Computed tomography, sometimes called computed tomography, computed tomography, or computerized axial tomography, involves the use of multiple X-ray images that are translated by a computer and converted into a three-dimensional image. This allows healthcare professionals to view an organ, injury, or growth from different angles. CT allows a more in-depth analysis than other imaging techniques, without the need for invasive interventions. It is used for a wide variety of reasons, such as tumor detection, blood clot detection, bone fracture evaluation, and more.
More than 70 million CT scans are performed annually in the United States, according to a study from Columbia University Medical Center in New York.
The purpose of the test
CT is a painless, non-invasive procedure that can be used to visualize almost any part of the body. Since the introduction of computed tomography technology in 1967, imaging has evolved from a medical diagnostic tool to a tool used in the prevention, detection, and treatment of disease. It is commonly used when an X-ray cannot provide sufficient details of the injury or disorder, especially in emergency situations where time is of the essence.
Among the many uses of CT scan:
- Abdominal CT can be used to look for growths in the liver, kidneys, or pancreas, or to look for causes of urinary tract bleeding ( hematuria ).
- Cardiovascular CT scans can be used to map blood flow ( CT angiography ) and to diagnose kidney disease , aortic aneurysm , atherosclerosis , or pulmonary edema .
- A CT scan of the heart can help diagnose and monitor coronary artery disease (CHD) or aid in valve replacement surgery.
- Head and brain CT scans can be used to look for tumors, bleeding, bone lesions, blocked blood flow, and brain calcifications (which are commonly seen in people with Parkinson's disease and dementia).
- CT of the lungs can help detect changes in the lung architecture that result from fibrosis (scarring), emphysema , tumors, atelectasis (collapsed lung), and pleural effusion .
- Skeletal CT can help diagnose spinal cord injuries, pathological fractures , tumors, or bone injuries, and can help evaluate a complex fracture , osteoporosis , or joint damage caused by arthritis.
With this in mind, your healthcare provider may order this test for a number of reasons, including reporting symptoms related to these or other problems, an event (such as a physical injury), other test results indicating the need for an evaluation. additional and / or the need to monitor the diagnosed problem.
Benefits and limitations
CT technology offers many benefits, especially in emergency situations where high-contrast images can be obtained in just a few minutes. This information can tell healthcare providers whether or not surgery is necessary.
In the context of emergency care, computed tomography is superior to X-rays, magnetic resonance imaging (MRI) , and positron emission tomography (PET) . Only ultrasound can compare with CT in speed, but it has limitations in the types of injuries or disorders it can diagnose.
That said, there are situations in which CT may be less effective. For example, MRI is much better at visualizing organs and soft tissues, including joints, ligaments, nerves, and spinal discs. In a non-emergency situation, MRI can provide more informative information than CT scan.
On the other hand, MRI costs twice as much and because it uses strong magnetic waves, it may not be suitable for people with metal implants (including some pacemakers, artificial joints, and cochlear implants).
In contrast, PET and CT technologies are often combined in a dual-use device called PET-CT . By providing anatomical and metabolic information, PET-CT scans can offer deeper insights when diagnosing or staging cancer .
Risks and contraindications.
While computed tomography is a valuable diagnostic and screening tool, it carries risks associated with an increased risk of cancer and response to contrast media.
The main problem many people have with CT scans is exposure to "high" radiation levels and the potential risk of cancer. While it is true that CT scans exposes you 100 to 1000 times more radiation than conventional X-rays, it does not necessarily translate into a commensurate increase in your risk of cancer.
According to the National Cancer Institute (NCI), the risk of cancer from a single CT scan is very small. Compared to the average lifetime cancer risk among Americans (one in five), the CT scan risk is approximately one in 2000. An additive exposure means a lifetime risk of approximately 20.05%, compared to an overall average of 20%.
Children may be at higher risk because they have a longer time to live after the procedure than, say, with someone in their 50s, 60s, or 70s. However, a 2012 review of studies questioned this assumption and found no clear link between medical radiation and cancer risk in children.
