CAT scan - arm; Computed axial tomography scan - arm; Computed tomography scan - arm; CT scan - arm
A computed tomography (CT) scan of the arm is an imaging method that uses x-rays to make cross-sectional pictures of the arm.
You will be asked to lie on a narrow table that slides into the center of the CT scanner.
Once you are inside the scanner, the machine's x-ray beam rotates around you. (Modern "spiral" scanners can perform the exam without stopping.)
A computer creates separate images of the arm area, called slices. These images can be stored, viewed on a monitor, or printed on film. Three-dimensional models of the arm can be created by adding the slices together.
You must be still during the exam. Movement can cause blurred images. You may be told to hold your breath for short periods of time.
The scan should take only 10 to 15 minutes.
How to Prepare for the Test
For some tests, you will need to have a special dye, called contrast, to be delivered into the body before the test starts. Contrast helps certain areas show up better on the x-rays.
- Contrast can be given through a vein (IV) in your hand or forearm. If contrast is used, you may also be asked not to eat or drink anything for 4 to 6 hours before the test.
- Let your health care provider know if you have ever had a reaction to contrast. You may need to take medicines before the test in order to safely receive this substance.
- Before receiving the contrast, tell your provider if you take the diabetes drug metformin (Glucophage). You may need to take special steps if you are on this medicine.
If you weigh more than 300 pounds (135 kilograms), find out if the CT machine has a weight limit. Too much weight can cause damage to the scanner's working parts.
You will be asked to remove jewelry and wear a hospital gown during the study.
How the Test will Feel
Some people may have discomfort from lying on the hard table.
Contrast given through an IV may cause a slight burning sensation, a metallic taste in the mouth, and a warm flushing of the body. These feels are normal. They will go away within a few seconds.
Why the Test is Performed
CT rapidly creates detailed pictures of the body, including the arms. The test may help detect or diagnose:
- An abscess or infection
- The cause of pain or other problems in the wrist, shoulder or elbow joints (usually when MRI cannot be done)
- A broken bone
- Masses and tumors, including cancer
- Healing problems or scar tissue following surgery
A CT scan may also be used to guide a surgeon to the right area during a biopsy.
Results are considered normal if no problems are seen in the images.
What Abnormal Results Mean
Abnormal results may be due to:
- Abscess (collection of pus)
- Blood clot in the arm (deep venous thrombosis)
- Bone tumors
- Broken or fractured bone
- Damage to the hand, wrist, or elbow joints
- Healing problems or development of scar tissue after surgery
Risks of CT scans include:
- Being exposed to radiation
- Allergic reaction to contrast dye
- Birth defect if done during pregnancy
CT scans expose you to more radiation than regular x-rays. Having many x-rays or CT scans over time may increase your risk for cancer. However, the risk from any one scan is small. You and your provider should weigh this risk against the benefits of getting a correct diagnosis for a medical problem.
Some people have allergies to contrast dye. Let your provider know if you have ever had an allergic reaction to injected contrast dye.
- The most common type of contrast given into a vein contains iodine. A person with an iodine allergy may have nausea or vomiting, sneezing, itching, or hives if given this type of contrast.
- If contrast is needed, you may get antihistamines (such as Benadryl) or steroids before the test.
- The kidneys help remove iodine out of the body. Those with kidney disease or diabetes may need to get extra fluids after the test to help flush the iodine out of the body.
Rarely, the dye may cause a life-threatening allergic response called anaphylaxis. If you have any trouble breathing during the test, let the scanner operator know right away. Scanners have intercom and speakers so the operator can hear you at all times.
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Thomsen HS, Reimer P. Intravascular contrast media for radiography, CT, MRI and ultrasound. In: Adam A, Dixon AK, Gillard JH, Schaefer-Prokop CM, eds. Grainger & Allison's Diagnostic Radiology: A Textbook of Medical Imaging. 6th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2015:chap 2.