Despite being outfitted with substantial hearing protection, 26 young and healthy volunteers with no history of auditory problems or ototoxic drug use suffered a temporary yet troublesome shift in hearing threshold after undergoing brain MRI in a study conducted in China and published online Aug. 16 in Radiology.

Jian Yang, PhD, and colleagues at Xi’an Jiaotong University in Shaanxi Province believe theirs is the first study of the effects of MRI loudness on hearing to carefully exclude subjects with any potential risk factors for heightened susceptibility to noise-induced hearing deficit.

They call for stronger measures to safeguard MRI patients’ hearing.

The researchers used a 3-T scanner to image 11 men and 15 women ranging in age from 18 to 26 years after equipping them with earplugs and motion-refraining sponge mats, which augment the earplugs’ noise-dampening effect.

The test scan lasted 51 minutes and included multiple sequences, including T1-weighted three-dimensional gradient-echo, T2-weighted fast spin-echo and diffusion-tensor imaging.

The researchers used automated auditory brainstem response (ABR) to measure the subjects’ hearing thresholds within 24 hours before the scan (for baseline), within 20 minutes after and, for follow-up, 25 days later.

In the ABR testing performed immediately after the scan, results showed a significantly increased mean threshold shift compared with the baseline study.

Specifically, the volunteers had an increased hearing threshold of 5.0 decibels ± 8.1 immediately after the scan, and, in 52 ears from 26 participants, 32 ears (61.5 percent) and 23 ears (44.2 percent) showed the threshold elevation of 5 decibels or greater and 10 decibels or greater, respectively.

This shift was marked enough to warrant concern even though it was not so severe that it rose above the 40- to 50-decibel shift level that would indicate cochlea nerve damage, the authors point out.

In the testing performed at day 25, there was no significant mean threshold shift, indicating the subjects’ hearing response had returned to normal by that time.

“With hearing protection, a 3-T MR neuroimaging examination with the acoustic noise at equivalent sound pressure level of 103.5 to 111.3 dBA (A-weighted decibels) lasting 51 minutes can cause temporary hearing threshold shift in healthy volunteers,” conclude the authors, who acknowledge their small sample as a limitation.

Their finding suggests that “appropriate hearing protection is crucial at clinical MR imaging,” they add, “and it identifies the need for more effective hearing-protective devices and imaging techniques with lowered acoustic noise and better monitoring of the real-time noise during the MR examination.”