CT (computed tomography) diagnostics | CLINICAL CENTRE

Unlike traditional imaging, computed tomography produces cross-sectional images taken from angles perpendicular to the long axis of the human body. In CT imaging a narrow beam of x-rays from an x-ray tube scans the affected body part or organs to generate cross-sectional images, then the x-rays shot through the body are picked up and measured using a detector.  The data are processed by a computer. The advantage of this method compared to traditional imaging is that it completely eliminates the superimposition of images of different structures, which makes is possible to examine the different structures individually.  If the structure of a tissue changes due to some pathogenic reaction, this change will often alter its radiopacity or radiolucency, which is detectable by imaging.  In some cases, setting up the diagnosis may require the use of contrast material. This is almost always necessary in thoracic and abdominal CT scanning, and also frequent in CT scanning of the head.  The use of contrast material helps visualize the blood supply of the individual organs or any change occurring in supply, which may be characteristic of certain disorders. During a CT scan, the patient lies on a bed that slowly moves through a circular opening into a large ring-shaped structure (the gantry), which is the scanner itself. What happens inside the ring cannot be seen by the patient, but in fact a unit emitting x-ray beams and x-ray detectors located directly opposite the x-ray source rotate around the table.  This way the machine assesses how much radiation is absorbed in the different parts of the cross-section. On the basis of the results the machine uses sophisticated mathematical and computing techniques to construct and display on the monitor a cross-sectional image of the body slice under investigation. The patient must lie motionless during scanning and must hold his/her breath if abdominal or thoracic scanning is done. Meanwhile he/she is directed from the control room. During the scan the table will incrementally (or continually) move forward into the gantry. Patients need to present for the examination on an empty stomach, that is they must not eat anything 4-6 hours before the scan as the contrast material may cause nausea.  Approximately one hour prior to abdominal scans patients need to drink contrast material (or some liquid, for example water) so that the bowels containing the contrast material can be definitely differentiated from the surrounding structures or abnormalities.  If the patient is pregnant or suspects to be pregnant at the time of the scan, she must inform the staff before scanning as in the first three months of pregnancy the developing fetus is especially susceptible to radiation exposure. Patients should also inform the investigator if they are sensitive to iodine. Orally taken contrast materials may have a laxative effect. CT scanning should only be performed in justified cases. It is often enough to perform a safe ultrasound examination to set up the same diagnosis. Although the received dose of radiation is low, it is only recommended to undergo scanning if it might reveal meaningful information or alter the course of treatment. Allergic reactions to contrast agents based on iodine are generally rare and mild, and include redness, rashes, or itching. However, allergy to contrast agents, just like allergies to medicines or chemicals, may also lead to life-threatening complications like anaphylaxis. The administration of the contrast material causes the discomfort of a needle stick.  After administration patients might experience flushes, nausea or a metallic taste in the mouth, which only last for a short time.