core (ie, the part of the ischemic field that is not already infarcted). PWI and DWI PWI can demonstrate ischemic regions of the brain while DWI reveals cytotoxic edema from infarction. The PWI-DWI mismatch refers to the presence of a relatively larger area of ischemia on PWI (ie, the penumbra or territory with critically low perfusion) relative to a smaller area of irreversible ischemic injury (ie, the infarction core) on DWI ( image 4 and image 5 and image 6). PWI quantifies the magnetic susceptibility effect from the passage of intravenously administered gadolinium-based contrast agent. Analysis of the characteristics of the https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 12/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate contrast bolus passage through brain tissue can yield maps of the cerebral perfusion, including cerebral blood flow, cerebral blood volume, mean transit time, time-to-peak of the contrast enhancement, and time-to-peak of the residue function. Aside from PWI, another MRI method to evaluate brain perfusion is arterial spin labeling (ASL). Instead of using an intravascular contrast agent, ASL magnetically labels the blood entering the brain. ASL imaging within 24 hours of stroke symptom onset can depict perfusion defects and mismatches of diffusion and perfusion [86]. In addition, asymmetry of perfusion on ASL appears to correlate with stroke severity and outcome. In the DEFUSE 3 trial, which studied patients with late-window (6 to 16 hours after the time last known to be well) acute ischemic stroke, either CT or MR perfusion imaging was used to select patients for mechanical thrombectomy [87]. The study demonstrated a benefit of endovascular thrombectomy regardless of whether CT or MRI was used for patient selection, but the benefit was greater for patients selected using PWI compared with CTP. (See "Mechanical thrombectomy for acute ischemic stroke".) Clinical-core mismatch Using MRI, a clinical-core mismatch (ie, clinical-DWI mismatch) is based on the concept that the neurologic deficits are an expression of both the core infarct and the ischemic penumbra. A mismatch is present if the severity of the neurologic deficits, as measured by the National Institutes of Health Stroke Scale (NIHSS), is greater than that expected from the core infarct, which corresponds to the DWI lesion [88]. An age-adjusted clinical-core mismatch was used to select patients for mechanical thrombectomy in the DAWN trial. (See "Mechanical thrombectomy for acute ischemic stroke".) Clinical-ASPECTS mismatch Using CT, a clinical-ASPECTS mismatch is present if the severity of the neurologic deficits, as measured by the NIHSS, is greater than expected from the severity of the core infarct, as assessed by ASPECTS [89]. In practice, the mismatch is present for patient with an NIHSS score 10 and an ASPECTS 6. DWI-FLAIR mismatch The DWI-FLAIR mismatch refers to evidence of a hyperintense lesion on DWI consistent with acute infarction but no corresponding signal abnormality on the FLAIR images ( image 7) [90]. This mismatch indicates that the stroke is relatively acute (ie, within 4.5 hours), since insufficient time has passed for development of hyperintense signal on FLAIR, a sign of vasogenic edema. DWI-FLAIR mismatch has been used in clinical trials to select patients for treatment with intravenous thrombolysis when the time of stroke onset is unwitnessed or unknown [91]. (See "Approach to reperfusion therapy for acute ischemic stroke", section on 'Benefit with imaging selection of patients'.) https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 13/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate IMAGING OF HEMORRHAGIC STROKE Acute or subacute hemorrhage on imaging is a contraindication to reperfusion therapy (intravenous thrombolysis and mechanical thrombectomy). Evaluation, diagnosis, and management are reviewed separately according to the location of hemorrhage: Intracerebral (see "Spontaneous intracerebral hemorrhage: Pathogenesis, clinical features, and diagnosis" and "Spontaneous intracerebral hemorrhage: Acute treatment and prognosis") Intraventricular (see "Intraventricular hemorrhage") Subarachnoid (see "Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis" and "Aneurysmal subarachnoid hemorrhage: Treatment and prognosis" and "Nonaneurysmal subarachnoid hemorrhage") Subdural (see "Subdural hematoma in adults: Etiology, clinical features, and diagnosis" and "Subdural hematoma in adults: Management and prognosis") Epidural (see "Intracranial epidural hematoma in adults") OTHER IMAGING MODALITIES Digital subtraction angiography Digital subtraction angiography (DSA) is a method of visualizing the cerebral vasculature using selective injections of contrast through a catheter placed