Synopsis

The signal-to-noise ratio (SNR) in MRI:

• definition of SNR
• analyzing the impact of acquisition parameters on SNR
• analyzing noise and signal statistics
• evaluating the SNR in MRI

Definition and application of the signal-to-noise ratio (SNR)

• SNR as metric of image quality
• Definition of the SNR as ratio of the mean value of the signal and the standard deviation of noise
• Alternative definitions of the SNR
• Applications of SNR in MRI

Influence of MR imaging parameters on the SNR

• Dependence on field strength, $$$B_0$$$; (over-)linear dependence of the SNR on $$$B_0$$$
• Dependence of voxel volume (matrix size, field of view)
• Dependence on “acquisition time” (cumulative read-out time, receiver bandwidth, number of averages)

Statistical and spatial distribution of noise in MRI

• Noise dependence on reconstruction algorithms (Fourier transform, magnitude images, sum-of-squares reconstruction of multi-coil data, parallel imaging reconstruction and g-factor, …)
• Statistical distribution of noise and signal in MRI (Gaussian, Rayleigh, Rician, non-central chi-distribution)
• Spatial distribution of noise in MRI (spatially uniform noise vs.non-uniform noise)

Measurement of the SNR in MRI

• Two-region approach
• Difference-image approach
• Multiple-acquisitions approach
• Noise-image approach
• Reconstruction in SNR units

Acknowledgements

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