The principle of CT examinations

Computed tomography (CT scan) technique

The patient is asked to lie on a special moveable bed, which is then shifted to the center of the CT scanner. Once inside the CT scanner around the patient begins to rotate the movable x-ray tube. In modern helical (multislice) CT scanners, the imaging procedure is performed in a single pass.

Small detectors inside the CT scanner measure the amount of x-ray radiation passed through the patient's body. The computer analyzes the received from the sensor information and converts it into images, called slices or layers. These images (slices) of the organs after the CT scan may be saved to disk for viewing by the attending physician of the patient on the monitor or printed on film. Three-dimensional models of organs and tissues can be reconstructed by computed tomography after the merger of several sequentially obtained by the imaging sections.

During the chest CT scan procedure patient should lie still, because movement can smear the obtained tomography image. This will cause difficulty for the radiologist during interpretation (description) obtained for the CT images. The patient may also be asked to briefly hold breath during the procedure.

In general, computed tomography (CT scan) procedure takes only a few minutes. The latest multislice CT scanner installed in our radiology department, can get an image of the whole body of the patient (starting from head and ending with feet) in less than 30 seconds.

Specific purpose computed tomography (CT scan) require the use of special dye, called contrast media. Contrast media is administered to the patient intravenously just before the procedure of scanning a particular organ. The contrast enhances specific areas of the body that gives further clear image during the computed tomography. If required to examine the patient's organs with contrast media, the drug he will be introduced intravenously through the veins of the elbow or on the wrist.

 

Patient preparation for computed tomography (CT scan)

Some patients are allergic to the contrast injected intravenously during a CT scan. Therefore, they needed the reception desensitizing drugs before performing the scan in order to further contrast was injected safely.

Contrast media can be introduced to the patient in different ways, because it depends on the type of the assigned computer tomography:

• intravenous contrast media administration through the veins of the elbow or wrist
• the introduction of contrast media via the rectum by enema
• oral intake (patient drinks a liquid contrasts media in advance before the CT scan procedure); contrast fluid has a chalk taste, therefore it is added flavoring components, which facilitates their reception; further contrast is completely eliminated from the body with stool

If it is planned to introduce contrast, the attending physician may ask the patient to refrain from taking food and fluids 4-6 hours before scheduled procedure.

Computed tomography of the previous generationthere were limitations on the weight (up to 130 kg). Too much weight patients could cause damage to certain parts of the device. At this stage, our radiology department has a new device for multislice computed tomography (MSCT), where physical limitations for assessment of patients with higher weight no longer exists.

Since x-ray radiation does not penetrate through metal, the patient before computed tomography (CT scan) are kindly asked to remove jewelry (chains, pendants, earrings, etc.).

 

Tolerability of computed tomography (CT scan)

Some of the studied patients may experience discomfort in the process of lying on a hard surface table of a computer tomograph.

Contrast media, injected intravenously before performing CT scan, may cause a feeling of heating in the vein, the sensation of heat in the body and a metallic taste in the mouth. These sensations are normal and usually disappear within a few seconds.

 

The risks of computed tomography (CT scan)

Computed tomography (CT) scans and other X-ray examination of such patients is strictly controlled in order to know exactly the amount of radiation received. Performed on modern imaging сomputed tomography gives the minimum dose of ionizing radiation, which has the potential to cause cancer and other complications. Risks associated with computed tomography small. This risk is increased only in the future, repeatedly iterative CT study.

In some cases, computed tomography scan of any organs and departments can be performed repeatedly to the patient. This may be necessary if the benefits of the resulting information at a given diagnosis is higher than the risk of complications, which is especially important at suspicion the presence of cancer in a patient.

Computed tomography of the upper abdomen is usually not recommended for pregnant women because it can harm the fetus. Therefore, a woman with suspected presence of her pregnancy should inform their physician to assign it a different kind of diagnosis (ultrasound, MRI).

Most types of contrast administered intravenously at computed tomography (CT scan), contain iodine. If the patient has an allergy to iodine (idiosyncrasy), the use of contrast during imaging may cause him nausea, vomiting, sneezing, itching and a rash (urticaria). Less contrast is administered at computed tomography (CT scan), can cause life-threatening anaphylactic reaction. If the patient has difficulty in breathing occur during computed tomography with contrast, he must immediately notify the radiologist or assistant conducting the study. All CT scanners equipped with intercom and audio speakers, so the doctor or his assistant always hear the patient.

In patients with renal insufficiency the contrast media can cause nephrotoxic effects. In this situation, the doctor will need to perform a preliminary preventive steps to protect the patient during his computed tomography scan with intravenous contrast media.