in the large arteries of the neck (ie, carotid and vertebral arteries) and head (cerebral arteries). DSA is rarely performed to triage patients in the setting of acute ischemic stroke for two main reasons. First, it is less available compared with CT angiography (CTA) and MR angiography (MRA). Second, DSA is associated with a risk of stroke, albeit low. The risk of stroke is estimated to be 0.14 to 1 percent, and the risk of transient ischemia is estimated to be 0.4 to 3 percent [92- 94]. DSA is an integral part of endovascular therapy procedures (ie, mechanical thrombectomy) for patients with acute ischemic stroke secondary to an occlusion of a large cerebral artery. The increased use of DSA started in 2015 after the publication of five major trials that demonstrated benefit of endovascular therapy up to six hours after stroke onset, and it has further increased since 2018 when two landmark trials were published that demonstrated benefit of mechanical https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 14/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate thrombectomy beyond the initial six-hour time window. (See "Mechanical thrombectomy for acute ischemic stroke".) DSA remains the gold standard for determining the severity of arterial stenosis and the presence of vasculopathy or vascular malformations [76]. In addition, it provides information about collateral flow and perfusion. Ultrasound methods Carotid duplex ultrasound (CDUS) and transcranial Doppler (TCD) ultrasound are noninvasive methods for neurovascular evaluation of the extracranial and intracranial large vessels, respectively. Carotid and vertebral duplex and TCD have traditionally been used independently in a predominantly elective, nonacute fashion to evaluate patients with transient ischemic attack (TIA) and ischemic stroke of possible large artery origin. Carotid and vertebral duplex Color flow guided duplex ultrasound is well established as a noninvasive examination to evaluate extracranial atherosclerotic disease. This topic is discussed separately. (See "Evaluation of carotid artery stenosis", section on 'Carotid duplex ultrasound'.) Transcranial Doppler TCD ultrasound uses low frequency (2 MHz) pulsed sound to penetrate bone and insonate intracranial vessels of the circle of Willis. Its use has gained acceptance as a noninvasive means to assess the patency of intracranial vessels. In patients with acute stroke, TCD is able to detect intracranial stenosis, identify collateral pathways, detect emboli on a real-time basis, and monitor reperfusion after thrombolysis [95-98]. Major drawbacks include operator dependence, poor acoustic windows (ie, inability to insonate flow in 15 percent of cases), and low sensitivity to flow in the vertebrobasilar arteries. Combined duplex and TCD The combination of urgent duplex and TCD has been described in a few small studies. As an example, a study of 150 patients found that the combination of duplex and TCD could be used effectively to detect arterial lesions amenable to interventional treatment [99]. A major limitation of this approach is that many centers are unable to perform these examinations emergently because of the lack of experienced sonographers. SOCIETY GUIDELINE LINKS Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Stroke in adults".) https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 15/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate INFORMATION FOR PATIENTS UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." th th The Basics patient education pieces are written in plain language, at the 5 to 6 grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more th th sophisticated, and more detailed. These articles are written at the 10 to 12 grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon. Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.) Basics topics (see "Patient education: Stroke (The Basics)") SUMMARY AND RECOMMENDATIONS Goals of imaging Immediate imaging of patients with suspected acute stroke is a priority because "time is brain" and because imaging provides essential information for selecting treatment. The goals of early neuroimaging are to distinguish ischemia from hemorrhage, exclude stroke mimics, detect signs of early infarction, depict the infarction core and ischemic penumbra, reveal the status of large cervical and intracranial arteries, and help determine patient eligibility for intravenous thrombolysis and mechanical thrombectomy. (See 'Goals of imaging' above and 'Urgency and scope of imaging' above.) Comparison of CT and MRI Noncontrast CT of the head is the standard imaging study for early acute stroke evaluation at most centers because of widespread availability, rapid scan times, and sensitivity for intracranial