How affected is oxygen metabolism in DWI lesions? A combined acute stroke PET-MR study

Objective: To use back-to-back diffusion-weighted imaging (DWI) and PET to obtain quantitative measures of the cerebral metabolic rate of oxygen (CMRO2) within DWI lesions, and to assess the perfusion-metabolism coupling status by measuring the cerebral blood flow and the oxygen extraction fraction within DWI lesions. Methods: Six prospectively recruited acute carotid-territory stroke patients completed the imaging protocol, which was commenced 7 to 21 hours from onset and combined DWI derived from state-of-the-art diffusion tensor imaging sequencing using a 3-T magnet and fully quantitative O-15-PET. The PET variables were obtained in individual DWI lesions in each patient. Results: Across patients, the CMRO2 was reduced in the DWI lesion relative to mirror (mean reduction 39.5%; p = 0.028). Examining individual DWI lesions, however, revealed considerable variability in the extent of this CMRO2 reduction. The flow-metabolism coupling pattern underlying the DWI lesion was also variable, including ongoing ischemia, mild oligemia, and partial or complete reperfusion. Discussion: Diffusion-weighted imaging (DWI) lesions generally reflect substantial disruption of energy metabolism. However, the degree of metabolic disruption is variable, indicating DWI lesions may not always represent irreversibly damaged tissue. Finally, because DWI lesions can persist despite reperfusion, assessment of perfusion is necessary for interpretation of DWI changes in acute stroke.