الفهرس 
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Abstract
Perfusion CT was introduced to help identify and quantify the presence and extent of a perfusion deficit in patients presenting with acute stroke symptoms. The level of perfusion to the ischemic tissues may help to determine the relative benefits and risks of a given therapy. The use of other perfusion imaging techniques such as MRI may be limited by their availability.
Although the concept of perfusion CT is not new, the ability to measure perfusion parameters with accuracy has been made possible with the development of high-speed multidetector CT scanners having solid-state detectors and a gantry design to contain the very high gravitational forces generated by high-speed rotation of the x-ray tube. Software development has allowed rapid electronic transfer of data from the detector arrays and rapid image reconstruction for perfusion analysis.
Perfusion CT can be performed quickly, monitoring the contrast agent through the cerebral vasculature with any multislice CT scanner. Changes in tissue attenuation that occur in the brain are measured after the contrast injection. Post-processing of the perfusion CT data allows the generation of color-coded maps of various perfusion parameters, including CBF, cerebral blood volume (CBV), mean transit time (MTT), and the time-to-peak (TTP), the time from the start of contrast agent injection to the time of maximum enhancement. The maps generated depend on the algorithm used in the processing of the perfusion CT data Even in an acute ischemic stroke, CBV can be either increased, normal, or decreased, depending on the severity of hypoperfusion and collateral flow. Thus, the perfusion CT technique was expanded to assess the whole dynamics of a contrast-agent transit curve (i.e., dynamic perfusion CT). Analysis software is commercially available, and algorithms have been developed to actually quantify flow in cerebral tissue. In acute ischemia, dynamic perfusion CT has been shown to be a reliable alternative to MR perfusion.
The primary proposed indication for the addition of perfusion CT in the evaluation of acute stroke is to differentiate between reversible and irreversible ischemic tissues as non-contrast CT is relatively insensitive in detecting acute and small cortical or subcortical infarctions. It can be performed during the same imaging session, completed within three to five minutes following the standard non-contrast CT scan.
A non-contrast computed tomography (CT) scan is regarded as the most important diagnostic tool in the assessment of patients with a suspected acute stroke to exclude hemorrhage and demonstrate early infarct signs. Additional perfusion imaging techniques may help to identify and quantify the presence and extent of a perfusion deficit; however, treatment should not be unduly delayed in order to facilitate vascular imaging. Perfusion CT scan may become part of the screening CT protocol in the future.