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ischemia [2026/04/27 17:23] – scottischemia [2026/05/26 17:16] (current) – [Case Examples] scott
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 ====Important Sequences for Identifying Ischemia==== ====Important Sequences for Identifying Ischemia====
  
 +===Diffusion Weighted Imaging (DWI)===
 +
 +DWI sequences are critical for identifying ischemia, and virtually the only sequence that can directly demonstrate the pathophysiologic changes due to hypoxia. While the mechanisms are not fully understood, when neural tissues experience hypoxia they tend to swell and water tends to move from extracellular to intracellular spaces, reducing the overall free diffusion of water. This physiologic change can be seen with __DWI ONLY__.
 +
 +The DWI sequence will produce 3 image series: a b0, b1000, and an Apparent Diffusion Coefficient (ADC) map. The 'b' represents a parameter known as the 'b value' which controls the strength and duration of the diffusion weighting gradients; higher b values means diffusion effects will have a stronger influence on image contrast. 
 +
 +Most commonly, EPI sequences with relatively long TE's are used to acquire diffusion weighted images; this means that a significant amount of T2 weighting will influence the image contrast. Therefore, any hyperintensity seen on the b0 or b1000 may represent edema, or edema + restricted diffusion. Truly restricted diffusion will appear as DARK on the ADC Map and is the only way to ensure that the hyperintensity is not just due to edema.
 +
 +True ischemia will have this imaging relationship: __BRIGHT b1000 and DARK ADC__
 +
 +====Case Examples====
 +
 +Ischemia has a few characteristics, aside from it's appearance on DWI's:
 +
 +  * Sharp margins of affected areas
 +  * Corresponds to known vascular territory
 +  * Edema on T2 and T2 FLAIR
 +  * If severe, T1 hypointensity, especially T1 GREs
 +
 +===MCA Ischemia===
 +{{::mcaischemia.png?600|}}
 +
 +=== More MCA Ischemia===
 +{{::dwi_b1000_mca.gif?}} {{::mca-b1000.gif?}}
 +
 +===Lacunar Infarct aka Small Vessel Ischemia; Thalamus===
 +{{::lacunarinfarct.png?600|}}