Noise SNR and CNR Types of noise Thermal noise SNR - definitions

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Presentation transcript:

Noise SNR and CNR Types of noise Thermal noise SNR - definitions Physiological Artifacts Thermal noise Averaging Bandwidth SNR - definitions Noise

SNR: why do we care? Typical BOLD contrast: 1% change Typical image SNR: 100:1 Typical CNR: 1! Noise

SNR: why do we care? Temporal averaging beats down noise: Noise

SNR: why do we care? Doubling SNR (CNR) = 4X reduction in scan time Noise

Types of noise Thermal Physiological noise Artifacts Random fluctuations in current in receive coil, amplifier … Spatially independent Physiological noise Respiration Cardiac Vasomotor Uncontrolled cognitive factors Artifacts Spikes Fluctuations in Nyquist ghost Segmentation ghosts Motion Noise

Ways to reduce thermal noise Refrigerate sample Noise

Ways to reduce thermal noise Refrigerate sample Average multiple image acquisitions Noise

Ways to reduce thermal noise Refrigerate sample Average multiple image acquisitions Decrease bandwidth (This should be a picture of one noisy image and one ugly image) Noise

Ways to reduce thermal noise Refrigerate sample Average multiple image acquisitions Decrease bandwidth Increase field of view (while maintaining resolution) Noise

Ways to reduce thermal noise Refrigerate sample Average multiple image acquisitions Decrease bandwidth Increase field of view (while maintaining resolution) Increase voxel size (increase S, rather than decrease N) Noise

Ways to quantify SNR mean(S) in sample region / stdev(noise) in background Noise

Ways to quantify SNR mean(S) in sample region / stdev(noise) in background mean(S) in sample region / stdev(S) in sample region Noise

Ways to quantify SNR mean(S) in sample region / stdev(noise) in background mean(S) in sample region / stdev(S) in sample region mean(S) in voxel / std(Svoxel) through time SNR ~ 15? Noise

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