The Diffusion-Weighted Lesion in Acute Stroke: Heterogeneous Patterns of Flow/Metabolism Uncoupling as Assessed by Quantitative Positron Emission Tomography

Abstract

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.