A study on improvement level of speech quality with covering bone conduction microphone for MRI examination

To overcome the loudness of a magnetic resonance imaging (MRI) scanner in operation, which can be 100 dB or more, the patient undergoing a scan is typically given an emergency buzzer to use in case of distress. Instead, we propose using a piezoelectric bone-conduction microphone. However, the MRI noise induces vibrations in the patient's body that degrade the speech quality. Our aim is to analyze the speech quality when using a bone-conduction microphone by estimating the effectiveness of shielding the microphone to make the patient's voice clearer against the noise. First, we calculate the level of improvement using a vibration propagation model and the approach of distributed constant on electronic circuit theory, and we design an experiment involving a human phantom made of ceramic and silicone. Next, we measure the vibration acceleration levels of a bone-conducted voice and MRI acoustic noise, and we calculate the level of improvement using the signal-to-noise ratio both with and without shielding the bone-conduction microphone. Here, the signal is the vibration acceleration level of the bone-conducted voice and the noise is the vibration acceleration level of the MRI acoustic noise. The SNR is -13 dB without shielding and -7 dB with 5600 mm² of shielding, which corresponds to an improvement in speech quality of 6 dB. This result shows that whoever is operating the MRI could hear a patient with a relatively quiet voice against 100 dB of MRI noise.