Imaging techniques

Computerized tomography examination involves the examined person lying on a moving table pushed in-and-out a ring-like machine. The circular machine contains the radiation source and the detector located opposite it. CT uses X-rays to image the human body in slices. Following image aquisition data is reconstructed using computer algorithms.

The advantage of CT technology is the more widespread accessibility than magnetic resonance Imaging, also the duration of the examination is much shorter, alas it is widely used in acute neurological diseases, such as diagnosing cerebral infarction or intracranial bleeding. It is also superior in the evaluation of bony structures. The major disadvantage is the high radiation dose, so in certain conditions such as in pregnancy it is contraindicated.

Magnetic resonance imaging involves the examined person lying on a table surrounded by a similar, but louder ring-like machine, somewhat similar to a CT examination. The test is based on nuclear magnetic resonance of hydrogen atoms, so it does not use ionizing radiation. However, due to the application of the strong magnetic field, special attention must be paid to metal devices in and around the human body, such as pacemakers, aneurysm clips, hearing-aids during the examination.

The advantage of MR imaging is its soft tissue resolution, being far superior to CT, making it ideal for examining the brain. For brain MR examinations, structural and functional imaging should be mentioned. Structural MR examination provides information on the presence of possible intracranial space occupying lesion, the volume of brain structures, and cortical thickness. The principle of functional imaging is that during certain activities, blood flow conditions change in the brain areas involved and this chage can be visualized with computer algorhythms. The functional MR examination is suitable for imaging brain areas operating during activity, as well as visualizing networks connecting brain structures.

During positron emission tomography, a positron-emitting radiopharmaceutical is injected into the body intravenously. The pharmaceutical agent accumulates in specific parts of the body. After a certain period of time, similar to CT and MR examinations, the examined person is imaged lying on a table in a ring-like machine containing detectors.The final result is detection of the radioisotope enhancement pattern throughout the body.

Beta-amyloid-specific PET tracers bind to amyloid fibrils indicating its presence. As the disease progresses, an increasingly stronger signal can be detected during the PET examination. Advantage of PET: a negative beta-amyloid PET test makes Alzheimer's disease unlikely as the underlying cause of dementia. However, a positive finding is not equal to the diagnosis of Alzheimer's disease, it can even be a normal phenomenon. Unfortunately, the test is extremely costly.

In this case, the tau-PET technique a positron-emitting tracer indicates the neurofibrillary bundles formed from hyperphosphorylated tau protein. The method is not specific, accumulation of this radiopharmaceutical can also be observed in other taupathies. Alzheimer's disease can be inferred from the pattern of enhancement. Furthermore, a positive finding definitely indicates pathology and suggests the presence of neurocognitive disease.

Transcranial Doppler ultrasound among adults, images are created through four so-called acoustic windows with the help of an ultrasound probe. These are the transtemporal, orbital, suboccipital and retromandibular windows. It is possible to examine cerebral vessels and brain structures.

Advantage of TCD is detection of intracranial space occupying lesion and midline shift. In addition, intracranial vascular circulation can be assessed, as reduced circulation is a risk for the development of stroke and dementia.

Examination of the arteries of the neck is suitable for analyzing the hemodynamic status of the 4 main vessels supplying the brain (right and left carotid and vertebrobasilar systems), which generally shows a strong correlation with nervous system blood supply.