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Blood-oxygen-level dependent

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Title: Blood-oxygen-level dependent  
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Subject: Magnetic resonance imaging, Amplitude of low frequency fluctuations, Signal enhancement by extravascular water protons, Susceptibility weighted imaging, Spinal fMRI
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Blood-oxygen-level dependent

Blood oxygenation level dependent (BOLD) relaxation: The transversal relaxation rate, R_2, of blood increases linear with the square of the concentration of deoxygenated hemoglobin

Blood-oxygen-level dependent contrast imaging, or BOLD-contrast imaging, is a method used in

  1. ^ a b E. Raichle, Marcus. "The Brain's Dark Energy". Scientific American. Retrieved 9 August 2013. The fMRI signal is usually referred to as the blood oxygen level–dependent, or BOLD, signal because the imaging method relies on changes in the level of oxygen in the human brain induced by alterations in blood flow. 
  2. ^ Raichle, ME (3 February 1998). "Behind the scenes of functional brain imaging: a historical and physiological perspective.". Proceedings of the National Academy of Sciences of the United States of America 95 (3): 765–72.  
  3. ^ Roche, [edited by] Richard A.P.; Commins, Seán (2009). Pioneering studies in cognitive neuroscience. Maidenhead, Berkshire: McGraw Hill Open University Press. p. 11.  
  4. ^ Chou, I-han. "Milestone 19: (1990) Functional MRI". Nature. Retrieved 9 August 2013. 
  5. ^ Theory of NMR signal behavior in magnetically inho...[Magn Reson Med. 1994] - PubMed Result
  6. ^ Langleben, Daniel D. (1 February 2008). "Detection of deception with fMRI: Are we there yet?". Legal and Criminological Psychology 13 (1): 1–9.  

Notes

The typical discarding the low-frequency signals in BOLD-contrast imaging came into question in 1995, when it was observed that the “noise” in the area of the brain that controls right-hand movement fluctuated in unison with similar activity in the area on the opposite side of the brain associated with left-hand movement.[1] BOLD-contrast imaging is only sensitive to differences between two brain states,[6] so a new method was needed to analyse these correlated fluctuations called Resting state fMRI.

Although most fMRI research uses BOLD contrast imaging as a method to determine which parts of the brain are most active, because the signals are relative, and not individually quantitative, some question its rigor. Other methods which propose to measure neural activity directly have been attempted (for example, measurement of the Oxygen Extraction Fraction, or OEF, in regions of the brain, which measures how much of the oxyhemoglobin in the blood has been converted to deoxyhemoglobin[5]), but because the electromagnetic fields created by an active or firing neuron are so weak, the signal-to-noise ratio is extremely low and statistical methods used to extract quantitative data have been largely unsuccessful so far.

Criticism and limitations

In 1990, three papers published by Seiji Ogawa and colleagues showed that hemoglobin has different magnetic properties in its oxygenated and deoxygenated forms, both of which could be detected using MRI.[4] This leads to magnetic signal variation which can be detected using an MRI scanner. Given many repetitions of a thought, action or experience, statistical methods can be used to determine the areas of the brain which reliably have more of this difference as a result, and therefore which areas of the brain are active during that thought, action or experience.

Neurons do not have internal reserves of energy in the form of sugar and oxygen, so their firing causes a need for more energy to be brought in quickly. Through a process called the hemodynamic response, blood releases oxygen to them at a greater rate than to inactive neurons. This causes a change of the relative levels of oxyhemoglobin and deoxyhemoglobin (oxygenated or deoxygenated blood) that can be detected on the basis of their differential magnetic susceptibility.

Theory

[3] and colleagues, who first used the technique in human participants in 1992.Kenneth Kwong Other notable pioneers of BOLD fMRI include [2] change of blood oxygenation could be detected with MRI.in vivo and colleagues in 1990, following an experiment which demonstrated that an Seiji Ogawa was provided by proof of concept Its [1]

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