CT Scan

Computed Tomography (CT) Scans General information -------------------------------------------------------------------------------- Table 3.3 Where It's Done Who Does It How Long It Takes Discomfort/Pain Hospital radiology unit or outpatient diagnostic clinic. Radiologist or technician. 30-45 minutes. None unless contrast medium is used; some people find it uncomfortable to remain still during the test. Results Ready When Special Equipment Risks/Complications Average Cost Often in a few hours; may take longer in some cases and other places. Revolving CT scanner (camera), X-ray and computer equipment, and monitor. Slight risk from radiation exposure; use of contrast agent (dye) can cause allergic reaction. £500.00 -------------------------------------------------------------------------------- Other names Computed axial tomograph (CAT) scans. Purpose To obtain a two-dimensional view of a cross section of the brain or other internal organ. To detect tumors, bleeding, and other abnormalities that may not show up on an ordinary X-ray. How it works Multiple X-rays are taken as the CT X-ray tube revolves around the patient. A computer calculates the amount of X-ray penetration through the specific plane(s) of the body part(s) examined, and gives each a numeric value (density coefficient). This information is fed into a computer, which translates the values into different shades of gray. These images are displayed on a television monitor and photographed as a series of two-dimensional images depicting a cross section of the part under examination. Preparation You will be shown the CT machine and asked to express any concerns. If you experience claustrophobia in small, enclosed spaces, you may be given a mild sedative to quell your anxiety. If an intravenous contrast agent is to be used, you will be asked to abstain from ingesting food and water for at least four hours beforehand. Before entering the unit, you will be asked to remove any jewelry or other objects that may interfere with clear X-ray images. Test procedure You will be asked to lie on a narrow examination table, which slides into the scanner (see figure 3.1). FIGURE 3.1 In CT scanning of the head, the X-ray tube revolves around the area being examined as the table slowly moves the patient across the area in question. As you lie as motionless as possible, the CT tube revolves slowly, taking multiple X-ray images, which are reconstructed into two-dimensional views of a cross section of the body. The table is then moved slightly to take another set of images through another plane of the body; typically, three to seven planes are imaged, but this varies according to the part of the body under examination. In some instances, the entire length of the body may be scanned; in others, only a relatively narrow section. Variations CT scanning may be performed in conjunction with other imaging studies and diagnostic procedures, such as X-rays of the joint or spinal column (eg, arthrography or myelography). This allows more detailed images of the entire joint structure than can be obtained from X-rays alone. A relatively new innovation is spiral CT imaging, which allows for continuous scanning as the gantry table slides through the unit. This technique cuts the amount of time needed for whole-body scanning. After the test You may be asked to wait while a radiologist quickly reviews the images to make sure that the part of the body under study has been adequately photographed. If necessary, you may be asked to return to the scanner for additional images. Otherwise, you will be able to resume normal activities. If an intravenous contrast medium was used, you will be instructed to drink extra fluids to speed its removal from the body. You should also watch for delayed allergic reactions, such as hives, a rash, itching, or perhaps a rapid heartbeat. Such symptoms usually appear within two to six hours; in severe cases, an antihistamine or steroid medication may be prescribed to ease discomfort. Factors affecting results Obesity, movement during the examination, and the presence of metallic objects can interfere with obtaining clear images. In some cases, excessive gas or fecal material in the intestines can give misleading results in an abdominal CT scan Interpretation A radiologist will interpret the scans. Advantages CT scanning provides a painless, noninvasive method of obtaining a detailed view of internal organs. In many instances, CT scanning eliminates the need for more invasive procedures Disadvantages The test is costly and may not be available in small hospitals and rural areas. It is contraindicated during pregnancy, and may not be suitable for those who are very obese. Based on The Yale University School of Medicine Patient's Guide to Medical Tests by Barry L. Zaret M.D., Senior Editor, Copyright (c) 1997 by Yale University School of Medicine and G. S. Sharpe Communications, Inc. Published under license from Houghton Mifflin Company.

Computed Tomography (CT) Scans

General information

Table 3.3

Other names

Computed axial tomograph (CAT) scans.

Purpose

• To obtain a two-dimensional view of a cross section of the brain or other internal organ.
• To detect tumors, bleeding, and other abnormalities that may not show up on an ordinary X-ray.

How it works

• Multiple X-rays are taken as the CT X-ray tube revolves around the patient.
• A computer calculates the amount of X-ray penetration through the specific plane(s) of the body part(s) examined, and gives each a numeric value (density coefficient).
• This information is fed into a computer, which translates the values into different shades of gray.
• These images are displayed on a television monitor and photographed as a series of two-dimensional images depicting a cross section of the part under examination.

Preparation

• You will be shown the CT machine and asked to express any concerns.
• If you experience claustrophobia in small, enclosed spaces, you may be given a mild sedative to quell your anxiety.
• If an intravenous contrast agent is to be used, you will be asked to abstain from ingesting food and water for at least four hours beforehand.
• Before entering the unit, you will be asked to remove any jewelry or other objects that may interfere with clear X-ray images.

Test procedure

• You will be asked to lie on a narrow examination table, which slides into the scanner (see figure 3.1).

  
  FIGURE 3.1
  In CT scanning of the head, the X-ray tube revolves around the area being examined as the table slowly moves the patient across the area in question.

   

• As you lie as motionless as possible, the CT tube revolves slowly, taking multiple X-ray images, which are reconstructed into two-dimensional views of a cross section of the body.
• The table is then moved slightly to take another set of images through another plane of the body; typically, three to seven planes are imaged, but this varies according to the part of the body under examination.
• In some instances, the entire length of the body may be scanned; in others, only a relatively narrow section.

Variations

• CT scanning may be performed in conjunction with other imaging studies and diagnostic procedures, such as X-rays of the joint or spinal column (eg, arthrography or myelography). This allows more detailed images of the entire joint structure than can be obtained from X-rays alone.
• A relatively new innovation is spiral CT imaging, which allows for continuous scanning as the gantry table slides through the unit. This technique cuts the amount of time needed for whole-body scanning.

After the test

• You may be asked to wait while a radiologist quickly reviews the images to make sure that the part of the body under study has been adequately photographed.
• If necessary, you may be asked to return to the scanner for additional images. Otherwise, you will be able to resume normal activities.
• If an intravenous contrast medium was used, you will be instructed to drink extra fluids to speed its removal from the body.
• You should also watch for delayed allergic reactions, such as hives, a rash, itching, or perhaps a rapid heartbeat. Such symptoms usually appear within two to six hours; in severe cases, an antihistamine or steroid medication may be prescribed to ease discomfort.

Factors affecting results

• Obesity, movement during the examination, and the presence of metallic objects can interfere with obtaining clear images.
• In some cases, excessive gas or fecal material in the intestines can give misleading results in an abdominal CT scan

Interpretation

A radiologist will interpret the scans.

Advantages

• CT scanning provides a painless, noninvasive method of obtaining a detailed view of internal organs.
• In many instances, CT scanning eliminates the need for more invasive procedures

Disadvantages

• The test is costly and may not be available in small hospitals and rural areas.
• It is contraindicated during pregnancy, and may not be suitable for those who are very obese.

Based on The Yale University School of Medicine Patient's Guide to Medical Tests by Barry L. Zaret M.D., Senior Editor, Copyright (c) 1997 by Yale University School of Medicine and G. S. Sharpe Communications, Inc. Published under license from Houghton Mifflin Company.