hemorrhage. MRI with diffusion-weighted imaging (DWI) is superior to CT for the detection of acute ischemic stroke and the exclusion of stroke mimics. In addition, MRI reliably detects acute intracranial hemorrhage. However, MRI is not as readily available for urgent imaging and is more limited by patient contraindications or intolerance. (See 'CT or MRI for initial imaging?' above.) Choosing initial imaging For patients who may be eligible for intravenous thrombolysis or mechanical thrombectomy ( algorithm 1), multimodal CT or MRI can provide crucial information to guide treatment decisions, including: https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 16/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate Whether there is cervical or intracranial large artery stenosis and occlusion The volume of the infarct core that is irreversibly damaged The volume of the ischemic penumbra that is salvageable with reperfusion The selection of initial neuroimaging studies can be guided by the time the patient was last known to be well and by local availability of advanced imaging with multimodal CT and MRI. Specifics are detailed above. (See 'Time-based selection of imaging' above.) Vessel imaging Neurovascular imaging with CT angiography (CTA) or MR angiography (MRA) is essential for confirming the presence of a large artery occlusion in patients who are candidates for mechanical thrombectomy. It is also important for assessing the potential sources of embolism and low flow in ischemic stroke. (See 'Vessel imaging' above.) Imaging the infarct core and ischemic penumbra Evaluation of the infarct core and ischemic penumbra with either DWI and perfusion-weighted imaging (PWI) or CT perfusion (CTP) imaging should be performed if the findings are likely to influence treatment decisions, such as mechanical thrombectomy in the late window (ie, >6 hours from the time last known to be well). (See 'Mismatch and salvageable brain tissue' above.) ACKNOWLEDGMENT The UpToDate editorial staff acknowledges Walter Koroshetz, MD, who contributed to an earlier version of this topic review. Use of UpToDate is subject to the Terms of Use. REFERENCES 1. Powers WJ, Rabinstein AA, Ackerson T, et al. Guidelines for the Early Management of Patients With Acute Ischemic Stroke: 2019 Update to the 2018 Guidelines for the Early Management of Acute Ischemic Stroke: A Guideline for Healthcare Professionals From the American Heart Association/American Stroke Association. Stroke 2019; 50:e344. 2. Molina CA, Saver JL. Extending reperfusion therapy for acute ischemic stroke: emerging pharmacological, mechanical, and imaging strategies. Stroke 2005; 36:2311. 3. Kamalian S, Lev MH. Stroke Imaging. Radiol Clin North Am 2019; 57:717. 4. Puig J, Shankar J, Liebeskind D, et al. From "Time is Brain" to "Imaging is Brain": A Paradigm Shift in the Management of Acute Ischemic Stroke. J Neuroimaging 2020; 30:562. https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 17/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate 5. Zerna C, Thomalla G, Campbell BCV, et al. Current practice and future directions in the diagnosis and acute treatment of ischaemic stroke. Lancet 2018; 392:1247. 6. Czap AL, Sheth SA. Overview of Imaging Modalities in Stroke. Neurology 2021; 97:S42. 7. von Kummer R, Bourquain H, Bastianello S, et al. Early prediction of irreversible brain damage after ischemic stroke at CT. Radiology 2001; 219:95. 8. Patel MR, Edelman RR, Warach S. Detection of hyperacute primary intraparenchymal hemorrhage by magnetic resonance imaging. Stroke 1996; 27:2321. 9. Fiebach JB, Schellinger PD, Gass A, et al. Stroke magnetic resonance imaging is accurate in hyperacute intracerebral hemorrhage: a multicenter study on the validity of stroke imaging. Stroke 2004; 35:502. 10. Kidwell CS, Chalela JA, Saver JL, et al. Comparison of MRI and CT for detection of acute intracerebral hemorrhage. JAMA 2004; 292:1823. 11. Simonsen CZ, Yoo AJ, Rasmussen M, et al. Magnetic Resonance Imaging Selection for Endovascular Stroke Therapy: Workflow in the GOLIATH Trial. Stroke 2018; 49:1402. 12. Shah S, Luby M, Poole K, et al. Screening with MRI for Accurate and Rapid Stroke Treatment: SMART. Neurology 2015; 84:2438. 13. S lling C, Ashkanian M, Hjort N, et al. Feasibility and logistics of MRI before thrombolytic treatment. Acta Neurol Scand 2009; 120:143. 14. Simonsen CZ, S rensen LH, Karabegovic S, et al. MRI before intraarterial therapy in ischemic stroke: feasibility, impact, and safety. J Cereb Blood Flow Metab 2014; 34:1076. 15. Ezzeddine MA, Lev MH, McDonald CT, et al. CT angiography with whole brain perfused blood volume imaging: added clinical value in the assessment of acute stroke. Stroke 2002; 33:959. 