Computed tomography scans
Computed tomography (CT) scans are completed with the use of a 360-degree x-ray beam and computer production of images. These scans allow for cross-sectional views of body organs and tissues.
CT scans are used to image a wide variety of body structures and internal organs. Since the 1990s, CT equipment has become more affordable and available.In some diagnoses, CT scans have become the first imaging exam of choice. Because the computerized image is so sharp, focused, and three-dimensional, manytissues can be better differentiated than on standard x rays. The CT scan can show details of sinusitis, and bone fractures. Physicians may order CT of the sinuses to provide an accurate map for surgery. Brain scans can detect tumors and strokes. The introduction of CT scanning, especially spiral CT, has helped reduce the need for more invasive procedures.
CT scans of the body will often be used to observe abdominal organs, such asthe liver, kidneys, adrenal glands, spleen, and lymph nodes, and extremities.CT scans can focus on the thoracic or abdominal aorta to locate aneurysms and other possible aortic diseases. CT scans of the chest are useful in distinguishing tumors and in detailing accumulation of fluid in chest infections.
Computed tomography, also called CT scan, CAT scan, or computerized axial tomography, is a combination of focused x-ray beams and computerized productionof an image. Introduced in the early 1970s, this radiologic procedure has advanced rapidly and is now widely used, sometimes in the place of standard x rays.
A CT scan may be performed in a hospital or outpatient imaging center. Although the equipment looks large and intimidating, it is very sophisticated and fairly comfortable. The patient is asked to lie on a gantry, or narrow table,that slides into the center of the scanner. The scanner looks like a doughnutand is round in the middle, which allows the x-ray beam to rotate around thepatient. The scanner section may also be tilted slightly to allow for certain cross-sectional angles.
Following the procedure, films of the images are usually printed for the radiologist and referring physician to review. A radiologist can also interpret CT exams on a special computer screen. The procedure time will vary in lengthdepending on the area being imaged. Average study times are from 30 to 60 minutes. Some patients may be concerned about claustrophobia but the width of the "doughnut" portion of the scanner is such that many patients can be reassured of openness.
While traditional x rays image organs in two dimensions, with the possibilitythat organs in the front of the body are superimposed over those in the back, CT scans allow for a more three-dimensional effect. Some have compared CT images to slices in a loaf of bread. Precise sections of the body can be located and imaged as cross-sectional views. The screen before the technologist shows a computer's analysis of each section detected by the x-ray beam. Thus, various densities of tissue can be easily distinguished.
Contrast agents are often used in CT exams and in other radiology proceduresto illuminate certain details of anatomy which may not be easily seen. Some contrasts are natural, such as air or water. Other times, a water-based contrast agent is administered for specific diagnostic purposes. Barium sulfate iscommonly used in gastroenterology procedures. The patient may drink this contrast, or receive it in an enema. Oral and rectal contrast are usually given when examining the abdomen or cells, and not given when scanning the brain orchest. Iodine is the most widely used intravenous contrast agent and is giventhrough an intravenous needle.
Spiral CT, also called helical CT, is a newer version of CT scanning which iscontinuous in motion and allows for three-dimensional recreation of images.For example, traditional CT allows the technologist to take slices at very small and precise intervals one after the other. Spiral CT allows for a continuous flow of images, without stopping the scanner to move to the next image slice. A major advantage of spiral CT is the ability to reconstruct images anywhere along the length of the study area. The procedure also speeds up the imaging process, meaning less time for the patient to lie still. The ability toimage contrast more rapidly after it is injected, when it is at its highest level, is another advantage of spiral CT's high speed.
Radiation exposure from a CT scan is similar to, though higher than, that ofa conventional x ray. This is a risk to pregnant women, but the exposure to other adults is minimal and should produce no effects. Although severe contrast reactions are rare, they are a risk of many CT procedures.
Normal findings on a CT exam show bone, the most dense tissue, as white areas. Tissues and fat will show as various shades of gray, and fluids will be gray or black. Air will also look black. Intravenous, oral, and rectal contrastappear as white areas. The radiologist can determine if tissues and organs appear normal by the sensitivity of the gray shadows. In CT, the images which can cut through a section of tissue or organ provide three-dimensional viewingfor the radiologist and referring physician.
Abnormal results may show different characteristics of tissues within organs.Accumulations of blood or other fluids where they do not belong may be detected. Radiologists can differentiate among types of tumors throughout the bodyby viewing details of their makeup.
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