Purpose: Attenuation correction (ATC) has been shown to improve the accuracy of thallium-201 single photon emission computed tomography (SPECT) for the detection and evaluation of patients with coronary artery disease. The purpose of this study was to evaluate the value of ATC for the assessment of infarct size in patients after myocardial infarction (MI).
Materials and methods: Tl-201 SPECT with ATC was performed on 39 patients with 49 previous MIs. This was followed by radionuclide ventriculography for the assessment of global and regional left ventricular function. Uncorrected and corrected 24-hour redistribution SPECT images were analyzed for regional perfusion using a 5-point segmental scoring scale from 0 (normal) to 4 (absent) thallium uptake.
Results: The mean number of segments with scores of >1 and 2 was significantly higher without ATC than with ATC (5.3 +/- 3.6 vs. 3.5 +/- 3.6, P = 0.0001 for scores >1; 3.8 +/- 3.6 vs. 2.5 +/- 3.0, P = 0.0001 for scores of >2, respectively). The mean total number of segments with scores of >1 assessed without ATC was significantly higher compared with that assessed with ATC (16.9 +/- 13.5 vs. 11.2 +/- 12.2, P = 0.0001). Evaluation without ATC demonstrated only a fair correlation between the SPECT parameters (number of segments with scores of >1 and >2, and total score of segments with scores of >1) and left ventricular regional and global function, whereas there was a clear improvement in all the parameters after ATC. With ATC, a decrease in infarct size was demonstrated in 27 of the 49 infarcts (55%).
Conclusions: The improved correlation with left ventricular function indicates that SPECT imaging with ATC provides a more accurate assessment of infarct size in post-MI patients. The use of nonattenuation-corrected SPECT imaging overestimates infarct size in a majority of patients.