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VERIFIED CONTENTConsultation: lek. Maciej Grymuza, a graduate of the Faculty of Medicine at the Medical University of K. Marcinkowski in Poznań.

Computed tomography (abbreviated to KT, CT or CT from English) is a radiological examination that uses electromagnetic (X-ray) rays, the machine carrying it out is a computer tomograph. The examination enables the mapping of sections - layers of the organ. It is worth finding out what computed tomography is, in what diseases it is ordered and whether it is safe.

Computed tomography - what is the examination?

Computed tomography is a commonly used diagnostic method. Its usefulness is determined by high availability, speed of execution and accuracy. This makes it the basic test for serious injuries where immediate damage assessment is essential. It is also used on a large scale, among others. in oncology or surgery.

Safety is also a big advantage, which is extremely important, there are no absolute contraindications for tomography. The tomograph consists of a table on which the patient is lying and a gantry, i.e. the actual device. The device contains one or more X-ray tubes, so the principle of imaging is the same as in the X-ray image.

The lamps rotate at high speed around the patient and at the same time move along the body to cover the entire examined area, during their movement they take many X-ray images in different planes and at different angles, so many sections and a layered image are created. Different tissues weaken the radiation in different ways, e.g. bones - very strongly, but the air is only minimal.

Based on the measurements of this weakening, the computer creates images of cross-sections of the patient's body, showing with high accuracy the body's tissues and organ structures. Then, an advanced computer program compares these photos with each other, sums them up, and thanks to the fact that it has many sections, it is possible to create an exact image of each layer of the examined person.

Tomography enables the assessment of anatomical structures and their possible abnormalities in the human body, currently the best devices have a resolution of up to 1 mm. The examination is facilitated by a special tomograph console that takes overcontrol over the machine. After entering the information about the examined anatomical area, it processes it in such a way as to obtain the most accurate images possible. Of course, it is necessary to supervise the operation of the machine.

As in any digital technique, in computed tomography it is possible to enlarge and divide the image as well as to perform its secondary reconstruction. The latest software also enables image reconstruction in other planes, and even in three-dimensional images.

Thanks to the most advanced devices, it is possible to examine the inside of cavities and the lumen of organs, as happens in virtual bronchoscopy or virtual colonoscopy. The resulting images are assessed by a radiologist and the result is in the form of a description.

Worth knowing

During one CT examination, the radiation dose to which the patient is exposed is many times greater than in the case of a traditional X-ray image.

For example, during a chest X-ray, the dose is approx. 0.02 mSv, and during KT - from 2 to 8 mSv, so the radiation dose is up to four hundred times higher.

For comparison, during the lifetime we consume a dose of 170 mSv, it comes from cosmic rays and everyday devices.

Computed tomography with contrast

Contrast tomography is based on exactly the same methods already described, with the difference that a contrast agent is administered to the body (commonly called contrast). Contrast is a substance based on iodine compounds (ionic or non-ionic), relatively neutral to the organism. Contrast very strongly, practically completely weakens X-rays, thanks to which the structures filled with contrast are bright and a very precise analysis of a given area is possible.

The contrast agent can be administered intravenously, orally and rectally, depending on what structures we want to evaluate. In the case of the gastrointestinal tract, we administer it orally or rectally, while in the assessment of the vascular system - intravenously. A precise amount of contrast is injected into the vessel with an automatic syringe when the subject is lying in the gantra, then after a predetermined time, the test is performed so that at the time of conducting the test, as much of the contrast as possible is in the vessel we want to visualize.

Contrast is removed unchanged from the gastrointestinal tract, it is not absorbed from the intestines, but the kidneys remove it from the blood, so before such an examination, its function should be checked by measuring the concentration of creatinine in the blood.

A very rare complication of contrast administration is post-contrast nephropathy, it can occur even in people with completely he althykidneys, risk factors include:

  • previously diagnosed renal failure,
  • diabetes,
  • diabetic kidney disease,
  • old age,
  • dehydration
  • and blood protein deficiency.

Computed tomography - indications

Computed tomography is always performed at the request of a doctor who knows whether this examination will be more beneficial in a given disease than ultrasound or magnetic resonance imaging. In emergency mode, the indications are primarily serious injuries: head, chest, abdominal cavity and pelvis. Depending on the extent of the injury and indications, individual examinations of each of these areas can be performed.

We distinguish, among others the following CT scans:

  • computed tomography of the abdominal cavity
  • computed tomography of sinuses
  • computed tomography of the chest
  • computed tomography of the lungs
  • computed tomography of the spine
  • computed tomography of the pelvis
  • computed tomography of bones.

In the most severe injuries, a simultaneous examination of the head, chest, abdomen and pelvis is used, it is the so-called "trauma scan", thanks to which it is possible to quickly assess all the injuries suffered by the patient and implement appropriate treatment.

The indications for the CT also include:

  • suspicion of cranial bleeding
  • before performing the lumbar puncture
  • suspected brain tumor
  • Congenital defects of the central nervous system and assessment of the anatomy of the structures of the central nervous system
  • osteoarthritis of the spine
  • diseases of the bones of the skull, sinuses, nasal cavities, pharynx and larynx
  • lung diseases: e.g. lung cancer, lung abscess, sarcoidosis, pulmonary infarction
  • pulmonary vascular disease, e.g. pulmonary embolism; when this disease is suspected, the so-called "angio-KT" is performed - tomography of the pulmonary arteries with contrast
  • diseases of the heart, pericardium and large vessels: cardiomyopathy, heart defects, heart tumors, aortic aneurysms
  • tumors in the abdominal cavity: liver cancer, pancreatic cancer, gallbladder cancer, kidney cancer, and spleen cancer. Thanks to this test, it is possible to assess the advancement of the tumor - is it limited to the primary organ only, whether there are metastases in the lymph nodes or other organs
  • pancreatitis and its complications
  • kidney diseases: inflammation, tumors, hydronephrosis, narrowing of the renal arteries, defects
  • cancers of the reproductive organs and bladder cancer.