16. Kloska SP, Nabavi DG, Gaus C, et al. Acute stroke assessment with CT: do we need multimodal evaluation? Radiology 2004; 233:79. 17. Hopyan J, Ciarallo A, Dowlatshahi D, et al. Certainty of stroke diagnosis: incremental benefit with CT perfusion over noncontrast CT and CT angiography. Radiology 2010; 255:142. 18. Campbell BC, Weir L, Desmond PM, et al. CT perfusion improves diagnostic accuracy and confidence in acute ischaemic stroke. J Neurol Neurosurg Psychiatry 2013; 84:613. 19. Tan JC, Dillon WP, Liu S, et al. Systematic comparison of perfusion-CT and CT-angiography in acute stroke patients. Ann Neurol 2007; 61:533. 20. Wintermark M, Rowley HA, Lev MH. Acute stroke triage to intravenous thrombolysis and other therapies with advanced CT or MR imaging: pro CT. Radiology 2009; 251:619. https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 18/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate 21. Althaus K, Dreyhaupt J, Hyrenbach S, et al. MRI as a first-line imaging modality in acute ischemic stroke: a sustainable concept. Ther Adv Neurol Disord 2021; 14:17562864211030363. 22. Vilela P, Rowley HA. Brain ischemia: CT and MRI techniques in acute ischemic stroke. Eur J Radiol 2017; 96:162. 23. Nael K, Yoo B, Salamon N, Liebeskind DS. Acute Ischemic Stroke: MR Imaging-Based Paradigms. Neuroimaging Clin N Am 2021; 31:177. 24. Thomalla G, Gerloff C. Acute imaging for evidence-based treatment of ischemic stroke. Curr Opin Neurol 2019; 32:521. 25. Simonsen CZ, Leslie-Mazwi TM, Thomalla G. Which Imaging Approach Should Be Used for Stroke of Unknown Time of Onset? Stroke 2021; 52:373. 26. Wardlaw JM, Mielke O. Early signs of brain infarction at CT: observer reliability and outcome after thrombolytic treatment systematic review. Radiology 2005; 235:444. 27. Truwit CL, Barkovich AJ, Gean-Marton A, et al. Loss of the insular ribbon: another early CT sign of acute middle cerebral artery infarction. Radiology 1990; 176:801. 28. von Kummer R, Meyding-Lamad U, Forsting M, et al. Sensitivity and prognostic value of early CT in occlusion of the middle cerebral artery trunk. AJNR Am J Neuroradiol 1994; 15:9. 29. Marks MP, Holmgren EB, Fox AJ, et al. Evaluation of early computed tomographic findings in acute ischemic stroke. Stroke 1999; 30:389. 30. Wijdicks EF, Diringer MN. Middle cerebral artery territory infarction and early brain swelling: progression and effect of age on outcome. Mayo Clin Proc 1998; 73:829. 31. Hacke W, Kaste M, Fieschi C, et al. Intravenous thrombolysis with recombinant tissue plasminogen activator for acute hemispheric stroke. The European Cooperative Acute Stroke Study (ECASS). JAMA 1995; 274:1017. 32. Wardlaw JM, Dorman PJ, Lewis SC, Sandercock PA. Can stroke physicians and neuroradiologists identify signs of early cerebral infarction on CT? J Neurol Neurosurg Psychiatry 1999; 67:651. 33. Patel SC, Levine SR, Tilley BC, et al. Lack of clinical significance of early ischemic changes on computed tomography in acute stroke. JAMA 2001; 286:2830. 34. Barber PA, Demchuk AM, Zhang J, Buchan AM. Validity and reliability of a quantitative computed tomography score in predicting outcome of hyperacute stroke before thrombolytic therapy. ASPECTS Study Group. Alberta Stroke Programme Early CT Score. Lancet 2000; 355:1670. https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 19/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate 35. Pexman JH, Barber PA, Hill MD, et al. Use of the Alberta Stroke Program Early CT Score (ASPECTS) for assessing CT scans in patients with acute stroke. AJNR Am J Neuroradiol 2001; 22:1534. 36. Coutts SB, Demchuk AM, Barber PA, et al. Interobserver variation of ASPECTS in real time. Stroke 2004; 35:e103. 37. Naylor J, Churilov L, Rane N, et al. Reliability and Utility of the Alberta Stroke Program Early Computed Tomography Score in Hyperacute Stroke. J Stroke Cerebrovasc Dis 2017; 26:2547. 38. Prakkamakul S, Yoo AJ. ASPECTS CT in Acute Ischemia: Review of Current Data. Top Magn Reson Imaging 2017; 26:103. 39. Na DG, Kim EY, Ryoo JW, et al. CT sign of brain swelling without concomitant parenchymal hypoattenuation: comparison with diffusion- and perfusion-weighted MR imaging. Radiology 2005; 235:992. 40. Butcher KS, Lee SB, Parsons MW, et al. Differential prognosis of isolated cortical swelling and hypoattenuation on CT in acute stroke. Stroke 2007; 38:941. 41. Herweh C, Ringleb PA, Rauch G, et al. Performance of e-ASPECTS software in comparison to that of stroke physicians on assessing CT scans of acute ischemic stroke patients. Int J Stroke 2016; 11:438. 42. Lee EJ, Kim YH, Kim N, Kang DW. Deep into the Brain: Artificial Intelligence in Stroke Imaging. J Stroke 2017; 19:277. 43. Qiu W, Kuang H, Teleg E, et al. Machine Learning for Detecting Early Infarction in Acute Stroke with Non-Contrast-enhanced CT. Radiology 2020; 294:638. 