Abstract WP92: Radiologist Inter-rater Reliability of Prehospital Alberta Stroke Program Early CT Scores on a Mobile Stroke Unit

Introduction: The computed tomography (CT) capabilities of mobile stroke units (MSUs) may facilitate prehospital triaging of patients with suspected large-vessel occlusion directly to thrombectomy-capable centers. However, little is known about the reliability of radiological interpretation of early ischemic changes on prehospital CTs. Methods: We identified all patients transported by the NewYork-Presbyterian MSU to Weill Cornell Medical Center with the diagnosis of acute ischemic stroke, transient ischemic attack, or stroke mimic between October 3, 2016 and December 31, 2017. All patients underwent noncontrast head CT on board the MSU using a CereTom® scanner. As controls, we matched these patients 1:1 by diagnosis to patients who were transported by standard ambulance and underwent noncontrast brain CT in our emergency department (ED) over the same period. Two neuroradiologists, blinded to patients’ characteristics and final diagnosis, independently calculated Alberta Stroke Program Early CT Scores (ASPECTS) on all scans. Weighted percent agreement and Cohen’s κ were used to assess inter-rater reliability, and paired t-tests were used to compare these metrics between MSU and ED scans. Results: Among 46 MSU patients and 46 ED patients, 52% had a diagnosis of acute ischemic stroke, 46% a diagnosis of stroke mimic, and 2% a diagnosis of transient ischemic attack. For ASPECTS score as a continuous outcome, the weighted inter-rater agreement was 98% for MSU scans versus 96% for ED scans (mean difference, 2%; 95% CI, -1% to 5%) and the weighted κ was 0.49 for MSU scans versus 0.54 for ED scans (mean difference, -0.05; 95% CI, -0.61 to 0.51). For ASPECTS score categorized as 0-4, 5-7, or 8-10, the weighted inter-rater agreement was 99% for MSU scans versus 97% for ED scans (mean difference, 2%; 95% CI, -2% to 7%) and the weighted κ was 0.66 for MSU scans versus 0.55 for ED scans (mean difference, 0.10; 95% CI, -0.87 to 1.08). Conclusions: In a sample of 96 patients, which limited our power to detect small differences, we found no substantial difference in the inter-rater reliability of ASPECTS scores obtained from MSU CTs versus ED CTs.