What is an MRI and how does it work?

Magnetic resonance imaging, or MRI, is a way of obtaining very detailed images of organs and tissues throughout the body without the need for x-rays or “ionizing” radiation. Instead, MRI uses a powerful magnetic field, radio waves, rapidly changing magnetic fields, and a computer to create images that show whether or not there is an injury, disease process, or abnormal condition present.

For this procedure, the patient is placed within the MR scanner—typically a large, tunnel or doughnut-shaped device that is open at both ends or a open MRI machine. The powerful magnetic field aligns atomic particles called protons that are present in most of the body’s tissues. The applied radio waves then cause these particles to produce signals that are picked up by a receiver within the MR scanner. The signals are specially characterized using the rapidly changing magnetic field, and, with the help of computer processing, very sharp images of tissues are created as “slices” that can be viewed in any orientation.

An MRI exam causes no pain, and the magnetic fields produce no known tissue damage of any kind. The MR scanner may make loud tapping or knocking noises at times during the procedure; using earplugs prevents problems that may occur with this noise. You will be able to communicate with the MRI technologist or radiologist at any time using an intercom system or by other means.

What are some common uses of the procedure?

MRI has become the preferred procedure for diagnosing a large number of potential problems or abnormal conditions in many different parts of the body. In general, MRI creates pictures that can show differences between healthy and unhealthy tissues. Physicians use MRI to examine:

  • brain, spine, joints, knee, shoulder, hip, wrist, and ankle
  • organs of the chest and abdomen—including the heart, liver, biliary tract, kidneys, spleen, bowel, pancreas and adrenal glands.
  • pelvic organs including the reproductive organs in the male (prostate and testicles) and the female (uterus, cervix and ovaries).
  • blood vessels (MR Angiography).
  • breasts.

Physicians use the MRI examination to help diagnose or monitor treatment for conditions such as:

  • tumors of the chest, abdomen or pelvis.
  • certain types of heart problems.
  • blockages, enlargements or anatomical variants of blood vessels, including the aorta, renal arteries, and arteries in the legs.
  • diseases of the liver, such as cirrhosis and tumors, and that of other abdominal organs, including the bile ducts, gallbladder, and pancreatic ducts.
  • diseases of the small intestine, colon, rectum and anus.
  • cysts and solid tumors in the kidneys and other parts of the urinary tract.
  • tumors and other abnormalities of the reproductive organs (e.g., uterus, ovaries, testicles, prostate).
  • causes of pelvic pain in women, such as fibroids, endometriosis and adenomyosis.
  • suspected uterine congenital abnormalities in women undergoing evaluation for infertility.
  • breast cancer and implants.
  • fetal assessment in pregnant women.

How should I prepare for my MRI exam?

You will typically receive a gown to wear during your MRI examination. Before entering the MRI system room, you and any accompanying friend or relative will be asked questions regarding the presence of implants and will be instructed to remove all metal objects from pockets and hair. Additionally, the accompanying individual will need to fill out a screening form to ensure that he or she may safely enter the MR system room.

Before the exam you will be asked to fill out a screening form asking about anything that might create a health risk or interfere with imaging. Items that may create a health hazard or other problem during an MRI exam include:

  • Cardiac pacemaker or implantable defibrillator
  • Catheter that has metal components that may pose a risk of a burn injury
  • A ferromagnetic metal clip placed to prevent bleeding from an intracranial aneurysm
  • An implanted or external medication pump (such as that used to deliver insulin or a pain-relieving drug)
  • A cochlear (inner ear) implant
  • A neurostimulation system

Items that need to be removed by patients and individuals before entering the MR system room include:

  • Purse, wallet, money clip, credit cards, cards with magnetic strips
  • Electronic devices such as beepers or cell phones
  • Hearing aids
  • Metal jewelry, watches
  • Pens, paper clips, keys, coins
  • Hair barrettes, hairpins
  • Any article of clothing that has a metal zipper, buttons, snaps, hooks, underwires, or metal threads
  • Shoes, belt buckles, safety pins

