Somatostatin-receptor scintigraphy in Graves' disease: Reproducibility andvariance of orbital activity

Somatostatin-receptor (SSTR) scintigraphy using the single photon emission computed tomography (SPECT) technique allows the assessment of orbital infl ammation inpatients with Graves' disease. Previous studies showed differenc es in orbital octreotide uptake already 4 hr after injection. In this study , analysis of inter-/intra-observer variance and reproducibility in the eva luation of orbital SPECT images was performed. First, SPECT data of one rep resentative female patient with clinically active Graves' ophthalmopathy (G O), obtained 4 hr after intravenous injection of 110 MBq In-111-pentetreoti de and processed by filtered backprojection, were analyzed. Transverse SPEC T images were reconstructed, an optimal orbital image was selected and pred etermined regions of interests (ROIs) for both orbits were positioned by th ree independent observers 15 to 19 times each. In a second step, SPECT data of 8 different patients with GO were evaluated in the same manner by four independent observers 3 to 4 times each. Variance component partitioning wa s used to compare the order of intra- and inter-observer variation. For the right and the left orbit, the inter-observer variance proportion was 90% a nd 79%, whereas intra-observer variance partition was 10% and 21%, respecti vely. The corresponding ratios 0.11 and 0.27 summarize the comparison of so urces of variance. The overall reliability was 84%, representing the patien ts influence on the total variance. Intra-observer reliability for both orb its was 88%, 89%, 97% and 98% (mean over orbits), respectively for observer s Ito IV Using the Spearman Brown prophecy formula it follows that two repl ications per patient are sufficient to ensure a minimum reproducibility of 90%, which is also confirmed by the low intra-observer variation. Furthermo re intra-class correlation as a measure of(multiple) observer reproducibili ty was 94%. In conclusion, due to the increased inter-observer variance pro portion and the high variation in intra-observer reliability, evaluations o f orbital SSTR scintigraphy have to be done by the same and experienced obs erver leading to comparable data. But an automatic and quantitative compute rized technique for evaluation of these SPECT data should be exactly reprod ucible and probably lead to more accurate and representative results.