Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2013 Nov 6;8(11):e77089.
doi: 10.1371/journal.pone.0077089. eCollection 2013.

On the definition of signal-to-noise ratio and contrast-to-noise ratio for FMRI data

Marijke Welvaert  1 , Yves Rosseel
Affiliations

On the definition of signal-to-noise ratio and contrast-to-noise ratio for FMRI data

Marijke Welvaert et al. PLoS One. .

Abstract

Signal-to-noise ratio, the ratio between signal and noise, is a quantity that has been well established for MRI data but is still subject of ongoing debate and confusion when it comes to fMRI data. fMRI data are characterised by small activation fluctuations in a background of noise. Depending on how the signal of interest and the noise are identified, signal-to-noise ratio for fMRI data is reported by using many different definitions. Since each definition comes with a different scale, interpreting and comparing signal-to-noise ratio values for fMRI data can be a very challenging job. In this paper, we provide an overview of existing definitions. Further, the relationship with activation detection power is investigated. Reference tables and conversion formulae are provided to facilitate comparability between fMRI studies.

PubMed Disclaimer

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Overview of reported SNR values in real data (left panel) and simulated data (right panel)., –.
Figure 2
Figure 2. Illustration of the notation in the SNR and CNR definitions: is the activation signal, the noise signal, defines the amplitude of the activation signal, and and indicate the standard deviation of the activation signal and noise signal respectively.
Figure 3
Figure 3. Percentage of the 119 simulation studies from the literature search that reported a specific SNR/CNR definition.
Figure 4
Figure 4. The relationship between power and the SNR/CNR definitions for 1% signal change.
Figure 5
Figure 5. tSNR results of the example data, illustrating how the definitions can be applied to real task-based and resting-state fMRI data.
Upper panel: tSNR results for a block design. Lower panel: tSNR results for the resting-state data.
See this image and copyright information in PMC

References

    1. Parrish T, Gitelman D, LaBar K, Mesulam M (2000) Impact of signal-to-noise on functional MRI. Magnetic Resonance in Medicine 44: 925–932. - PubMed
    1. Edelstein W, Glover G, Hardy C, Redington R (1986) The intrinsic signal-to-noise ratio in NMR imaging. Magnetic Resonance in Medicine 3: 604–618. - PubMed
    1. Gudbjartsson H, Patz S (1995) The rician distribution of noisy MRI data. Magnetic Resonance in Medicine 34: 910–914. - PMC - PubMed
    1. Redpath T (1998) Signal-to-noise ratio in MRI. British Journal of Radiology 71: 704–707. - PubMed
    1. Duyn J (2012) The future of ultra-high field MRI and fMRI for study of the human brain. NeuroImage 62: 1241–1248. - PMC - PubMed