contrast dye

Definition of contrast material
National Cancer Institute

contrast material

(KON-trast muh-TEER-ee-ul)
A dye or other substance that helps show abnormal areas inside the body. It is given by injection into a vein, by enema, or by mouth. Contrast material may be used with x-rays, CT scans, MRI, or other imaging tests.

Source: NCI Dictionary of Cancer Terms