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Noise, Part II: physiology and artifacts

Explore the different types of noise, including thermal, physiological, and artifacts, and their impact on MR imaging. Learn about respiration, motion, segmentation, and navigation in relation to noise.

maryrbowen
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Noise, Part II: physiology and artifacts

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  1. Noise, Part II: physiology and artifacts • Types of noise • Thermal • Physiological • Artifacts • Physiological noise • Respiration • Motion • Segmentation and navigation Noise

  2. 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 Noise

  3. Last week: thermal SNR SNR Noise

  4. This week: physiological noise Noise

  5. Noise

  6. Global B0 shift = spatial offset due to phase roll Phase errors accumulate through time FLASH: RO direction EPI: PE direction Noise

  7. Global B0 shift = spatial offset due to phase roll + = Noise

  8. Global B0 shift = spatial offset due to phase roll + = Noise

  9. Global B0 shift = spatial offset due to phase roll + = Noise

  10. Simulated respiration effects (on edge voxels) thermal noise thermal noise + B0 shift Noise

  11. Motion (during k-space acquisition) Simulated early (t = 15ms) in EPI acquisition Middle (t = 30ms) (Much more relevant in 3D MP-RAGE and segmented EPI) Late (t = 45ms) Noise

  12. Segmented EPI Noise

  13. Segmented EPI 1st shot 2nd shot Noise

  14. Segmented EPI – imperfect timing Phase shift added to 1st shot 2nd shot Noise

  15. Segmented EPI – respiration or motion Phase roll added to 1st shot 2nd shot Noise

  16. Segmented EPI pulse sequence with navigators NPE/NSEG TE RF GSS GPE GRO DAC Noise

  17. Segmented EPI and Navigation 1st shot Phase information from navigators is compared to correct between-segment errors 2nd shot Noise

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