IV Contrast Flow and Timing

Knowing how long it takes for IV contrast to reach certain anatomical structures is key to understanding why certain CT protocols are setup the way they are.

It is also helpful when critiquing your images to ensure you have scanned at the correct delay time.

So I would like to present to you my (extremely nerdy) IV contrast flow and timing chart! The times depicted in the each circle is how long it takes for IV contrast to reach the anatomical structure. Blue is venous, red is arterial. Obviously these numbers would vary depending on the patient's cardiac output and (to a lesser extent) your selected flow rate. So let's assume these numbers represent an average patient, normal cardiac and renal function, with an injection rate of 3 ml/sec.

Injection speed really only plays a part in timing before it reaches the aorta (i.e. for a CTPA). Once the contrast is in the left ventricle, it will only move as fast as the heart can pump it out. It will, however, determine the density of the contrast bolus and therefore how bright the contrast will appear on the images.