Yes, Hearing loss after an MRI is normal. A magnetic resonance imaging (MRI) provides a way to diagnose a various condition which includes multiple sclerosis, acoustic neuromas, strokes, traumatic brain injury and also many other conditions and it produces sounds like a knocking and tapping. The main source of loud noise in an MRI scanner is a movement of gradient coil because of rapid alterations in electrical current.
This device produces loud noise that damage patients and operators hearing and cause a different type of hearing loss such as temporary, permanent, unilateral, bilateral, as well as with or without symptoms of tinnitus. It also causes anxiety, difficulty in verbal communication, changes in blood pressure, pulse rate.
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Working of MRI
As the human body consists of 70% of water. The MRI scans the body of a patient. Any part of the body can be scanned with the help of the MRI. An MRI scanner scans the body with the help of a magnetic field. The magnetic field applied in a body is about 0.2 to 3 teslas. This magnetic field allows to proton spins.
As protons have a positive charge so they act like small magnets. The magnetic field created by an MRI is 1000 times stronger than the earth`s magnetic field. The radio signals beam radio waves on spinning proton.
For creating an image MRI detects the radio signals coming back from the protons. MRI plots the protons proper locations and creates a 3D image.
Why MRI noises so much?
An MRI is so noisy because of the magnetic field generated by an electromagnet. In this, an electrical current via a coiled wire is forward to an electromagnet. When the current is supplied there is an outward force all along with the coil. The force is very huge because the magnetic field is so strong.
The force on the magnetic field rises from zero to huge in milliseconds. As a result, the coil expands slightly which makes a noise of a click. When MRI plots an image the current is switched on and off rapidly. This results in a rapid clicking noise which is amplified by the enclosed space where the person or patient lies.
MRI creates sounds of 125db. The protection given to the patient is of 15db only. Remaining 110db of noise is heard by the patients. The exposure to 110db of noise should not exceed more than 89 seconds. But MRI takes more time to imitate an image.
Sources of acoustic noises during MRI procedure
- The vibration produced by the gradient magnetic.
- Alternating currents within the gradient coil of the system.
- RF hearing
- Noise From Subsidiary Systems – Patient comfort fans and cryogen reclamation systems associated with superconducting magnets of MR systems.
- Thermoelastic expansion
Reason for hearing loss after an MRI procedure
The frequency of noise created by MRI device, however, is usually below 4 kHz (mostly less than 2 KHz). The WHO states that exposure to noise levels of 100 dB, is safe for no more than 15 minutes. These sounds may be as loud as 125 decibels.
An MRI creating sounds at 125db where you have the hearing protection that only provides 15db of protection means you effectively have a healthcare provider exposing you to 110db of noise, which you should not have exposure to for more than 89 seconds.
The high-intensity noise produced by modern 3-Tesla (3T) MRI scanners that can reach peak sound pressure levels of 125.7 to 130.7 dB and have an average equivalent intensity of 110 to 115 dB.
The intensity of noise produced by MRI scanners generally has a positive correlation with the magnetic field strength (i.e., 3T scanners are louder than 1.5T scanners). The human ear is a highly sensitive wide-band receiver, with the typical frequency range for normal hearing being between 20-Hz to 20,000-Hz.
Method of hearing protection during MRI:
Patients during magnetic resonance imaging (MRI) can protect their hearing by using various methods. A staff, as well as patients of the laboratory or hospital, must need to use earplug and other hearing protection which include these.
- Ear-plugs
- Headphones
- Ear-muffs
- washcloths, towel or put sponges to the ear.
Recovery from the effects of noise occurs in a relatively short period of time. However, if the noise insult is particularly severe, full recovery can take up to several weeks. If the noise is sufficiently injurious, a permanent threshold shift at specific frequencies may occur.
What does the research tell?
Scientists in China discovers that the people who do not suffer from hearing loss when exposed to MRI, then they have the symptoms of hearing loss even after wearing the hearing protection. The studied 26 people by putting them in 3T MRI with noise levels between 103.5 and just over 111 decibels. The study participants are kept protected by the earplugs and earmuffs. After the study completed they recorded that the people suffer from the temporary hearing loss after MRI