Postcontrast

Postcontrast refers to imaging data acquired after the administration of a contrast agent with the aim of improving visualization of anatomy and pathology. Contrast agents work by altering the way tissues or vessels appear on the chosen imaging modality, increasing lesion conspicuity, delineating margins, and highlighting vascularity. Postcontrast imaging is used across several modalities, including computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, and, less commonly, nuclear medicine techniques.

In CT, iodinated contrast is injected and images are obtained during predefined phases, such as arterial, portal venous, and delayed phases. These phases help characterize lesions, assess perfusion, and evaluate vessel patency. In MRI, gadolinium-based contrast agents shorten T1 signals, enabling T1-weighted postcontrast sequences that highlight enhancement patterns. Dynamic contrast-enhanced MRI can track contrast uptake over time to characterize tissues. In ultrasound, microbubble contrast agents enhance echogenicity and can improve assessment of perfusion and lesion vascularity. Postcontrast ultrasound is used for focal liver lesions, renal lesions, and some cardiovascular indications.

Safety considerations include the risk of allergic reactions and, with gadolinium agents, potential nephrogenic systemic fibrosis in patients with advanced kidney disease. Iodinated contrast carries a risk of contrast-induced nephropathy, particularly in patients with preexisting renal impairment. Careful patient selection, hydration, and monitoring are standard precautions. The interpretation of postcontrast images relies on the timing of acquisition, the agent used, and expected enhancement patterns for specific tissues or lesions, aiding diagnosis and treatment planning.