Diffusion-Weighted MRI

Diffusion-Weighted MRI

A patient is loaded into an MRI machine.
A patient is loaded into an MRI machine. Morsa Images/Getty Images

Diffusion-weighted MRI (magnetic resonance imaging) is a type of MRI sequence used to identify areas of an organ, such as the brain, which have recently been damaged or injured, often by a stroke.

Stroke can be caused either by an ischemic stroke (where a clot blocks the flow of blood to the brain) or by a hemorrhagic stroke (where a blood vessel ruptures, preventing blood flow to the brain. A transient ischemic attack, or "mini stroke", is caused by a temporary clot.

Effects of Stroke

If a stroke occurs and blood flow can't reach the area that controls a particular body function, that part of the body stops working as it should. If the stroke occurs toward the back of the brain, for example, it's likely that some level of vision will be impaired.

The effects of a stroke depend on several factors, including the location of the blockage and how much brain tissue is affected. However, because one side of the brain controls the opposite side of the body, a stroke affecting one side will result in neurological complications on the side of the body it affects. For example, if the stroke occurs in the brain's right side, the left side of the body (and the left side of the face) will be affected, which could produce any or all of the following:

  • Paralysis on the left side of the body
  • Vision problems
  • Quick, inquisitive behavioral style
  • Memory loss

If the stroke occurs in the left side of the brain, the right side of the body will be affected, producing some or all of the following:

  • Paralysis on the right side of the body
  • Speech/language problems
  • Slow, cautious behavioral style
  • Memory loss

When stroke occurs in the brain stem, depending on the severity of the injury, it can affect both sides of the body and may leave someone in a ‘locked-in’ state. When a locked-in state occurs, the patient is generally unable to speak or achieve any movement below the neck.

Diffusion-Weighted MRI

Diffusion-weighted MRI is also known as DWI MRI or DWI Sequence. During a diffusion-weighted MRI, the MRI machine is set to detect small restrictions in the movement of water molecules inside the injured areas. These small changes, which are commonly referred to as "areas of restricted diffusion," are detected by the MRI machine and ultimately appear as bright spots inside the organ being investigated.

Areas of acute stroke look like bright spots on DWI MRI.

DWI is a better imaging method than conventional MRI in detecting early ischemic lesions in stroke patients. In a study of diffusion-weighted MRI, researchers concluded that DWI is a better imaging method than conventional MRI in detecting early ischemic lesions in stroke patients. Lesion size as measured on DWI scans are potential parameters for predicting clinical outcome in acute stroke patients.

Reference:

American Stroke Association.

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