What is the role of diffusion-weighted imaging (DWI) in the workup of acute stroke?

Updated: Dec 19, 2018
  • Author: Souvik Sen, MD, MPH, MS, FAHA; Chief Editor: Helmi L Lutsep, MD  more...
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Answer

Diffusion-weighted imaging (DWI) is sensitive to the microscopic random motion of the water molecule protons, a value known as the apparent diffusion coefficient (ADC), which is measured and captured by this type of imaging. The water molecules move in the direction of the magnetic field gradient; they accumulate a phase shift in their transverse magnetization relative to that of a stationary one, and this phase shift is directly related to the signal attenuation of the image. (See the image below.)

The diffusion-weighted MRI reveals a region of hyp The diffusion-weighted MRI reveals a region of hypointensity in the distribution of the right middle cerebral artery. Flanking the anterior and posterior regions of this abnormality are regions of hyperintensities, which represent regions of new infarct. The contiguity of these regions suggests that they are extensions of the old infarct.

Numerous studies have shown that ADCs in ischemic areas are lower by 50% or more compared with those of normal brain areas, and they appear as bright areas (ie, hyperintensities) on DWI (see the image below). Studies have demonstrated that changes in the ADC occur as early as 10 minutes following the onset of ischemia.

Magnetic resonance imaging in acute stroke. Left: Magnetic resonance imaging in acute stroke. Left: Diffusion-weighted MRI in acute ischemic stroke performed 35 minutes after symptom onset. Right: Apparent diffusion coefficient (ADC) map obtained from the same patient at the same time.

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