The basics

Research output: Contribution to journalArticle

Abstract

The basic elements of NMR and its subspecialty magnetic resonance spectroscopy (MRS) are presented at a graduate course level, for the purpose of providing a background to common concepts in chapters that follow. Nuclei eligible for NMR have an odd number of either protons or neutrons, which endows them with a quantum mechanical magnetic moment. When placed in a magnetic field (B0), such nuclei align and precess about B0 at discrete quantized orientations and resonant frequencies. Flips between orientations result in radio frequency (RF) emissions and absorptions at the resonant frequency. These transitions can be excited by a circularly polarized RF field (B1) perpendicular to B0, and detected as an RF voltage using a tuned RF coil. The NMR signal decays with characteristic time constants T1 and T2 that can be measured using various sequences of B1 pulses. The T1 and T2 relaxation times are properties of the molecular-level motion at the nuclei, and form the basis of tissue contrast in NMR imaging. Furthermore, intramolecular variations in the local B0 due to the presence of chemical bonds produces characteristic shifts of parts-per-million in the NMR frequencies of subgroups of magnetically equivalent nuclei, or moieties. These chemical shifts allow identification of specific biochemicals in MRS experiments employing the Fourier transform of the decaying NMR time signal. The signals from chemically shifted moieties may be enhanced or suppressed by decoupling, Overhauser enhancement, and solvent suppression techniques. The moiety's concentration and volume, B0, and the NMR receiver's performance are key determinants of the signal-to-noise ratio (SNR), currently limiting detection to about 10-6 of the 1H signal from water. Because the NMR signal ?B0 2 and the noise ?B0 if sample noise is dominant or v B0 if coil noise dominates, the SNR?B0 1 or B0 1.75.

Original languageEnglish (US)
Pages (from-to)505-524
Number of pages20
JournaleMagRes
Volume4
Issue number2
DOIs
StatePublished - 2015

Fingerprint

Radio
Nuclear magnetic resonance
Noise
Signal-To-Noise Ratio
Magnetic resonance spectroscopy
Magnetic Resonance Spectroscopy
Neutrons
Fourier Analysis
Magnetic Fields
Natural frequencies
Signal to noise ratio
Protons
Magnetic Resonance Imaging
Chemical bonds
Chemical shift
Water
Magnetic moments
Relaxation time
Fourier transforms
Tissue

Keywords

  • Bloch equations
  • Chemical shift
  • NMR
  • Relaxation
  • Signal-to-noise ratio
  • Spin-spin coupling
  • Water suppression

ASJC Scopus subject areas

  • Analytical Chemistry
  • Spectroscopy
  • Biomedical Engineering
  • Biochemistry
  • Radiology Nuclear Medicine and imaging

Cite this

The basics. / Bottomley, Paul A.

In: eMagRes, Vol. 4, No. 2, 2015, p. 505-524.

Research output: Contribution to journalArticle

Bottomley, Paul A. / The basics. In: eMagRes. 2015 ; Vol. 4, No. 2. pp. 505-524.
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