Evaluation of interoperator variance in shunt fraction calculation after transcolonic scintigraphy for diagnosis of portosystemic shunts in dogs and cats

Objective-To determine interoperator variance in shunt fraction calculation . Design-Case series. Sample Population-101 transrectal portoscintigraphic studies. Procedure-Results of dynamic portoscintigraphic studies were reviewed by 4 radiologists without knowledge of signalment, history, or medical profile. Results were judged to be negative or positive on the basis of the dynamic scan. Composite images were formulated, and hand-drawn regions of interest were determined for the heart and liver. Time-activity curves were generate d, time-zero points were selected, curves were integrated during a 10-secon d interval, and shunt fractions were calculated. Results-Radiologists were in agreement regarding positive versus negative r esults for 99 of 101 studies. Interoperator variance in shunt fraction calc ulation ranged from 0.4 to 59.6%. For 51 studies with positive results, var iance ranged from 2.5 to 59.6% (mean +/- SD, 22.8 +/- 14.5%); differences a mong reviewers were significant. For 48 studies with negative results, vari ance in shunt fraction ranged from 0.4 to 25.9% (mean, 5.3 +/- 5.8%); signi ficant differences among reviewers were not detected. Shunt fraction calcul ations were not exactly reproducible among radiologists in 94 and 100% of s tudies with negative or positive results, respectively. Conclusions and Clinical Relevance-Results suggest that shunt fraction valu es are not reproducible among operators. Range in variability was greater i n studies with positive results. This factor may be of particular clinical importance in reassessment of patients after incomplete shunt ligation.