© 2016, German Acoustical Society (DEGA). All rights reserved. The acoustical driving noise of a magnetic resonance imaging (MRI) device is loud. A bone conduction microphone is used to transmit the patient's voice because it works better than other microphones during an MRI examination. However, when the patient becomes unwell, the doctor cannot understand the transmitted voice of the patient because the voice is faint and the MRI acoustical noise is loud. The MRI acoustical noise generates a vibration in the patient body. The vibration propagates to the microphone and deteriorates the communication quality. Our goal is to explore the relation between the shielding area of the bone conduction microphone and the communication quality. We propose a theoretical formula for the characteristic of the vibration propagation and the ratio of the vibration acceleration to the sound pressure based on a distributed constant. The communication quality in the case of the shielding the bone conduction microphone was verified using the theoretical formula. The estimated communication quality was equal to the experimental communication quality with high accuracy. The results show that the communication quality could be improved by a shielding area, such as an earmuff, to a level where the doctor could recognize the patient's faint voice.