A computed tomography (CT or CAT) scan allows doctors to see inside your body. It uses a combination of X-rays and a computer to create pictures of your organs, bones, and other tissues. It shows more detail than a regular X-ray.
You can get a CT scan on any part of your body. The procedure doesn't take very long, and it's painless.
A CT scanner machine uses an X-ray that rotates around your body to get views from all angles that are put together for a 3D image. (Photo Credit: Kaliantye/Dreamstime)
What is a CT scan machine?
The CT scan machine is an imaging device that uses a motorized X-ray to take three-dimensional (3D) digital images.
There are several important parts of a CT scan machine. You lie on a movable table and will slide through the center of a gantry. That is the ring-shaped part of the scanner where the X-ray tube and digital X-ray detectors are. The detectors are opposite the X-ray source. When they capture the X-rays, the detectors send the information to a computer. The computer turns the data into detailed images.
CT scan vs. MRI
A CT scan and MRI are both imaging machines used to help doctors see inside your body. For both of these tests, you&#;ll lie on a moving table that passes through a doughnut-shaped machine.
A CT scan uses X-rays to image the body. An MRI uses radio waves and a powerful magnet to create similar images. CT scans are helpful in showing where things are &#; where one organ ends and another begins, for instance. An MRI is geared toward showing normal and abnormal tissue.
CT scans are often used to find cancer, bone fractures, internal bleeding, blood clots, and injuries to the spine and brain. An MRI shows certain diseases that a CT scan can&#;t. For instance, uterine, prostate, and certain liver cancers are hard to see on a CT scan. Also, an MRI is used to diagnose injuries to the soft tissues or joints and injury to organs like the heart, brain, and digestive organs.
PET scan vs. CT scan
A positron emission tomography (PET) scan is an imaging tool, like a CT scan and MRI, that produces images of your organs and tissues. But it works differently. In a PET scan, you&#;re injected with a safe radioactive chemical called a radiotracer. After the radiotracer has had a chance to get into your bloodstream, cells, and tissues, you&#;ll lie on a moving table, similar to one for a CT scan. In places where your body has increased metabolic activity, more of the radiotracer is absorbed. The scan picks that up to show areas where something may be wrong, such as heart disease, cancer, or a brain disorder. A PET scan is able to find cellular changes in your body in real time (even before a CT scan or an MRI can detect anything wrong).
A PET scan is able to measure vital functions such as blood flow, oxygen use, and blood sugar metabolism. It identifies organs and tissues that aren&#;t working as they should much earlier than a CT scan can find these issues.
The whole PET scan process usually takes 2 hours to complete, longer than a CT scan. Part of that time is waiting for your body to absorb the radiotracer.
Computed tomography (CT) of the body uses sophisticated x-ray technology to help detect a variety of diseases and conditions. CT scanning is fast, painless, noninvasive and accurate. In emergency cases, it can reveal internal injuries and bleeding quickly enough to help save lives.
Tell your doctor if there's a possibility you are pregnant and discuss any recent illnesses, medical conditions, medications you're taking, and allergies. You will be instructed not to eat or drink anything for a few hours beforehand. If you have a known allergy to contrast material, your doctor may prescribe medications to reduce the risk of an allergic reaction. Leave jewelry at home and wear loose, comfortable clothing. You may be asked to wear a gown.
Computed tomography, more commonly known as a CT or CAT scan, is a diagnostic medical imaging test. Like traditional x-rays, it produces multiple images or pictures of the inside of the body.
A CT scan generates images that can be reformatted in multiple planes. It can even generate three-dimensional images. Your doctor can review these images on a computer monitor, print them on film or via a 3D printer, or transfer them to a CD or DVD.
CT images of internal organs, bones, soft tissue, and blood vessels provide greater detail than traditional x-rays. This is especially true for soft tissues and blood vessels.
Using specialized equipment and expertise to create and interpret CT scans of the body, radiologists can more easily diagnose problems such as cancer, cardiovascular disease, infectious disease, appendicitis, trauma and musculoskeletal disorders.
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CT imaging is:
In pediatric patients, CT imaging is often used to evaluate:
Radiologists and radiation oncologists often use the CT examination to:
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Wear comfortable, loose-fitting clothing to your exam. You may need to change into a gown for the procedure.
Metal objects, including jewelry, eyeglasses, dentures, and hairpins, may affect the CT images. Leave them at home or remove them prior to your exam. Some CT exams will require you to remove hearing aids and removable dental work. Women will need to remove bras containing metal underwire. You may need to remove any piercings, if possible.
Your doctor may instruct you to not eat or drink anything for a few hours before your exam if it will use contrast material. Tell your doctor about all medications you are taking and if you have any allergies. If you have a known allergy to contrast material, your doctor may prescribe medications (usually a steroid) to reduce the risk of an allergic reaction. To avoid unnecessary delays, contact your doctor well before the date of your exam.
Also tell your doctor about any recent illnesses or other medical conditions and whether you have a history of heart disease, asthma, diabetes, kidney disease, or thyroid problems. Any of these conditions may increase the risk of an adverse effect.
Women should always inform their physician and the CT technologist if there is any possibility that they may be pregnant. See the CT Safety During Pregnancy page for more information.
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The CT scanner is typically a large, donut-shaped machine with a short tunnel in the center. You will lie on a narrow table that slides in and out of this short 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 in a separate control room. This is where the technologist operates the scanner and monitors your exam in direct visual contact. The technologist will be able to hear and talk to you using a speaker and microphone.
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In many ways, a CT scan works like other x-ray exams. Different body parts absorb x-rays in different amounts. This difference allows the doctor to distinguish body parts from one another on an x-ray or CT image.
