MRI interpretation
Contrast agents

Key points

  • Gadolinium is the most common contrast agent used for MRI – it can be given intravenously or injected directly into a body part
  • Abnormal tissue may enhance more than surrounding normal tissue following intravenous gadolinium
  • Abnormal tissue may also retain gadolinium longer than normal tissue

Additional information can sometimes be gained by use of a contrast agent.

The most common contrast agent is gadolinium, a para-magnetic substance which produces very high T1 signal. It is usually given intravenously, but can also be injected directly into a body part, such as a joint.

Intravenous gadolinium

Pre and post-gadolinium T1-weighted images are compared in order to assess 'enhancement' of tissues. Abnormal tissue, such as inflamed or cancerous tissue, is often more vascular than surrounding tissue and so 'enhances', appearing brighter on post-gadolinium images

MRI with gadolinium (brain)

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MRI with gadolinium (brain)

  • The pre-gadolinium image shows only an indistinct area of abnormality in the left cerebral hemisphere
  • The post-gadolinium image of the brain shows a very well-defined area of enhancement – in this case due to a malignant brain tumour

Delayed gadolinium enhancement

In some clinical settings, delayed imaging is used to see if gadolinium is retained within abnormal tissue.

Cardiac MRI

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Cardiac MRI

  • This image was acquired after a delay of 15 minutes following intravenous injection of gadolinium
  • An area of the myocardium remains ‘enhanced’ (arrows)
  • This ‘delayed enhancement’ indicates cell death in this area of the heart following myocardial infarction
  • A normal example is shown for comparison – gadolinium is not retained by normal myocardial tissue (arrowheads)

Direct gadolinium

Gadolinium can be injected directly into a body part. For example, a joint can be injected to help visualise joint structures (MRI arthrogram).

MRI arthrogram – shoulder

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MRI arthrogram – shoulder

  • Fluid containing gadolinium has been injected into the shoulder joint revealing displacement of the anterior glenoid labrum in this patient with recurrent shoulder dislocation
  • G = Glenoid of scapula
  • H = Head of humerus