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Monitoring electromagnetic signals in the brain with MRI: Technique could be used to detect light or electrical fields in living tissue.

Researchers commonly study brain function by monitoring two types of electromagnetism — electric fields and light. Contudo, most methods for measuring these phenomena in the brain are very invasive. MIT engineers have now devised a new technique to detect either electrical activity or optical signals in the brain using a minimally invasive sensor for magnetic resonance imaging (MRI).

MRI is often used to measure changes in blood flow that indirectly represent brain activity, mas a equipe do MIT desenvolveu um novo tipo de sensor de ressonância magnética que pode detectar pequenas correntes elétricas, bem como luz produzida por proteínas luminescentes. (impulsos eléctricos surgem de comunicações internas do cérebro, e sinais ópticos podem ser produzidos por uma variedade de moléculas desenvolvidas por químicos e bioengineers.)

“MRI oferece uma maneira de sentir as coisas do lado de fora do corpo de uma forma minimamente invasiva,”, Diz Aviad Hai, um pós-doutorado MIT e autor principal do estudo. “It does not require a wired connection into the brain. We can implant the sensor and just leave it there.”

This kind of sensor could give neuroscientists a spatially accurate way to pinpoint electrical activity in the brain. It can also be used to measure light, and could be adapted to measure chemicals such as glucose, dizem os pesquisadores.

Alan Jasanoff, an MIT professor of biological engineering, cérebro e ciências cognitivas, and nuclear science and engineering, and an associate member of MIT’s McGovern Institute for Brain Research, is the senior author of the paper, que aparece na outubro. 22 emissão de Nature Biomedical Engineering. Postdocs Virginia Spanoudaki and Benjamin Bartelle are also authors of the paper.

Detecting electric fields

Jasanoff’s lab has previously developed MRI sensors that can detect calcium and neurotransmitters such as serotonin and dopamine. Nesse artigo, they wanted to expand their approach to detecting biophysical phenomena such as electricity and light. atualmente, the most accurate way to monitor electrical activity in the brain is by inserting an electrode, which is very invasive and can cause tissue damage. Electroencephalography (EEG) is a noninvasive way to measure electrical activity in the brain, but this method cannot pinpoint the origin of the activity.

To create a sensor that could detect electromagnetic fields with spatial precision, the researchers realized they could use an electronic device — specifically, a tiny radio antenna.

MRI works by detecting radio waves emitted by the nuclei of hydrogen atoms in water. These signals are usually detected by a large radio antenna within an MRI scanner. Para este estudo, the MIT team shrank the radio antenna down to just a few millimeters in size so that it could be implanted directly into the brain to receive the radio waves generated by water in the brain tissue.

The sensor is initially tuned to the same frequency as the radio waves emitted by the hydrogen atoms. When the sensor picks up an electromagnetic signal from the tissue, its tuning changes and the sensor no longer matches the frequency of the hydrogen atoms. Quando isso acontece, a weaker image arises when the sensor is scanned by an external MRI machine.

The researchers demonstrated that the sensors can pick up electrical signals similar to those produced by action potentials (the electrical impulses fired by single neurons), or local field potentials (the sum of electrical currents produced by a group of neurons).

“We showed that these devices are sensitive to biological-scale potentials, on the order of millivolts, which are comparable to what biological tissue generates, especially in the brain,” Jasanoff says.

The researchers performed additional tests in rats to study whether the sensors could pick up signals in living brain tissue. For those experiments, they designed the sensors to detect light emitted by cells engineered to express the protein luciferase.

Normalmente, luciferase’s exact location cannot be determined when it is deep within the brain or other tissues, so the new sensor offers a way to expand the usefulness of luciferase and more precisely pinpoint the cells that are emitting light, dizem os pesquisadores. Luciferase is commonly engineered into cells along with another gene of interest, allowing researchers to determine whether the genes have been successfully incorporated by measuring the light produced.

Smaller sensors

Uma grande vantagem deste sensor é que ele não precisa de realizar qualquer tipo de fonte de alimentação, porque os sinais de rádio que os emite scanner de ressonância magnética externas são suficientes para alimentar o sensor.

é, que vai se juntar a faculdade da Universidade de Wisconsin em Madison em janeiro, pretende miniaturizar adicionalmente os sensores de modo a que mais de entre eles podem ser injectados, permitindo que a imagem da luz ou campos eléctricos sobre uma área maior do cérebro. Nesse artigo, os investigadores realizaram modelagem que mostrou que um sensor 250 mícrons (a few tenths of a millimeter) should be able to detect electrical activity on the order of 100 millivolts, similar to the amount of current in a neural action potential.

Jasanoff’s lab is interested in using this type of sensor to detect neural signals in the brain, and they envision that it could also be used to monitor electromagnetic phenomena elsewhere in the body, including muscle contractions or cardiac activity.

“If the sensors were on the order of hundreds of microns, which is what the modeling suggests is in the future for this technology, then you could imagine taking a syringe and distributing a whole bunch of them and just leaving them there,” Jasanoff says. “What this would do is provide many local readouts by having sensors distributed all over the tissue.”

A pesquisa foi financiada pelo National Institutes of Health.


Fonte:

http://news.mit.edu, por Anne Trafton

Sobre Marie

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