Computed Tomography

Computed tomography (CT) is a very useful imaging method for detection of many diseases and pathological conditions. It is usually used when the ultrasound or X-ray do not give us all desired information.


The most basic principle of the examination is a simple X-ray. The CT device can produce many images that are transferred to the computer, viewed and evaluated. While a classic X-ray is just one image, the CT creates a lot of cuts. The examined body part is metaphorically “cut to slices”. More advanced machines are even capable of creating a three-dimensional image of the examined organ or tissue.


CT scans can be performed with or without contrast agent. The CT with contrast is done after the contrast substance is administered orally or intravenously (or both ways). The contrast significantly improves the result of the examination.


The actual examination takes place in a special room with the CT device. The patient lies on a special examining pad. The CT device is ring-shaped and moves around the patient scanning the desired body part. The examination lasts several minutes and it is completely painless.


The CT performed without contrast does not need any special preparation. However, abdominal computed tomography should be done on empty stomach. It is different in computed tomography with contrast agent. Contrast may cause allergic reaction including possible anaphylactic shock. Therefore, any contrast-CT should be done on empty stomach and after preventive administration of anti-allergic drugs. When an acute allergic reaction is imminent, it is possible to immediately administer a high dose of corticosteroids.


It is also necessary to remember that the contrast agent is usually nephrotoxic (dangerous to kidneys) and the patient should drink plenty of fluids after the procedure to avoid dehydration. Dehydration after the computed tomography with used contrast agent can cause kidney damage including the acute renal failure.


The examination is widely used in modern medical practice. Computed tomography of the brain can find subdural and epidural hematoma, subarachnoid hemorrhage, strokes, brain tumors and brain metastases. Computed tomography of the chest may help to diagnose local tumors and many disorders of lungs (pulmonary fibrosis, lung cancer, lung metastases, pneumonia, etc.). Abdominal computed tomography may help to find many abdominal pathologies including local tumors, metastases, inflamed areas, abscesses and many, many more. Computed tomography of the vertebral column and spine is used to find local injuries, spinal disc herniation, infections and tumors with metastases.


The main disadvantage is a significant exposure to radiation. Average abdominal CT is comparable to the dose of about 200 chest X-rays. Therefore, it is advisable to cautiously indicate any CT examination and perform it only when really necessary. Other specific problems with the used contrast agents are mentioned above - it is the risk of allergic reaction and contrast-induced nephropathy (kidney damage). Contrast-mediated CT must be very cautiously indicated in patients with acute renal failure or known chronic renal failure.


Computed tomography is extremely useful for physicians in terms of confirmation or exclusion of many common diseases and pathological conditions. The examination is quick, painless and in developed countries, it is widely available in every major hospital.


Jiri Stefanek, MD  Author of texts: Jiri Stefanek, MD
 Sources: basic text sources