Bolus tracking

Bolus tracking is a technique used in computed tomography imaging, to visualise vessels more clearly. A small bolus of radio-opaque contrast media is injected into a patient via a peripheral intravenous cannula. Depending on the vessel being imaged, the volume of contrast is tracked using a region of interest (abbreviated "R.O.I.") at a certain level and then followed by the CT scanner once it reaches this level. Images are acquired at a rate as fast as the contrast moving through the blood vessels.

This method of imaging is used primarily to produce images of arteries, such as the aorta, pulmonary artery, cerebral, carotid and hepatic arteries. The image shown illustrates this technique on a sagittal MPR (multi planar reformat). The image is demonstrating the blood flow through an abdominal aortic aneurysm or AAA. The bright white on the image is the contrast. You can see the lumen of the aorta in which the contrast is contained, surrounded by a grey 'sack', which is the aneurysm. Images acquired from a bolus track, can be manipulated into a MIP (maximum intensity projection) or a volume rendered image.

...
Wikipedia