Computerized Tomography

Computerized tomography (CT) is an imaging technique that utilizes X-rays. This technology is used for both medical and research purposes. During a test that utilizes a CT scanner, a patient lies on his or her back on a bench-like structure and a scanner rotates around the patient taking several pictures using X-rays. These X-rays are then sent to a computer, which converts them into a picture, known as cross-sectional images. From the cross-sectional images, a physician or researcher can determine the amount of fat, muscle, and bone a patient has as well as if certain diseases are present.

CT scans can be used as a diagnostic tool for many medical conditions. It is often used along with other imaging techniques such as traditional X-rays. In the medical field, CT scans have been employed to diagnose problems in the brain, lungs, heart, and gastrointestinal tract (digestive system). Some diseases it may be used to diagnosis include cancers of any of the above-mentioned organs, internal bleeding in the brain, emphysema or pulmonary embolism in the lungs, heart disease, pancreatitis, or any bowel obstruction.

CT scans are useful in body composition research, an important component in the study of obesity. CT scans are able to determine how much fat, muscle, and bone a patient has. CT scans can distinguish the types of tissue because each of these tissues has a different density, and subsequently, the X-rays will travel through each of these body tissues at different speeds. CT scans can also provide measurements about organ size such as the liver, kidney, and spleen. Organ sizes are often used as references for body composition measurements. Data from CT scans are presented in Hounsfield units; an image with low Hounsfield values will signify a greater amount of fat present, while an image with high Hounsfield values will signify a greater amount of muscle present.

CT scans can also provide data about how fat is distributed in the body. It is useful for determining the regional distribution of fat (i.e., subcutaneous fat—below the skin; visceral fat—around the organs of the abdomen; intermuscular fat—fat between the muscles). CT scans along with magnetic resonance imaging (MRI) are considered good research tools for the measurement of human body composition. Learning about body composition has been critical in understanding how fat and muscle tissue relate to the development of many diseases such as heart disease, diabetes, and hypertension (high blood pressure).

A major disadvantage of this test is its utilization of X-rays, which exposes a patient to radiation. Therefore, this test is limited in the populations in which it can be used. Children and pregnant women should be limited to the amount of radiation to which they are exposed. MRIs are an alternative option for measuring body composition in these populations because no radiation is used during this test. Additionally, this test is expensive and laborious which limits where it is utilized. Therefore, CT scans tend to be found in most major medical and research centers, but not commonly found in physicians' offices.