Introduction:
Options for imaging in acute stroke are expanding with the potential to select therapy based on imaging targets, as well as providing additional diagnostic and prognostic information. Multimodal CT has been used to image the ischemic penumbra, infarct core, and to detect leptomeningeal collateral flow although the optimum way to image these variables is not clear.
Methods:
In addition to a systematic literature review of imaging for leptomeningeal collaterals, Data from observational studies of acute stroke which employed multimodal CT imaging on admission and follow up was used to evaluate feasibility of acute stroke imaging with CT and MRI, Perfusion thresholds for core and ischemic penumbra, methods to quantify leptomeningeal collateral flow and sensitivity of non contrast CT for detecting infarct core pixels.
Results:
Advanced imaging in acute stroke and at follow up was more feasible with CT compared to MRI with the possible suggestion that imaging with MRI alone could introduce a bias regarding age and clinical severity for patients entered into clinical studies
Heterogeneity in grading and detecting collateral flow was found in the literature providing an opportunity to devise a novel assessment method.
Well developed collaterals were associated with imaging and clinical markers for good outcome as well as some potential biomarkers including atrial fibrillation and blood fibrinogen level.
Relative cerebral blood flow and delay time were found to be the best predictors on infarct core and ischemic penumbra after derivation of optimum perfusion thresholds and subsequent validation in independent patient groups.
Pixel based comparison of infarct core on CT perfusion and non contrast CT highlighted the lack of sensitivity of CT for detecting infarct core based on Hounsfield unit value alone.
Conclusion:
Multimodal CT for acute stroke assessment offers the potential for measuring infarct core, ischemic penumbra and leptomeningeal collateral flow status rapidly according to novel grading scales and thresholds and provides information on tissue viability which cannot be detected on non-contrast CT. Further evaluation on the impact additional imaging should have in clinical practice is needed
