Bolus

A bolus is a single, concentrated dose of a substance, such as a contrast agent or medication, injected rapidly into a vein. In contrast-enhanced ultrasound, a bolus of microbubble contrast agent is injected intravenously and then tracked as it flows through the blood vessels and organs, providing detailed information about blood flow patterns and tissue perfusion. The timing of the bolus injection relative to the ultrasound imaging is important because different tissues enhance at different times, allowing sonographers to characterize liver lesions, evaluate transplant organ viability, and detect areas of abnormal blood flow. Contrast-enhanced ultrasound has become increasingly important as a diagnostic tool that avoids the radiation and contrast risks associated with CT and MRI.