = .0007, and at redistribution 84 (8) to 88 (6), P = .01; women at stress 86 (7) t o 90 (5), P = .0002, and at redistribution 87 (5) to 88 (7), P = .3; p atients combined at stress 84 (8) to 88 (6), P = .0004, and at redistr ibution 85 (7) to 87 (7), P = .03. Inferior/anterior count ratio for m en at stress increased after correction from 0.82 to 0.99 and septal/l ateral count ratio from 0.94 to 1.02. Inferior/anterior count ratio fo r men at redistribution increased from 0.86 to 1.06 and septal/lateral count ratio from 0.97 to 1.04. Inferior/anterior count ratio for wome n at stress increased from 0.95 to 1.03 and septal/lateral count ratio from 0.93 to 1.00. Inferior/anterior count ratio for women at redistr ibution increased from 1.04 to 1.10, and septal/lateral count ratio de creased from 1.02 to 1.00. Conclusion. Improvement in image homogeneit y was demonstrated with this attenuation correction method with a card iac phantom and for patients with low likelihood of coronary artery di sease, The slight relative increase in inferior mall counts at redistr ibution was most likely caused by scatter from the relatively higher l iver activity compared with the situation during stress and emphasizes the need for scatter correction, The close similarity in count distri bution for the mean male and female polar maps supports use of a sex-i ndependent normal database for quantitative analysis. The reduced vari ation in corrected images from patient to patient implies increased ac curacy for detection of myocardial defects.