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What imaging technique measures changes in blood oxygen levels

Published: 02.07.2022

what imaging technique measures changes in blood oxygen levels

Blood oxygen level-dependent imaging

Blood oxygen level dependent imaging ,or BOLD contrast imaging ,is a method that is used in the functional magnetic resonance imaging (fMRI) to observe different areas of the brain a> u other organs whi are found active at a given time, what imaging technique measures changes in blood oxygen levels. [1]

Neurons have no internal reserves of energy in the form of sugar and oxygen,so their activation triggers the need to bring in more energy quickly. Through a process called haemodynamic response,the blood releases oxygen to them at a higher rate than to inactive neurons. This causes a ange in the relative levels of oxyhemoglobin and deoxyhemoglobin ( blood oxygenated or deoxygenated ) that can be detected as a function of its magnetic susceptibility differential.

In 1990, three articles published by Seiji Ogawa and colleagues showed that hemoglobin has different magnetic properties in its oxygenated forms and deoxygenated (deoxygenated hemoglobin is paramagnetic and oxygenated hemoglobin is diamagnetic ), whi could be detected by magnetic resonance imaging. [2] This leads to a variation of the magnetic signal that can be detected by a magnetic resonance imaging scanner. Given many repetitions of a thought, action or experience, statistical methods can be used to determine the areas of the brain that reliably have more of this difference as a result and, therefore, whi areas of the brain are more active during that thought, action or experience. experience.

Although most functional magnetic resonance imaging resear uses BOLD contrast imaging as a method to determine whi parts of the brain are most active, due to the signals being relative and not quantitative individually, some question its rigor. Other methods have been attempted that propose to measure neural activity directly (for exame, the measurement of the oxygen extraction fraction, or OEF, in brain regions, whi measures the amount of oxyhemoglobin in the blood that has been converted to deoxyhemoglobin < sup> [3]). ), but due to the fact that the electromagnetic fields created by a neuron active or triggered are so weak, the signal-to-noise ratio is extremely low and the methods statistics used to extract quantitative data have not been successful so far.

The typical discard of low-frequency signals in BOLD contrast images was called into question in 1995, when it was observed that "noise" in the area of ​​the brain that controls right-hand movement fluctuated in unison with an activity similar in the area. on the opposite side of the brain associated with left hand movement. [1] BOLD contrast images are only sensitive to differences between two states cerebral, [4] so a new method was needed to analyze these fluctuations correlated called resting-state fMRI.

Its proof of concept of blood oxygen level-dependent contrast imaging was provided by Seiji Ogawa and colleagues in 1990, after an experiment that proved that an in vivo ange in blood oxygenation could be detected with MRI. [5] In Ogawa's experiments, the oxygen-level dependent images on blood from a rodent brain cut contrast in different air components. At elevated magnetic fields, the water proton magnetic resonance images of brains of live mice and rats under anesthesia have been measured by means of a sequence of gradient eo pulses. The experiments showed that when the oxygen content in the breathable gas anged gradually, the contrast of these images anged gradually. Ogawa proposed and demonstrated that oxyhemoglobin and deoxyhemoglobin is the main contribution of this difference. [6]

Other notable pioneers of BOLD fMRI include Kenneth Kwong and colleagues, who first used the tenique in human participants on 1992. [7]

Published: 02.07.2022 | Исправлено: 02.07.2022

Есик Лежняков, Рудный
02.07.2022 в 11:44
Похудеть за один день - это вообще возможно? Да! И сделать это можно, не моря себя голодом, а вдобавок еще и очистить свой организм от токсинов. Специальная однодневная овсяная диета сделает это возможным.

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