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Why Is MRI Scan So Noisy?

Magnetic resonance imaging (MRI) has become in recent years one of the most requested tests within a diagnostic imaging service thanks to its great potential to differentiate the different tissues that make up the human body, but why is it so noisy. It is the question that many patients ask themselves at the end of the test.

The Magnetic Resonance imaging machine is basically composed of a powerful magnet, mostly superconductors, with a transmitter and a radio wave receiver, in addition to all the electronics needed to coordinate its operation. The magnet creates a powerful magnetic field even more powerful than that of the earth, the transmitter, in turn, emits radio waves that are directed towards the patient, these waves excite the protons of the different tissues and the receiver picks up the emitted signal with which will create the image.

There are four magnets, one main, the largest and most powerful, and the other three smaller ones are the gradients, which are inside a large metal coil called the gradient coil. This coil is composed of copper electromagnets that create a secondary magnetic field in each of the three directions of space and fulfill a fundamental function since they are responsible for spatially locating the Magnetic Resonance signal and encoding it to create the image that is performed by MRI scan centre in East Delhi.

Why so much acoustic noise? To generate the magnetic field an electric current has to be applied and when it is applied in the presence of a static magnetic field they produce variable magnetic forces that act on the gradient coil (mechanical vibration) and causes it to expand and contract rapidly in a matter of milliseconds producing movements or vibrations generating the noise that is manifested throughout the room, so we can say that the main reason the noise generated by the RM machine present in the MRI test labs in Delhi are the gradient coils.

There are other factors that contribute to generate noise such as the modification of acquisition parameters, acoustic noise tends to improve with the decrease of the thickness of cut, the field of vision (FOV), TR (repetition time) and TE ( echo time) but this may affect the resulting image.

On the other hand, the characteristics of the acoustic noise have a spatial dependence depending on the position and the size of the patient the levels can vary in about 10dB.

Studies conducted including a variety of pulse sequences where several gradients are applied resulted in this type of sequence (3D and GR) being among the strongest with levels ranging from 103 - 113 dB. Other studies also measured the acoustic noise generated by the echo-planar (EPI) and the FSE (fast spin-echo) sequences in 1.5T, noise levels ranging from 114 to 115 dB and at 3T levels in the range of 126 to 131 dB for these noise levels the use of hearing protection is recommended.

General Electric GE developed a technology called Silent Scan a few years ago that allows to reduce acoustic noise to a level similar to that of ambient sound, if we take into account that an RM scanner without this technology generates a noise of approximately 100 dB, depending on several factors, this decrease of almost 30 dB causes greater patient satisfaction and generates a more pleasant silent and comfortable experience.

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