This test is also used quite often before surgery in order to plan it -verification of the extent and assessment of anatomical structures. The computed tomography technique also enables its use in the so-called interventional tests, i.e. CT biopsy (puncture and removal of a small part of a specific organ for histopathological examination), puncture or abscess drainage.

Computed tomography - examination price

Computed tomography is not a cheap research.The cost depends mainly on the place of performance - it can be from 200 to 1,000 PLN.When the test is performed privately, the cost of the visit should be added to its price.

Computed tomography - preparation for the examination

Most tests are performed without any special preparation, sometimes on an empty stomach (i.e. 6 hours before you should eat nothing, and 4 hours before drinking), but after taking medications on a regular basis. If the test is carried out with the use of a contrast medium, you should have the result of creatinine measured in your blood and sometimes also the result of the TSH test. In this case, you should also remember about proper hydration before the tomography (at least 2 liters of fluids a day for 2 days before the test).

If the patient suffers from renal insufficiency, the CT scan should be reconsidered and often a different contrast medium should be used, and the patient should be properly prepared. Additionally, in the case of gastrointestinal diagnostics, it is sometimes necessary to drink the contrast agent about 2 hours before the examination or clean the large intestine the day before the tomography, if virtual colonoscopy is performed.

Detailed information on the preparation is provided when scheduling the examination.

Performing a CT scan can be problematic for people with claustrophobia as the gantra inside is quite small. Similarly in the case of young children - before the examination, they are given sedatives, and sometimes even general anesthesia.

Very rarely before the examination, it is necessary to perform other imaging tests (X-ray pictures, ultrasound examinations), but if such examinations were performed for any reason, it is worth providing these results, because they often facilitate the interpretation of the CT performed. However, if a tomography has been performed before, it is necessary to have this result with you.

Before starting the CT scan, be sure to report:

  • pregnancy

And if the test is carried out with the use of contrast, additionally:

  • occurrence of allergies after contrast agents or medications
  • kidney disease
  • thyroid disease
  • bleeding tendency

Computed tomography - the course of the examination

You do not need to undress for the tomography, but it is necessary to remove all metal objects (earrings, buckles, watches), including getting rid of the phone and wallet, as they significantly distort the image. During the tomography, the subject lies motionless on a narrow, sliding table and gradually moves into the tunnel. The person conducting the test instructs on the behavior, e.g. about breathing, in key moments it is recommended to hold the breath.

Following the recommendations shortens the examination, and the images obtained then are of much better quality.

For this purpose, most devices are equipped with an intercom, i.e. a simple method of voice communication between the patient and the person performing the test, or with LEDs that light up when the patient should hold his breath. Continuous contact of the examined person with the examiner is also possible during the examination, it is necessary in case of disturbing symptoms.

You should report anything you are concerned about immediately: sudden symptoms (e.g. claustrophobia), any symptoms after intravenous contrast injection (dyspnoea, nausea, swelling of the face).

Computed tomography - how long does it take?

Tomography usually lasts from several to several dozen minutes, depending on the extent of the examined area. However, it is worth booking more time, because depending on the area and the type of research, the stay in the studio may last from half to more than 3 hours.

After tomography there are no contraindications to driving a car, unless sedatives or general anesthesia were used during it. The result of the outpatient examination is issued after a few days, if it is an examination as part of a hospital stay, much faster. The description should be shown to the referring physician and he or she will interpret it properly.

It should be remembered that after the contrast test, spend several dozen minutes under the supervision of staff to make sure that it has not caused any serious adverse effects.

Computed tomography - examination security

Tomography itself is painless, safe and carries no risks associated with the examination. Concerns about exposure to radiation usually include concerns about carcinogenicity. As mentioned earlier, KT is not the only source of radiation, and the dose delivered by the tomograph is small compared to the radiation we absorb from other sources.

It is therefore considered that the dose adsorbed during the test is not harmful,all the more so because modern apparatuses modify it so that the radiation is as low as possible. In addition, when conducting the test, it is necessary to follow the ALARA principle (as low as reasonably achievable), which says that the lowest dose that gives an appropriate image should be used.

Sometimes we also have the option of performing HRCT (high-resolution tomography) or low-dose KT, which additionally reduce exposure to radiation.

If it is not absolutely necessary, however, the test should not be repeated too often.

Ailments very rarely appear when a contrast test is performed and it may be the cause of complications. A common symptom of warmth after administration of a contrast agent is normal and is not a cause for concern.

The side effects include:

  • swelling,
  • skin redness,
  • rash,
  • vomiting,
  • weakness,
  • shortness of breath,

Each of them should be reported immediately, exceptionally, a drop in blood pressure or even an anaphylactic reaction may occur. Tomography can be performed at any age, but it should not be done in pregnant women as it may cause birth defects in the baby. The test should be avoided in women in the second half of the menstrual cycle, in whom it was possible to become pregnant.

Bow. Maciej GrymuzaA graduate of the Faculty of Medicine at the Medical University of K. Marcinkowski in Poznań. He graduated from university with an over good result. Currently, he is a doctor in the field of cardiology and a doctoral student. He is particularly interested in invasive cardiology and implantable devices (stimulators).

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