CT with and without contrast: how to do computed tomography correctly

When is CT indicated?

Computed tomography, or computed axial tomography, is an X-ray imaging technique that can make cross-sectional images of the human body, including the head, lumbar and sacral spine, and other organs.

The method works by combining a series of x-rays that radiologists try to take from different angles. The images are then processed by a computer to create cross-sectional images – very thin “sections” of bones, muscles and blood vessels become visible. This allows the doctor to literally look inside the body. Figuratively speaking, as if an apple was cut in half.

This procedure was able to make a real revolution in radiation diagnostics, because thanks to it it is possible to see tissues, blood vessels, bones and foci of infections in different parts of the body in detail.

This type of scan is prescribed by a doctor both as an independent diagnostic method and in addition to others, for example, a thorough examination of the sacral spine.

Some symptoms make a scan appointment more preferable. These are frequent and severe headaches, sudden loss of speech, hearing and vision, frequent inflammation of the sinuses, pain in the back, neck and limbs, poor joint mobility, pain in the abdomen, sacro-lumbar, abdominal and retroperitoneal regions, sinus injuries or eye area, as well as head injuries and, in general, any severe injuries. Scanning will clarify the diagnosis and help determine further treatment tactics.

Indications and contraindications

Scanning is indicated in cases where it is necessary to carefully examine the bones, internal organs and soft tissues, including the abdominal and sacro-lumbar region, blood vessels or suspicious growths. This type of x-ray can detect certain types of cancer and benign tumors, compound fractures, blood clots, heart disease, intestinal disorders (blockage, Crohn’s disease), diseases or injuries of the brain and spinal cord, and all types of internal bleeding. It clearly shows the gaps between the insides and departments, which in some cases is especially important.

Health professionals consider CT to be generally safe, including for the brain, sacro-lumbar, and retroperitoneal cavity. However, with frequent x-rays, the risk is higher than with conventional x-rays, since this procedure uses higher ionizing radiation. Allergic reactions to the contrast agent may also occur.

In general, scanning is completely contraindicated only for pregnant women, since images of the pelvis and retroperitoneal cavity can harm the fetus. In these cases, an ultrasound or MRI may be recommended.

How to prepare for CT

On the day of the CT scan, you should arrive at the medical facility at least 20 minutes before the scan. The day before, you should ask your doctor if you need to take medicines as usual, if they are prescribed.

It is best to wear comfortable clothing, especially if a lumbar scan is scheduled. Most likely, you will have to change into a bathrobe, take off your watch and jewelry. Lightning bolts and metal objects can interfere with scanning.

If contrast is to be used, the doctor should give specific advice on how to prepare for the contrast. Sometimes it may be necessary to take a blood test before a scheduled CT scan, especially of the sacral spine.

There are restrictions in nutrition: you need to take only clear liquids within four hours before CT. This helps prevent nausea when the contrast medium is injected. You can eat broth, drink tea or coffee, fruit juices and soft drinks.

Allergy sufferers may need to take a steroid the night before and the morning of the procedure along with an antihistamine to avoid a reaction to the contrast agent. But amateur performance is useless here, on this issue it is necessary to consult a doctor.

Differences between CT and MRI

Unlike MRI, scanning is completely silent. X-rays are used to make it, while MRI does not use any radiation and is based solely on the effect of a magnetic field – with the help of radio waves, internal organs and the head are visualized.

Computed tomography creates more detailed images of bones, cavities and regions, including the abdomen and sacro-lumbar, than conventional x-rays. But it is not as accurate at detecting soft tissue damage, such as in the chest, as MRI. At the same time, this method is low in cost in comparison with MRI.

The advantage is that the procedure is very fast, usually the scan takes no more than 5-10 minutes, although this depends on the part of the body.

How is the procedure

To perform the procedure, the patient must remove all metal or other items that may interfere with the examination, such as glasses or dentures.

The health care provider may use a special dye called a contrast agent, given as a drink or injected into a vein. The contrast in the images appears white, allowing blood vessels, tissues, or other structures to be seen. In exceptional cases, a contrast agent is injected into the cavity or rectum.

During the CT scan, the subject must lie on a table or on a special stretcher. Doctors and technicians are in the next room, where there is a computer and monitors. The patient can communicate with them through the intercom.

When the scan starts, the stretcher or table is slowly moved into the scanner and the X-ray machine rotates around the patient. Each rotation generates multiple views of the body, such as the chest or abdomen, in section.

The procedure can last from 5 minutes to 1 hour. At this stage, you need to remain as still as possible, because movement can blur images. The scanner will take pictures of the area, such as the sacral spine, that the health worker needs to see. When the examination is completed, the stretcher or table will slide out of the scanner. The radiologist will then converge and analyze the images.

How often can you do

Any exposure carries a small relative risk. There is no set number of scan sessions that can be completely safe for humans. There are also many types of scans, and each exposes the patient to a different dose of radiation depending on the target and body part being scanned.

However, as established in the course of studies, in the absence of impaired renal function CT scan of any part of the body and its divisions can safely be done twice a year. But that doesn’t mean you have to do two scans every year. If you have recently done such a procedure, it is advisable to carry out the next one no earlier than six months later. Do not expose yourself to more radiation than is absolutely necessary.

Features of CT of different organs

Computed tomography (CT) of the abdominal organs. With this procedure, abscesses, tumors, foci of infection, enlarged lymph nodes, foreign bodies, bleeding, appendicitis, diverticulitis can be detected in the abdominal and retroperitoneal cavity. Doctors use it to diagnose the cause of abdominal or pelvic pain. With its help, diseases of the small and large intestines, pyelonephritis, fluid accumulations, ulcerative colitis, pancreatitis, cirrhosis, cancer of the liver, kidneys, pancreas, ovaries and bladder, as well as lymphomas, kidney and bladder stones, abdominal aortic aneurysms are found, injuries in the abdominal and retroperitoneal cavity, diseases of the spleen.

brain CT

A CT scan of the brain can provide more detailed information about brain tissue and brain structures than standard x-rays of the head. The procedure is performed to evaluate the brain for tumors, trauma, intracranial bleeding, and structural abnormalities such as hydrocephalus, infections, brain dysfunction, and many other pathological conditions. It is used to assess the effect of treatment on tumors and to detect blood clots in the brain. Based on the CT scan results, brain surgery or tissue biopsy may be recommended.

Computed tomography of the chest

It can reveal problems in the lungs, heart, esophagus, aortic artery, or tissues in the center of the chest. It can detect infections, lung cancer, pulmonary embolism, and aneurysms. It is indispensable for diagnosing various pathological conditions of the chest – the causes of unexplained cough, shortness of breath, chest pain, fever and other chest symptoms.

Chest tomography helps to see even very small nodules and cavities in the examined organs located inside the chest. The procedure is especially effective for diagnosing various types of lung cancer at the earliest, most treatable stage.

Computed tomography of the lungs

This is a non-invasive x-ray examination, with which layer-by-layer detailed images of the tissues of the lungs, arteries, bronchi, various cavities and the structure of the mediastinum are obtained. CT is often a preventative measure that helps diagnose lung cancer at an early stage when it is still highly treatable. However, this method is of limited value for people under 45 years of age.

Getting Results

Analysis of scan results usually takes 24 hours. A radiologist who specializes in reading and interpreting CT scans will review the images and prepare a report for the doctor. In emergency situations, such as chest injuries, results can be available within an hour.

After the radiologist and the attending physician review the images in detail, as a rule, an appointment is made after the procedure, at which the attending physician discusses the results with the patient.