ITMO: Researchers Create MRI Antennas That Allow Higher MRI Scans | India Training, Training Information India, Training Information

Magnetic resonance imaging (MRI) has several uses. Everyone knows about the importance of MRI in healthcare, where it is used for high-precision diagnostics. However, this technology also plays a huge role in research – scientists analyze scans from volunteers to better understand the functions of a particular organ or to track the mechanisms behind disease or syndromes development.

The scanners used in healthcare generally have a relatively weak magnetic field. This parameter is measured in Tesla, units named after the famous scientist. In clinical MRI machines, the strength of the magnetic field is 1.5 to 3 Tesla, which is completely sufficient for most diagnostic procedures. However, such a field is not sufficient for scientific purposes. Therefore, researchers use devices with a field of 7 or more Tesla. This improves the signal-to-noise ratio and therefore enables a clearer picture. However, a problem arises here which is related to the principle of how scanners work.

At the center of MRT technology is a special antenna that irradiates the patient with electromagnetic waves of a certain frequency. This causes the patient’s body to react with resonances that are registered by the recipient. Based on this received signal, the scanner creates its images. The frequency of the electromagnetic waves used in MRI is directly related to the power of the magnetic field. The problem is that the higher the frequency, the shorter the electromagnetic waves – this is a law of physics. At the same time, in the language of physics, the human body is an optically dense substance. Simply put, once the patient is in the patient, they get even shorter.

“In the 3 Tesla range, as with good clinical scanners, the wavelength is around 0.4 meters,” explains Georgiy Solomakha, doctoral student at ITMO. “In the 7 Tesla range, the wavelength in air is one meter, and when it penetrates the human body, it is shortened to 10 to 12 centimeters. Under such conditions, the standard equipment for clinical scanners stops working and the field distribution becomes uneven, resulting in both a reduction in image quality and a reduction in the safety of this procedure for volunteers. “

New antennas
Due to the fact that the length of electromagnetic waves in the human body is so much shorter, research scanners use several of them rather than one large antenna that sends and receives the signal. They are placed on the patient’s body and work together as a single antenna array. However, there is also a difficulty here: in addition to the electromagnetic field of these antennas, there is not only a magnetic field that stimulates magnetic resonance in the patient’s body, but also an electric field. It doesn’t electrocute the person, but it does cause heating that can get very intense.

To prevent volunteers from getting burns in the scanner, less voltage is applied to the device than would be possible. This also affects the image quality. This means that the expensive scanner is not fully utilized.

Researchers at ITMO University, in collaboration with their colleagues from the consortium, proposed a solution to these problems. Instead of the dipole antennas now in use, they proposed a different design.

Illustration from the article. Photo credit: nature.com
Illustration from the article. Photo credit: nature.com
“Now scanners are equipped with classic dipole antennas, which are similar to those of telephones, WLAN routers and TVs,” says Georgiy Solomakha, lead author of the paper. “Such antennas match half the wavelength, which enables resonance, so the antennas emit a strong signal. However, this is not the only possible approach. There are also leaky wave antennas that are used in radio direction finding and radar equipment. Our idea is that we have put many small antennas in series through which a wave propagates. Each element gives off part of the power so that together they form the total radiation. Thanks to non-resonant (leaky wave) radiation, it is possible to reduce heating. As part of our work, we developed and examined the world’s first leaky wave antenna for MRI. “

The design of the antenna is specially adapted for MR scanning. To do this, the researchers created each cell (i.e., a small antenna) that makes up the array in a specific way. At the same time, the prototype was manufactured using standard printed circuit board technology, which reduced the cost and labor intensity of its production. According to the developers of the antenna, it could open a new page in the history of MRI research applications. Finally, it is possible to increase the power consumed by the scanner as the heating is significantly reduced. This in turn further improves the image quality.

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