A magnetic resonance imaging (MRI) scanner operates at a noise level of 100 dB or more. When a patient uses a piezoelectric bone conduction microphone to communicate with the doctor, the MRI vibrations deteriorate the quality of the patient's speech. Our aim was to improve the quality of the patient's speech when communicating with a doctor from within the noisy MRI environment. Shielding of the bone conduction microphone improved the signal-to-noise ratio (SNR) to −7 dB; however, it was not sufficient to understand the patient's voice accurately. In this paper, the effective SNR required to understand the patient's voice accurately was clarified. First, we measured the relationship between the force applied on the microphone and the percentage of the patient's answers that were correctly understood. Next, we measured the relationship between the SNR, from three types of MRI noise and the percentage of correct answers that were obtained at the optimum applied force. The results showed that the SNR needs to be over 0 dB to achieve accurate communication with the patient when using the most effective force on the microphone.