What is a CT scan and what is it for?

The Computed axial tomography (CT scan) is a radiological diagnostic and imaging test, which is used to evaluate the anatomical conditions of various parts of the human body. This can be done under two modalities that provide somewhat different sources of information: with contrast and without contrast. In both cases, serial tomographic images are obtained, that is, series of images obtained layer on successive layer from the scan of an organ or a structure on which the radiation emanating from the tomograph is focused.

What is a CT scan?

Although they have characteristics in common, a CT scan is not the same as an MRI, and its advantage is derived from the speed with which the analysis of a lesion can be carried out by means of a CT, compared to a tomography, which takes longer to resolve and implies spending a long time inside a resonance machine, confined in a space minimum that many patients do not tolerate, especially if they are children.

The first tomographs were designed to scan the brain exclusively and precisely, at different angles and at different depths. Over time, his resolve was extended to scan the rest of the body.

Let’s analyze a little more in depth the principle that governs CT as a diagnostic test and see what its usefulness is in the diagnosis of diseases and health conditions.

What is a Computed Axial Tomography?

The TAC is based on an X-ray scan in the form of serial axial slices of an organ or structure. Unlike the only image obtained from a conventional radiograph, CT produces a group of successive images in parallel planes, originating from the emission of many X-ray beams emitted in different directions and multiple angular planes, which can change at will. of the imaging technician.

The superimposed product of the sum of the images obtained in the different planes is integrated with the help of a computer, thus obtaining a complete and detailed result of the layered image of the evaluated organ.

Because each type of tissue has a different density and hydration level, each one differentially absorbs the radiation emitted by the tomograph, and from these differences the algorithm that is handled in the computer is fed with information, producing the images in black and white gradation that characterize the typical “slices” of CT scans. The latest generation tomographs are also capable of integrating serial section planes and produce three-dimensional images of the scanned object.

Sometimes, the complementary use of contrast media (iodine, barium, methylcellulose, polyethylene glycol, mannitol, air and CO2) is necessary to achieve a better resolution, which improves the precision of the diagnostic capacity of the test.

What is the usefulness of TAC?

As a diagnostic test, a CT It is the most accurate method to detect signs of certain types of diseases with preference over others. Among the diagnoses that are more accurate with the use of a CT scan we have:

  • Detect injuries to the thoracic and abdominal organs (heart, lungs, liver, spleen, kidneys, stomach, gallbladder, intestines and the circulatory system) or congenital malformations in all of them.
  • It is especially useful in cases of traumatic injuries resulting from accidents, because through it it is possible to determine the level of injury to an organ and the presence and extent of inflammation and internal bleeding.
  • Make the diagnosis of the presence and extent of a tumor, and certain special types of cancer, such as lymphomas and neuroblastoma, as well as malignant and benign tumors of the kidney and adrenal glands.
  • It is useful in the non-invasive evaluation of pathologies related to the spinal cord and the nervous system, in general.
  • It serves as a non-invasive guide for the performance of biopsies, and for the planning and final evaluation of certain types of surgical interventions.
  • It is used as a guideline during the drainage of internal abscesses and the diagnosis of certain types of infections; it is especially useful in cases of acute appendicitis.
  • It is used to plan targeted radiation treatments for cancerous tumors and to guide the delivery of targeted radiation at the time of treatment.
  • It is used in the evaluation of the evolution of the response to certain chemotherapy treatments by some internal organs.
  • It is useful in determining bone density as a screening test for osteoporosis, and to verify the presence or absence of osteopenia.
  • It is also very useful in the diagnosis and recognition of inflammatory bowel disease.
  • In general, it is used to verify doubtful diagnoses from the physical examination of a patient, since it is an exact and detailed test, non-invasive, rapid, painless, with wide use in many medical fields and a variety of organs and conditions. The only limitation is that it is a test of lower sensitivity and level of resolution than an MRI.


Undergoing a CT scan involves receiving a certain dose of radiation, so the risks associated with its use include a minimal chance of developing cancer. Likewise, there is a risk of a anaphylactic shock in people allergic to contrast media, when its use is necessary to refine the diagnosis, or there may be risk of kidney damage for its use.


The TAC is prohibited in case of pregnancy or if its existence is suspected, due to the radiation to which the fetus would be exposed. It is also recommended to limit its use in children, especially in the version in which contrast is used for diagnosis; however, it is very useful in verifying the presence of certain types of childhood cancer, such as lymphomas and neuroblastomas.

CT with contrast is also not indicated in people with kidney risks, since it produces a certain level of transient toxicity which could impair kidney function. For his part, contrast medium can be toxic to certain allergy sufferers.

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