Computerized Axial Tomography Scanner

Nicholas K. Birech

March, 2006

A computerized axial tomography scan is more commonly known by its abbreviated name, CAT scan or CT scan. It is an x-ray procedure which combines many x-ray images with the aid of a computer to generate cross-sectional views and, if needed, three-dimensional images of the internal organs and structures of the body. The operating setup of a CAT Scanner.

A fan shaped beam of x-rays is directed to an array of stationary 360 degree ring of detectors that are fixed in position relative to the x-ray source. The fan shaped x-ray beam rotated around the patient directed at detectors in a non-fixed relationship. X-ray slice data is generated as the X-ray source rotates around the object/patient; the X-ray sensors positioned on the opposite side of the circle from the X-ray source pick up the data. Many data scans are progressively taken as the object is gradually passed through the gantry. They are combined together by the mathematical procedure known as tomographic reconstruction.

Newer machines with faster computer systems and newer software strategies can process not only individual cross sections but continuously changing cross sections as the gantry, with the object to be imaged, is slowly and smoothly slid through the X-ray circle. These are called helical or spiral CT machines. Their computer systems integrate the data of the moving individual slices to generate three dimensional volumetric information (3D-CT scan), in turn viewable from multiple different perspectives on attached CT workstation monitors.

Traditional CAT scanners use one X-ray source that rotates around the organ being imaged, but modern scanners combines two rotating x-ray sources and two array of detectors, significantly improving the quality of information each scan produces

Medical Use of CAT Scans
CAT scans are performed to analyze the internal structures of various parts of the body. This includes:

The head, where traumatic injuries, (such as blood clots or skull fractures), tumors, and infections can be identified.
The spine: the bony structure of the vertebrae can accurately be defined, as can the anatomy of the intervertebral discs and spinal cord. Occasionally, contrast material (an x-ray dye) is placed into the spinal fluid to further enhance the scan and the various structural relationships of the spine, the spinal cord, and its nerves.
CAT scans are also used in the chest to identify tumors, cysts, or infections that may be suspected on a chest x-ray.
CAT scans of the abdomen are extremely helpful in defining body organ anatomy, including visualizing the liver, gallbladder, pancreas, spleen, aorta, kidneys, uterus, and ovaries. CAT scans in this area are used to verify the presence or absence of tumors, infection, abnormal anatomy, or changes of the body from trauma.

Risks in Obtaining a CAT Scan
A CAT scan is a very low-risk procedure. The technique is painless and can provide extremely accurate images of body structures in addition to guiding the radiologist in performing certain procedures, such as biopsies of suspected cancers, removal of internal body fluids for various tests, and the draining of abscesses which are deep in the body. Many of these procedures are minimally invasive and have markedly decreased the need to perform surgery to accomplish the same goal.

However, adverse reaction to intravenous contrast material may occur. Intravenous contrast is usually an iodine-based liquid given in the vein, which makes many organs and structures, such as the kidneys and blood vessels much more visible on the CAT scan. There may be resulting itching, a rash, hives, or a feeling of warmth throughout the body. These are usually self-limiting reactions and go away rather quickly. If needed, antihistamines can be given to help relieve the symptoms.

Toxicity to the kidneys which can result in kidney failure is an extremely rare complication of the intravenous contrast used in CAT scans. Diabetics, dehydrated individuals, or patients who already have impaired kidney function are most prone to this reaction. Newer intravenous contrast agents have been developed, such as Isovue, which have nearly eliminated this complication.

The amount of radiation a person receives during a CAT scan is minimal. In men and non-pregnant women, it has not been shown to produce any adverse effects. If a woman is pregnant, there may be a potential risk to the fetus.

References and Sources