Session Item

Earplugs used for hearing protection in diagnostic MRI can be too large  for paediatric patients who are exposed to noise when undergoing MRI for radiotherapy (RT). Thermoplastic shells do not allow for the use of alternative devices

The acoustic noise levels with 3 types of hearing protection were measured, to minimise clinically significant noise levels, maximise patient compliance and optimise RT paediatric MRI workflow.

Acoustic noise measurements were performed in a 1.5T Philips Ingenia Ambition using an OptiSLM 100 sound meter with Optimic 1150 microphone, Figure 1. 3 different hearing protection types were tested: silicone earplugs (SEP; Boots Soft Silicone®), otological putty (OP; Oto-soft®) and foam earplugs (SFEP; Acro Essentials®). Sound Pressure Levels (SPL) were recorded during scanning and a Single Number Rating (SNR) was calculated as a difference between the mean Sound Pressure Level (A-weighted) without and with protection. Acoustic noise at ear was calculated using HSE noise calculator, manufacturer-quoted SNR values where available and highest SPL value (C-weighted) recorded at the scanner centre without the funnel. The results were compared to the Medicines and Healthcare products Regulatory Agency (MHRA) guidelines that hearing protection must reduce noise at the eardrum to below 85dB.

The investigation showed the efficacy of various hearing protection tested. Table 1 shows the SPL measured along with the calculated SNR and manufacturer-quoted SNR. SFEP showed the most attenuation. SEP and OP had a similar performance

The recorded  levels of the scanner exceed 80dB, therefore hearing protection must be worn  to reduce the SPL at the ear drum to 85dB(A). SEP is preferred over OP, although the acoustic noise results is 2dB above the recommended level, 87dB, it does not require specialist training to fit unlike the putty. The risk of damaging the hearing of patients fitted with SEP is minimal given short scan times.

In RT there has been little research into appropriate hearing protection for paediatrics. SEP, are recommended for use. These measured a minimally greater noise level than OP. However, OP requires specialist training to fit, which is inappropriate for RT workflow. This work is not only very important in the context of having of having a dedicated MRI in  RT but also future proofing patient welfare as we move towards MR only planning.

Future work to be undertaken to ensure exam times do not exceed 45mins and that staff are trained appropriately to fit the recommended earplugs.