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hemodynamic status may be obtained by modern imaging studies.85 Neuroimaging tests might improve selection of patients who could be treated with reperfusion therapies by identifying those with regions of salvageable brain tissue, a low risk for hemorrhagic transformation, or occlusions of large arteries that might or might not be amenable to therapy. CT and magnetic resonance imaging (MRI) are being used as initial imaging options. The most commonly obtained brain imaging test is noncontrast CT, but individual centers able to obtain MRI with efficiency equal to that of CT are using an MRI strategy in patients without MR contraindications.86–90 Additional research is required.91,92 As a result, it is generally agreed that the performance of these tests should not delay treatment with intravenous rtPA.86,91–93 1. Non–Contrast-Enhanced CT Scan of the Brain It is agreed that emergency, non–contrast-enhanced CT scanning of the brain accurately identifies most cases of intracranial hemorrhage and helps discriminate nonvascular causes of neurological symptoms (eg, brain tumor). The prior guidelines recommended that CT be the primary diagnostic brain imaging study for evaluation of patients with suspected stroke.94 Although CT is the “criterion standard” with which other brain imaging studies are compared, it is relatively insensitive in detecting acute and small cortical or subcortical infarctions, especially in the posterior fossa.95 In most cases, the use of a contrast infusion does not provide additional information and is not necessary unless it is required for CT angiography (and, more recently, CT perfusion) or concern exists about a brain tumor or infectious process. With the advent of rtPA treatment, interest has grown in using CT to identify subtle, early signs of ischemic brain injury (early infarct signs) or arterial occlusion (hyperdense vessel sign) that might affect decisions about treatment. In addition, the loss of the gray-white differentiation in the cortical ribbon (particularly at the lateral margins of the insula) or the lentiform nucleus and sulcal effacement can often be detected within 6 hours in up to 82% of patients with large-vessel anterior circulation occlusions.96,97 These signs are associated with poorer outcomes.98,99 In addition, widespread signs of early infarction are correlated with a higher risk of hemorrhagic transformation after treatment with thrombolytic agents. In combined data from 2 trials of intravenous rtPA administered within 3 hours of symptom onset, CT evidence of early edema or mass effect was accompanied by an 8-fold increase in the risk of symptomatic hemorrhage.66 In a second analysis, early infarct signs involving more than one third of the territory of the middle cerebral artery (MCA) were not independently associated with increased risk of adverse outcome after rtPA treatment, and as a group these patients still benefited from therapy.100 In a European trial in which thrombolytic therapy was administered within 6 hours of symptom onset, patients estimated to have involvement of more than one third of the territory of the MCA had an increased risk of intracerebral hemorrhage, whereas those with less involvement benefited the most from thrombolytic treatment.99,101 However, physicians’ ability to reliably and reproducibly recognize the early CT changes is variable.102–106 Use of scoring systems for early CT changes may improve identification of cerebral ischemia and may provide valuable prognostic information but is not validated for outcome or patient selection for acute treatments.107,108 Further studies are needed to determine the significance of early infarct signs and their role in treatment decision making.109 For patients who are candidates for treatment with rtPA, the goal is to complete the CT examination within 25 minutes of arrival at the ED, with the study interpreted within an additional 20 minutes (door-to-interpretation time of 45 minutes).61 A subsequent CT scan often is obtained if the patient worsens neurologically and may be especially helpful in identifying hemorrhagic transformation after administration of rtPA.66 2. Multimodal CT Recent technological advances have led to increased interest in more sophisticated multimodal approaches to
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