Reproducibility of myocardial thallium-201 washout in studies applying a standardized dipyridamole stress protocol

Thallium-201 (²⁰¹T1) washout analysis was proposed as an adjunctive tool to improve the detection of coronary artery disease (CAD). Since reproducibility of ²⁰¹T1 washout in dipyridamole (DPM) stress studies is unknown, this item was evaluated in 32 patients (24 with CAD, 8 without CAD), who were scintigraphed twice within 1–2 weeks. At 2 minutes following DPM infusion (0.5 mg/kg/5 min), 2 mCi ²⁰¹T1 were injected. Global and segmental washout were calculated by comparing circumferential profiles of respective background-corrected stress (left anterior oblique (LAO) 45°: 8 min postinfusion (p.i.), 35 min p.i.; anterior (ANT): 17 min p.i.; LAO 70°: 26 min p.i.) and redistribution (4 h p.i.) images. Whereas visual findings were comparable for study I and II, reproducibility of ²⁰¹T1 washout was low, indicated by comparing variances among patients with variance between studies, which were 28.8 and 71.2% of total variance, respectively. Mean differences of segmental washout between the studies ranged from 9.75 to 19.24% with only minor differences with regard to the different views and segments evaluated. Variability was lower using the intermediate instead of the initial scintigram as reference for the redistribution image (12.87±11.64% vs. 18.59±14.43%, n = 85; p<0.01). Variability was higher for nonstenosed compared to stenosed segments (14.54 ± 11.41%, n=32 vs. 9.89±8.03%, n=28, p<0.05). Correspondent with results of visual interpretation, variance of relative differences of washout values between neighboring segments was lower than variance statistically expected from variability of washout values between study I and II (12.79%, n=216 vs. 21.55%, n=270; F=2.76, p<0.01). It is suggested, that considerable washout variability might explain the controversially discussed diagnostic value of ²⁰¹T1 washout analysis in DPM stress studies.