03:54 PM Abstract No. 341 Imaging triage of lower gastrointestinal bleed: assessing utility of selected contrast phases of multiphasic CTA

Abstract

Many institutions advocate for obtaining arterial (Art), non-contrast (NC), and delayed (Del) phases when assessing for active lower gastrointestinal bleed (LGIB) on multiphasic computed tomography arteriograms (CTA). We aimed to evaluate the necessity of all three phases of CTA for accurate diagnosis of active LGIB. This study is IRB approved and HIPAA compliant. We identified all CTA exams for LGIB performed at our institution from Oct 2012 to Oct 2017. We selected a random sample of 50 exams positive for active LGIB as well as an age/sex/protocol-matched cohort of 50 exams with no evidence of LGIB based on initial interpretation and throughout workup. A randomized experimental block design was used where three interventional radiologists blinded to patient data each assessed all exams using (1) Art only, (2) Art/NC, and (3) Art/NC/Del phase configurations accounting for presence of active LGIB, location, source vessel, and time required for interpretation. Evaluations were spaced one month apart. This experimental design allowed for estimation of incremental benefit of additional phases while controlling for carryover effects. Sensitivity and specificity were powered for equally (50/50). Generalized estimating equations (GEE) with sandwich estimation were used to estimate the relative difference of each phase using SAS 9.4. Mean patient age was 73.8 years. Specificity increased with added contrast phases (Art only 0.72; Art/NC 0.86; Art/NC/Del 0.95, p<0.001) without sacrifice in sensitivity (Art only 0.72; Art/NC 0.70; Art/NC/Del 0.72, p=0.3047) or increased mean time required per study (sec, Art only 31.7; Art/NC 30.6; Art/NC/Del 32.9, p=0.1813). Overall agreement among readers (Kappa) similarly increased (Art only 0.47; Art/NC 0.65; Art/NC/Del 0.79). When assessing for LGIB on multiphasic CTA, additional non-contrast and delayed phases incrementally increase specificity without decreased sensitivity or increased time required per study. In addition, the overall agreement between readers for diagnosis of LGIB as well as identifying bleed source and location increases with additional phases per exam, altogether supporting use of triphasic CTA in diagnosing LGIB.