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Use in Diagnosis

CT scans for brain imaging

A CT (Computed Tomography) scan is usually the first radiologic test done when a patient presents with neurologic symptoms suggesting a stroke or TIA. It is used to exclude the presence of hemorrhage, which is an essential step if the administration of "clot-busting" drugs is being considered.

A CT scan produces a picture of a slice of the brain. Features are made distinct by their differing attenuation (i.e., absorption or deflection) of x-rays passed through them. Detectors positioned around the circumference of the scanner collect attenuation readings from multiple angles. This numerical information is fed into a computer which constructs a gray-scale visual image of the brain slice. These images of the brain are optimized to show the subtle tissue differences between gray and white matter. (The major reason for this difference is the large amount of "fatty" (lipid-rich) myelin surrounding axons in the white matter in comparison to the gray matter, in which non-myelinated structures like neuron cell bodies and dendrites are also present.)

Simplified Display of CT Brain Tissue Image Characteristics

* Recall that the choroid plexi are specialized tissues that produce the CSF and are associated with specific parts of the ventricular system. In most adults, certain regions of the choroid plexi become calcified.

** The pineal gland is a single, unpaired structure that lies in the midline of the brain. It is located just rostral to the superior colliculus and has the shape of a little pine cone that is oriented with its tip pointing toward the occipital lobes (posterior). It also becomes partially calcified by the teenage years. 

By convention, images are always shown as though you were standing below the patient's head and looking up at the brain--this means that the patient's left is on the right side of the image.