While it shouldn't be said that this is not without risk, when used correctly the benefits of CT scans almost always outweigh the potential risks. If you have had one or more CT scans in the past, it is important to let your doctor know if a new scan will be ordered.
Contrast agents , also known as X-ray contrast agents or contrast dyes, are used in computed tomography to highlight structures that are difficult to distinguish from their surroundings, such as the brain, spine, liver, or kidneys. . Most are iodine-based and are given intravenously (into a vein) before the scan.
Some gastrointestinal exams may require an oral solution or an enema. The most widely used are barium sulfate and iodine-based gastrographin (diatrizoate).
According to a study published in the International Journal of Angiology , side effects from contrast media can occur in 1% to 12% of cases, depending on the agent used. Side effects can range in severity from mild to life threatening. between one hour and seven days after the dose.
Common side effects include:
- Runny nose
- Abdominal cramps
- Threw up
Diabetes, asthma, heart disease, thyroid disease, and kidney failure can increase the risk of side effects.
People with a known allergy to radiopaque contrast agents should be treated with antihistamines and steroids prior to contrast agent administration.
Life-threatening allergic reactions known as anaphylaxis can occur in 0.01-0.2% of cases. Symptoms include shortness of breath, hives, facial swelling, rapid breathing, shortness of breath, abdominal cramps, and a feeling of impending seizure. Rock. If not treated right away, anaphylaxis can lead to seizures, coma, shock , and even death.
According to the NCI, between 5 and 9 million CT scans are being performed on children in the United States, including infants and toddlers. Although the risk of developing cancer in children with a single computer scan is low, the NCI recommends adjusting the procedure so that the radiation dose is as low as possible to achieve clear imaging results.
This will include:
- Perform CT scan only when needed
- Consideration of other methods that do not emit radiation, such as ultrasound and magnetic resonance imaging (MRI)
- Radiation level adjustment based on the child's height and weight.
- Reduce the scan to the minimum required area
- Lower the scan resolution when high-quality images are not absolutely essential
If more than one CT scan is recommended, discuss the benefits and risks with your doctor and don't hesitate to ask if there are other means of making a reliable diagnosis.
Considerations about pregnancy
If you are pregnant or suspect that you are pregnant or are trying to become pregnant, tell your doctor. In general, if an examination of the abdomen or pelvis is not performed, the risk to the fetus is minimal. According to the American College of Obstetricians and Gynecologists (ACOG) guidelines, if a CT scan covers the abdomen or pelvis, the risk to your child is still considered small.
Also, oral and rectal contrast agents are not absorbed into the bloodstream and cannot harm the fetus. Although intravenous agents can cross the placenta and enter the fetal bloodstream, animal studies to date have shown no evidence of harm.
No matter how small the risk, it is always best to speak with your doctor about any procedure performed during pregnancy so that you can make an informed decision.
When it comes to breastfeeding, barium is not absorbed into the bloodstream and is not passed to your baby through breast milk. Although less than 1% iodine-based solution can be passed into breast milk, ACOG has concluded that this amount is not harmful to the baby and does not require interruption of breastfeeding.
However, some mothers may prefer a more conservative approach and refuse to breastfeed for 24 to 48 hours after the test. (In such cases, pumping a couple days in advance can help.)
CT scans should almost always be avoided during pregnancy unless the benefits of the test clearly outweigh the potential risks.
Other contraindications may include:
In practice, obesity can preclude the use of CT scans, since most machines can only support 425 to 450 pounds of weight and less than 28 inches between the back and the abdomen.
Before the test
Preparation for a CT scan can vary depending on the type of condition being diagnosed and whether or not a contrast agent is used. Your healthcare professional will provide you with specific instructions based on the purpose of the test.
From arrival to completion, the appointment will last from one to two hours, depending on the necessary preparations. The scan itself without contrast agent will take 15 to 30 minutes. New machines can start scanning in just a few minutes.
If a contrast agent is used, it may take several minutes to an hour for the solution to fully circulate through the bloodstream or gastrointestinal tract. Be prepared for delays in scheduling your exam and try to arrive 15 minutes early to register.