A conventional x-ray exam directs a small amount of radiation through the body part under examination. A special electronic image recording plate captures the image. Bones appear white on the x-ray. Soft tissue, such as the heart or liver, shows up in shades of gray. Air appears black.
With CT scanning, several x-ray beams and electronic x-ray detectors rotate around you. These measure the amount of radiation being absorbed throughout your body. Sometimes, the exam table will move during the scan. A special computer program processes this large volume of data to create two-dimensional cross-sectional images of your body. The system displays the images on a computer monitor. CT imaging is sometimes compared to looking into a loaf of bread by cutting the loaf into thin slices. When the computer software reassembles the image slices, the result is a very detailed multidimensional view of the body's interior.
Nearly all CT scanners can obtain multiple slices in a single rotation. These multi-slice (multidetector) CT scanners obtain thinner slices in less time. This results in more detail.
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Modern CT scanners can image large sections of the body in just a few seconds, and even faster in small children. Such speed is beneficial for all patients. Speed is especially beneficial for children, the elderly, and critically ill &#; anyone who finds it difficult to stay still, even for the brief time necessary to obtain images.
For children, the radiologist will adjust the CT scanner technique to their size and the area of interest to reduce the radiation dose.
Some CT exams use a contrast material to enhance visibility in the body area under examination.
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The technologist begins by positioning you on the CT exam table, usually lying flat on your back. They may use straps and pillows to help you maintain the correct position and remain still during the exam.
Many scanners are fast enough to scan children without sedation. In special cases, children who cannot hold still may need sedation. Motion may cause blurring of the images and degrade image quality the same way that it affects photographs.
The exam may use contrast material, depending on the type of exam. If so, it will be swallowed, injected through an intravenous line (IV) or, rarely, administered by enema.
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 for the actual CT scan. Depending on the type of CT scan, the machine may make several passes.
The technologist may ask you to hold your breath during the scanning. Any motion, including breathing and body movements, can lead to artifacts on the images. This loss of image quality can resemble the blurring seen on a photograph taken of a moving object.
When the exam is complete, the technologist will ask you to wait until they verify that the images are of high enough quality for accurate interpretation by the radiologist.
The CT examination is usually completed within 30 minutes. The portion requiring intravenous contrast injection usually lasts only 10 to 30 seconds.
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CT exams are generally painless, fast, and easy. Multidetector CT reduces the amount of time that the patient needs to lie still.
Though the scan is painless, you may have some discomfort from remaining still for several minutes or from placement of an IV. If you have a hard time staying still, are very nervous, anxious, or in pain, you may find a CT exam stressful. The technologist or nurse, under the direction of a doctor, may offer you some medication to help you tolerate the CT exam.
If the exam uses iodinated contrast material, your doctor will screen you for chronic or acute kidney disease. The doctor may administer contrast material intravenously (by vein), so you will feel a pin prick when the nurse inserts the needle into your vein. You may feel warm or flushed as the contrast is injected. You also may have a metallic taste in your mouth. This will pass. You may feel a need to urinate. However, these are only side effects of the contrast injection, and they subside quickly.
If you swallow oral contrast material, you may find the taste mildly unpleasant. However, most patients can easily tolerate it. If you receive an enema, you can expect to experience a sense of abdominal fullness. You may also feel an increasing need to expel the liquid. If so, be patient; the mild discomfort will not last long.
When you enter the CT scanner, you may see special light lines projected onto your body. These lines help ensure that you are in the correct position on the exam table. With modern CT scanners, you may hear slight buzzing, clicking and whirring sounds. These occur as the CT scanner's internal parts, not usually visible to you, revolve around you during the imaging process.
You will be alone in the exam room during the CT scan, unless there are special circumstances. For example, sometimes a parent wearing a lead shield may stay in the room with their child. However, the technologist will always be able to see, hear and speak with you through a built-in intercom system.
With pediatric patients, a parent may be allowed in the room but may need to wear a lead apron to minimize radiation exposure.
After a CT exam, the technologist will remove your intravenous line. They will cover the tiny hole made by the needle with a small dressing. You can return to your normal activities immediately.
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A radiologist, a doctor specially trained to supervise and interpret radiology exams, will analyze the images. The radiologist will send an official report to the doctor who ordered the exam.
You may need a follow-up exam. If so, your doctor will explain why. Sometimes a follow-up exam further evaluates a potential issue with more views or a special imaging technique. It may also see if there has been any change in an issue over time. Follow-up exams are often the best way to see if treatment is working or if a problem needs attention.
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There is no conclusive evidence that radiation at small amounts delivered by a CT scan causes cancer. Large population studies have shown a slight increase in cancer from much larger amounts of radiation, such as from radiation therapy. Thus, there is always concern that this risk may also apply to the lower amounts of radiation delivered by a CT exam. When a CT scan is recommended by your doctor, the expected benefit of this test outweighs the potential risk from radiation. You are encouraged to discuss the risks versus the benefits of your CT scan with your doctor or radiologist, and to explore whether alternative imaging tests may be available to diagnose your condition.
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Soft-tissue details in areas such as the brain, gallbladder, internal pelvic organs, and joints (such as knees and shoulders) can often be better evaluated with magnetic resonance imaging (MRI). In pregnant women, while CT can be performed safely, other imaging exams not involving radiation, such as ultrasound or MRI, are preferred but only if they are likely to be as good as CT in diagnosing your condition.
A person who is very large may not fit into the opening of a conventional CT scanner. Or, they may be over the weight limit&#;usually 450 pounds&#;for the moving table.
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