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Why does a doctor use contrast dye with an MRI?

Sometimes a substance called contrast or dye is used. This helps to show different parts of the body in even more detail. Contrast or dye is given as an injection through a tiny tube called a catheter (also known as an IV) which is inserted into a vein, usually in the back of the hand or the front of the arm at the elbow.

Most types of body imaging use injectable contrast, or dyes. MRI is no different. What is different, however, is the type of contrast used, how it works and why it is used.

The contrast or dye materials used in procedures such as X-rays and CT scans work in the same way. Both use X-rays and these dyes work by preventing the X-ray photons from passing through areas where the dye has been injected. The X-ray photons, therefore, cannot reach the X-ray film. This results in different levels of density on the X-ray/CT film. The dyes have no direct physiologic impact on the body's tissue.

The contrast dye used in an MRI is fundamentally different.

MRI dyes work by altering the tissue's local magnetic field. Normal and abnormal tissue will respond differently to the slight alteration, giving doctors differing signals. These varied signals are transferred to the MRI images, allowing doctors to visualize many types of tissue abnormalities and disease processes. An MRI can do this better than possible without the contrast dye.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.