Computed tomography (CT) was developed in the 1970s. This imaging technique makes use of the same imaging principles as does traditional x-ray imaging in which ionizing radiation is projected through the body onto a special photographic plate. CT, however, uses special equipment to obtain images from many different angles. The information from these images is then processed by a computer and used to create a cross-section of body tissues and organs. In its early development, computed tomography took several hours to assemble a single image or "slice." These images were also restricted to horizontal or "axial" cross-sections of the body (hence the original term "Computed Axial Tomography" or "CAT scan"). However, there have been many major advances in the past 25 years, such that CT scans are now much faster, while at the same time showing greater detail.

The use of CT can be divided into two categories: CT of the head and CT of the body. Head CT is used for a wide variety of reasons. These include locating skull fractures and brain damage (head injury), detecting a blood clot or bleed within the brain (stroke or leaking aneurysm), determining the extent of bone and soft tissue damage (facial trauma), detecting some brain tumors, illuminating enlarged brain cavities or ventricles (hydrocephalus), and evaluating for sinus inflammation or other changes (sinusitis). Potential uses of body CT include diagnosing and planning treatment for many different cancers, (such as lung, liver, and pancreatic cancer), diagnosing and treating spinal problems and injuries to the hands, feet and other skeletal structures, measuring bone mineral density for the detection of osteoporosis, identification of injuries (trauma) to the liver, spleen, kidneys, or other internal organs, and the diagnosis and treatment of vascular diseases.

A CT scan consists of placing the patient on a movable table, which then moves the patient through the donut-like scanner. Cross-sectional slices are then sent immediately to a computer, where they can be adjusted to specific parameters (called "windows") in order to best visualize the organs of interest. The images are then interpreted by a radiologist who views them either on printed films or on a special imaging computer. CT scans at UAMS are read solely on computers.

The main advantage of CT imaging over plain film (x-ray) is that the images created have much better resolution and diagnostic utility. By viewing a series of CT scans, a doctor can know exactly where in the body an injury or tumor is, in addition to knowing how large it is, and what internal organs are affected. Unlike traditional x-rays, CT can also offer detailed views of many different kinds of tissue, including lungs, bones, soft tissues and blood vessels. The detail provided by CT means that this non-invasive modality can eliminate the need for invasive exploratory surgery and surgical biopsy. CT is the preferred imaging modality in cases of head injury, especially when a bleed into the brain is suspected. In the emergency setting, CT was once considered too slow to be of any immediate benefit. However, improved equipment means that CT scans can now be conducted in a matter of minutes to assess the extent of injury and help save lives.

The major concern patients have about CT is the risk of radiation exposure. Like traditional x-ray techniques, CT scans expose the body to ionizing radiation, too much of which can increase cancer risk. Because of the multiple images that must be taken, CT does expose the body to more radiation than does x-ray. The amount of ionizing radiation used in a CT scan is equivalent to the amount of background radiation that the average person receives over 8 months (head CT) to 3 years (body CT). However, in terms of diagnosing a possibly life-threatening condition, the benefit of this procedure far outweighs the potential risk. In addition, special care is taken to minimize the amount of radiation exposure. The other concern about CT has to do with the use of contrast material, which is injected into the body to highlight particular structures, usually blood vessels. IV contrast can cause further damage to already weakened kidneys and can cause an allergic reaction, although this is rarely severe.

Images from CT scans can now be reconstructed into a 3-dimensional (3D) image by "stacking" slices on top of each other. Though a trained radiologist will be able to make diagnoses without this 3D reconstruction, a 3D image is often helpful in appreciating the extent of a particular problem. CT has also recently been combined with angiography to gain more anatomically accurate data about blood flow through vessels.

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