1. Psy 8960, Spring ’07 Introduction to MRI1 Introduction to MRI: NMR Physics reminders –Nuclei and atoms –Electromagnetic spectrum and Radio Frequency –Magnets –Vectors NMR phenomena –nuclei, atoms and electron clouds (molecular environment) –excitation and energy states, Zeeman diagram –precession and resonance quantum vs. classical pictures of proton(s)

2. Psy 8960, Spring ’07 Introduction to MRI2 Electromagnetic spectrum http://www.nps.gov

3. Psy 8960, Spring ’07 Introduction to MRI3 Electromagnetic spectrum www.yorku.ca/eye/spectru.htm c = = 3 x 10 8 m/s /

4. Psy 8960, Spring ’07 Introduction to MRI4 RF Antennae vs. RF coils www.yorku.ca/eye/spectru.htm Antennae disperse energyCoils focus energy

5. Psy 8960, Spring ’07 Introduction to MRI5 Nuclei and subatomic particles

6. Psy 8960, Spring ’07 Introduction to MRI6 Stern-Gerlach experiment: discovery of spin http://www.upscale.utoronto.ca/GeneralInterest/Harrison/SternGerlach/SternGerlach.html Discovery of magnetic moment on particles with spins Electron beam has (roughly) even mix of spin-up and spin-down electrons –Beam should be bent to the side because a force is exerted on moving charge in a magnetic field –Beam was also split vertically, because electrons posses inherent magnetic moment

7. Psy 8960, Spring ’07 Introduction to MRI7 Spin and magnetic moment Sub-atomic particles have intrinsic angular momentum (spin), L Aligned with L is , a magnetic moment The quantum number I determines how many spin states a particle might be found in –For a nucleus, the number of protons and neutrons determines I L and  are related by , the gyromagnetic ratio

8. Psy 8960, Spring ’07 Introduction to MRI8 Periodic table: some nuclei are magnetic

9. Psy 8960, Spring ’07 Introduction to MRI9 Water www.lsbu.ac.uk/water/

10. Psy 8960, Spring ’07 Introduction to MRI10 Magnets Dipole in a static field B NSNS NSNS Lowest energy Highest energy Units of magnetic field: 1 Tesla = 10 4 Gauss 0.5 G = earth’s magnetic field ~50 G = refrigerator magnet

11. Psy 8960, Spring ’07 Introduction to MRI11 Magnets Proton in a static magnetic fieldDipole in a static field B NSNS NSNS Lowest energy Highest energy  : magnetic dipole

12. Psy 8960, Spring ’07 Introduction to MRI12 Nucleus in magnetic fieldNucleus in free space B E Single spin-1/2 particle in an external magnetic field All orientations possess the same potential energy Spin-up and spin-down are different energy levels; difference depends linearly on static magnetic field

13. Psy 8960, Spring ’07 Introduction to MRI13 Resonant frequency B E Transition emits energy Excitation promotes transition Resonant frequency is determined by gyromagnetic ratio, a property of the nucleus At 3T, protons resonate at ~128 MHz At 7T, protons resonate at ~300 MHz

14. Psy 8960, Spring ’07 Introduction to MRI14 Electromagnetic spectrum www.yorku.ca/eye/spectru.htm c = = 3 x 10 8 m/s /

15. Psy 8960, Spring ’07 Introduction to MRI15 Hydrogen spectrum: electron transitions http://csep10.phys.utk.edu/astr162/lect/light/absorption.html 1 electron volt = 1.6 × 10 -19 J Fixed energy transitions result in discrete absorption lines

16. Psy 8960, Spring ’07 Introduction to MRI16 B E Precession and resonant frequency Spin-up and spin-down are different energy levels; difference depends linearly on static magnetic field Torque exerted by magnetic force on dipole creates precession.

17. Psy 8960, Spring ’07 Introduction to MRI17 Gyromagnetic (magnetogyric) ratio

18. Psy 8960, Spring ’07 Introduction to MRI18 B M: net (bulk) magnetization M MM M || From spin-1/2 particles to bulk magnetization Equilibrium: ~ 1 ppm excess in spin-up (low energy) state creates a net magnetization Excitation affects phase and distribution between spin-up and spin-down, rotating bulk magnetization isochromat

19. Psy 8960, Spring ’07 Introduction to MRI19 Information in proton NMR signal Resonant frequency depends on Static magnetic field Molecule Relaxation rate depends on physical environment Microscopic field perturbations –Tissue interfaces –Deoxygenated blood Molecular environment –Gray matter –White matter –CSF Relaxation Excitation

20. Psy 8960, Spring ’07 Introduction to MRI20 Proton NMR spectrum: ethanol /grupper/KS-grp/microarray/slides/drablos/Structure_determination