CT Scan

Before, During and After a CT Scan

CT scan, CT scan image, CT scan of kidneys, Renal CT.
A CT Scan of Kidney Cysts. Image: National Institute of Health

CT Scan Explained

A CT scan, also known as Computer Tomography or a CAT scan, is an imaging test.  The images produced are similar to that of an x-ray, but they are three dimensional, meaning the images look more like a human body than a flat photo.

The images are then sent to a computer, which allows a physician to look at the images from a variety of viewpoints.   The “reading” or interpretation of a CT scan is typically done by a radiologist, a physician trained in reading imaging tests.

  Another physician, such as a surgeon, may also 

A CT scan can look deep within the body and can see a wide variety of tissue including internal organs, soft tissues such as ligaments and tendons, as well as bone and blood vessels.  This type of scan is more sensitive than an x-ray, and may be able to detect small breaks that a standard x-ray cannot. 

Why a CT Scan is Performed

A CT scan is a quick, versatile and accurate way to look inside the human body.  It may be performed to look at the brain to determine if a stroke or some type of injury has occured. A CT may be done to determine if a patient is bleeding internally, to examine the lungs to determine why a patient is having difficulty breathing, or may be used to determine which tissue in the pelvis is causing pain or discomfort.  Other reasons include staging cancers and determining if a mass is responding to treatment, monitoring the digestive tract, or making sure that blood vessels are 

The CT scan is very versatile, and is used to diagnose many types of injuries and illness.  It can also be used to rule out a serious illness. For example, if a patient is suddenly unconscious, a CT can be done quickly to determine if the patient is having a stroke or has had a traumatic brain injury.

CT With Contrast

During some CT scans, depending on the nature of the suspected problem, contrast medium may be used to obtain better images.  One type of contrast dye is given through an IV, and allowed to circulate through the body.  Another type of contrast is given as a drink, and is given half an hour or longer before the scan is performed. 

For some patients, an initial scan is performed without contrast, followed by the administration of the contrast dye, and a second scan with the contrast. 

During a CT Scan

A CT scan isn’t painful, but it does require the patient to remain still during the test.  It also requires that metal and jewelry be removed, including piercings, dental work, underwire bras and other forms of metal.  What needs to be removed depends on the site being scanned, but in general it is requested that all jewelry be removed.  Individuals with implanted metal, such as pacemakers or joint replacements, can safely have a CT scan.

The patient will lie on a small bed that moves in and out of the CT machine.

  The machine is often shaped like a doughnut, with the bed moving in and out of the center.  Other machines are shaped like a box.  The CT machine does not touch the patient during the scan.

Some procedures are done with CT guidance, meaning that the CT machine is used to insure that the physician is in the right area.  For example, a CT may be used to guide a biopsy procedure, to make sure the right area of the organ is being sampled.  

Risks of CT Scans

  • Individuals who are allergic to shellfish may also be allergic to contrast medium.  Any allergies should be reported prior to the scan.
  • CT scans, like surgery, are not recommended for pregnant women unless the risk of not performing the scan is greater than the potential benefit of diagnosis.
  • Women should not breastfeed for at least 48 hours after having a CT scan with contrast.
  • Very large patients, typically weighing greater than 400 pounds, may not fit inside the CT scanning machine. 
  • A CT scan may lead to an MRI scan if a problem is identified that needs more evaluation. 
  • Patients who cannot be still for the examination may require sedation.
  • Radiation is produced by a CT scan.  For this reason, a CT scan should only be done when necessary.


CT Scan. Medline Plus.  Accessed October, 2015. https://www.nlm.nih.gov/medlineplus/ctscans.html#cat51

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