Objects that may interfere with image quality if close to the area being scanned include:

  • Metallic spinal rod
  • Plates, pins, screws, or metal mesh used to repair a bone or joint
  • Joint replacement or prosthesis
  • Metal jewelry including those used for body piercing
  • Some tattoos or tattooed eyeliner (these alter MR images, and there is a chance of skin irritation or swelling; black and blue pigments are the most troublesome)
  • Bullet, shrapnel, or other type of metal fragment
  • Metallic foreign body within or near the eye (such an object generally can be seen on an x-ray; metal workers are most likely to have this problem)
  • Dental fillings (while usually unaffected by the magnetic field, they may distort images of the facial area or brain; the same is true for orthodontic braces and retainers)

How is the procedure performed?

You will be positioned on the moveable examination table. Straps and bolsters may be used to help you stay still and maintain the correct position during imaging.

Small devices that contain coils capable of sending and receiving radio waves may be placed around or adjacent to the area of the body being studied.

If a contrast material will be used in the MRI exam, a nurse or technologist will insert an intravenous (IV) line into a vein in your hand or arm. A saline solution may be used. The solution will drip through the IV to prevent blockage of the IV line until the contrast material is injected.

You will be moved into the magnet of the MRI unit and the radiologist and technologist will leave the room while the MRI examination is performed.

If a contrast material is used during the examination, it will be injected into the intravenous line (IV) after an initial series of scans. Additional series of images will be taken during or following the injection.

When the examination is completed, you may be asked to wait until the technologist or radiologist checks the images in case additional images are needed.

Your intravenous line will be removed.

MRI exams generally include multiple runs (sequences), some of which may last several minutes.

Depending on the type of exam and the equipment used, the entire exam is usually completed in 15 to 45 minutes.

What will I experience during and after the procedure?

MRI exams are painless, however, some patients find it uncomfortable to remain still during MR imaging. Others experience a sense of being closed-in (claustrophobia).

It is normal for the area of your body being imaged to feel slightly warm, but if it bothers you, notify the radiologist or technologist. It is important that you remain perfectly still while the images are being recorded, which is typically only a few seconds to a few minutes at a time. For some types of exams, you may be asked to hold your breath. You will know when images are being recorded because you will hear tapping or thumping sounds when the coils that generate the radiofrequency pulses are activated. You will be able to relax between imaging sequences, but will be asked to maintain your position as much as possible.

You will usually be alone in the exam room during the MRI procedure. However, the technologist will be able to see, hear and speak with you at all times using a two-way intercom. Many MRI centers allow a friend or parent to stay in the room as long as they are also screened for safety in the magnetic environment.

You may be offered or you may request earplugs to reduce the noise of the MRI scanner, which produces loud thumping and humming noises during imaging. Children will be given appropriately sized earplugs or headphones during the exam. MRI scanners are air-conditioned and well-lit. Some scanners have music to help you pass the time.

You may resume your usual activities and normal diet immediately after the exam. A few patients experience side effects from the contrast material, including nausea and local pain. Very rarely, patients are allergic to the contrast material and experience hives, itchy eyes or other reactions. If you experience allergic symptoms, a radiologist or other physician will be available for immediate assistance.

How safe is MRI?

The powerful magnetic field of the MRI system will attract iron-containing (also known as ferromagnetic) objects and may cause them to move suddenly and with great force. This can pose a possible risk to the patient or anyone in an object’s “flight path.” Great care is taken to be certain that objects such as ferromagnetic screwdrivers and oxygen tanks are not brought into the MRI system area. It is vital that you remove all metallic belongings in advance of an MRI exam, including watches, jewelry, and items of clothing that have metallic threads or fasteners.

