CT Scan

What is a CT Scan

A computed tomography (CT) scan which was originally known as a computed axial tomography (CAT) scan is an imaging method where advanced x-ray technology is used to take two-dimensional pictures of slices of an object. Then using tomography and digital geometry processing a three-dimensional image is generated of the inside of the object from the series of images.

The procedure works by passing controlled amounts of x-ray radiation through the body where different tissues absorb the radiation at different rates. These rays are then absorbed by an array of detectors rather then the film used in a common x-ray. The CT scanner is composed of a rotating tube which has an x-ray machine mounted on side and the detector across from it. During each 360 degree rotation 1,000 images are taken which creates the image of a thin section. "You might think of it as a loaf of bread cut into thin slices. When the image slices are reassembled by computer, the result is a very detailed, multidimensional view of the body's interior." With the traditional CT small abrasions can go undetected if a patient moves slightly or breathes differently between scans. This problem has been corrected using a technique known as spiral CT. Spiral CT scans are taken using multiple detectors to allow higher resolution and faster scanning. The spiral CT was given this name because of the way the procedure works. During a spiral CT the moving table moves steadily through the scanner as the x-ray machine also rotates steadily. This traces a spiral path which avoids any gaps between images.

Leading up to having a CT scan the subject is often asked to avoid food especially if contrast materials, which are dyes used to highlight the images, are used. Then just before the scan the subject is asked to remove all metallic items as well as other objects which may interfere with the image quality. Then the subject lies down on a movable table and the table slides into the donut-shaped machine in position based on what part of the body is being scanned. The scan can take anywhere from half an hour to two hours. Minimizing body movement is very important to avoid image degredation.

Common Uses

CT scans provide us with a great way to analyze the internal structures of the human body. CT scans are used most commonly in healthcare although they can be used in other areas as well such as nondestructive material testing. CT scans are useful because they can show all types of tissues in great detail and aid in diagnosing all kinds of cancers, diseases, and trauma.

Procedures

Cranial CT

The cranial CT scan is most frequently used to diagnose intracranial hemorrhaging after accidents. Cranial CT scans are also used to detesct tumors, skull fractures, and surgical planning.
Chest CT
The chest CT scan is used to diagnose lung problems such as pneumonia, cancer, emphysema, pulmonary emoblisms, etc.
Abdominal and pelvic CT
The abdominal and pelvic CT scan is used to diagnose various abdominal diseases, monitor the progression of cancer, and investigaget other abdominal pain.
Extremities
CT scans are often used to analyze fractures, especially those around joints which are relatively complex.

Risks

Although CT scans offer a quick, non-invasive, and excellent imaging of a wide variety of tissues there are still several risks associated with them. The main risk is the exposure to x-rays which can be damaging although the common CT scan only exposes you to 10 mSv of radiation which is equivalent to the amount an average person receives from background radiation in three years.(4) Other risks include pregnant and nursing mothers who should let their doctor know before undergoing a CT scan. Finally since contrast mterials are often used people risk serious allergic reaction to the iodine in these materials although this is not very common.

References

Dale Neufeld