Psy 8960, Spring ‘07 SNR1 Definition Averaging uncorrelated noise Thermal vs. physiological.

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Presentation transcript:

Psy 8960, Spring ‘07 SNR1 Definition Averaging uncorrelated noise Thermal vs. physiological

Psy 8960, Spring ‘07 SNR2 Averaging to beat down noise If noise is uncorrelated:

Psy 8960, Spring ‘07 SNR3 Signal-to-Noise Ratio (SNR) Thermal noise (  th ) is uncorrelated and normally and uniformly distributed Imaging noise Physiological noise (  phys ) has all sorts of correlations and is different in gray matter, white matter … Brain noise

Psy 8960, Spring ‘07 SNR4 Caveat: estimating zero-mean noise in magnitude images Gaussian distributionRician distribution

Psy 8960, Spring ‘07 SNR5 Small voxel: low SNR

Psy 8960, Spring ‘07 SNR6 Big voxel: dominated by phys. noise SNR lower in gray matter Phys. noise masked by thermal noise