Post-processing speech recordings during MRI

TL;DR

This paper presents a post-processing spectral filtering method to reduce noise in speech recordings made during MRI scans, addressing challenges posed by MRI noise and equipment limitations.

Contribution

It introduces an adaptive spectral filtering algorithm for noise reduction in MRI speech recordings and analyzes the impact of MRI environment on speech formants.

Findings

The algorithm effectively reduces noise in MRI speech recordings.

Significant frequency-dependent discrepancies in formant data are observed.

MRI environment influences speech acoustics, causing external formants at specific frequencies.

Abstract

We discuss post-processing of speech that has been recorded during Magnetic Resonance Imaging (MRI) of the vocal tract. Such speech recordings are contaminated by high levels of acoustic noise from the MRI scanner. Also, the frequency response of the sound signal path is not flat as a result of severe restrictions on recording instrumentation due to MRI technology. The post-processing algorithm for noise reduction is based on adaptive spectral filtering. The speech material consists of samples of prolonged vowel productions that are used for validation of the post-processing algorithm. The comparison data is recorded in anechoic chamber from the same test subject. Formant analysis is carried out for the post-processed speech and the comparison data. Artificially noise-contaminated vowel samples are used for validation experiments to determine performance of the algorithm where using true data would be difficult. The properties of recording instrumentation or the post-processing algorithm do not explain the consistent frequency dependent discrepancy between formant data from experiments during MRI and in anechoic chamber. It is shown that the discrepancy is statistically significant, in particular, where it is largest at 1 kHz and 2 kHz. The reflecting surfaces of the MRI head and neck coil are suspected to change the speech acoustics which results in "external formants" at these frequencies. However, the role of test subject adaptation to noise and constrained space acoustics during an MRI examination cannot be ruled out.