Incremental value of dedicated [

Background: Rest/stress [ Methods: In this retrospective study, we analyzed 174 patients-totaling 2,958 myocardial segments-who underwent both protocols. Intermodality correlation was assessed, and the rates of segmental and patient-level reclassification (segments converting from <50% maximum uptake on sestamibi to ≥50% maximum uptake on thallium) were quantified. Results: While a moderately high correlation was observed between the baseline uptake scores of the two modalities (Spearman's r = 0.817 for rest sestamibi vs. thallium), thallium imaging provided substantial additional information, with 48.0% of segments classified as fixed defects on sestamibi SPECT demonstrating improved uptake on thallium SPECT. At the patient level, 78.9% of individuals who had fixed defects on the initial sestamibi SPECT had at least one segment reclassified. Receiver operating characteristic analysis showed that a rest sestamibi uptake score of <20% predicted a lack of reclassification with 99% specificity, although with low sensitivity (12%). Conclusion: In a selected cohort of patients presenting with fixed defects on standard rest/stress sestamibi SPECT MPI, supplementary imaging with thallium myocardial CZT SPECT provided incremental data, altering the clinical interpretation in nearly 80% of patients. However, in the absence of an independent viability reference standard, this finding represents intertracer diagnostic reclassification rather than proven functional recovery. A rest sestamibi uptake of <20% demonstrated high specificity for non-reclassification; however, this cutoff should be interpreted cautiously as a potential gatekeeping finding when considering downstream testing rather than a rigid rule for omitting further myocardial viability evaluation.