The patient will be asked to lie on a narrow table (gantry) that slides into the center of the scanner. Depending on the study being performed, the patient may need to lie on his/her stomach, back, or side. If contrast media (dye) is to be administered, intravenous access will be placed in a small vein of a hand or arm.

Much like standard photographic cameras, subject motion causes blurred images in CT. Therefore, the technologist operating the scanner and supervising the patient will give instructions through an intercom when to hold one's breath and not move.

As the exam takes place, the gantry will advance small intervals through the scanner. Modern "spiral" scanners can perform the examination in one continuous motion of the gantry. Generally, complete scans will only take a few minutes, however, additional contrast-enhanced or higher-resolution scans will add to the scan time. The newest multi-detector scanners can image the entire body, head to toe, in under 30 seconds.

The health care provider may advise you to avoid eating or drinking for 4 to 6 hours prior to the scan, if contrast dye is to be used.

The CT scanner has a weight limit to prevent damage to the mechanized gantry. Have the health care provider contact the scanner operator if you weigh more than 300 pounds.

Metal interferes with the X-rays, so you may be asked to remove jewelry and wear a hospital gown during the study.

For infants and children:
The preparation you can provide for this test depends on your child's age and previous experience. For specific information regarding how you can prepare your child, see the following topics:

• infant test or procedure preparation (birth to 1 year)
• toddler test or procedure preparation (1 to 3 years)
• preschooler test or procedure preparation (3 to 6 years)
• schoolage test or procedure preparation (6 to 12 years)
• adolescent test or procedure preparation (12 to 18 years)

The X-rays are painless. The primary discomfort may be from the need to lie still on the table.

If intravenous contrast dye is given, the patient may initially feel a slight burning sensation within the injected arm, a metallic taste in the mouth, and a warm flushing of the body. These sensations are normal and usually go away within a few seconds.

• when there is a chest injury
• when a tumor or mass (clump of cells) is suspected
• to determine the size, shape, and position of internal organs
• to look for bleeding or fluid collections in the lungs or other areas

• enlarged lymph nodes (lymphadenopathy)
• abnormalities of the structure or position of the heart, lungs, or blood vessels
• bronchiectasis
• tumors, nodules, or cysts within the chest
• the stage of some lung tumors or esophageal cancer
• aortic aneurysm (thoracic)
• pleural effusion
• pneumonia
• accumulations of blood or fluid

• alcoholic cardiomyopathy
• asbestosis
• atrial myxoma; left
• atrial myxoma; right
• cardiac tamponade
• coarctation of the aorta
• dilated cardiomyopathy
• echinococcus
• heart failure
• histoplasmosis
• hypertensive heart disease
• idiopathic cardiomyopathy
• infective endocarditis
• ischemic cardiomyopathy
• left-sided heart failure
• mesothelioma (malignant)
• metastatic cancer to the lung
• mitral regurgitation; acute
• mitral regurgitation; chronic
• mitral valve prolapse
• pericarditis; bacterial
• pericarditis; constrictive
• pericarditis; post-MI
• peripartum cardiomyopathy
• pulmonary edema
• restrictive cardiomyopathy
• senile cardiac amyloid
• SVC obstruction