44. Wolff L, Berkhemer OA, van Es ACGM, et al. Validation of automated Alberta Stroke Program Early CT Score (ASPECTS) software for detection of early ischemic changes on non-contrast brain CT scans. Neuroradiology 2021; 63:491. 45. Mair G, White P, Bath PM, et al. External Validation of e-ASPECTS Software for Interpreting Brain CT in Stroke. Ann Neurol 2022; 92:943. 46. Coutts SB, Lev MH, Eliasziw M, et al. ASPECTS on CTA source images versus unenhanced CT: added value in predicting final infarct extent and clinical outcome. Stroke 2004; 35:2472. 47. Parsons MW, Pepper EM, Chan V, et al. Perfusion computed tomography: prediction of final infarct extent and stroke outcome. Ann Neurol 2005; 58:672. 48. Hill MD, Buchan AM, Canadian Alteplase for Stroke Effectiveness Study (CASES) Investigators. Thrombolysis for acute ischemic stroke: results of the Canadian Alteplase for Stroke Effectiveness Study. CMAJ 2005; 172:1307. https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 20/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate 49. Demchuk AM, Hill MD, Barber PA, et al. Importance of early ischemic computed tomography changes using ASPECTS in NINDS rtPA Stroke Study. Stroke 2005; 36:2110. 50. Dzialowski I, Hill MD, Coutts SB, et al. Extent of early ischemic changes on computed tomography (CT) before thrombolysis: prognostic value of the Alberta Stroke Program Early CT Score in ECASS II. Stroke 2006; 37:973. 51. Puetz V, Sylaja PN, Coutts SB, et al. Extent of hypoattenuation on CT angiography source images predicts functional outcome in patients with basilar artery occlusion. Stroke 2008; 39:2485. 52. Tei H, Uchiyama S, Usui T, Ohara K. Posterior circulation ASPECTS on diffusion-weighted MRI can be a powerful marker for predicting functional outcome. J Neurol 2010; 257:767. 53. Schellinger PD, Bryan RN, Caplan LR, et al. Evidence-based guideline: The role of diffusion and perfusion MRI for the diagnosis of acute ischemic stroke: report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology. Neurology 2010; 75:177. 54. Warach S, Gaa J, Siewert B, et al. Acute human stroke studied by whole brain echo planar diffusion-weighted magnetic resonance imaging. Ann Neurol 1995; 37:231. 55. Sorensen AG, Buonanno FS, Gonzalez RG, et al. Hyperacute stroke: evaluation with combined multisection diffusion-weighted and hemodynamically weighted echo-planar MR imaging. Radiology 1996; 199:391. 56. Li F, Han S, Tatlisumak T, et al. A new method to improve in-bore middle cerebral artery occlusion in rats: demonstration with diffusion- and perfusion-weighted imaging. Stroke 1998; 29:1715. 57. Gonz lez RG, Schaefer PW, Buonanno FS, et al. Diffusion-weighted MR imaging: diagnostic accuracy in patients imaged within 6 hours of stroke symptom onset. Radiology 1999; 210:155. 58. Fiebach JB, Schellinger PD, Jansen O, et al. CT and diffusion-weighted MR imaging in randomized order: diffusion-weighted imaging results in higher accuracy and lower interrater variability in the diagnosis of hyperacute ischemic stroke. Stroke 2002; 33:2206. 59. Chalela JA, Kidwell CS, Nentwich LM, et al. Magnetic resonance imaging and computed tomography in emergency assessment of patients with suspected acute stroke: a prospective comparison. Lancet 2007; 369:293. 60. Brazzelli M, Sandercock PA, Chappell FM, et al. Magnetic resonance imaging versus computed tomography for detection of acute vascular lesions in patients presenting with stroke symptoms. Cochrane Database Syst Rev 2009; :CD007424. https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 21/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate 61. Brunser AM, Hoppe A, Illanes S, et al. Accuracy of diffusion-weighted imaging in the diagnosis of stroke in patients with suspected cerebral infarct. Stroke 2013; 44:1169. 62. Simonsen CZ, Madsen MH, Schmitz ML, et al. Sensitivity of diffusion- and perfusion- weighted imaging for diagnosing acute ischemic stroke is 97.5%. Stroke 2015; 46:98. 63. Ay H, Buonanno FS, Rordorf G, et al. Normal diffusion-weighted MRI during stroke-like deficits. Neurology 1999; 52:1784. 64. Sylaja PN, Coutts SB, Krol A, et al. When to expect negative diffusion-weighted images in stroke and transient ischemic attack. Stroke 2008; 39:1898. 65. Schulz UG, Briley D, Meagher T, et al. Diffusion-weighted MRI in 300 patients presenting late with subacute transient ischemic attack or minor stroke. Stroke 2004; 35:2459. 66. Beauchamp NJ Jr, Barker PB, Wang PY, vanZijl PC. Imaging of acute cerebral ischemia. Radiology 1999; 212:307. 67. Leys D, Pruvo JP, Godefroy O, et al. Prevalence and significance of hyperdense middle cerebral artery in acute stroke. Stroke 1992; 23:317. 