The diffusion-weighted lesion in acute stroke: Heterogeneous patterns of flow/metabolism uncoupling as assessed by quantitative positron emission tomography

Background: To investigate what the hyperintense lesion in diffusion- weighted imaging ( DWI) of acute ischaemic stroke represents metabolically, we prospectively imaged acute carotid- territory stroke patients with DWI along with fully quantitative positron emission tomography ( PET), which gives physiological maps of cerebral blood flow ( CBF), the cerebral metabolic rate of oxygen (CMRO2) and the oxygen extraction fraction ( OEF). Method: Of 10 patients who consented, 5 ( 3 males, 2 females, 53 - 84 years, NIHSS 6 - 16) completed the imaging protocol of back- to- back DWI and PET within 21 ( mean 15.7, range 7 - 21) h of stroke onset. All images were co-registered with the DWI lesion forming a region of interest (ROI) that was transferred to the PET parametric maps ( OEF, CBF, CMRO2). Patterns of blood flow and metabolism were assessed within the DWI ROI. Results: Within the DWI lesions, the following patterns were observed: very low CBF and CMRO2/variable OEF; low CBF/ high OEF, and high CBF/ low OEF. There was a heterogeneity of patterns between and within DWI lesions. In addition, areas of hyperperfusion ( with low OEF) and areas of hypoperfusion ( with high OEF) were seen outside the DWI lesions. Conclusion: The DWI lesion does not have a single flow/ metabolism counterpart, suggesting that it reflects various stages of the ischaemic process.