Physics · MU Sofia

18. Nuclear magnetic resonance (NMR)

Explains nuclear magnetic resonance as the absorption and re-emission of electromagnetic radiation by nuclei placed in a magnetic field, and why it matters for MRI and molecular analysis. Covers the nuclear properties of charge, mass and spin, the alignment of magnetic moments, the precession relation with the gyromagnetic ratio, and the role of radiofrequency pulses. Closes with the Zeeman effect, including the energy-difference formula and the meaning of its terms.

Inside: 1 section · 4 labelled pictures · 8 flashcards · 3 min

Topic 19 of 42 in the MU Sofia syllabus for Physics (Medicine, Year 1). The free AceMed note covers it in 1 section, about 428 words (3 min of reading), with 8 flashcards.

In this note

  1. Introduction

Introduction

Summary

  • Nuclear Magnetic Resonance (NMR) is a physical phenomenon where nuclei in a magnetic field absorb and re-emit electromagnetic radiation. This method is critical in medical imaging, particularly in MRI, to study the composition and properties of organic molecules and molecular physics in various states, including crystals. The effectiveness of NMR depends on the magnetic properties of the nucleus, such as charge, mass, and spin, which affects how nuclei align in a magnetic field and respond to radiofrequency pulses.
  • Nuclear Magnetic Resonance (NMR): the absorption of electromagnetic radiation by a nucleus having a magnetic moment when in an external magnetic field, used mainly as an analytical technique and in diagnostic body imaging.
  • Nucleus Composition:
  • Charge: Causes motion and creates a magnetic field.
  • Mass: Composed of protons and neutrons, which have similar mass.
  • Spin: A fundamental property of all elements which determines electron positions and can induce a permanent magnetic moment along the spin direction.
  • Magnetic Moments:
  • Nucleons and the nucleus itself can have magnetic moments that align either parallel or antiparallel to an applied magnetic field.
  • The nucleus spins at an angular velocity expressed as ω = γ*B(0), where γ represents the gyromagnetic ratio and B(0) the magnetic field strength.
  • Conditions for Nuclear Magnetic Resonance:
  • The human body primarily consists of fat and water, materials suitable for NMR analysis.
  • Proper positioning of the patient and maintaining the correct distance are crucial to capture a clear image.
  • Application of a Radiofrequency (RF) pulse is necessary to provoke the resonance needed for imaging.
  • Applications and Importance:
  • Medical Imaging: NMR is extensively used in MRI to form images of the internal structures of the body.
  • A procedure that uses radio waves, a powerful magnet, and a computer to make a series of detailed pictures of areas inside the body.
  • Molecular Study: It aids in the study of the structure of organic molecules and molecular physics in crystals.
  • Zeeman Effect:
  • Describes the splitting of a spectral line into several components when in the presence of a static magnetic field, which is a key aspect of NMR's functionality in different applications.
  • splitting of levels due to an external magnetic field
  • This diagram will explain the energy difference between two zeeman states formula :
  • The energy difference formula is given by ΔE = g(μB) Bm
  • g is the Landé g-factor, which is 1 for the normal Zeeman effect,
  • μB is the Bohr magneton,

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