MRI stands for Magnetic Resonance Imaging. It is a method of viewing the insides of structures such as living organisms or geological structures. It's most important use is in medical imaging to detect alterations in living tissue due to certain stimuli.

In clinical practice, it plays an important role as it can be used to distinguish healthy cells from tumurs and other abnormalities. According to current knowledge, it is completely harmless to the patient. It is still generally used conservatively however due to both cost and the risk that unknown side effects do exist.

It's main difference from CT is that CT can detect spatial resolution. This is the distance between two distinct structures. MRI's strength is that it can detect far better contrast resolution. This is the ability to distinguish between different tissue types.