68. Flacke S, Urbach H, Keller E, et al. Middle cerebral artery (MCA) susceptibility sign at susceptibility-based perfusion MR imaging: clinical importance and comparison with hyperdense MCA sign at CT. Radiology 2000; 215:476. 69. Rovira A, Orellana P, Alvarez-Sab n J, et al. Hyperacute ischemic stroke: middle cerebral artery susceptibility sign at echo-planar gradient-echo MR imaging. Radiology 2004; 232:466. 70. Huang P, Chen CH, Lin WC, et al. Clinical applications of susceptibility weighted imaging in patients with major stroke. J Neurol 2012; 259:1426. 71. Halefoglu AM, Yousem DM. Susceptibility weighted imaging: Clinical applications and future directions. World J Radiol 2018; 10:30. 72. Hsu CC, Kwan GNC, Hapugoda S, et al. Susceptibility weighted imaging in acute cerebral ischemia: review of emerging technical concepts and clinical applications. Neuroradiol J 2017; 30:109. 73. Khaladkar SM, Chanabasanavar V, Dhirawani S, et al. Susceptibility Weighted Imaging: An Effective Auxiliary Sequence That Enhances Insight Into the Imaging of Stroke. Cureus 2022; 14:e24918. 74. Belachew NF, Dobrocky T, Aleman EB, et al. SWI Susceptibility Vessel Sign in Patients Undergoing Mechanical Thrombectomy for Acute Ischemic Stroke. AJNR Am J Neuroradiol 2021; 42:1949. 75. Menon BK. Neuroimaging in Acute Stroke. Continuum (Minneap Minn) 2020; 26:287. https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 22/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate 76. Latchaw RE, Alberts MJ, Lev MH, et al. Recommendations for imaging of acute ischemic stroke: a scientific statement from the American Heart Association. Stroke 2009; 40:3646. 77. Leng X, Fang H, Leung TW, et al. Impact of Collateral Status on Successful Revascularization in Endovascular Treatment: A Systematic Review and Meta-Analysis. Cerebrovasc Dis 2016; 41:27. 78. Menon BK, d'Esterre CD, Qazi EM, et al. Multiphase CT Angiography: A New Tool for the Imaging Triage of Patients with Acute Ischemic Stroke. Radiology 2015; 275:510. 79. Goyal M, Demchuk AM, Menon BK, et al. Randomized assessment of rapid endovascular treatment of ischemic stroke. N Engl J Med 2015; 372:1019. 80. Lee KY, Latour LL, Luby M, et al. Distal hyperintense vessels on FLAIR: an MRI marker for collateral circulation in acute stroke? Neurology 2009; 72:1134. 81. Grosch AS, Kufner A, Boutitie F, et al. Extent of FLAIR Hyperintense Vessels May Modify Treatment Effect of Thrombolysis: A Post hoc Analysis of the WAKE-UP Trial. Front Neurol 2020; 11:623881. 82. MacLellan A, Mlynash M, Kemp S, et al. Perfusion Imaging Collateral Scores Predict Infarct Growth in Non-Reperfused DEFUSE 3 Patients. J Stroke Cerebrovasc Dis 2022; 31:106208. 83. Allmendinger AM, Tang ER, Lui YW, Spektor V. Imaging of stroke: Part 1, Perfusion CT overview of imaging technique, interpretation pearls, and common pitfalls. AJR Am J Roentgenol 2012; 198:52. 84. Vagal A, Wintermark M, Nael K, et al. Automated CT perfusion imaging for acute ischemic stroke: Pearls and pitfalls for real-world use. Neurology 2019; 93:888. 85. Heit JJ, Wintermark M. Perfusion Computed Tomography for the Evaluation of Acute Ischemic Stroke: Strengths and Pitfalls. Stroke 2016; 47:1153. 86. Chalela JA, Alsop DC, Gonzalez-Atavales JB, et al. Magnetic resonance perfusion imaging in acute ischemic stroke using continuous arterial spin labeling. Stroke 2000; 31:680. 87. Albers GW, Marks MP, Kemp S, et al. Thrombectomy for Stroke at 6 to 16 Hours with Selection by Perfusion Imaging. N Engl J Med 2018; 378:708. 88. D valos A, Blanco M, Pedraza S, et al. The clinical-DWI mismatch: a new diagnostic approach to the brain tissue at risk of infarction. Neurology 2004; 62:2187. 89. Bouslama M, Bowen MT, Haussen DC, et al. Selection Paradigms for Large Vessel Occlusion Acute Ischemic Stroke Endovascular Therapy. Cerebrovasc Dis 2017; 44:277. 90. Thomalla G, Fiebach JB, stergaard L, et al. A multicenter, randomized, double-blind, placebo-controlled trial to test efficacy and safety of magnetic resonance imaging-based thrombolysis in wake-up stroke (WAKE-UP). Int J Stroke 2014; 9:829. https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 23/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate 91. Thomalla G, Simonsen CZ, Boutitie F, et al. MRI-Guided Thrombolysis for Stroke with Unknown Time of Onset. N Engl J Med 2018; 379:611. 92. Johnston DC, Chapman KM, Goldstein LB. Low rate of complications of cerebral angiography in routine clinical practice. Neurology 2001; 57:2012. 93. Willinsky RA, Taylor SM, TerBrugge K, et al. Neurologic complications of cerebral angiography: prospective analysis of 2,899 procedures and review of the literature. Radiology 2003; 227:522. 94. Kaufmann TJ, Huston J 3rd, Mandrekar JN, et al. Complications of diagnostic cerebral angiography: evaluation of 19,826 consecutive patients. Radiology 2007; 243:812. 