The test is usually done in a hospital or a separate radiology center. The new CT systems consist of a large donut-shaped unit and a motorized scanning table that moves in and out of the scanner. In the center of the tunnel (gantry) is a row of X-ray emitters and detectors. They are much less noisy and claustrophobic than older systems.
The radiologist will perform CT scans from the radiation-proof control room adjacent to the examination room.
What to wear
Depending on the part of your body being scanned, some or all of your clothing may need to be removed. Wear comfortable clothing without zippers, buttons, rivets, or buttons (like a tracksuit).
While there may be a locked storage space, leave all valuables at home. Since you will need to remove all metal from the scan site (including glasses, jewelry, and piercings), it is best to leave all non-essential accessories at home.
Food and drink
Some CT scan procedures may require food and drink restrictions, especially with contrast media. In such cases, you may be asked to stop eating or drinking six to eight hours earlier.
You may also need to temporarily stop taking certain medications. Tell your doctor about all the medicines you take, whether they are prescription, over-the-counter, or for fun.
If you have been prescribed a rectal contrast medium, you will need a bowel prep the day before your procedure, which includes dietary restrictions and laxatives to help completely remove stool from the intestine.
Be sure to bring your ID and insurance card when you enter the lab. If your child is being screened, you can bring a stuffed animal if he is particularly concerned.
If a rectal contrast agent is ordered, you may want to carry a sanitary pad with you to prevent anal leakage after the solution has been evacuated from the colon.
Cost and health insurance
The cost of a conventional CT scan without contrast material ranges from $ 600 to $ 1,500, depending on the state you live in and the institution you choose. A broader estimate with contrast can be as high as $ 5,000.
Generally, CT scans require prior authorization from insurance. Your healthcare provider can make this request for you. If a scan is denied, ask for the reason in writing. You can then take the letter to your state consumer protection office for help filing an appeal. Your healthcare provider should also give you additional motivation as to why the test is so important.
If approved, be sure to find out what your personal expenses will be. If you are not insured or not sufficiently insured, buy at the best prices. Generally speaking, radiology departments in hospitals are more expensive than independent ones.
You can also ask if the lab offers flexible payment options. If you are not insured, ask if they have a patient assistance program with a tiered pricing structure.
During the exam
The test will be performed by a specially trained radiologist in the exam room. A nurse may also be present.
On the day of the test, after logging in and confirming your insurance information, you may be asked to sign a consent form stating that you understand the purpose and risks of the procedure. Then they will take you to the dressing room to change.
If you have a conventional CT scan, you are now ready to sit in the CT room. But if your doctor ordered a contrast agent test, you will need to make some additional preparations:
- If IV contrast is ordered , it will be placed on a table in the exam room and an IV will be inserted into a vein, usually in the arm or groin, and then the contrast will be injected. In some cases, the agent can be injected directly into the joint (arthrogram) or the lower part of the spine (myelogram). You may experience momentary redness or a metallic taste in your mouth. Depending on the part of the body you are scanning, you may need to wait a few minutes or more in a reclined or prone position. Line IV remains in place until the end of the scan.
- If an oral contrast agent has been prescribed , you will be asked to drink a chalky (barium) or watery (gastrografin) substance before entering the exam room. Depending on the part of the body you are examining, you may need to wait 30 to 60 minutes before the scan can be done. Notify your nurse or radiologist if you experience nausea or distress.
- If rectal contrast is ordered , it will be placed on a table in the exam room and your rectum will be lubricated. An enema tube will be inserted to gradually fill the colon with contrast agent (and sometimes air ). You may be given an injection of Buscopan (butylscopolamine) to relieve muscle cramps. The balloon is then inflated at the end of the tube to prevent leakage and is kept there until the scan is complete.
Depending on the results of the test, you may be asked to lie on your back, on your side, or on your stomach. The table can be raised or lowered, and straps and cushions can be used to hold it in position and help it stay in place during the test. While immobility during scanning is imperative, newer CT systems with multiple detectors operate quickly and easily, reducing the time required to hold a position.