The powerful magnetic field of the MRI system will pull on any iron-containing object in the body, such as certain medication pumps or aneurysm clips. Every MRI facility has a comprehensive screening procedure and protocol that, when carefully followed, ensures that the MRI technologist and radiologist knows about the presence of metallic implants and materials so that special precautions can be taken. For example, the MRI exam will not be performed if a ferromagnetic aneurysm clip is present, because there is a risk of the clip moving or being dislodged. In some cases, certain medical implants can heat substantially during the MRI examination as a result of the radiofrequency energy that is used during the procedure. Therefore, it is very important to inform the MRI technologist about any implant or other internal object that you may have.

The magnetic field of the MR systems may damage an external hearing aid or cause a heart pacemaker or electrical stimulator, or neurostimulator, to malfunction or cause patient injury. If you have a bullet or other metallic fragment in your body (e.g., any metallic foreign body) there is a potential risk that it could change position, possibly causing injury.
In addition, a metallic implant or other object may cause signal loss or distort the MR images. This may be unavoidable, but if the radiologist knows about it, allowances can be made when interpreting the MR images.

Pregnancy and MRI

If you are pregnant or suspect you are pregnant, you should inform the MRI technologist and/or radiologist during the screening procedure before the MRI examination. In general, there is no known risk of using MRI in pregnant patients. However, MRI is reserved for use in pregnant patients only to address very important problems or suspected abnormalities. In any case, MRI is safer for the fetus than imaging with x-rays or CT.

You should inform your radiologist if you are breast-feeding at the time of a scheduled MRI study and may need to receive an MRI contrast agent. One option under this circumstance is to pump breast milk before the study, to be used until injected contrast material has cleared from the body, which typically takes about 24 hours.

What is a CT Colonography?

CT scanning—sometimes called CAT scanning—is a noninvasive medical test that helps physicians diagnose and treat medical conditions.

CT scanning combines special x-ray equipment with sophisticated computers to produce multiple images or pictures of the inside of the body. These cross-sectional images of the area being studied can then be examined on a computer monitor, printed or transferred to a CD.

CT scans of internal organs, bones, soft tissue and blood vessels provide greater clarity and reveal more details than regular x-ray exams.

CT colonography, also known as virtual colonoscopy, uses low dose radiation CT scanning to obtain an interior view of the colon (the large intestine) that is otherwise only seen with a more invasive procedure where an endoscope is inserted into the rectum and passed through the entire colon.

What are some common uses of the procedure?

The major reason for performing CT colonography is to screen for polyps or cancers in the large intestine. Polyps are growths that arise from the inner lining of the intestine. Some polyps may grow and turn into cancers.

The goal of screening with CT colonography is to find these growths in their early stages, so that they can be removed before cancer has had a chance to develop. The American Cancer Society (ACS) recommends that women and men undergo screening for colon cancer or polyps beginning at age 50. As part of its recommendation, ACS suggests a colonoscopy once every 10 years or CT colonography once every five years. Individuals at increased risk or with a family history of colon cancer may start screening at age 40 or younger and may be screened at shorter intervals (for example, every five years). Risk factors for the disease include a history of polyps or having a family history of colon cancer. Signs and symptoms of colon cancer include a persistent change in bowel habits, the presence of blood in the stool, abdominal discomfort or pain, bloating and unexplained weight loss.

How should I prepare?

You should wear comfortable, loose-fitting clothing to your exam. You will be given a gown to wear during the procedure.

Women should always inform their physician and the CT technologist if there is any possibility that they are pregnant. The bowel-cleansing regimen for CT colonography is similar to that for a colonoscopy. Your diet will be restricted to clear liquids the day before the examination. It is very important to clean out your colon the night before your CT colonography examination so that the radiologist can clearly see any polyps that might be present. You will be asked to take either a set of pills or a cathartic liquid. Some common preparations are NuLytely®, Go-Lytely® (Polyethylene glycol electrolyte solutions) or Magnesium Citrate or bisacodyl tablets. Additional agents may also be taken the day before the exam. These may include small quantities of barium and iodinated liquids. These agents help the radiologist better distinguish stool from polyps by “tagging” the remaining stool and fluid.

