CT Scan – All You need to know about Computed Tomography


Andrada Costache

Radiology Specialist

A computerized tomography (CT or CAT) is a non-invasive method of diagnosing diseases that could otherwise not be diagnosed without surgery or autopsy.

The computerized tomography (CT scan) is also known as a CAT – axial computerized tomography or CAT scan. [1]

What is CT Scan (Computed Tomography) and how it works

The tomograph is a device that uses a combination of X-rays that are processed by computer software and can render parts or the whole human body in 3D images, thus allowing doctors to see in detail internal organs, blood vessels or bone structure. [2]

Etymologically, the word tomography has its roots in the Greek word “tomos” which means “section” or “slice” and “graphos” which means “writing”. This procedure was independently invented by two researchers – Godfrey Hounsfield, EMI Laboratories in England [3] and Allan Cormack – Tufts University, Massachusetts [4]. For this discovery that marked modern medicine, the two received the Nobel Prize in 1979. [5]

What is the difference between a CT scan – computerized tomography – and MRI – magnetic resonance imaging?

The main difference between the two methods of examination is the technology used. In the case of an MRI, a combination of a magnetic field and a radio wave is used to obtain an image of the organs or other structures in the body. In contrast, a CT uses X-rays to do this.  [6]

In some situations, it may also be necessary to use iodine-based contrast agents to better highlight certain areas, organs or structures, such as the main vascular system, tumors or other pathological entities.

The contrast substance can be administered intravenously (in the arm) or introduced to other parts of the body – intrarectal, intra-articular or administered orally. The contrast substance can be administered orally (on the mouth) to allow a better delimitation of the anatomical formations called handles (which are located in the large and small intestine) from the other structures that surround them and also to be able to verify and better visualize the inside of the digestive tract.

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What is the operating principle of  CT Scan?

The X-ray machine emits X-radiation that crosses the body. These rays are absorbed by tissues differently, depending on their density. Thus, each tissue and each area will react differently, and the colored image in shades of gray that they produce will be cast beyond the body, on a special plate, either photographic or electronic, the final result being the x-ray we all know.

In the case of a CT-Scan the device is more complex. The patient is seated on a table and is easily inserted into the device. A device that emits X-rays is constantly rotating around and transmits real time information to the computer, which in turn performs a series of complex mathematical calculations and then displays the final image on the device screen. Thus, images of the sections are obtained in any plane of the desired area – 3D organs can be recreated or the bone can be removed for a better visibility of the other tissues.

Because the examination is very precise, the patient is asked to remain very still throughout the examination, which usually only lasts a few minutes. The procedure is not painful, and usually does not involve other preparations, unless it’s necessary to use contrast substance. In this situation, the patient must come to the clinic an hour or 90 minutes before the examination, in order for the administered substance to have time to reach the target area (for example in the entire intestine and in all its handles).

Depending on the area examined, it is possible to ask the patient not to consume food or drink for 4 hours before surgery.

What areas or parts of the child can be examined with the help of a CT?

This procedure is very comprehensive, allowing a full body scan and can cover all segments – head, chest, abdomen, cervical area, pelvis, arms and legs. Also, organs such as heart, lungs, liver, pancreas, kidneys, stomach, intestines, bladder, adrenal glands, spinal cord, blood vessels and bone system can be checked. [7]

What is the range of CT exams?

CT head – imaging different structures of the brain when there are symptoms indicating tumors, strokes, different abnormalities of blood vessels or intracranial bleeding, as well as enlarged lymph nodes and enlarged glands. This large group of head computerized tomography includes: cerebral angio-CT / neck region, frontal bone CT, skull / cerebral CT, internal ear CT, mastoid CT, sinus CT, temporal bone CT.

Abdominal CT – provides a detailed visualization of the abdominal and pelvic organs, such as liver, pancreas, kidney, spleen, adrenal glands, but also the stomach and intestines. Included here: Angio-CT abdomen, CT abdomen, CT abdomen and pelvis, Colo-CT (virtual colonoscopy).

Spine CT – is used to correctly identify the causes of pain in the back, neck, arms or legs. It enables the correct diagnosis of disc hernias or the narrowing of the spinal canal (spinal stenosis). Also with the help of a computerized tomography, spinal fractures or cracks can be detected. There are several types of CT included in this area: cervical spine CT, dorsal spine CT, lumbar spine CT, spine segment CT.

Limbs CT – allows to obtain a clear and detailed image of the limbs to correctly identify the causes of afflictions in these areas: arms, shoulders, elbows, wrist joint, hand joint, legs, hip, knee, ankles, foot. This category includes: Limb Angio-CT, arm / forearm CT, joint (shoulder, elbow, knee, ankle) CT, 3D Reconstruction.

Chest CT – focused on the chest area and internal organs located here: heart, lungs, respiratory tract, etc. This category includes: chest angio CT , chest CT and High-resolution CT.

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What are the risks of a CT scan?

Such a medical examination involves, like any other medical procedure, certain risks, some of them common, others specific to it. Many of these are related to the general condition of the patient and the medical situation they are in.

The doctor, along with the patient, will analyze each situation prior to the tomography and will compare the benefits and the risks of performing the examination and only afterwards will make the best possible decision.

The patient also has the obligation to inform the doctor about any illness or extra information – for example, if a patient is pregnant.


Among the most frequently asked questions about the risks of a CT scan are radiation related.

Every human being is exposed during life to different sources of irradiation, the sun being for example one of the largest.

Computerized tomography and radiography, because they are based on X-rays, expose the person to an extra dose of radiation. [8] This is not a big dose, but it is not recommended to carry out a large number of such examinations.

The amount of radiation is strictly dosed so that it is optimal to give correct and conclusive images, without the level being higher than necessary.

The risk associated with too high and prolonged exposure to these radiation is the increased likelihood of developing cancer. This is why before each tomography the advantages of its accomplishment and the risks of not doing it are put into balance.

Pregnant women need to be more careful, because the fetus is more sensitive to these radiation than the adult. A CT scan can be performed on a pregnant woman if the situation requires it and the benefits are much greater than this potential risk.

Contrast substance.

The contrast substance is a iodized pharmaceutical substance that, due to its properties, helps in better visibility of the tissues, especially those in the abdomen or blood vessels. It is generally given orally (drank) or intravenously. It is naturally eliminated – usually through the urine – within a few hours of administration. It is not radioactive.

The risks associated with the use of the contrast substance consist of adverse reactions that it can generate. In rare cases, of 1%, these reactions occur in the form of nausea, vomiting, hives, headaches. Usually they pass very quickly after the administration of the substance. In very rare cases – 0.01% – 1 case per 10,000 patients – the reactions may be more severe, manifesting themselves in the form of anaphylactic shock and requiring the intervention of specialized doctors. However, these reactions cannot be predicted. [9]

This is why it is very important that when a doctor recommends using this kind of substance, a patient answers very diligently and accurately to each question in order to prevent unwanted consequences.

References :

[1] https://www.webmd.com/cancer/what-is-a-ct-scan#1

[2] https://www.healthline.com/health/ct-scan

[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5144463/

[4] https://www.britannica.com/biography/Allan-MacLeod-Cormack

[5] https://www.nobelprize.org/prizes/medicine/1979/summary/

[6] https://www.medicinenet.com/ct_scan_vs_mri/article.htm

[7] https://patient.info/treatment-medication/ct-scan#nav-1

[8] https://www.mayoclinic.org/tests-procedures/ct-scan/expert-answers/ct-scans/faq-20057860

[9] https://www.radiologyinfo.org/en/info.cfm?pg=safety-contrast#safety-benefits-risks