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MedTech Outlook | Monday, May 29, 2023
Data collection techniques have been updated, machine learning has been used in image reconstruction, and research is being conducted on the BOLD signal to improve future MRI applications.
FREMONT, CA: In medicine, MRI was already widely used to provide precise anatomical pictures, and MRI scanners could be found in hospitals worldwide. By installing new software on these current devices, fMRI experiments could be carried out. However, the method has its limits. One is that it doesn't detect brain activity in the brain. While neurons fire in milliseconds, changes in blood oxygenation might take many seconds. This questions whether there is a consistent link between neuronal activity and blood oxygenation throughout the brain and how exactly neural activity affects variations in blood oxygen levels.
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Additionally, blood flow-related disorders, including cardiovascular disease and Alzheimer's disease, are difficult for fMRI to visualize. BOLD-based fMRI monitors blood flow variations and cannot differentiate between neuronal and vascular abnormalities. This complicates the understanding and management of illness.
Certain researchers are looking at alternative approaches to measuring brain activity. Like EEG or MEG, one technique, current neural imaging, detects the electromagnetic fields produced by neuronal electrical activity. Because the fields created are so tiny, MRI has a difficult time detecting them. Researchers have shown that the method is theoretically feasible by demonstrating the use of MRI to detect electromagnetic signals in post-mortem turtle brains. However, scientists have yet to have much luck with human brains. Another method researchers use to identify neural function is monitoring physiological changes. Neurons momentarily enlarge as they get information from other active neurons. Diffusion MRI, a method that tracks the motion of water molecules, can be used to find this. Although the precise process by which changes in neuronal swelling are detected by diffusion MRI is still unknown, one theory is that cell swelling changes how water molecules cluster around neuronal membranes. Meanwhile, scientists have also developed approaches to enhance fMRI without giving up neurovascular coupling.
One significant development relates to the hardware. Stronger magnets enable researchers to gather better data because they lower the signal-to-noise ratio and enable pictures to be produced at higher spatial and temporal resolutions. Some of the earliest human fMRI investigations took place in 1.5-tesla magnetic fields, which are 30,000 times stronger than Earth's magnetic field. Up to 10.5 Tesla magnets have been employed in human neuroimaging investigations, and ever-more-powerful ones are being developed. In February, a group of Dutch research institutes said they would build the strongest human MRI scanner with a magnetic field intensity of 14 teslas. Additionally, many methods of observing blood flow via the brain have been used by researchers.
BOLD is more sensitive to blood flow via major veins, which drain deoxygenated blood away from the areas with large blood vessels, such as capillaries, since it depends on changes in blood oxygen levels. This presents a problem when scientists wish to examine the brain more closely. Researchers developed methods like vascular space occupancy, which evaluate changes in blood volume rather than blood oxygenation, to get around this issue. With such technologies, neuroscientists have achieved more spatial resolution than they could with traditional BOLD fMRI, allowing them to examine neuronal activity variations across different cerebral cortex layers.
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