Neuroradiology is a medical discipline that includes in-depth knowledge and skills in the radiological diagnosis of diseases, injuries, and malformations in the central nervous system both in the head and the back. Specialist in neuroradiology also requires knowledge, skills and attitudes which are required to run radiology diagnostic.
There are several different techniques to study the functions and structures of the brain. The oldest method is the conventional x-ray imaging, which gives some information about the structure but no information about electroencephalography, developed in 1929 by Berger, measured through small electrodes the nerve impulses of neurons in the brain. The method of the “cognitive evoked potentials” is to measure electrical brain activity differences when the patient is subject to cognitive tests. Because the brain still has electrical activity even when it rests, there is background noise, which scrambles the signal, tests are repeated many times to allow the experimenter to make the average of the measured signals (and this generally on several subjects). The obtained average signal is called “evoked potential”. This method has the advantage of making measurements of reaction time for the brain to specific tests, which gives an idea of the complexity of the treatment and to differentiate between successive activities separated by a few milliseconds. On the other hand, this type of testing” does not detect signals from fairly deep brain areas, since they are too attenuated.
The magneto-encephalography measures magnetic fields due to the electrical activity of neurons, without direct contact with the head of the subject. These magnetic fields are much smaller than the Earth’s magnetic field and thus MEG requires a shielded room, to which the helium liquid cooling with a hundred of ultra-sensitive superconductive sensors are added, which involves a very large investment. This technique allows, in addition to the benefits of the EEG to measure signals of deep and full of effectively areas the results achieved by the fMRI.
Imaging by functional magnetic resonance (fMRI) indirectly measures the increase in blood flow (which follows the activation of neurons, but with a lag of a few seconds), using the property of hemoglobin deprived of oxygen (the Deoxyhemoglobin) to disrupt a magnetic field. The obtained signal called BOLD (Blood Oxygenation Level Dependent) provides access to a section of the brain. A heavy treatment is then to overlay different cuts (it takes approximately 40 cuts for whole brain), to correct any movements of the subject, and then to make a comparison with the brain standard indications. Responses to each stimulus are combined with sections of the brain to get a statistical color 3D card that evolves in time. The resulting image is more accurate than with the EEG and MEG, but the disadvantages are numerous: containment of the topic, noise important device, strong magnetic field, many repetitions of the experiment, heavy computer processing.
Positron Emission Tomography (PET) is injected to the subject a radioactive marker (water or glucose) that will disintegrate into positrons (antiparticuls associated with electrons) and this especially as the area of the brain is irrigated in blood. Energy from the reaction of positrons with electrons is detected and analyzed to identify precisely the activated areas of the brain. This method is almost as good as fMRI while being more visual, but requires the manufacture of radioactive solution on-site and experiments limited to the authorized radioactive dose.
Among modern medical advances, those involving brain imaging are particularly important and spectacular. They allow us to observe the organization of our neurons and their exchanges of information with more details.
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