Be sure to inform your physician if you have heart, liver or kidney disease to be certain that the bowel prep will be safe. Your physician can advise you on dietary restrictions prior to the exam. You will be able to resume your usual diet immediately after the exam.

What does the equipment look like?

The CT scanner is typically a large, box like machine with a hole, or short tunnel, in the center. You will lie on a narrow examination table that slides into and out of this tunnel. Rotating around you, the x-ray tube and electronic x-ray detectors are located opposite each other in a ring, called a gantry. The computer workstation that processes the imaging information is located in a separate room, where the technologist operates the scanner and monitors your examination.

During CT colonography, you will be asked to lie on your back and then on your stomach or side.

How does the procedure work?

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 large volume of data to create two-dimensional cross-sectional images of your body, which are then displayed on a monitor. This technique is called helical or spiral CT.

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 capabilities.

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 but especially children, the elderly and critically ill.

For CT colonography, the computer generates a detailed 3-D model of the abdomen and pelvis, which the radiologist uses to view the bowel in a way that simulates traveling down the colon. This is why the procedure is often called a virtual colonoscopy. Two dimensional (2-D) images of the inside of the colon as well as the rest of the abdomen and pelvis are obtained and reviewed at the same time.

How is the procedure performed?

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

A very small, flexible tube will be passed two inches into your rectum to allow air to be gently pumped into the colon using a hand-held squeeze bulb. Sometimes an electronic pump is used to deliver carbon dioxide gas into the colon. Sometimes a retention balloon is inflated on the rectal tube to help keep the tube positioned correctly. The purpose of the gas is to distend the colon as much as possible to eliminate any folds or wrinkles that might obscure polyps from the physician’s view.

Next, the table will move through the scanner. Patients are asked to hold their breath for about 15 seconds before turning over and lying on their back or side for a second pass that is made through the scanner. In some centers the sequence of positions may be the opposite: facing upward first and then facing down. Once the scan is done, the tube is removed.

The entire examination is usually completed within 15 minutes.

What will I experience during and after the procedure?

The vast majority of patients who have CT colonography report a feeling of fullness when the colon is inflated during the exam, as if they need to pass gas. Significant pain is uncommon, occurring in fewer than 5 percent of patients. A muscle-relaxing drug may be injected intravenously or subcutaneously to lessen discomfort, but this is seldom necessary. The scanning procedure itself causes no pain or other symptoms.

When you enter the CT scanner, special lights may be used to ensure that you are properly positioned. With modern CT scanners, you will hear only slight buzzing, clicking and whirring sounds as the CT scanner revolves around you during the imaging process.

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

After a CT exam, you can return to your normal activities.

Who interprets the results and how do I get them?

A physician, usually a radiologist with expertise in supervising and interpreting radiology examinations, will analyze the images and send a signed report to your primary care physician or the physician who referred you for the exam, who will discuss the results with you.In some cases, information about whether you have polyps is available immediately. Some imaging centers are equipped to perform colonoscopy and polyp removal the same day as the CT colonography.

Follow-up examinations are often necessary, and your doctor will explain the exact reason why another exam is requested. Sometimes a follow-up exam is done because a suspicious or questionable finding needs clarification with additional views or a special imaging technique. A follow-up examination may be necessary so that any change in a known abnormality can be detected over time. Follow-up examinations are sometimes the best way to see if treatment is working or if an abnormality is stable over time

What are the benefits vs. risks?


