Magnetic Resonance Imaging (MRI) is a diagnostic tool that uses a powerful magnetic field and radio waves to create detailed images of organs and tissues. Tinnitus is the perception of noise or ringing in the ears, such as buzzing, clicking, or roaring sounds that are not externally produced. The environment inside an MRI machine is notably loud, and this acoustic energy raises safety concerns regarding potential noise-induced hearing changes. Understanding the source of this operational noise is essential for appreciating the safety protocols designed to protect hearing.
Why MRI Scanners Are Loud
The intense noise produced by an MRI scanner is a direct consequence of the physics required to generate high-resolution images. The primary source of the sounds is the rapid pulsing and switching of the gradient coils, which are necessary to localize the signal and create the images. These coils are powerful electromagnets operating within the machine’s main static magnetic field. When electrical current is quickly ramped up and down in the gradient coils, strong Lorentz forces cause the coils to vibrate, producing the distinct, loud banging and clicking sounds.
The sound pressure levels inside the scanner bore are substantial, with typical levels frequently exceeding 100 decibels (dB) and sometimes reaching peaks of 120 dB or more in modern, high-field strength machines. This noise level is comparable to a jackhammer or a loud rock concert. The specific pulse sequence used for imaging—the pattern of electrical current switching—determines the characteristic sound and intensity for each part of the scan.
Quantifying Auditory Risk and Protection Protocols
The high noise levels generated by the MRI process pose a risk for acoustic trauma, necessitating strict safety protocols in imaging facilities. Most noise exposure during a properly conducted MRI, where protection is worn, results in a temporary threshold shift (TTS). This TTS is a short-term change in hearing sensitivity that usually recovers. Permanent hearing damage directly resulting from an MRI is statistically rare, but the potential for it without adequate protection is real due to the intense sound levels.
To mitigate this risk, patients are routinely provided with hearing protection, typically involving foam earplugs, specialized MRI-compatible headphones, or both. Well-fitted earplugs reduce sound exposure by approximately 25 to 30 decibels, and combining them with headphones offers greater attenuation. This reduction aims to keep noise exposure below damaging levels, generally aiming for a level under 99 dB, even during the loudest sequences.
Several factors influence the actual risk level, including the specific sequence being run, the strength of the scanner’s main magnet, and the procedure’s duration. Faster, more complex sequences, such as echo planar imaging (EPI), require rapid gradient switching and tend to be the loudest. Studies on volunteers undergoing prolonged, loud MRI protocols have noted a temporary reduction in hearing sensitivity immediately following the scan, which typically resolves within a few weeks. This highlights the importance of correct and verified deployment of hearing protection to ensure effectiveness throughout the scan.
Addressing Tinnitus Symptoms After an MRI
Patients may experience new or temporarily worsened tinnitus immediately after an MRI due to intense noise exposure. This sensation is often a sign of a temporary threshold shift, where the delicate structures of the inner ear are briefly overstimulated. In most cases, this temporary noise-induced tinnitus will fade and resolve completely within a few hours.
If the ringing or hearing change persists for more than 24 to 48 hours following the scan, or if it is accompanied by symptoms like vertigo or noticeably muffled hearing, a follow-up with a medical professional is warranted. This includes consulting an audiologist or an Ear, Nose, and Throat (ENT) doctor. While persistent new-onset tinnitus is an infrequent complication, a medical evaluation can help confirm the nature of the symptoms and rule out other causes. Management for any persistent noise-induced tinnitus often focuses on habituation, including sound therapy using white or pink noise, and counseling to reduce distress.