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Preparing for a CT Scan

Preparing for the CT Scan

Wear comfortable, loose-fitting clothing to your exam.  You may be given a gown to wear during the scan.

Metal objects including jewelry, eyeglasses, dentures and hairpins may affect the CT images and should be left at home or removed prior to your exam.  You may also be asked to remove hearing aids and removable dental work.

You may be asked not to eat or drink anything for several hours before your scan, especially if a contrast material will be used in your exam.  You should inform your physician of any medications you are taking and if you have any allergies, especially to contrast materials.

Also inform your doctor of any recent illnesses or medical conditions, and if you have a history of heart disease, asthma, diabetes, kidney disease or thyroid problems.  Any of these conditions may increase the risk of an unusual adverse effect.

Please bring a list of your current medications:  prescriptions, over the counter medications, and vitamins.
Women should always inform their physician or technologist if there is any possibility that they are pregnant.

If your infant or young child is having a spiral CT, there are measures that can be taken to ensure that the test will not cause anxiety for either the child or parent.

Understanding the CT Scan

In many ways CT scanning works very much like other X-ray examinations.  X-rays are a form of radiation-like light or radio waves-that can be directed at the body.  Different body parts absorb the X-rays in varying degrees.

In a conventional X-ray exam, a small burst of radiation is aimed at and passes through the body, recording an image on photographic film or a special image recording plate.  Bones appear white on the X-ray, soft tissue shows up in shades of gray and air appears black.

With CT scanning, numerous X-ray beams and a set of electronic X-ray detectors rotate around you, measuring the amount of radiation being absorbed throughout your body.  At the same time, the examination table is moving through the scanner, so that the X-ray beam follows a spiral path.  A special computer program processes this series of pictures, or slices of the body, to create two-dimensional cross-sectional images, which are then displayed on a monitor.

CT imaging is sometimes compared to looking into a loaf of bread by cutting the loaf into thin slices.  When the image slices are reassembled by computer software, the result is a very detailed multidimensional view of the body's interior.

Refinements in detector technology allow new CT scanners to obtain multiple slices in a single rotation.  These scanners, called "Multislice CT" or "multidetector CT," allow thinner slices to be obtained in a shorter period of time, resulting in more detail and additional view capability.

Modern CT scanners are so fast that they can scan through large sections of the body in just a few seconds. Such speed is beneficial for all patients, especially children, the elderly and critically ill.

For some CT exams, a contrast material is used to enhance visibility in the area of the body being studied.

How the CT Scan is Performed

The technologist begins by positioning you on the CT examination table, usually lying flat on one's back, on the side or stomach. Straps and pillows may be used to help maintain the correct position and to hold still during the exam.

If a contrast material is used, it will be injected through an intravenous line (IV) into an arm vein during the procedure. A scan of the lower spine may also be done after injecting contrast material into the spinal canal (usually well below the bottom of the spinal cord) during a lumbar puncture. This will help to detect tumors or locate areas of inflammation or nerve compression.

Next, the table will move quickly through the scanner to determine the correct starting position for the scans. Then, the table will move slowly through the machine as the actual CT scanning is performed.

You may be asked to hold your breath during the scanning.

When the examination is completed, you will be asked to wait until the technologist determines that the images are of high enough quality for the radiologist to read.

The CT scanning is usually completed within 30 minutes.

Expectations During and After the Scan

Most CT exams are painless, fast and easy.  With spiral CT, the amount of time that the patient needs to lie still is reduced.

Though the scanning itself causes no pain, there may be some discomfort from having to remain still for several minutes.  If you have a hard time staying still, are claustrophobic or have chronic pain, you may find a CT exam to be stressful.  The technologist or nurse may offer you a mild sedative to help.

If an intravenous contrast material is used, you will feel a slight prick when the needle is inserted into the vein.   A warm, flushed sensation may be felt during the injection of the contrast materials and a metallic taste in your mouth that lasts for a few minutes.  

Occasionally, patients develop hives and an itch, which can be relieved with medication.  If you become light-headed or experience difficulty breathing, the technologist or nurse should be notified immediately, as it may indicate a more severe allergic reaction.

When entering the CT scanner, special lights may be used to properly position you, and you may hear slight buzzing, clicking and whirring sounds as the CT scanner moves during the imaging process.

During the CT scan, you will be alone in the exam room, however, the technologist will be able to see, hear and speak with you at all times.

With pediatric patients, a parent may be allowed in the room, but will be required to wear a lead apron to prevent radiation exposure.
After a CT exam, you may return to normal activities. If a contrast material was given, special instructions may follow.


A radiologist, a physician specifically trained to supervise and interpret radiology examinations, will analyze the images and send a signed report to your primary care or referring physician, who will share the results with you.

Benefits vs. Risks?


