Studying brain function by measuring the level of electromagnetic signals within brain cells helps researchers and scientists study and understand brain function. Magnetic Resonance Imaging (MRI) diagnostic technology that measure changes in blood flow and brain activity is known to be highly invasive.
As revealed by MIT News, Engineers at MIT have now found a way to study electric fields and light in the brain with the use of a new device. The device which is an MRI sensor — a little smaller than the size of a micro SD card— uses a new technique to detect either electrical activity or optical signals in the brain.
This small implantable antenna is designed to function just like the antenna built into the MRI machine. The antenna is designed to pick up radio signals that hydrogen atoms emit in their normal state. This antenna is very visible under an MRI scan.
Electromagnetic fields in the region surrounding the chip, emitted by neurons firing, interfere with the antenna’s tuning which doesn’t match the emitted signals thereby making the antenna poorly visible when scanned by the MRI.
MRI is often used to measure changes in blood flow that indirectly represent brain activity, and this new type of MRI sensor can detect tiny electrical currents, as well as light produced by luminescent proteins.
Special molecules developed by chemists and bioengineers produce electrical impulses and optical signals which come from the brain’s internal communications and interactions with them.
Lead author of the study and MIT postdoctoral fellow, Aviad Hai says this new MRI sensor does not require a wired connection to the human brain and can be safely implanted there in a minimally invasive fashion.
According to the researchers, 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, proteins, and other biomolecules.
MRI Sensor Detects Electric Fields
Lead Researcher and MIT professor of biological engineering, brain and cognitive sciences, and nuclear science and engineering, Alan Jasanoff 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).
The research which was published in the October issue of Nature Biomedical Engineering 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.
This new MRI sensor does not require a wired connection to the human brain and can be safely implanted there in a minimally invasive fashion.
Although Jasanoff has previously developed MRI sensors that can detect calcium and neurotransmitters such as serotonin and dopamine, in this research, they wanted to expand their approach to detecting biophysical phenomena such as electricity and light.
At the moment, the most accurate way to monitor electrical activity in the brain is by inserting an electrode (also known as an Electroencephalograph, EEG), which is very invasive, can cause tissue damage and 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. For this study, 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. When this happens, 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).
Professor Jasanoff says:
“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 and his colleagues performed additional tests in rats to study whether the MRI sensor could pick up signals in living brain tissue. To carry out the experiments, they designed the sensors to detect light emitted by cells engineered to express the protein luciferase.
Typically, the precise location of luciferase cannot be determined when it is deep within the brain or other tissues. The researchers say that this new sensor offers a way to expand the usefulness of luciferase and more precisely pinpoint the cells that are emitting light.
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 Sized MRI Sensors
Apart from its small size, a major advantage of this new sensor is it does not require power supply. This is because the external MRI scanner emits radio signals which are sufficient to power the device.
Hai, intends to make the sensors size even smaller so they ca be injectable, thereby enabling the imaging of light or electrical fields over a larger brain area.
To carry out this research, the scientists performed modeling that showed that a 250-micron sensor (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.
“What this would do is provide many local readouts by having sensors distributed all over the tissue.”
News Source: MIT News