BOLD Noise Assumptions in fMRI

Wink, Alle Meije; Roerdink, Jos B. T. M.

doi:https://doi.org/10.1155/IJBI/2006/12014

International Journal of Biomedical Imaging

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Recent Advances in Mathematical Methods for the Analysis of Biomedical Images

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Volume 2006 | Article ID 012014 | https://doi.org/10.1155/IJBI/2006/12014

BOLD Noise Assumptions in fMRI

Alle Meije Wink¹and Jos B. T. M. Roerdink^2,3

Received30 Jan 2006

Revised13 Jun 2006

Accepted17 Jun 2006

Published30 Jul 2006

Abstract

This paper discusses the assumption of Gaussian noise in the blood-oxygenation-dependent (BOLD) contrast for functional MRI (fMRI). In principle, magnitudes in MRI images follow a Rice distribution. We start by reviewing differences between Rician and Gaussian noise. An analytic expression is derived for the null (resting-state) distribution of the difference between two Rician distributed images. This distribution is shown to be symmetric, and an exact expression for its standard deviation is derived. This distribution can be well approximated by a Gaussian, with very high precision for high SNR, and high precision for lower SNR. Tests on simulated and real MR images show that subtracting the time-series mean in fMRI yields asymmetrically distributed temporal noise. Subtracting a resting-state time series from the first results in symmetric and nearly Gaussian noise. This has important consequences for fMRI analyses using standard statistical tests.

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Copyright

Copyright © 2006 Alle Meije Wink and Jos B. T. M. Roerdink. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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