Detection of ischemic penumbra using combined perfusion and T2 * oxygen challenge imaging

Background Acute ischemic stroke is common and disabling, but there remains a paucity of acute treatment options and available treatment (thrombolysis) is underutilized. Advanced brain imaging, designed to identify viable hypoperfused tissue (penumbra), could target treatment to a wider population. Existing magnetic resonance imaging and computed tomography‐based technologies are not widely used pending validation in ongoing clinical trials. T2 * oxygen challenge magnetic resonance imaging, by providing a more direct readout of tissue viability, has the potential to identify more patients likely to benefit from thrombolysis – irrespective of time from stroke onset – and patients within and beyond the 4·5 h thrombolysis treatment window who are unlikely to benefit and are at an increased risk of hemorrhage. Aims This study employs serial multimodal imaging and voxel‐based analysis to develop optimal data processing for T2 * oxygen challenge penumbra assessment. Tissue in the ischemic hemisphere is compartmentalized into penumbra, ischemic core, or normal using T2 * oxygen challenge (single threshold) or T2 * oxygen challenge plus cerebral blood flow (dual threshold) data. Penumbra defined by perfusion imaging/apparent diffusion coefficient mismatch (dual threshold) is included for comparison. Methods Permanent middle cerebral artery occlusion was induced in male S prague‐ D awley rats ( n  = 6) prior to serial multimodal imaging: T2 * oxygen challenge, diffusion‐weighted and perfusion imaging (cerebral blood flow using arterial spin labeling). Results Across the different methods evaluated, T2 * oxygen challenge combined with perfusion imaging most closely predicted 24 h infarct volume. Penumbra volume declined from one to four‐hours post‐stroke: mean ±  SD , 77 ± 44 to 49 ± 37 mm 3 (single T2 * oxygen challenge‐based threshold); 55 ± 41 to 37 ± 12 mm 3 (dual T2 * oxygen challenge/cerebral blood flow); 84 ± 64 to 42 ± 18 mm 3 (dual cerebral blood flow/apparent diffusion coefficient), as ischemic core grew: 155 ± 37 to 211 ± 36 mm 3 (single apparent diffusion coefficient threshold); 178 ± 56 to 205 ± 33 mm 3 (dual T2 * oxygen challenge/cerebral blood flow); 139 ± 30 to 168 ± 38 mm 3 (dual cerebral blood flow/apparent diffusion coefficient). There was evidence of further lesion growth beyond four‐hours (T2‐defined edema‐corrected infarct, 231 ± 19 mm 3 ). Conclusions In conclusion, T2 * oxygen challenge combined with perfusion imaging has advantages over alternative magnetic resonance imaging techniques for penumbra detection by providing serial assessment of available penumbra based on tissue viability.