Computed tomography is one of the modern methods of detecting and diagnosing many diseases. The essence of computed tomography is mapping organs in cross-section, i.e. taking pictures of individual layers of the organ. These layers have a very thin diameter (from 2 to 10 mm), which allows to detect even a few-millimeter changes in the structure of the organ.
The basis of a CT scan is X-rays, the same radiation used in a regular X-ray. The lamps that emit this radiation move along the patient’s body.
The radiation is absorbed differently by different tissues and parts of the body, allowing them to be distinguished from each other. In addition, contrast – usually iodine compounds – is administered to increase the differences between different tissues.
The information about the amount of absorbed radiation is transferred to the computers of the tomograph. Special programs convert this information into an image and this is how the tomogram – the result of the examination – is created.
Preparation for the computed tomography examination
- The patient should be fasting for 6 to 8 hours before the examination.
- You should report to the CT laboratory half an hour before the scheduled examination time.
- The examination lasts 10-30 minutes, depending on the body parts being scanned.
Course of computed tomography examination
The examination is performed in a supine, immobile position. The patient lies in a special tunnel. The tunnel is made up of a table, casing and instrumentation. Due to the fact that the patient must lie still, small children or agitated people are given sedatives.
The doctor performing the examination should ask the patient if he or she suffers from a fear of being confined, as an attack of such anxiety can make the examination difficult.
- primarily for diagnosis of diseases of the brain and spine, especially for diagnosis of discopathy
- suspected brain tumor
- For cranial injuries – allows the detection of hematomas formed during the injury
- when aortic aneurysms are suspected
- for diagnosing non-traumatic brain lesions, such as aneurysms, hydrocephalus or bleeds
- chest CT scan – a very important examination in case of suspicion of lung cancer, it informs about the extent of cancerous changes, assesses whether the lymph nodes are also enlarged; this examination decides about further treatment and allows to establish the extent of the operation
- CT examination of the abdomen and pelvis allows for the detection of pathological changes, primarily tumors of such organs as the liver, pancreas, kidneys, spleen, abdominal lymph nodes (in this case contrast is administered)
- in the diagnosis of ovarian, prostate, uterine and bladder cancer.
- Computed tomography is not suitable for the diagnosis of intestinal diseases, because the accumulation of gases in the intestines prevents the evaluation of changes in this organ.
Positron emission tomography (PET)
In addition to the above-described X-ray computed tomography, there are other variations of CT. The most modern of these is the PET technique – positron emission tomography.
Instead of X-rays, this technique uses the phenomenon of annihilation (loss of mass, disappearance) of positrons. Special radioactive substances are administered to the patient. These substances decay in the body and release positrons, or positively charged electrons. These electrons collide with electrons in the body and lose mass, accompanied by the emission of magnetic radiation. This radiation is recorded in digital form by a computer and processed into an image.
Preparation for the examination – computed tomography
For 6 hours before the examination you should refrain from eating and drinking, except for pure water.
Pregnant and diabetic patients should report this to the referring doctor.
Before the examination a radioactive agent, e.g. fluorine F-18, is administered, and after waiting for 1 hour you should drink 1 liter of still mineral water.
The examination takes about 3 hours.
Applications of PET
- Diagnosis of cancer – it is most often used in the case of: lung cancer, brain tumors, colorectal cancer, lymphoma, melanoma, breast cancer, cervical cancer, bone and muscle tumors, head and neck; in addition, PET is also used to monitor the treatment of these cancers
- Searching for inflammatory foci and metastases
- Diagnosis of brain diseases – most importantly for brain lesions, PET allows detection of Alzheimer’s disease approximately 13 months before the diagnosis based on clinical symptoms, and allows differentiation of Parkinson’s disease from brain infarction
- Diagnosis of heart disease – PET enables detection of necrotic lesions in the heart muscle and detection of coronary artery disease, as well as determination of the degree of cardiac ischemia.
- Early diagnosis of Huntington’s disease is also possible with PET.
Safety – computed tomography
X-rays used in CT scans pose a potential health risk if overexposed. A patient is irradiated with 100 to 1,000 times more dose during a CT scan than during a regular X-ray.
The basic principle of radiation protection is not to expose a person to more radiation than necessary. Therefore, physicians should remember not to order a CT scan unless it is necessary. When CT is used rationally, it does not pose a threat to a patient’s life or health.
Adverse effects may occur only after the administration of contrast.
- anaphylactic shock
- cardiovascular collapse.
The described complications are not dose-dependent and may occur regardless of all precautions taken. Therefore, during the examination, patients are under the professional care of radiologists (and anesthesiologists if necessary), and X-ray rooms are equipped to provide the necessary assistance immediately.