1. Basic MRI Chapter 1 Lecture

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

3. MR Images The image is a display of the radiofrequency (RF) signal intensity 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.” 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 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 Magnetization is changed during imaging, and the rate of change depends on tissue characteristics

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

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

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

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

8. Spatial Characteristics Slices Slices Voxels Voxels Pixels Pixels

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

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