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Basic MRI

Basic MRI. Chapter 1 Lecture. Introduction. MRI uses radio waves and a magnetic field to make images Other methods make images in other ways Radiography – x-ray attenuation CT – x-ray with computer NM – gamma rays from radionuclides US – sound waves. MR Images.

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Basic MRI

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  1. Basic MRI Chapter 1 Lecture

  2. Introduction • MRI uses radio waves and a magnetic field to make images • Other methods make images in other ways • Radiography – x-ray attenuation • CT – x-ray with computer • NM – gamma rays from radionuclides • US – sound waves

  3. MR Images • The image is a display of the radiofrequency (RF) signal intensity • The source of the RF signal from the patient is the “condition of magnetization produced when the patient is placed in the magnetic field.” • Magnetization occurs when magnetic nuclei (like H nuclei or protons) are present • Magnetization is changed during imaging, and the rate of change depends on tissue characteristics

  4. Tissue Characteristics • PD • T1 • T2 • Flow • Diffusion • Spectroscopy/chemical shift

  5. Major Tissue Characteristics • PD– proton density • T1– longitudinal relaxation time; spin-lattice relaxation time • T2– transverse relaxation time; spin-spin relaxation time

  6. Minor Tissue Characteristics • Flow • Diffusion • Spectroscopy/chemical shift

  7. What do you see on an MR image? • RF signal intensity, influenced by • Tissue magnetization, including saturation pulses • Proton (hydrogen nuclei) density • Relaxation effects from T1 and T2

  8. Spatial Characteristics • Slices • Voxels • Pixels

  9. Image Quality • Detail/Resolution • Noise/Signal-to-Noise ratio • Artifacts

  10. In-Plane Resolution This is a photo that has been taken at 165x256 resolution

  11. In-Plane Resolution This is a photo that has been taken with 329x512 resolution

  12. In-Plane Resolution • Original Resolution 720x1150

  13. Signal-to-Noise

  14. Signal-to-Noise

  15. Signal-to-Noise

  16. Signal-to-Noise

  17. Aliasing: Example

  18. Wraparound Artfacts in 3D

  19. Chemical Shift Effect

  20. Chemical Shift

  21. Chemical Shift - Example

  22. Chemical Shift Artifacts

  23. Signal Truncation

  24. Truncation Artifacts

  25. Partial Volume Effect

  26. Motion Artifacts - Periodic

  27. Motion Artifacts - Periodic

  28. Motion Artifacts - Random

  29. Flow Motion Artifacts - CSF

  30. Magic Angle Artifacts

  31. FT of Realistic RF Signal

  32. RF Zipper Artefact

  33. RF Feed through Zipper Artifact

  34. RF Noise

  35. Magnetic Inhomogeneity Artifacts

  36. Diamagnetic Susceptibility Artifact

  37. Paramagnetic Effect of Deoxyhemoglobin

  38. Ferromagnetic Susceptibility Artifacts

  39. Susceptibility Artifacts

  40. Gradient Non-linearity

  41. Geometric Distortion: Gradient Non-Linearity

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