Silent echo-planar imaging for auditory FMRI.
BACKGROUND
The effect of the acoustic scanner noise produced by gradient coil switching on the auditory evoked BOLD signal represents a well-known problem in auditory functional MRI (FMRI). In this paper, a new low-noise echo-planar imaging (EPI) sequence is presented that is optimized for auditory FMRI measurements.


METHODS
The sequence produces a narrow-band acoustic frequency spectrum by using a sinusoidal readout echo train and a constant phase encoding gradient. This narrow band is adapted to the frequency response function of the MR scanner by varying the switching frequency of the sinusoidal readout gradient.


RESULTS
Compared to a manufacturer-provided standard EPI sequence, the acoustic noise reduction amounts to up to 20 dBA. Using a simple block design paradigm contrasting presentation of a pure tone during ON blocks and "silence" (absence of the tone) during OFF blocks, the new low-noise sequence was evaluated and compared to the standard EPI sequence. Statistical parametric mapping (SPM) resulted in higher levels of significance of auditory activation for the low-noise sequence.


CONCLUSIONS
These findings strongly suggest that the low-noise sequence may generate enhanced BOLD contrasts compared to the standard EPI sequences commonly used in FMRI.
Schmitter
S
S
Division of Medical Physics in Radiology, German Cancer Research Center, Im Neuenheimer Feld 280, 69120, Heidelberg, Germany. s.schmitter@dkfz.de
Diesch
E
E
Amann
M
M
Kroll
A
A
Moayer
M
M
Schad
L R
LR
D000161:Acoustic Stimulation; D000328:Adult; D001303:Auditory Cortex / Q000033:anatomy & histology* / Q000502:physiology*; D017352:Echo-Planar Imaging / Q000379:methods* / Q000706:statistics & numerical data; D004867:Equipment Design; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D009622:Noise