CT Head Slices …..8mm Spacing Copy

CT HEAD GENERAL CONCEPTS

The computed tomography ( CT ) scan is developed by passing a rotating beam of X-Rays through the patient. Thousands of X-Ray detectors in the donut shaped scanner measure the attenuation of the X-Rays by different tissue densities. Computer processing of this information result in images of cross sections or slices of the patient. The “cross sections” will reveal images proportionate to the tissue radiodensity and will follow a color coding similar to that previously discussed :

bone………………………………………………..whiter

fresh blood………………………………………. white

CSF …………………………………………………gray

infarcted brain tissue…………………………..grayer

air……………………………………………………..black

As a further refinement of “radiodensity coding “, we will introduce the concept of Hounsfield Unit later in this module. This will be used as a quantitative measure of the radiodensity of a given tissue. The CT scan basically takes a slice of the body part ( head, chest, abdomen, pelvis, bone, joint ) and presents an image reflecting the content of the tissues at that level. The interpreter then decides what these images probably represent according to their location, shape, Hounsfield Units, ( shade of black-white), e.g., a white area of the CT might represent…… bone calcified area (tumor, choroid plexus, etc.) acute hemorrhage ( intracerebral, subdural, subarachnoid, epidural ) contrast material foreign material .