  • This new minimally invasive test provides both 2-D and 3-D images that can depict many polyps and other lesions as clearly as when they are directly seen by conventional colonoscopy.
  • CT colonography has a markedly lower risk of perforating the colon than conventional colonoscopy. Most of those examined do not have polyps, and can be spared having to undergo a full colonoscopy.
  • CT colonography is an excellent alternative for patients who have clinical factors that increase the risk of complications from colonoscopy, such as treatment with a blood thinner or a severe breathing problem.
  • Elderly patients, especially those who are frail or ill, will tolerate CT colonography better than conventional colonoscopy.
  • CT colonography can be helpful when colonoscopy cannot be completed because the bowel is narrowed or obstructed for any reason, such as by a large tumor.
  • If conventional colonoscopy cannot reach the full length of the colon—which occurs up to 10 percent of the time—CT colonography can be performed on the same day because the colon has already been cleansed.
  • CT colonography provides clearer and more detailed images than a conventional barium enema x-ray examination.
  • CT colonography can detect abnormalities outside of the colon, including early-stage malignancies and potentially dangerous conditions, such as abdominal aortic aneurysms.
  • CT colonography is tolerated well. Sedation and pain relievers are not needed, so there is no recovery period.
  • CT colonography is less costly than colonoscopy.
  • No radiation remains in a patient’s body after a CT examination.
  • X-rays used in CT scans usually have no immediate side effects.


  • There is a very small risk that inflating the colon with air could injure or perforate the bowel. This has been estimated to happen in fewer than one in 10,000 patients.
  • There is always a slight chance of cancer from excessive exposure to radiation. However, the benefit of an accurate diagnosis far outweighs the risk.
  • The effective radiation dose for this procedure varies. See the Safety page for more information about radiation dose.
  • Women should always inform their physician and x-ray or CT technologist if there is any possibility that they are pregnant.
  • CT scanning is, in general, not recommended for pregnant women unless medically necessary because of potential risk to the baby.

What are the limitations of CT Colonography?

A person who is very large may not fit into the opening of a conventional CT scanner or may be over the weight limit for the moving table which is usually about 450 pounds.

CT colonography is strictly a diagnostic procedure. If any clinically significant polyps are found, they will have to be removed by conventional colonoscopy.The ability of CT colonography to differentiate stool from artifacts and smaller polyps may not be as good as that of conventional colonoscopy.

CT colonography is not recommended for patients who have active Crohn’s disease, ulcerative colitis, inflammatory bowel disease or diverticulitis, because of increased risk of perforating the colon. Patients with a history of bowel perforation and those experiencing severe pain or cramps on the day of the examination should not undergo CT colonography.

Some insurance companies do not cover CT colonography as a screening test for colonic polyps, but they may cover the cost if a patient has symptoms related to the colon.

Pregnancy and x-rays

As with any aspect of medical care, knowing that a patient is or could be pregnant is important information. Pregnancy, for example, might explain certain symptoms or medical findings. When a pregnant patient is ill or injured, the physician will carefully select medications to avoid potential risks to the developing child. This is also true of x-rays.

While the vast majority of medical x-rays do not pose a critical risk to a developing child, there may be a small likelihood of causing a serious illness or other complication. The actual risk depends on how far along the pregnancy is and on the type of x-ray. Ultrasound studies, for example, don’t use x-rays and have never demonstrated any potential risk to pregnancy. X-ray studies of the head, arms, legs and chest do not usually expose the baby directly to x-rays and typically the technologist who takes the x-rays will implement special precautions to ensure that the baby of a pregnant patient is not directly exposed.

Sometimes patients need examinations of the abdomen or pelvis while they are pregnant. When studies of the abdomen or pelvis are required, the physician may prefer to order a different type of exam for a pregnant patient or reduce the number of x-rays from that which is normally acquired. Therefore, it is important that you inform your physician or the x-ray technologist about your reproductive status before the x-ray study is performed.

Most standard x-ray examinations of the abdomen are not likely to pose a serious risk to the child. Some abdominal and pelvic studies such as CT deliver greater amounts of radiation to a developing pregnancy. Informing the radiologist that you are or might be pregnant is important so that your medical care can be planned with both you and your baby in mind. Remember, this is done to optimize medical care by reducing any potential risk.

Radionuclide exams, also known as nuclear medicine, use an x-ray-like radiation. The method of use, however, is quite different from x-rays and produces very different looking images. The same advice for informing your physician or the nuclear medicine technologist about any possible pregnancy before the examination begins is important.

