Imaging of Intracranial Atherosclerosis: Stenoses and Collateral Perfusion 颅内动脉粥样硬化的影像学检查管腔狭窄与侧枝灌注,David S Liebeskind, MD,Associate Professor of Neurology & Director of Stroke Imaging Co-Director, UCLA Cerebral Blood Flow Laboratory Associate Neurology Director, UCLA Stroke Center,No potential conflicts to disclose,NIH/NINDS K23NS054084,June 20, 2009,Tiantan International Stroke Conference, Beijing, China,Objectives 目的,Overview of current imaging in intracranial atherosclerosis Consider arterial lesions beyond degree of luminal stenosis Underscore the paramount role of collateral perfusion Explore how imaging of intracranial atherosclerosis may provide insight on many other aspects of ischemic stroke,Ischemia 缺血,Ischemia as principal pathophysiologic event, collaterals may avert any detrimental effect of thrombosis or plaque Vast majority of efforts focus on restoration of antegrade flow, anti-thrombotics or arterial manipulation,Hemorrhagic transformation 出血性转化,Severe ischemia and neurovascular compromise Reperfusion rate ischemic pre- and post-conditioning driven via collaterals, DSL,Time is not brain!,Across population of stroke cases studied from onset to chronic phase, not in a given patient during early phases Time of symptom onset time of vascular occlusion Collaterals prone to failure over time, DSL,Moyamoya,Ideal model of collaterals in chronic cerebral ischemia Striking consistency in stenotic arterial features Universal dependence on leptomeningeal collaterals Strokes are typically limited in extent, allowing for recovery TIA without stroke should be goal Recurrent ischemia and temporal features easily studied,Imaging,Tools to understand physiology, mechanisms Not TCD vs. CTA vs. MRA vs. DSA etc. Distinct features emphasized by each modality Anatomy Flow,Trials,SONIA in parallel with WASID SAMMPRIS Opportunity to discern mechanisms Not just % stenosis Flow at lesion QMRA TCD with embolus detection Collaterals on DSA,N of 1- intracranial atherosclerosis,Diagnosis, rational selection of therapy Peri-procedural/serial imaging Opportunity to revise treatment strategy,Lesion/stenosis,Length and architecture of plaque,TCD beyond velocities,MFV, PI, AUC Current TCD velocity criteria for diagnosis of intracranial stenosis are insensitive to age- and gender-related changes in cerebral blood flow TCD diagnosis based on published criteria may overestimate disease prevalence Lab-specific norms may need to be established to account for demographic features of population,CTA,CTA Specifics,Luminal contents identified by filtering of image data based on Hounsfield units Contrast opacification errors due to administration, dosing, body habitus, injection rate, bolus tracking Window width and center levels are critical Measurement of stenoses Erroneous fusion of different structures Automated bone segmentation Calcifications,CTA Specifics,Predominantly anatomical angiographic images Insensitivity to flow physiology Lack of temporal resolution,Future of CTA,Improved image quality with increasing multidetector capability Possible temporal resolution Contrast modifications Alternative agents Refined dosing schemes,CTA of Stented Artery,MRA,Flow-sensitive nature of MRI Gradient echo imaging rapid scan acquisition with particular sensitivity to flow-related effects MRA techniques include time-of-flight (TOF) and phase contrast (PC) imaging,Time-of-Flight (TOF) MRA,Inflow of fully magnetized spins into a slice saturated by a radiofrequency pulse 2D TOF MRA thicker slices, lower signal-to-noise ratios 3D TOF MRA thin slices, higher signal-to-noise ratios Signal intensity dependent on slice thickness, flip angle, TE Magnetization transfer contrast for background suppression Multiple overlapping thin slab angiography (MOTSA),Time-of-Flight (TOF) MRA,Gadolinium-Enhanced MRA,Improves vascular signal intensity Reduces signal dropout due to slow flow Dynamic or time-resolved MRA Temporal resolution offset by limited spatial resolution,Gadolinium-Enhanced MRA,Phase Contrast (PC) MRA 相位对比MRA,PC MRA employs gradients that induce phase shifts in flowing blood with subsequent background subtraction Gradient modifications allow for determination of flow direction and flow rate Mapping of flow direction Measurement of flow rates Differentiating slow flow from frank thrombosis,MRA Specifics,Inferior spatial resolution Limited depiction of arterial structures beyond the proximal cerebral vessels Flow-related artifacts due to slow or turbulent flow Susceptibility artifact induced by metal clips or objects Patient motion may limit diagnostic utility,MRA Artifacts,Willisian collateralization,DSA,Methodology/critical appraisal?,Frequently encounter case series biased by other selection biases SONIA Not how we generally use techniques Rule-out disease,Intracranial vascular calcification,Plaque stability,USPIO Vessel wall imaging T1-weighted post-contrast images,GRE and phase imaging,FVH,Slow collateral flow distal to severe lesions Relatively rare,