A multicenter trial on interobserver and intraobserver reproducibility of segmental scoring of thallium-201 planar myocardial imaging before and after reinjection

Inter- and intraobserver reproducibility (R) of segmental ²⁰¹Tl scores after stress (ST), redistribution (RD) and reinjection (RI) planar imaging were evaluated. Methods: Images were examined from 396 patients with suspected coronary artery disease, demonstrated by means of post-ST imaging of at least one perfusion defect. To eliminate external sources of variability, the same gamma camera, acquisition protocol and computer software were used in this multicenter study. Thallium-201 images of the anterior, left anterior oblique and left lateral projections were obtained immediately, 4 hr after exercise and 30 min after the injection of additional ²⁰¹Tl either on the same day or on a different day. The left ventricle was divided into 15 segments and evaluated by three independent observers, blinded to clinical data, according to a five-point scale. Results: The R score for ST, RD and RI images, expressed as an intraclass correlation coefficient, was 0.76, 0.74 and 0.72, respectively. After averaging multiple observer scores, R increased to 0.91, 0.90 and 0.89, respectively. Individual observer measurement of the R score was 0.48, 0.51 and 0.32 for ST-RD, ST-RI and RD-RI image pairs, respectively, and multiple observer scores showed R increases to 0.74, 0.76 and 0.58. Conclusion: This qualitative scale reliably assesses the severity of ²⁰¹Tl perfusion defects, particularly when multiple-observer scores are averaged. Individual observer change scores should be taken with great caution, especially in studies involving the visual evaluation of RD-RI image changes.