95. Alexandrov AV, Demchuk AM, Wein TH, Grotta JC. Yield of transcranial Doppler in acute cerebral ischemia. Stroke 1999; 30:1604. 96. Gao S, Wong KS, Hansberg T, et al. Microembolic signal predicts recurrent cerebral ischemic events in acute stroke patients with middle cerebral artery stenosis. Stroke 2004; 35:2832. 97. Saqqur M, Shuaib A, Alexandrov AV, et al. Derivation of transcranial Doppler criteria for rescue intra-arterial thrombolysis: multicenter experience from the Interventional Management of Stroke study. Stroke 2005; 36:865. 98. Sharma VK, Wong KS, Alexandrov AV. Transcranial Doppler. Front Neurol Neurosci 2016; 40:124. 99. Chernyshev OY, Garami Z, Calleja S, et al. Yield and accuracy of urgent combined carotid/transcranial ultrasound testing in acute cerebral ischemia. Stroke 2005; 36:32. Topic 1085 Version 40.0 https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 24/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate GRAPHICS Early ischemic changes on noncontrast head CT scan Findings of EIC in a 59-year-old man who presented with acute left hemiparesis. (A and B) NCCT 3.5 hours after symptom onset shows hypodensity and cortical swelling with sulcal effacement. There is loss of gray- white matter differentiation in the right frontal operculum, right temporal operculum, right insular cortex, and right frontoparietal lobes (arrowheads). CT: computed tomography; EIC: early ischemic changes; NCCT: noncontrast-enhanced computed tomography. From: Prakkamakul S, Yoo AJ. ASPECTS CT in Acute Ischemia: Review of Current Data. Top Magn Reson Imaging 2017; 26:103. DOI: 10.1097/RMR.0000000000000122. Copyright 2017. Reproduced with permission from Wolters Kluwer Health. Unauthorized reproduction of this material is prohibited. Graphic 121623 Version 2.0 https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 25/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate Evolution of early ischemic changes on head CT scan Evolution of early ischemic changes over time in a 35-year-old woman who presented with acute aphasia. (A) NCCT at one hour after symptom onset shows loss of gray white matter differentiation in the left frontal and temporal operculum and insular cortex and hypodensity in the lentiform nucleus (ASPECTS was 4 points for involvement of insula, lentiform, M1-3, M5). (B and C) NCCT and CTA-SI at two hours after symptoms onset and IV rtPA administration show more conspicuous hypodensity and mild effacement of cortical sulci compared with https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 26/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate NCCT at one hour after symptoms onset. (D) NCCT at eight hours after symptoms onset shows frank hypodensity in the infarcted areas. The extent of the hypodense areas remains the same but is more conspicuous than prior NCCT studies. CT: computed tomography; NCCT: noncontrast-enhanced computed tomography; ASPECTS: The Alberta Stroke Program Early CT score; CTA-SI: computed tomography angiography source image; IV: intravenous; rtPA: recombinant tissue plasminogen activator. From: Prakkamakul S, Yoo AJ. ASPECTS CT in Acute Ischemia: Review of Current Data. Top Magn Reson Imaging 2017; 26:103. DOI: 10.1097/RMR.0000000000000122. Copyright 2017. Reproduced with permission from Wolters Kluwer Health. Unauthorized reproduction of this material is prohibited. Graphic 121624 Version 2.0 https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 27/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate ASPECTS study form The ASPECTS value is calculated from two standard axial CT cuts: one at the level of the thalamus and basal ganglia (left), and one just rostral to the basal ganglia (right). A: anterior circulation; P: posterior circulation; C: caudate; L: lentiform; IC: internal capsule; I: insular ribbon; MCA: middle cerebral artery; M1: anterior MCA cortex; M2: MCA cortex lateral to insular ribbon; M3: posterior MCA cortex; M4, M5, and M6 are anterior, lateral, and posterior MCA territories immediately superior to M1, M2, and M3, rostral to basal ganglia Reproduced with permission from: Barber, PA, Demchuk, AM, Zhang, J, Buchan, AM. Validity and reliability of a quantitative computed tomography score in predicting outcome of hyperacute stroke before thrombolytic therapy. ASPECTS Study Group. Alberta Stroke Programme Early CT Score. Lancet 2000; 355:1670. Copyright 2000 The Lancet. Graphic 72190 Version 1.0 https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 28/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate ASPECTS study form and MCA variants (A and B) Right hemisphere, observer variations: lower and upper ASPECTS slices show as shaded areas the minimal and maximal variations in size of the cortical areas of the MCA (M1-M6) chosen by six expert observers. Left hemisphere, ASPECTS study form: A = anterior circulation; P = posterior circulation; C = caudate head; L = lentiform nucleus; IC = internal capsule; I = insular ribbon; MCA = middle cerebral artery; M1 = anterior MCA cortex; M2 = MCA cortex lateral to insular ribbon; M3 = posterior MCA cortex; M4, M5, and M6 are anterior, lateral, and posterior MCA territories, respectively, approximately 2 cm superior to M1, M2, and M3, respectively, rostral to basal ganglia. (C and D) Cortical MCA area variations with change of baseline. In the right hemisphere, the baseline is parallel to the inferior OML; in the left hemisphere, the baseline is the superior OML. OML=orbitomeatal line. (E and F) Normal vascular variations in MCA size on the two ASPECTS slices. The right hemisphere shows the larger normal variations described by van der Zwan* (light https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 29/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate shading). The left hemisphere of each shows the smaller, textbook , variations (dark shading). References van der Zwan, A, Hillen, B, Tulleken, AF, et al. Variability of the territories or the major cerebral arteries. J Neurosurg 1992; 77:927. Osborn, AG. Neuroradiology, Mosby, St. Louis 1995. Reproduced with permission from: Pexman, JH, Barber, PA, Hill, MD, et al. Use of the Alberta Stroke Program Early CT Score (ASPECTS) for assessing CT scans in patients with acute stroke. AJNR Am J Neuroradiol 2001; 22:1534. Copyright 2001 American Society of Neuroradiology. Graphic 63480 Version 1.0 https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 30/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate Multiphase CTA images (A) Images in a patient with a left M1 MCA occlusion (arrow) and good collaterals (backfilling arteries). (B) Images in a patient with a left M1 MCA occlusion (dashed arrow) and intermediate collaterals. (C) Images in a patient with a right M1 MCA occlusion (arrowhead) and poor collaterals (minimal backfilling arteries). CTA: computed tomography angiography. https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 31/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate Reproduced with permission from: Menon BK, d'Esterre CD, Qazi EM, et al. Multiphase CT angiography: A new tool for the imaging tria patients with acute ischemic stroke. Radiology 2015; 275:510. Copyright 2015 RSNA. Graphic 121648 Version 1.0 https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 32/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate Classic pattern of DWI-PWI mismatch Representative case with classic pattern of mismatch. (A) Diffusion weighted-image (DWI). (B) DWI abnormal lesion (shown in red) and hypoperfusion lesion (shown in green) superimposed on DWI. (C) DWI abnormal lesion and hypoperfusion lesion with brain image (DWI) removed. PWI: perfusion-weighted image. Reproduced with permission from: Ogata T, Nagakane Y, Christensen S, et al. A topographic study of the evolution of the MR DWI/PWI mismatch pattern and its clinical impact: a study by the EPITHET and DEFUSE Investigators. Stroke 2011; 42:1596. Copyright 2011 Lippincott Williams & Wilkins. Graphic 82701 Version 5.0 https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 33/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate Brain MRI showing large core-penumbra mismatch on diffusion- and perfusion- weighted sequences in a patient with acute ischemic stroke Diffusion- and perfusion-weighted brain MRI showing a large core-penumbra mismatch in a patient with an acute ischemic stroke. Diffusion-weighted MRI (panel A) indicates the infarction core in red as tissue with apparent diffusion coefficient <620 that measures 17 mL in volume. Perfusion-weighted MRI (panel B) indicates the ischemic penumbra in green as tissue with T volume. The mismatch volume is 122 mL and the mismatch ratio is 8.2. >6.0 seconds that measures 139 mL in max MRI: magnetic resonance imaging. Glenn A Tung, MD, FACR. Graphic 129431 Version 2.0 https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print 34/40 7/5/23, 12:16 PM Neuroimaging of acute stroke - UpToDate Brain MRI showing a small core-penumbra mismatch on diffusion- and perfusio weighted sequences in a patient with acute ischemic stroke Diffusion- and perfusion-weighted brain MRI showing a small core-penumbra mismatch in a patient with an acute ischemic stroke. Diffusion-weighted MRI (panel A) indicates the infarction core in red as tissue with apparent diffusion coefficient <620 that measures 151 mL in volume. Perfusion-weighted MRI (panel B) indicates the ischemic penumbra in green as tissue with Tmax >6.0 seconds that measures 177 mL in volume. The mismatch volume is 26 mL and the mismatch ratio is 1.2.