However, in nuclear medicine another precaution is advised for women who are breast-feeding a child. Some of the pharmaceuticals that are used for the study can pass into the mother’s milk and subsequently the child will consume them. To avoid this possibility, it is important that a nursing mother inform her physician and the nuclear medicine technologist about this before the examination begins.

What are contrast materials and how do they work?

Contrast materials, also called contrast agents or contrast media, are used to improve pictures of the inside of the body produced by x-rays, computed tomography (CT), magnetic resonance (MR) imaging, and ultrasound. Often, contrast materials allow the radiologist to distinguish normal from abnormal conditions.

Contrast materials are not dyes that permanently discolor internal organs. They are substances that temporarily change the way x-rays or other imaging tools interact with the body.

When introduced into the body prior to an imaging exam, contrast materials make certain structures or tissues in the body appear different on the images than they would if no contrast material had been administered. Contrast materials help distinguish or “contrast” selected areas of the body from surrounding tissue. By improving the visibility of specific organs, blood vessels or tissues, contrast materials help physicians diagnose medical conditions.

Contrast materials enter the body in one of three ways. They can be:

  • swallowed (taken by mouth or orally)
  • administered by enema (given rectally)
  • injected into a blood vessel (vein or artery; also called given intravenously or intra-arterially)

Following an imaging exam with contrast material, the material is absorbed by the body or eliminated through urine or bowel movements.

There are several types of contrast materials:

  • Iodine-based and barium-sulfate compounds are used in x-ray and computed tomography (CT) imaging exams.

Contrast materials can have a chemical structure that includes iodine, a naturally occurring chemical element. These contrast materials can be injected into veins or arteries, within the disks or the fluid spaces of the spine, and into other body cavities.

Barium-sulfate is the most common contrast material taken by mouth, or orally. It is also used rectally and is available in several forms, including:

  • powder, which is mixed with water before administration
  • liquid
  • paste
  • tablet

When iodine-based and barium-sulfate contrast materials are present in a specific area of the body, they block or limit the ability of x-rays to pass through. As a result, blood vessels, organs and other body tissue that temporarily contain iodine-based or barium compounds change their appearance on x-ray or CT images.

  • Gadolinium is the key component of the contrast material most often used in magnetic resonance (MR) exams. When this substance is present in the body, it alters the magnetic properties of nearby water molecules, which enhances the quality of MR images.
  • Saline (salt water) and air are also used as contrast materials in imaging exams. Microbubbles and microspheres have been administered for ultrasound imaging exams, particularly exams of the heart.

Which imaging exams use contrast materials?

Oral Contrast Materials

Barium-sulfate contrast materials that are swallowed or administered by mouth (orally) are used to enhance x-ray and CT images of the gastrointestinal (GI) tract, including:

  • pharynx
  • esophagus
  • stomach
  • the small intestine
  • the large intestine (colon)

In some situations, iodine-based contrast materials are substituted for barium-sulfate contrast materials for oral administration.

Rectal Contrast Materials

Barium-sulfate contrast materials that are administered by enema (rectally) are used to enhance x-ray and CT images of the lower gastrointestinal (GI) tract (colon and rectum).

In some situations, iodine-based contrast materials are substituted for barium-sulfate contrast materials for rectal administration.

Intravenous Contrast Materials

Iodine-based and Gadolinium-based

Iodine-based contrast materials injected into a vein (intravenously) are used to enhance x-ray and CT images. Gadolinium injected into a vein (intravenously) is used to enhance MR images. Typically they are used to enhance the:

  • internal organs, including the heart, lungs, liver, adrenal glands, kidneys, pancreas, gallbladder, spleen, uterus, and bladder
  • gastrointestinal tract, including the stomach, small intestine and large intestine
  • arteries and veins of the body, including vessels in the brain, neck, chest, abdomen, pelvis and legs
  • soft tissues of the body, including the muscles, fat and skin
  • brain
  • breast

How safe are contrast materials?