  • Spinal CT scanning is a rapid procedure and offers an accurate evaluation of bone and most soft tissues. Using the latest equipment, the spine may be displayed in multiple planes and three-dimensional imaging is an option.
  • CT scanning is painless, noninvasive and accurate.
  • A major advantage of CT is that it is able to provide detailed images of bone, lungs and other soft tissue and blood vessels all at the same time.
  • CT examinations are fast and simple; in emergency cases, they can reveal internal injuries and bleeding quickly that helps save lives.
  • CT is shown to be a cost-effective imaging tool for a wide range of clinical problems.
  • CT may be less expensive than MRI. In addition, it is less sensitive to patient movement.
  • CT can be performed if you have an implanted medical device of any kind, unlike MRI.
  • CT provides real-time imaging, making it a good tool for guiding minimally invasive procedures such as needle biopsies and needle aspirations of many areas of the body, particularly the lungs, abdomen, pelvis and bones.
  • A diagnosis determined by CT scanning may eliminate the need for exploratory surgery and surgical biopsy.
  • No radiation remains in a patient's body after a CT examination.
  • X-rays used in CT scans usually have no side effects.


  • There is always a slight chance developing from radiation exposure. However, the benefit of an accurate diagnosis outweighs the risk.
  • The effective radiation dose from CT imaging is about 10 mSv, which is about the same as the average person receives from background radiation in three years.   Background radiation is natural radiation from earth and space.
  • Women should always inform their physician or CT technologist if there is any possibility that they are pregnant.
  • CT scanning is, in general, not recommended for pregnant women because of potential risk to the baby.
  • Nursing mothers should wait for 48 hours after contrast material injection before breast feeding.
  • The risk of serious allergic reaction to contrast materials that contain iodine is rare, and radiology departments are well equipped to deal with them.
  • Children should have a CT study only if it is essential for making a diagnosis and should not have repeated CT studies unless absolutely necessary.

Will the CT Imaging Examination Hurt?

No, CT imaging itself should cause no pain.  The CT examination itself causes no bodily sensation.  However, CT imaging requires that the patient remain still.  For some patients, keeping still for some time may be uncomfortable. 

CT imaging examinations that require the patient to receive iodine contrast injection may cause slight, temporary discomfort while the intravenous needle is placed.

Is CT Imaging Safe?

Yes, CT imaging is considered a safe examination.  In general, the diagnostic benefit of a CT scan usually outweighs the risk of X-ray radiation exposure or injections of imaging contrast and use of sedatives during the scan.  Patients should inform the radiologist or technologist if they have a history of allergies (especially to medications, previous iodine injections, or shellfish), diabetes, asthma, a heart condition, kidney problems, or thyroid conditions.

How Long Will the CT Examination Take?

Depending on the type of exam you will receive, the length of the actual procedure will typically be between 10 minutes and 45 minutes.  A few involved CT examinations take longer than 45 minutes.

Also, many CT exams require the patient to hold their breath several times.  This helps to eliminate blurring from the images, which can be caused by breathing or other patient motion. Please ask specific questions about your CT imaging examination's duration with the technologist before your exam.

Do I need a Referral (Prescription) to Receive a CT Examination?

Yes, your doctor must give you a referral (prescription) in order for you to receive a computed tomography (CT) imaging examination.  However, CT can often be performed on an outpatient basis without having to admit the patient to the hospital.

Can I Move While I Am in the CT Scanner?

You should not move when you are on the CT table and the images are being acquired. It is important that you not move the body part being imaged until the entire CT exam is complete.  CT exams of the chest and abdomen require the patient to hold their breath for a short period of time, perhaps 10 to 25 seconds.  This eliminates blurring in the image caused by breathing or other patient motion.

Can I Talk With Anyone During the CT Scan?

You may talk to the technologists or ask a question in between CT data acquisitions.

Can I Bring a Friend or a Relative into the CT Scan Room With Me?

No, CT uses X-rays and only the person being imaged should be in the CT scanner room during the examination.

Do I Need an Injection of Contrast for my CT Exam?

Not everyone needs an injection for CT imaging. When a contrast injection is needed, a pharmaceutical contrast agent made of iodine is used.  This is only done when the radiologist and/or the referring physician have determined that it is necessary for diagnostic purposes. Iodine contrast is used to make specific organs; blood vessels or tissue types "stand out" with more image contrast in the resulting picture.  The referring doctor provides the CT department with information about the patient's medical condition and the goal of the CT imaging procedure being ordered.  The decision to use or not to use an injection of CT contrast is made based on this information and the body part being examined.

If I'm Nursing an Infant, Can I Breast Feed After an Injection of CT Contrast?

Typically, patients are instructed to wait for 48hours after receiving the CT contrast injection before breast-feeding again.  Patients may wish to pump breast milk prior to the CT exam and store it for use during this 48-hour period.  Always check with the radiologist and the CT department for their specific recommendations.

Can I Have a CT Imaging Exam if I Am Pregnant?

Pregnant woman should not have a CT exam or any X-ray examination, especially if the woman is in her first trimester (first three-month period of pregnancy).  Depending on the condition, there may be other exams available, such as ultrasound, to help diagnose a medical condition.  Pregnant women should always inform their imaging technologist or radiologist that they are pregnant, or may be pregnant.

What Happens After the Procedure?

After your CT scan is completed, you may resume all of your normal activities. There should be no ill-side effects and you will be able to drive.

The only thing we recommend is that you drink plenty of liquids/water after your test is complete (if given contrast).  This is so that the contrast dye can be quickly flushed from your body and you do not become dehydrated.