[P3–371]: INTRA‐ VERSUS INTEROBSERVER CONCORDANCE IN DOPAMINE TRANSPORTER SPECT SCANS FOR EXAMINATION OF EXTRAPYRAMIDAL PARKINSONIAN SYNDROMES

Background:Numerous studies of qualitative visual approaches for interpreting dopamine transporter SPECT scans of symptomatic patients withParkinsonian syndromes (PS), havedemonstratedgoodoverall accuracy (876 6%) and fair inter-observer reproducibility (approx. 75%, when a substantial cohort of subjects unafflicted by PS is included) – though the latter has generally been measured between observers at a single institution, and therefore reflects training and/or interpretive approaches that may share greater commonality than would be expected to exist across the field of clinical interpreters. In this study, we examined intervs. intra-institutional concordance rates between mutually blinded interpreters, and inter-operator degrees of concordance when employing a quantitative approach. Methods: Visual analyses were conducted independently by three interpreters – an experienced board-certified radiologist/neuroradiologist at one institution, and an experienced board-certified NuclearMedicine physician/neuronuclear imaging specialist, as well as a recent trainee, at another institution – who read all scans blinded to each others’ assessments. Quantified analyses were also conducted independently by operators blinded to these visual assessments, as well as to patients’ clinical data. Results: Diagnostic assessments on a patient-by-patient basis – to determine the presence of Parkinson’s Disease on the basis of a gradient of decreasing DaT activity observed from anterior to posterior striatum in one or both cerebral hemispheres (the most specific biomarker) – made by the interpreters at the same institutionwere highly concordant and did not significantly differ between those interpreters (p1⁄40.75). In contrast, concordance was diminished between interpreters who were trained and practicing at separate institutions, and significant differences in patient-by-patient diagnostic assessments emerged (p1⁄40.001). Quantitative assessments of ratios of anterior putamen to posterior putamen activity of the right and left striatal structures across operators were highly correlated (p1⁄40.004 and p<0.0001, respectively). Conclusions: Inter-observer concordance within an institution was substantially higher across institutions, even with the latter comparison beingmade between highly experienced clinical imaging physicians. These results raise the possibility that inter-observer concordance rates reported in the peer-reviewed literature, when they rely only upon observers located at a single institution, may frequently represent overestimates of concordance rates that could reasonably be expected to be achieved in actual clinical practice.