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Comprehensive Introduction to MRI: Understanding Neural Coding with Electromagnetic Spectrum and NMR Physics

Delve into the vast world of Magnetic Resonance Imaging (MRI) to grasp the fundamental concepts of neural coding, NMR phenomena, and the electromagnetic spectrum. Explore the history, physics, and neural environment interactions, unraveling the complexities of proton behavior and resonance quantum. Discover the significance of the Gyromagnetic ratio, bulk magnetization, and proton NMR spectrum in decoding molecular environments for precise imaging. Uncover the secrets of excitation, relaxation, and resonance frequency variations that shape MRI signals, offering a unique view into the neural structures. Immerse yourself in the realm of MRI to master the art of decoding neural activities and creating high-quality images.

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Comprehensive Introduction to MRI: Understanding Neural Coding with Electromagnetic Spectrum and NMR Physics

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  1. Introduction to MRI: NMR • MRI - big picture • Neuroimaging alternatives • Goal: understanding neurall coding • Electromagnetic spectrum and Radio Frequency • X-ray, gamma ray, RF • NMR phenomena • History (NMR, imaging, BOLD) • Physics • nuclei, molecular environment • excitation and energy states, Zeeman diagram • precession and resonance quantum vs. classical pictures of proton(s) Introduction to MRI

  2. Related readings • Huettel, Chapter 1 • History, resonance phenomena described (pp. 11 - 22) • Definitions of contrast and resolution (pp. 6 - 11) • Example (of what I don’t like … pp. 12, 13) • Buxton, pgs. 64 - 72, 124 - 131 • Haacke, Ch. 1, 2 & 25 Introduction to MRI

  3. Neuroimaging Introduction to MRI

  4. Nuclei Introduction to MRI

  5. Periodic table Introduction to MRI

  6. Hydrogen spectrum: electron transitions 1 electron volt = 1.6 × 10-19 J http://csep10.phys.utk.edu/astr162/lect/light/absorption.html Introduction to MRI

  7. Magnets Dipole in a static field Dipole-dipole interactions Lowest energy Highest energy Lowest energy Highest energy B N S N S N S N S N S N S Introduction to MRI

  8. The Zeeman effect • The dependence of electronic transition energies on the presence of a magnetic field reveals electron spin (orbital angular momentum) http://csep10.phys.utk.edu/astr162/lect/light/zeeman-split.html Introduction to MRI

  9. Stern-Gerlach experiment • Discovery of magnetic moment on particles with spins • Electron beam has (roughly) even mix of spin-up and spin-down electrons http://www.upscale.utoronto.ca/GeneralInterest/Harrison/SternGerlach/SternGerlach.html Introduction to MRI

  10. NMR - MRI - fMRI timeline 1922 Stern-Gerlach Electron spin 1952 Nobel prize Felix Bloch, Edward Purcell NMR in solids 1993 Seiji Ogawa, et al. BOLD effect 1902 Pieter Zeeman Radiation in a magnetic field 1937 Isidor Rabi Nuclear magnetic resonance 1973 Paul Lauterbur, Peter Mansfield NMR imaging 1936 Linus Pauling Deoxyhemoglobin electronic structure Introduction to MRI

  11. Single spin-1/2 particle in an external magnetic field E B Nucleus in free space Nucleus in magnetic field Spin-up and spin-down are different energy levels; difference depends linearly on static magnetic field All orientations possess the same potential energy Introduction to MRI

  12. E B Resonant frequency, two ways Spins in static magnetic field precess, with  = B or  = B where ,  = precession frequency (radians, Hz) ,  = gyromagnetic ratio (in rad/T or Hz/T) B = static (external) magnetic field (Tesla) Transition from high to low energy state emits radiation with characteristic frequency: Proton gyromagnetic ratio:  = 42.58 MHz/T  = 2 =267,000,000 rad/T Introduction to MRI

  13. Gyromagnetic ratio Introduction to MRI

  14. Many spin-1/2 particles in an external magnetic field B M: net (bulk) magnetization Excitation affects phase and distribution between spin-up and spin-down, rotating bulk magnetization M|| M Equilibrium: ~ 1 ppm excess in spin-up state creates a net magnetization M Introduction to MRI

  15. 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 Excitation Relaxation Introduction to MRI

  16. Proton NMR spectrum: ethanol /grupper/KS-grp/microarray/slides/drablos/Structure_determination Introduction to MRI

  17. Water www.lsbu.ac.uk/water/ Introduction to MRI

  18. Magnetic Resonance Imaging • An MR image is (usually) a map of water protons, with intensity determined by local physical environment • Contrast and image quality are determined by • Pulse sequence • Field strength • Shim quality • Acquisition time Introduction to MRI

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