|Factors affecting the appearance|
Similar to the use of intravenous contrast in CT, the conspicuity of and contrast between structures of similar composition can be augmented by the use of intravenous contrast in MRI.
The contrast used in MRI is made of gadolinium, a paramagnetic substance with a strong magnetic field. Gadolinium affects the appearance of tissues on T1 weighted images, causing tissues which take it up to appear brighter on T1 weighted images. Gadolinium is administered to the patient by intravenous injection. Tissues that appear brighter on images obtained after gadolinium are said to "enhance".
The images above are T1 weighted axial images of the abdomen. The image on the right was obtained after intravenous gadolinium was administered. Note that the kidneys, aorta and pancreas are brighter due to the gadolinium. In addition, the renal medulla and cortex can be differentiated on the enhanced images, as they have taken up different amounts of gadolinium. Tumors and other abnormal tissues take up gadolinium differently from normal tissues, and gadolinium is to augment detection of these.