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. 2005 Mar;53(3):739-44.
doi: 10.1002/mrm.20398.

Extraction of overt verbal response from the acoustic noise in a functional magnetic resonance imaging scan by use of segmented active noise cancellation

Kwan-Jin Jung  1 , Parikshit Prasad, Yulin Qin, John R Anderson
Affiliations

Extraction of overt verbal response from the acoustic noise in a functional magnetic resonance imaging scan by use of segmented active noise cancellation

Kwan-Jin Jung et al. Magn Reson Med. 2005 Mar.

Abstract

A method to extract the subject's overt verbal response from the obscuring acoustic noise in an fMRI scan is developed by applying active noise cancellation with a conventional MRI microphone. Since the EPI scanning and its accompanying acoustic noise in fMRI are repetitive, the acoustic noise in one time segment was used as a reference noise in suppressing the acoustic noise in subsequent segments. However, the acoustic noise from the scanner was affected by the subject's movements, so the reference noise was adaptively adjusted as the scanner's acoustic properties varied in time. This method was successfully applied to a cognitive fMRI experiment with overt verbal responses.

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Figures

FIG. 1
FIG. 1
A block diagram of the fMRI paradigm.
FIG. 2
FIG. 2
An experiment using a phantom subject. (a) Acoustic noise from the scanner. (b) Processed waveform using the synchronization pulse for the segmentation. (c) and (d) Processed waveforms using template matching with a constant and a dynamic reference noise, respectively. The segment corresponding to the reference noise is nulled and the scanner's acoustic noise before the reference noise is left un-processed.
FIG. 3
FIG. 3
An experiment using a human subject without voluntary movements. (a) Waveform before processing. (b) and (c) Waveforms after processing with a constant and a dynamic reference noise, respectively.
FIG. 4
FIG. 4
An experiment using a human subject with voluntary movements. (a) Waveform before processing. (b) and (c) Waveforms after processing with a constant and a dynamic reference noise, respectively.
FIG. 5
FIG. 5
Spectral power of the acoustic noise from the scanner before and after processing with the dynamic reference noise for one segment in Fig. 3.
FIG. 6
FIG. 6
Histogram of the RMS ratios of remnant noise processed with dynamic reference noise to that processed with constant reference noise for a total of 164 runs from 14 subjects.
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