Relative Diffusion Rstriction - A New Framework for the Interpretation of the Apparent Diffusion Coefficent in Clinical Brain MRI
Friday, September 18, 2015 — Poster Session IV
- John Butman
Diffusion weighted imaging (ADC) is an essential component of clinical neuroimaging. Because diffusion weighted imaging combines T2 and diffusion effects, the apparent diffusion coefficient (ADC) is typically computed to remove the confound of T2 and generate a "pure" diffusion measurement. Interpretation of the ADC map is typically referenced to the diffusivity of normal brain. Thus, a region has abnormally low diffusivity (diffusion restriction) if the ADC of the lesion is less than that of normal brain. Conversely a lesion has high diffusivity if the ADC is greater than that of normal brain. This interpretation is overly simplistic, and neglects to take into account the high correlation of T2 and ADC with increasing water content as is seen with interstitial (vasogenic) edema and gliosis. Here we show a number of diverse pathologies in which this correlation is broken, so that the ADC is RELATIVELY low with respect to that expected based on the T2 value of the lesion. In these cases the ADC may still be higher than that of normal brain. Current radiologic interpretation is that the diffusion is elevated in such a lesion. The new proposition is that such lesions should be considered to have relatively low diffusivity, given the T2 signal. This new concept can help distinguish amongst otherwise similar lesions, particularly in the context of white matter diseases. The pathophysiologic basis of this is as yet unclear.
Category: Biomedical Engineering and Biophysics