SPREADING OF VASOGENIC EDEMA AND CYTOTOXIC EDEMA ASSESSED BY QUANTITATIVE DIFFUSION AND T2 MAGNETIC-RESONANCE-IMAGING

Background and Purpose The apparent diffusion coefficient (ADC) of wat er should be sensitive to the cytotoxic edema triggered by energy fail ure during ischemia. Elevated values of T2, the nuclear MR transverse relaxation time of water, seen on T2 nuclear MR images detect vasogeni c edema and infarcted areas. The temporal and spatial changes in ADC a nd T2 abnormalities after occlusion of the middle cerebral artery (MCA O) were therefore estimated by these two quantitative techniques. Meth ods Permanent MCAO was performed on rats. Quantitative ADC and T2 maps of brain water were obtained, from which the ischemic volumes were ca lculated at various times up to 48 hours after MCAO. Results The areas of decreased ADC represented 36+/-7% of the final infarct volume (24 hours) at 0.5 hours and 64+/-4% at 5 hours after MCAO, suggesting that there is recruitment of peripheral areas with disturbed energy metabo lism and cytotoxic edema. The ADC and T2 contours closely matched at 3 .5, 24, and 48 hours after MCAO. Conclusions T2 imaging can assess isc hemic insults as well as ADC imaging, but only 3.5 hours after the ons et of ischemia. Assessment of edematous swelling (approximate to 24.5% of total infarcted volume) demonstrates that ADC and therefore T2 ima ging detect all the tissue that will become infarcted approximately 7 hours after occlusion. The spread of ADC and T2 abnormalities would th erefore stop at approximately 7 hours, and any further increase in vol ume observed on the images would be mainly due to edematous swelling.