Diffusion-weighted imaging in acute ischemic stroke
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Diffusion weighted imaging is commonly performed in MRI imaging for evaluation of an acute ischaemic stroke, and is excellent at detecting small and early infarcts. Conventional (T1 / T2/T2) MRI sequences may not demonstrate an infarct for 6 hours, and small infarcts may be hard to appreciate on CT for days, especially without the benefit of prior imaging.
For a general discussion of pathogenesis and radiographic features please refer to ischaemic stroke.
Decreased diffusion in ischaemic brain tissue is observed within a few minutes after arterial occlusion and progresses through a stereotypic sequence of ADC reduction, followed by subsequent increase, pseudo normalisation and, finally, permanent elevation.
Reported sensitivity ranges from 88 - 100-100% and specificity ranges from 86 - 100-100%
Radiographic features
The appearance of DWI / ADC/ADC depends on the timing.
Acute (0 - 7-7 days)
- ADC value decreases with maximal signal reduction at 1 to 4 days
- marked hyperintensity on DWI (a combination of T2 and diffusion weighting), less hyperintensity on exponential images, and
hypo-intensityhypointensity on ADC images. - subsequently, release of inflammatory mediators from ischaemic brain tissue leads to vasogenic oedema with extravasation of water molecules from blood vessels to expand the interstitial space, where water molecule diffusion is highly unrestricted.
Subacute (1 - 3-3 weeks)
- ADC pseudonormalisation occurs in the second week (7
- 15-15 days)- ADC values to rise and return to near baseline
- irreversible tissue necrosis is present despite normal ADC values
- DWI remains hyperintense due to T2 shine through
- after 2 weeks ADC values continue to rise above normal parenchyma and the region appears hyperintense 2
Chronic (>3 weeks)
- ADC signal high
- DWI signal low (as T2 hyperintensity and thus T2 shine through resolve).
-<p><strong>Diffusion weighted imaging</strong> is commonly performed in MRI imaging for evaluation of an acute <a href="/articles/ischaemic-stroke" title="Ischaemic stroke">ischaemic stroke</a>, and is excellent at detecting small and early infarcts. Conventional (T1 / T2) MRI sequences may not demonstrate an infarct for 6 hours, and small infarcts may be hard to appreciate on CT for days, especially without the benefit of prior imaging. </p><p>For a general discussion of pathogenesis and radiographic features please refer to <a href="/articles/ischaemic-stroke" title="Ischaemic stroke">ischaemic stroke. </a></p><p>Decreased diffusion in ischaemic brain tissue is observed within a few minutes after arterial occlusion and progresses through a stereotypic sequence of ADC reduction, followed by subsequent increase, pseudo normalisation and, finally, permanent elevation.</p><p>Reported sensitivity ranges from 88 - 100% and specificity ranges from 86 - 100%</p><h4>Radiographic features</h4><p>The appearance of DWI / ADC depends on the timing. </p><h5>Acute (0 - 7 days)</h5><ul>-<li>ADC value decreases with maximal signal reduction at 1 to 4 days</li>-<li>marked hyperintensity on <a href="/articles/diffusion-weighted-imaging-1" title="DWI">DWI </a>(a combination of T2 and diffusion weighting), less hyperintensity on exponential images, and hypo-intensity on ADC images. </li>-<li>subsequently, release of inflammatory mediators from ischaemic brain tissue leads to vasogenic oedema with extravasation of water molecules from blood vessels to expand the interstitial space, where water molecule diffusion is highly unrestricted. </li>-</ul><h5>Subacute (1 - 3 weeks) </h5><ul>-<li>ADC pseudonormalisation occurs in the second week (7 - 15 days)<ul>-<li>ADC values to rise and return to near baseline</li>-<li>irreversible tissue necrosis is present despite normal ADC values</li>-<li>DWI remains hyperintense due to <a href="/articles/t2-shine-through" title="T2 shine through">T2 shine through</a>-</li>- +<p><strong>Diffusion weighted imaging</strong> is commonly performed in MRI imaging for evaluation of an acute <a href="/articles/ischaemic-stroke">ischaemic stroke</a>, and is excellent at detecting small and early infarcts. Conventional (T1/T2) MRI sequences may not demonstrate an infarct for 6 hours, and small infarcts may be hard to appreciate on CT for days, especially without the benefit of prior imaging. </p><p>For a general discussion of pathogenesis and radiographic features please refer to <a href="/articles/ischaemic-stroke">ischaemic stroke.</a></p><p>Decreased diffusion in ischaemic brain tissue is observed within a few minutes after arterial occlusion and progresses through a stereotypic sequence of ADC reduction, followed by subsequent increase, pseudo normalisation and, finally, permanent elevation.</p><p>Reported sensitivity ranges from 88-100% and specificity ranges from 86-100%</p><h4>Radiographic features</h4><p>The appearance of DWI/ADC depends on the timing. </p><h5>Acute (0-7 days)</h5><ul>
- +<li>ADC value decreases with maximal signal reduction at 1 to 4 days</li>
- +<li>marked hyperintensity on <a href="/articles/diffusion-weighted-imaging-1">DWI </a>(a combination of T2 and diffusion weighting), less hyperintensity on exponential images, and hypointensity on ADC images.</li>
- +<li>subsequently, release of inflammatory mediators from ischaemic brain tissue leads to vasogenic oedema with extravasation of water molecules from blood vessels to expand the interstitial space, where water molecule diffusion is highly unrestricted.</li>
- +</ul><h5>Subacute (1-3 weeks) </h5><ul>
- +<li>ADC pseudonormalisation occurs in the second week (7-15 days)<ul>
- +<li>ADC values to rise and return to near baseline</li>
- +<li>irreversible tissue necrosis is present despite normal ADC values</li>
- +<li>DWI remains hyperintense due to <a href="/articles/t2-shine-through">T2 shine through</a>
- +</li>
-</li>- +</li>
-</li>- +</li>
-<li>ADC signal high</li>-<li>DWI signal low (as T2 hyperintensity and thus T2 shine through resolve). </li>- +<li>ADC signal high</li>
- +<li>DWI signal low (as T2 hyperintensity and thus T2 shine through resolve). </li>
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