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Why is Magnetic Resonance so Noisy?

In past years, magnetic resonance imaging (MRI diagnostic labs in Delhi) has become 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 machine basically consists of a powerful magnet, mostly superconductors, with a transmitter and a radio wave receiver, in addition to all the electronics necessary 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 signal emitted 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 a 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 RM signal and coding it in order to create the image.

What is so much acoustic noise? To create the magnetic field an electric current has to be applied and when this is applied in the presence of a static magnetic field they produce variable magnetic forces that act on the gradient coil (mechanical vibration) and cause it to expand and contract rapidly in a matter of milliseconds producing movements or vibrations generating noise that is manifested throughout the room, so we can say that the main responsible for the noise generated by the magnetic resonance machine 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 reduction of the thickness of cut, the field of vision (FOV), RT (repetition time) and ET (echo time) but this may affect the resulting image.

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

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

When the patient asks about technical issues like this we cannot use a very technical language since the patient would not understand us, we have to find a way to make ourselves understood in order to satisfy their curiosity. A patient informed about the MRI test cost in Noida that is going to be performed tends to collaborate and feel safer.

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