Adding non-contrast and delayed phases increases the diagnostic performance of arterial CTA for suspected active lower gastrointestinal bleeding.

Objectives: When assessing for lower gastrointestinal bleed (LGIB) using CTA, many advocate for acquiring non-contrast and delayed phases in addition to an arterial phase to improve diagnostic performance though the potential benefit of this approach has not been fully characterized. We evaluate diagnostic accuracy among radiologists when using single-phase, biphasic, and triphasic CTA in active LGIB detection.

Method And Materials: A random experimental block design was used where 3 blinded radiologists specialty trained in interventional radiology retrospectively interpreted 96 CTA examinations completed between Oct 2012 and Oct 2017 using (1) arterial only, (2) arterial/non-contrast, and (3) arterial/non-contrast/delayed phase configurations. Confirmed positive and negative LGIB studies were matched, balanced, and randomly ordered. Sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, positive and negative predictive values, and time to identify the presence/absence of active bleeding were examined using generalized estimating equations (GEE) with sandwich estimation assuming a binary distribution to estimate relative benefit of diagnostic performance between phase configurations.

Results: Specificity increased with additional contrast phases (arterial 72.2; arterial/non-contrast 86.1; arterial/non-contrast/delayed 95.1; p < 0.001) without changes in sensitivity (arterial 77.1; arterial/non-contrast 70.2; arterial/non-contrast/delayed 73.1; p = 0.11) or mean time required to identify bleeding per study (s, arterial 34.8; arterial/non-contrast 33.1; arterial/non-contrast/delayed 36.0; p = 0.99). Overall agreement among readers (Kappa) similarly increased (arterial 0.47; arterial/non-contrast 0.65; arterial/non-contrast/delayed 0.79).

Conclusion: The addition of non-contrast and delayed phases to arterial phase CTA increased specificity and inter-reader agreement for the detection of lower gastrointestinal bleeding without increasing reading times.

Key Points: • A triphasic CTA including non-contrast, arterial, and delayed phase has higher specificity for the detection of lower gastrointestinal bleeding than arterial-phase-only protocols. • Inter-reader agreement increases with additional contrast phases relative to single-phase CTA. • Increasing the number of contrast phases did not increase reading times.