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Intracranial atherosclerosis is a major cause of ischemic stroke. Patients with a high degree of stenosis have a significant rate of stroke despite medical therapy. Two randomized trials of stenting have failed to show benefit. Improving periprocedural complication rates and patient selection may improve stenting outcomes. Fractional flow reserve (FFR), intravascular ultrasound (IVUS), and optical coherence tomography (OCT) are intravascular imaging techniques employed to improve patient selection and stent placement in interventional cardiology. FFR has been shown to improve cardiovascular outcomes when used in patient selection for intervention. Studies of FFR in intracranial atherosclerosis show that the measure may predict which plaques lead to stroke. IVUS is used in cardiology to quantify stenosis and assist with stent placement. Comparisons with histology show that it can reliably characterize plaques. Several case reports of IVUS in intracranial arteries show the technique to be feasible and indicate it may improve stent placement. Plaque characteristics on IVUS may help identify vulnerable plaques. In interventional cardiology, OCT provides excellent visualization of vessel geometry and is useful periprocedurally. Images reliably identify thin-capped fibroatheromas and other plaque features. Case reports indicate that OCT is safe for use in intracranial arteries. OCT can be used to identify perforator vessels and so may be useful in avoiding perforator strokes, a common complication of stenting. Plaque characteristics on OCT may be useful in patient selection.

Background Following reperfusion treatment in ischemic stroke, CT imaging at 24-hours is widely used to assess radiological outcomes. Even without visible hyperattenuation, occult angiographic contrast may persist in the brain and confound Hounsfield Unit-based imaging metrics such as Net Water Uptake (NWU). Aims We aimed to assess the presence and factors associated with retained contrast post-thrombectomy on 24-hour imaging using Dual Energy CT (DECT), and its impact on the accuracy of NWU as a measure of cerebral edema. Methods Consecutive patients with anterior circulation large vessel occlusion who had post-thrombectomy DECT performed 24-hours post-treatment from two thrombectomy stroke centers were retrospectively studied. NWU was calculated by interside comparison of Hounsfield Units of the infarct lesion and its mirror homolog. Retained contrast was quantified by the difference in NWU values with and without adjustment for iodine. Patients with visible hyperdensities from hemorrhagic transformation or visible contrast retention, and bilateral infarcts were excluded. Cerebral edema was measured by relative hemispheric volume (rHV) and midline shift (MLS). Results Of 125 patients analyzed (median age 71 [IQR 61-80], baseline NIHSS 16 [IQR 9.75-21]), reperfusion (defined as extended-Thrombolysis-In-Cerebral-Infarction 2b-3) was achieved in 113 patients (90.4%). Iodine-subtracted NWU was significantly higher than unadjusted NWU (17.1% vs 10.8%, p<0.001). In multivariable median regression analysis, increased age (p=0.024), number of passes (p=0.006), final infarct volume (p=0.023) and study site (p=0.021) were independently associated with amount of retained contrast. Iodine-subtracted NWU correlated with rHV (rho=0.154, p=0.043) and MLS (rho=0.165, p=0.033) but unadjusted NWU did not (rHV rho=-0.035, p=0.35; MLS rho=0.035, p=0.347). Conclusions Angiographic iodine contrast is retained in brain parenchyma 24-hours post-thrombectomy, even without visually obvious hyperdensities on CT, and significantly affects NWU measurements. Adjustment for retained iodine using DECT is required for accurate NWU measurements post-thrombectomy. Future quantitative studies analyzing CT after thrombectomy should consider occult contrast retention.