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leoliuf / MRiLab

A Numerical Magnetic Resonance Imaging (MRI) Simulation Platform
https://leoliuf.github.io/MRiLab/
BSD 2-Clause "Simplified" License
204 stars 63 forks source link

SNR and noise level #51

Closed jukeeva closed 1 year ago

jukeeva commented 1 year ago

Hi, I was wondering how is the noise level measured? Is the value in db or is it the(SNR) ratio of the average signal intensity over the standard deviation of the noise? The formula in the manual is hard to follow and it would be nice to have some kind of measurement unit also. Thank you.

DreymaR commented 1 year ago

SNR is the ratio of signal in a given region (S) to noise in that region, which is commonly taken to be the signal deviation σ of the signal (in a non-zero signal region). It's really a bit more complex, but that's the gist of it.

Since it is a ratio of signals, it has no unit.

jukeeva commented 1 year ago

ah thank you! so it is just background noise. Because there is this formula from user guide and it seems like Noise level and SNR are not the same thing, so, I got confused image

DreymaR commented 1 year ago

They are indeed not the same thing. As I said, SNR is the ratio of signal S to Noise N in your voxel or whatever.

The formula contains factors that affect this ratio: Some affect S, some N and some both. B0, for instance, increases S, as does the square root of NEX. Bandwidth increases N by its square root. Etc etc.

jukeeva commented 1 year ago

ok, thank you!