Psy 8960, Fall ‘06 Noise1 SNR and CNR Types of noise –Thermal –Physiological –Artifacts...
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Transcript of Psy 8960, Fall ‘06 Noise1 SNR and CNR Types of noise –Thermal –Physiological –Artifacts...
![Page 1: Psy 8960, Fall ‘06 Noise1 SNR and CNR Types of noise –Thermal –Physiological –Artifacts Thermal noise –Averaging –Bandwidth SNR - definitions.](https://reader030.fdocuments.us/reader030/viewer/2022032522/56649d625503460f94a44c15/html5/thumbnails/1.jpg)
Noise 1Psy 8960, Fall ‘06
Noise
• SNR and CNR• Types of noise
– Thermal– Physiological– Artifacts
• Thermal noise– Averaging– Bandwidth
• SNR - definitions
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Noise 2Psy 8960, Fall ‘06
SNR: why do we care?
• Typical BOLD contrast: 1% change• Typical image SNR: 100:1• Typical CNR: 1!
![Page 3: Psy 8960, Fall ‘06 Noise1 SNR and CNR Types of noise –Thermal –Physiological –Artifacts Thermal noise –Averaging –Bandwidth SNR - definitions.](https://reader030.fdocuments.us/reader030/viewer/2022032522/56649d625503460f94a44c15/html5/thumbnails/3.jpg)
Noise 3Psy 8960, Fall ‘06
SNR: why do we care?
• Temporal averaging beats down noise:
![Page 4: Psy 8960, Fall ‘06 Noise1 SNR and CNR Types of noise –Thermal –Physiological –Artifacts Thermal noise –Averaging –Bandwidth SNR - definitions.](https://reader030.fdocuments.us/reader030/viewer/2022032522/56649d625503460f94a44c15/html5/thumbnails/4.jpg)
Noise 4Psy 8960, Fall ‘06
SNR: why do we care?
• Doubling SNR (CNR) = 4X reduction in scan time
![Page 5: Psy 8960, Fall ‘06 Noise1 SNR and CNR Types of noise –Thermal –Physiological –Artifacts Thermal noise –Averaging –Bandwidth SNR - definitions.](https://reader030.fdocuments.us/reader030/viewer/2022032522/56649d625503460f94a44c15/html5/thumbnails/5.jpg)
Noise 5Psy 8960, Fall ‘06
Types of noise
• Thermal– 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
![Page 6: Psy 8960, Fall ‘06 Noise1 SNR and CNR Types of noise –Thermal –Physiological –Artifacts Thermal noise –Averaging –Bandwidth SNR - definitions.](https://reader030.fdocuments.us/reader030/viewer/2022032522/56649d625503460f94a44c15/html5/thumbnails/6.jpg)
Noise 6Psy 8960, Fall ‘06
Ways to reduce thermal noise
• Refrigerate sample
![Page 7: Psy 8960, Fall ‘06 Noise1 SNR and CNR Types of noise –Thermal –Physiological –Artifacts Thermal noise –Averaging –Bandwidth SNR - definitions.](https://reader030.fdocuments.us/reader030/viewer/2022032522/56649d625503460f94a44c15/html5/thumbnails/7.jpg)
Noise 7Psy 8960, Fall ‘06
Ways to reduce thermal noise
• Refrigerate sample• Average multiple image acquisitions
![Page 8: Psy 8960, Fall ‘06 Noise1 SNR and CNR Types of noise –Thermal –Physiological –Artifacts Thermal noise –Averaging –Bandwidth SNR - definitions.](https://reader030.fdocuments.us/reader030/viewer/2022032522/56649d625503460f94a44c15/html5/thumbnails/8.jpg)
Noise 8Psy 8960, Fall ‘06
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)
![Page 9: Psy 8960, Fall ‘06 Noise1 SNR and CNR Types of noise –Thermal –Physiological –Artifacts Thermal noise –Averaging –Bandwidth SNR - definitions.](https://reader030.fdocuments.us/reader030/viewer/2022032522/56649d625503460f94a44c15/html5/thumbnails/9.jpg)
Noise 9Psy 8960, Fall ‘06
Ways to reduce thermal noise
• Refrigerate sample• Average multiple image acquisitions• Decrease bandwidth• Increase field of view (while maintaining resolution)
![Page 10: Psy 8960, Fall ‘06 Noise1 SNR and CNR Types of noise –Thermal –Physiological –Artifacts Thermal noise –Averaging –Bandwidth SNR - definitions.](https://reader030.fdocuments.us/reader030/viewer/2022032522/56649d625503460f94a44c15/html5/thumbnails/10.jpg)
Noise 10Psy 8960, Fall ‘06
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)
![Page 11: Psy 8960, Fall ‘06 Noise1 SNR and CNR Types of noise –Thermal –Physiological –Artifacts Thermal noise –Averaging –Bandwidth SNR - definitions.](https://reader030.fdocuments.us/reader030/viewer/2022032522/56649d625503460f94a44c15/html5/thumbnails/11.jpg)
Noise 11Psy 8960, Fall ‘06
Ways to quantify SNR
• mean(S) in sample region / stdev(noise) in background
![Page 12: Psy 8960, Fall ‘06 Noise1 SNR and CNR Types of noise –Thermal –Physiological –Artifacts Thermal noise –Averaging –Bandwidth SNR - definitions.](https://reader030.fdocuments.us/reader030/viewer/2022032522/56649d625503460f94a44c15/html5/thumbnails/12.jpg)
Noise 12Psy 8960, Fall ‘06
Ways to quantify SNR
• mean(S) in sample region / stdev(noise) in background• mean(S) in sample region / stdev(S) in sample region
![Page 13: Psy 8960, Fall ‘06 Noise1 SNR and CNR Types of noise –Thermal –Physiological –Artifacts Thermal noise –Averaging –Bandwidth SNR - definitions.](https://reader030.fdocuments.us/reader030/viewer/2022032522/56649d625503460f94a44c15/html5/thumbnails/13.jpg)
Noise 13Psy 8960, Fall ‘06
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?