What is a ct scan used to detect? How long does it take for a ct scan?

What is a CT scan? 

"CT" stands for "computerized tomography." A newer way of looking inside the human body, it uses pencil like x-ray beams to scan the section of the body being studied. It combines the speed of a computer with the sensitivity of the x-ray detectors. Sometimes you will hear the terms tomographic scanner, ACTA scanner ("ACTA" stands for "automatic computerized transverse axial scanner"), or CAT ("computerized axial tomography"). They all mean the same thing.

How does the CT scanner work? 

The CT takes a three dimensional look inside the body. The scanner has an arm which directs the beam through the body as it rotates around you. The x-rays pass through the body and are detected by an electronic device. About 160 scans are made in one position; then the detectors are rotated and the 160 scans are repeated.

What does the computer do? 

As the beam moves around the body in the same plane, a minicomputer analyzes how much of the x-rays are absorbed as they pass through the various internal organs and structures. Up to eight slices 1 centimeter apart may be taken at any one time. Each target area in the slice has between 100 and 200 x-ray beams going through it. The approximately 100,000 bits of information are fed into a computer that performs a billion calculations to convert the data into an image. The image can be seen on a TV screen or in printed form.

How does the CT scan differ from the standard x-ray? 

X-ray machines send a broad x-ray beam over a large area. CT scanners direct a pencil point thin line of electromagnetic energy through a narrow cross section or slice of the body. Ordinary x-rays take a "flat" view, superimposing organs in the front of the body on organs in the back, giving a two dimensional picture. CTs give a three dimensional picture. CTs also give better pictures of soft tissues than do x-rays.

What is ECAT? 

ECAT stands for "emission computerized axial tomograph. " It is a cousin of the CT. Patients swallow radioactive material. The charged particles (positrons) given off from deep inside the body are recorded on the ECAT scanner, giving the doctor a picture taken from the inside ofwhatever organ is under study.

What is MRI? 

MRI, which stands for "magnetic resonance imaging," is a new diagnostic device which produces pictures of the body's internal tissues that are similar to the computerized, crosssectional x-rays made by CT scanners. The MRI method, which uses electromagnets instead of x-ray tubes, is safer than established techniques that depend on x-rays, injected contrast solutions, and radioactivity. Sharper pictures, with more distinction than CT scanners produce, are possible, especially for difficult areas such as the brain, liver, heart, and spinal cord. Brain scans, for example, are far more detailed than those from the best CT scanners. Without injecting anything into the body or exposing the body to radiation, the MRI pictures clearly show blood vessels and contours of brain tissue and distinguish between different types of soft tissues. MRI can show structure as well as function. It is capable of distinguishing normal from abnormal tissue but at present cannot distinguish a benign tumor from a malignant one. Repeated scans can be done without risk of excessive radiation. Presently, the costly MRI machine is available on a limited basis at major medical centers.

What’s the Difference Between an MRI and a CT?


Is it uncomfortable to have a CT scan? 

There should be little discomfort. The total time needed to complete a series of scans making up a complete examination is about an hour. Sometimes contrast material is used. If it is needed, an intravenous needle is put in your vein and the solution passed through it.

Can I move during the CT scan? 

No. It is very important that you not move during the examination. If you do, the examination may have to be repeated.

Do I need any special preparation? 

Ordinarily not. If your head is being scanned, however, an elasticized stocking cap will be put over your scalp to assist the technician in positioning your head for the examination. Tape will also be used to ensure proper positioning. You will be asked to remove all jewelry, ornaments, dentures, and other similar objects in the head and neck area so that they will not interfere with the scanning examination. If the scan is of your chest, stomach, pelvic area, arms, or legs, you will be given a gown to wear.

Who will do the actual scan? 

The technician will prepare you and position you for the examination, and will be operating the equipment. The diagnostic radiologist will view and interpret the scanning information. The report of the examination will be given to your doctor by the radiologist.

Has the CT scan taken the place of other tests? 

The hospitals with CT scanners have reduced the number of pneumoencephalograms and angiograms significantly. Both are conventional brain x-rays using contrast media, and both are high risk procedures because of the injection of contrast medium. A CT scan is not considered a highrisk procedure.

How much radiation do you get from a CT scanner? 

Some radiologists claim that the thin x-ray beams expose patients to less radiation than a conventional x-ray examination. They do not expose the patient to more radiation than the conventional x-ray. And the scan avoids the risks associated with the injections of contrast dyes needed in some of the conventional procedures.

How long does it take to do a CT scan? 

It depends upon the question the doctor wants to have answered by the scan. A single scan takes anywhere from a few seconds to a couple of minutes, depending upon the type of scanner and the extent of the examination. A full body exam could take from 15 minutes to an hour, depending upon the questions to be answered. The CT scan can be done on an outpatient basis, with a minimum amount of discomfort.

What are CT scanners used for? 

Originally, CT scanning was used only to see brain abnormalities. Today it is a tool which can be used for cancers such as those of the lung, bladder, prostate, liver, and pancreas. It is used to spot tumors, detect organ disorders and abnormal structures, follow blood vessels, spot blocked ducts, differentiate between normal and abnormal tissues, and see blood clots. It can detect small differences in the physical characteristics of tissues. It can tell the difference between white matter and gray matter and between blood and water. It can be used by radiologists in making out treatment plans because it can provide detailed information about the absorption of radiation by a particular tumor. Some scanners now take the scans in color, but these are not usually used for routine diagnosis, since the black and white image at this time gives more detail.


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