A Preliminary Results of Acoustic Noise Effect due to Gradient Pulsing in Functional MRI

ABSTRACT

PURPOSE: In functional MRI(fMRI), the acoustic noise effects of gradient pulsing are analyzed with two different combinations of readout and phase-encoding gradients for sagittal-view images. MATERIALS AND METHODS: Series of sagittal-view EPI images for fMRI obtained from five healthy volunteers. In order to show the effect of gradient pulsing noise, this study was duplicated for the Y readout / Z phase-encoding gradients and the Z readout / Y phase-encoding gradients. The first 7 images were obtained with visual stimulation. This sequential paradigm without and with visual stimulation was repeated 4 times, and was followed by the last 7 images being obtained without visual stimulation. In order to compare the visual cortex activation according to the combination of readout and phase-encoding gradients, the number of activated pixels and the average intensities of the activated pixels were analyzed, where the total activation is defined by multiplying the number of activated pixels by the average intensities of the activated pixels. RESULTS: The experimental results show that the combination of Z readout and Y phase-encoding gradients produce larger visual cortex activation than the combination of Y readout and Z phase-encoding gradients when a sagittal-view fMRI is performed. CONCLUSION: This experiment result represents that visual cortex response can be affected by acoustic noise. Therefore, the combination of the Z readout and Y phase encoding gradients is efficient for sagittal view fMRI because it has less acoustic noise.