Contrast materials are safe drugs; adverse reactions ranging from mild to severe do occur but severe reactions are very uncommon. While serious allergic or other reactions to contrast materials are rare, radiology departments are well-equipped to deal with them.

How should I prepare for my imaging procedure with contrast material?

Because contrast materials carry a slight risk of causing an allergic reaction or adverse reaction, you should tell your doctor about:

  • allergies to contrast materials, food, drugs, dyes, preservatives, or animals
  • medications you are taking, including herbal supplements
  • recent illnesses, surgeries, or other medical conditions
  • history of asthma and hay fever
  • history of heart disease, diabetes, kidney disease, thyroid problems or sickle cell anemia

You will be given specific instructions on how to prepare for your exam.

How should I prepare for my imaging procedure with contrast material?

Because contrast materials carry a slight risk of causing an allergic reaction or adverse reaction, you should tell your doctor about:

  • allergies to contrast materials, food, drugs, dyes, preservatives, or animals
  • medications you are taking, including herbal supplements
  • recent illnesses, surgeries, or other medical conditions
  • history of asthma and hay fever
  • history of heart disease, diabetes, kidney disease, thyroid problems or sickle cell anemia

You will be given specific instructions on how to prepare for your exam.

Side effects and adverse and allergic reactions

Barium Sulfate Contrast Materials

You should tell your doctor if these mild side effects of barium-sulfate contrast materials become severe or do not go away:

  • stomach cramps
  • diarrhea
  • nausea
  • vomiting
  • constipation

Tell your doctor immediately about any of these symptoms:

  • hives
  • itching
  • red skin
  • swelling of the throat
  • difficulty breathing or swallowing
  • hoarseness
  • agitation
  • confusion
  • fast heartbeat
  • bluish skin color

You are at greater risk of an adverse reaction to barium-sulfate contrast materials if:

  • you have a history of asthma, hay fever, or other allergies, which will increase your risk of an allergic reaction to the additives in the barium-sulfate agent.
  • you have cystic fibrosis, which will increase the risk of blockage in the small bowel.
  • you are severely dehydrated, which may cause severe constipation.
  • you have an intestinal blockage or perforation that could made worse by a barium-sulfate agent.

Iodine-based Contrast Materials

Mild reactions include:

  • nausea and vomiting
  • headache
  • itching
  • flushing
  • mild skin rash or hives

Moderate reactions include:

  • severe skin rash or hives
  • wheezing
  • abnormal heart rhythms
  • high or low blood pressure
  • shortness of breath or difficulty breathing

Severe reactions include:

  • difficulty breathing
  • cardiac arrest
  • swelling of the throat or other parts of the body
  • convulsions
  • profound low blood pressure

A very small percentage of patients may develop a delayed reaction with a rash which can occur hours to days after an imaging exam with an iodine-based contrast material. Most are mild, but severe rashes may require medication after discussion with your physician.

Contrast-Induced Nephropathy

Patients with impaired kidney (renal) function should be given special consideration before receiving iodine-based contrast materials by vein or artery. Such patients are at risk for developing contrast-induced nephropathy, in which the pre-existing kidney damage is worsened.

At-Risk Patients

Some conditions increase the risk of an allergic or adverse reaction to iodine-based contrast materials. These include:

  • previous adverse reactions to iodine-based contrast materials
  • history of asthma
  • history of allergy
  • heart disease
  • dehydration
  • sickle cell anemia, polycythemia and myeloma
  • renal disease
  • the use of medications such as Beta blockers, NSAIDs, interleukin 2
  • having received a large amount of contrast material within the past 24 hours

Being at increased risk for an allergic or adverse reaction to contrast material does not necessarily mean a patient cannot undergo an imaging exam with contrast materials. Medications are sometimes given before the contrast material is administered to lessen the risk of an allergic reaction in susceptible patients.


