Imaging that depends on blood oxygen levels , or BOLD contrast imaging , is a method used in functional magnetic resonance imaging (fMRI) to observe different areas of the brain or other organs, which are found active at any given time.
Video Blood-oxygen-level dependent imaging
Theory
Neurons do not have internal energy reserves in the form of sugar and oxygen, so burning causes more energy to be brought in quickly. Through a process called hemodynamic response, blood releases oxygen to them to a greater extent than the inactive neurons. This leads to changes in the relative levels of oxyhemoglobin and deoxyhemoglobin (oxygenated or deoxygenated blood) that can be detected based on their differential magnetic susceptibility.
In 1990, three papers published by Seiji Ogawa and colleagues showed that hemoglobin has different magnetic properties in the form of oxygen and deoxygenated (deoxygenated hemoglobin is paramagnetic and oxygenated diamagnetic hemoglobin), both of which can be detected using MRI. This causes variations in magnetic signals that can be detected using the MRI scanner. Given the many repetitions of thought, action or experience, statistical methods can be used to determine which areas of the brain have more of these differences as a result, and therefore which areas of the brain are most active during thought, action or experience.
Maps Blood-oxygen-level dependent imaging
Criticisms and restrictions
Although most fMRI studies use BOLD contrast imaging as a method to determine which part of the brain is most active, since the signal is relative, and not individually quantitative, some questions are assertiveness. Other methods that propose to measure direct neural activity have been tried (eg, measurement of Oxygen Extraction Fraction, or OEF, in brain regions, which measure how much oxyhemoglobin in the blood has been converted to deoxyhemoglobin), but because of the electromagnetic fields created by active neurons the firing is very weak, the signal-to-noise ratio is very low and the statistical methods used to extract quantitative data are largely unsuccessful so far.
The typical disposal of low frequency signals in BOLD contrast imaging was questioned in 1995, when it was observed that the "noise" in the area of ​​the brain that controls the movement of the right hand fluctuates along with similar activity in the area. on the opposite side of the brain associated with the movement of the left hand. BOLD contrast imaging is only sensitive to differences between the two brain states, so a new method is needed to analyze these correlated fluctuations called fMRI resting states.
History
The evidence of the oxygen-level contrast-dependent blood-dependent imaging concept was provided by Seiji Ogawa and Colleagues in 1990, after experiments showing that in vivo blood oxygenation changes could be detected with MRI. Ogawa's experiment, blood-oxygen-dependent imaging of rat brain fragments contrasted in various air components. In high magnetic fields, magnetic resonance images of live mouse water proton rats and mice under anesthesia have been measured with a sequence of gradient echo pulses. Experiments show that when the oxygen content in the respiratory gas changes gradually, the contrast of these images changes gradually. Ogawa proposes and proves that oxyhemoglobin and deoxyhemoglobin are the major contributions of this difference.
Other notable pioneers of BOLD fMRI include Kenneth Kwong and colleagues, who first used this technique on human participants in 1992.
Note
Source of the article : Wikipedia
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