CT Near-Miss Events Caused by Superior Vena Cava Contrast Artifacts: Mechanisms, Triggering Errors, and Prevention

Abstract

Near-miss events are increasingly recognized as key indicators of safety in modern diagnostic imaging. In thoracic CT angiography, one of the most frequent—yet underreported—near-miss events arises during the bolus-tracking phase when highly concentrated contrast medium enters the superior vena cava (SVC). The extreme attenuation gradients and turbulent inflow within this vessel generate a complex pattern of beam-hardening and streak artifacts that destabilize Hounsfield Unit (HU) measurements within the bolus-tracking region of interest (ROI). These fluctuations may be misinterpreted by automated triggering algorithms as true arterial enhancement, causing premature scan initiation. Although adverse outcomes are often avoided by repeating the acquisition, these episodes still fulfill the definition of a near-miss and expose a significant vulnerability in automated timing systems. This review provides an expanded analysis of the physical mechanisms responsible for SVC artifacts, their impact on triggering accuracy, and the preventive strategies required to mitigate diagnostic risk. By reframing SVC-induced triggering errors as true near-miss events—rather than minor technical inconveniences—this work establishes a structured foundation for recognizing, reporting, and preventing a frequently overlooked safety issue in thoracic CT angiography. Key preventive measures include optimized ROI placement, adherence to evidence-based injection timing recommendations, and standardized saline-chaser protocols.