Definition Computed tomography of the chest is a non-invasive imaging method that combines x-rays with computer technology. X-ray beams from a variety of angles are used to create a series of detailed cross sectional images.
Who is a candidate for the test? Computed tomography can provide detailed views of several types of tissue including lung, bone, soft tissue and blood vessels. For this reason, this technique is an excellent method for determining the size and location of growths that are suspected to be cancer. It is also used to guide radiation therapy, biopsies, and other minimally invasive procedures. Conditions of the lungs and chest wall frequently diagnosed with chest CT include:
tumours and other abnormal growths, including lung cancer
is allergic to shellfish, or foods with added iodine such as table salt
has experienced claustrophobia, or anxiety in enclosed spaces. If this is a problem, mild sedating medication may be given.
A woman will be asked if there is a possibility she might be pregnant. Frequently, a urine pregnancy test will be performed on females of child-bearing age before the CT scan.
The person having the test will lie on a flat table. The CT technologist may use pillows or other devices to help support the individual's body in the proper position. As the test begins, the table will move slowly into a donut-shaped machine. This device delivers x-ray beams through the person's chest cavity from a variety of angles.
Often, special substances called "contrast agents" are used to enhance internal structures and improve image quality on the final image.
For a chest CT, contrast agents are most commonly injected into a vein or swallowed. If contrast is administered, the patient may experience mild nausea, flushing, itching or a metallic taste in the mouth. Most of these sensations disappear within a few minutes.
A conventional chest CT test takes approximately 30 to 45 minutes. More advanced CT devices, known as helical or spiral CT machines, reduce the imaging time dramatically. To prevent distortion of the final images, the person must lie very still for the duration of the test.
After the test, the person will be asked to wait until the pictures are examined to see if more images are needed. The person will be observed for any delayed allergic reactions to the medication used as the contrast agent. Also, the individual will be encouraged to drink extra fluids to help flush the contrast material from the body.
What is involved in preparation for the test? The person having a CT will need to refrain from eating or drinking at least 4 hours prior to the test. The CT technologist will explain the procedure to the individual. People who are prone to claustrophobia will be administered with a calming drug before the examination.
What do the test results mean? A doctor specially trained in analysing CT images, called a radiologist, will examine the results of the test. The radiologist will forward a report of the findings to the individual's doctor.
Some of the conditions a chest CT can reveal include:
tumours of the lungs, chest wall, bone and soft-tissue, such as lung cancer
fluid or inflammation of the membranes around the heart, known as pericardial effusion
fluid or inflammation of the membranes around the lungs, known as pleural effusion
rib or spine fractures
stomach problems, such as hiatal hernia or conditions of the oesophagus
enlarged lymph nodes
conditions of the aorta such as calcification, dilation, or tears
Author: Stephanie Slon, BA Reviewer: HealthAnswers Australia Medical Review Panel Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia Last Updated: 1/10/2001 Contributors Potential conflict of interest information for reviewers available on request
