Computerized Tomography

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CT is obtained urgently to exclude intracerebral hemorrhage and to identify whether imaging evidence of acute infarction exceeds one-third of the middle cerebral artery territory. In the presence of hemorrhage or large stroke, thrombolytic therapy is contra-indicated. A "hyperdense MCA sign'' (Fig. 2) may indicate thrombus within the middle cerebral artery and correlates with a worse outcome. Early changes of stroke may not be evident on CT for several hours after the stroke. Sudden deterioration may suggest hemor-rhagic transformation of a stroke, a repeated episode of bleeding from subarachnoid hemorrhage, expansion of the size of ischemic infarction, repeated embolic infarction, deterioration due to brain swelling, or many other possibilities. Because CT is widely available and can be obtained very rapidly, it is frequently used for reassessment after such changes. In uncooperative patients, in patients that require ventilatory assistance (or other hardware that may not be exposed to the strong magnetic field of an MR machine), and in emergency situations, CT is still the test of choice.

Mca Sign Brain

Figure 2 Acute ischemic stroke, CT, and diffusion weighted MR. The top images are slices from a CT scan obtained within hours after an acute middle cerebral artery (MCA) stroke. The "dense MCA sign'' can be seen (top left, arrow), but little evidence of stroke is noted (top right, arrow). In contrast, the acute diffusion weighted MRI shows substantial hyperintensity in the ischemic area [adapted with permission from R. Bakshi and L. Ketonen, Brain MRI in clinical neurology. In Baker's Clinical Neurology (R. J. Joynt and R. C. Griggs, Eds.). Copyright Lippincott, Williams & Wilkins, 2001].

Figure 2 Acute ischemic stroke, CT, and diffusion weighted MR. The top images are slices from a CT scan obtained within hours after an acute middle cerebral artery (MCA) stroke. The "dense MCA sign'' can be seen (top left, arrow), but little evidence of stroke is noted (top right, arrow). In contrast, the acute diffusion weighted MRI shows substantial hyperintensity in the ischemic area [adapted with permission from R. Bakshi and L. Ketonen, Brain MRI in clinical neurology. In Baker's Clinical Neurology (R. J. Joynt and R. C. Griggs, Eds.). Copyright Lippincott, Williams & Wilkins, 2001].

Three advances in CT have increased its clinical utility. First, contrast agents provide important information about the integrity of the blood-brain barrier. In malignancy, infection, inflammatory disorders, and subacute stroke, contrast material will often escape from the vessels, producing enhancement. Contrast enhancement begins about 3 days after a stroke and may persist for weeks. Second, CT angiography is now available. Vascular contrast agents attenuate the CT signal so that high-quality images of cerebrovascular anatomy can be derived using this technique. Third, contrast materials may be combined with CT to produce quantitatively accurate information about the volume of blood within a specific brain area. The inflow (time to peak) or washout (clearance) of contrast material (e.g., Xe or iodinated contrast agents) provide quantitative information about CBF through a brain area or vessel. These techniques are becoming more widely available and are increasingly important for acute stroke management.

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