If you are traveling with a child, you should wear a protective apron to minimize your radiation exposure. During the actual scan, you will be in the control room with the technician, but you will be able to communicate with your child through a two-way speaker.
Throughout the test
When it's time to start, the technician will let you know by contacting you over the speaker. At first, the motorized table will quickly go in and out of the scanner. This is to ensure that the table is in the correct starting position and that the scan covers the entire area of the body being examined. You will also see special lines of light projected onto your body to make sure you are in the correct position.
From this point on, the table will move slowly through the scanner. The portal will rotate around you as the X-ray emitters create a series of beams. The rays will pass through your body and will be received by the appropriate detectors.
Remember to stay still during each scan. In some cases, you may be asked to hold your breath. Its position can also be changed to get different views. Unlike older CT scanners, newer devices only emit a slight buzz, buzz, or click. You will not feel the pain of the scan itself.
If you need to sneeze, scratch, or cramp, tell your healthcare professional. There is no problem to stop the test instantly. In some cases, a technician can make you more comfortable without interfering with your viewing.
The computer then converts the signals into a series of cross-sectional (tomographic) images called slices. Using geometric digital processing, 2D slices can be converted into a final 3D image.
Once the scan is complete, the radiologist will double check to make sure the images are clearly displayed.
- If an intravenous contrast medium has been used , the intravenous line will be removed and the puncture wound will be bandaged.
- If an oral contrast medium has been used, you will be given a glass of water and asked to drink plenty of fluids.
- If a rectal contrast medium has been used , the solution will be drawn from the colon through an enema tube. After the tube has been removed, you will be taken to the bathroom to flush the rest down the toilet. A sanitary napkin can be provided to protect your garment from leaks. A laxative may also be suggested to cleanse the intestines and prevent constipation.
In most cases, you can change your clothes again and go home or to work.
After the test
Most iodine-based contrast agents have a half-life of two to four hours. This means that they are completely eliminated from your body within a day or two. Most of the solution is excreted in the urine, so you should drink plenty of fluids.
If you have been given a barium solution, you may experience constipation in the short term and your stools may become chalky for a day or two. If you have not had a bowel movement after two days, call your doctor. A barium enema can sometimes cause blockages and lead to a bowel obstruction. A special enema may be required to clear the plug.
Radiation from a CT scan will not stay in the body, and you will not harm anyone who touches, kisses, or stands next to it.
Regardless of the type of CT scan, call your doctor if you develop unusual symptoms, such as fever, chills, vomiting, shortness of breath, or rapid heartbeat.
interpretation of results
Your healthcare provider should get the results of the CT scan in a day or two. In addition to the images, the radiologist will prepare a detailed report showing normal and abnormal results.
Computed tomography can sometimes provide definitive evidence of disease, especially fractures; kidney stones; clots or narrowing (stenosis) of your blood vessels, airways, or intestines.
In other cases, the scan can only guess what is happening. This is especially true for abnormal growths, lesions, and tumors. More research is often required to determine whether the growth is benign or malignant and what types of cells may be involved.
In some cases, the problem cannot be detected. This does not mean that it is necessarily in clear light. It simply indicates that nothing was found due to limitations of CT technology.
Based on the results, your healthcare provider may suggest a treatment plan or recommend more tests.
If more tests are needed, the diagnosis may include blood tests, urinalysis, cultures, tissue biopsies, other imaging tests, or even diagnostic surgery.
If cancer is suspected, a combined PET-CT scan can provide more definitive evidence of malignancy along with a biopsy of the lesion itself.
Get the word of drug information
As accurate and fast as computed tomography can be, the results are sometimes open to interpretation. If your symptoms persist despite a "normal" result, discuss other testing options with your doctor or request a referral to a specialist who can further investigate. Never be afraid of getting another doctor's opinion or having your records sent to another healthcare provider.
Today, CT images are stored as electronic data files and can be sent via email or other means as required.