The contrast material used in MR called gadolinium is less likely to produce an allergic reaction than the iodine-based materials used for x-rays and CT scanning. Very rarely, patients are allergic to gadolinium-based contrast materials and experience hives and itchy eyes. Reactions usually are mild and easily controlled by medication. Severe reactions are rare.

Nephrogenic systemic fibrosis (NSF), a thickening of the skin, organs and other tissues, is a rare complication in patients with kidney disease that undergo an MR with contrast material. Gadolinium-based contrast material may be withheld in some patients with severe kidney disease.

What will I experience before and after receiving contrast material?

Barium-Sulfate Oral and Rectal Contrast Material

If a barium-sulfate contrast material (given orally or rectally) will be used during your exam, you will be asked not to eat for several hours before your exam begins. If the contrast material will be given rectally, you may also be asked to cleanse your colon with a special diet and medication (possibly including an enema) before your exam.

If you swallow the contrast material, you may find the taste mildly unpleasant; however, most patients can easily tolerate it.

If your contrast material is given by enema, you can expect to experience a sense of abdominal fullness and an increasing need to expel the liquid. The mild discomfort will not last long.

It is a good idea to increase your fluid intake after an imaging exam involving a barium-based contrast material to help remove the contrast material from your body.
Barium-sulfate contrast materials are expelled from the body with feces. You can expect bowel movements to be white for a few days. Some patients may experience changes in their normal bowel movement patterns for the first 12 to 24 hours.

Iodine-based Contrast Material

When an iodine-based contrast material is injected into your bloodstream, you may have a warm, flushed sensation and a metallic taste in your mouth that lasts for a few minutes.

The needle may cause you some discomfort when it is inserted. Once it is removed, you may experience some bruising.

It is a good idea to increase your fluid intake after an imaging exam involving an iodine-based contrast material to help remove the contrast material from your body.

Gadolinium-based Contrast Material

When the gadolinium is injected, it is normal to feel coolness at the site of injection, usually the arm for a minute or two.

The needle may cause you some discomfort when it is inserted. Once it is removed, you may experience some bruising.

For all of the above administrations of contrast material (barium sulfate, iodine-based, and gadolinium-based):

If you have not been sedated, no recovery period is necessary. You may resume your usual activities and normal diet immediately after the exam. Increased fluid intake will help eliminate the contrast material from your body.

Pregnancy and contrast materials

Prior to any imaging exam, women should always inform their physician or x-ray technologist if there is any possibility that they are pregnant. Many imaging tests and contrast material administrations are avoided during pregnancy to minimize risk to the baby.

For CT imaging, if a pregnant woman must undergo imaging with an iodine-based contrast material, the patient should have a discussion with her referring physician and radiologist to understand the potential risks and benefits of the contrast-enhanced scan.

For MR imaging, gadolinium contrast material administration is usually avoided due to unknown risk to the baby, but may be used when critical information must be obtained that is only available with the use of gadolinium-based contrast material.

Intravenous Contrast Material (Iodine and Gadolinium) and Breast-feeding:

Manufacturers of intravenous contrast indicate mothers should not breast-feed their babies for 24 to 48 hours after contrast medium is given. However, both the American College of Radiology (ACR) and the European Society of Urogenital Radiology note that the available data suggest that it is safe to continue breast-feeding after receiving intravenous contrast. The Manual on Contrast Media from the ACR states:

“Review of the literature shows no evidence to suggest that oral ingestion by an infant of the tiny amount of gadolinium contrast medium excreted into breast milk would cause toxic effects. We believe, therefore, that the available data suggest that it is safe for the mother and infant to continue breast-feeding after receiving such an agent.

If the mother remains concerned about any potential ill effects, she should be given the opportunity to make an informed decision as to whether to continue or temporarily abstain from breast-feeding after receiving a gadolinium contrast medium. If the mother so desires, she may abstain from breast-feeding for 24 hours with active expression and discarding of breast milk from both breasts during that period. In anticipation of this, she may wish to use a breast pump to obtain milk before the contrast study to feed the infant during the 24-hour period following the examination.”


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