A Review of MRI Acoustic Noise Outputs and Hearing Protection Device Performance.

The acoustic noise outputs of MR equipment typically require a hearing protection device (HPD) to minimize the likelihood of patient hearing loss. Several different ways to quantify HPD performance have been developed and adopted over many years in different countries across the world (eg, NRR, SNR, SLC80). These HPD evaluations are done in controlled laboratory conditions, following different standardized methodologies, producing different performance ratings for the same HPD, and consequently of a variable relationship with achieved real-world usage performance assessments. Conversely, the MR manufacturers follow one standard (NEMA MS-4) which strives to produce a worst-case peak and average acoustic noise output measurement. Measuring the acoustic output of MR equipment is a complex undertaking in the confined patient space, especially when considering the variability of what is in the patient imaging space. Given both the MR equipment acoustic output measurements and the HPD performance rating, it is theoretically possible to estimate the worst-case patient exposure level, subject to the uncertainty of how successfully the protection was applied and population variability. An assessment, shown here, suggests that the worst-case outputs from the loudest MR equipment requires the best passive HPD performance presently available in order to meet patient protection guidelines, but only when the HPD is properly deployed. However, when considering government agency derating recommendations that estimate protection achieved during practical application, the various metrics are not consistent in confirming that the best HPD provide sufficient protection. This paper reviews the challenges of determining and providing sufficient hearing protection. The correct deployment of HPD, and its verification, is thus a critical factor in ensuring adequate patient protection and the main concern of this review. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 5.