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Related Concept Videos

NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...
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When proton-coupled carbon-13 spectra are simplified by a broadband proton decoupling technique, structural information about the coupled protons is lost. Distortionless enhancement by polarization transfer (DEPT) is a technique that provides information on the number of hydrogens attached to each carbon in a molecule. While the DEPT experiment utilizes complex pulse sequences, the pulse delay and flip angle are specifically manipulated. The resulting signals have different phases depending on...
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Organic molecules primarily contain carbon and hydrogen atoms. While all the hydrogen isotopes are NMR-active, protium or hydrogen-1 is the most abundant. It has a significant energy separation between its nuclear spin states due to its large gyromagnetic ratio. As per Boltzmann's distribution, an increase in the energy separation implies a greater excess population of nuclei available for excitation, resulting in a strong NMR absorption signal.
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The atomic mass of an element varies due to the relative ratio of its isotopes. A sample's relative proportion of oxygen isotopes influences its average atomic mass. For instance, if we were to measure the atomic mass of oxygen from a sample, the mass would be a weighted average of the isotopic masses of oxygen in that sample. Since a single sample is not likely to perfectly reflect the true atomic mass of oxygen for all the molecules of oxygen on Earth, the mass we obtain from this particular...

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Quantitative Mapping of Specific Ventilation in the Human Lung using Proton Magnetic Resonance Imaging and Oxygen as a Contrast Agent
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Correction of systematic errors in quantitative proton density mapping.

Steffen Volz1, Ulrike Nöth, Ralf Deichmann

  • 1Brain Imaging Center, University of Frankfurt, Frankfurt, Germany. volz@med.uni-frankfurt.de

Magnetic Resonance in Medicine
|December 7, 2011
PubMed
Summary
This summary is machine-generated.

Accurate brain proton density mapping is crucial. This study reveals insufficient magnetic field spoiling causes errors, but bias field correction improves accuracy, aligning with literature values.

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Area of Science:

  • Magnetic Resonance Imaging (MRI)
  • Neuroimaging
  • Quantitative MRI

Background:

  • Quantitative brain tissue proton density mapping is increasingly important for MRI.
  • Accurate measurement of receiver coil sensitivity profiles is a significant challenge.
  • Existing methods often rely on the reciprocity theorem, assuming identical receive and transmit sensitivities.

Purpose of the Study:

  • To determine quantitative proton density maps using an optimized variable flip angle method for T(1) mapping at 3 Tesla (3 T).
  • To investigate systematic errors in proton density measurements caused by insufficient spoiling of transverse magnetization.
  • To compare receiver coil sensitivity mapping methods: reciprocity theorem versus bias field correction.

Main Methods:

  • Utilized an optimized variable flip angle method for T(1) mapping at 3 T.
  • Investigated the impact of insufficient transverse magnetization spoiling on proton density quantification.
  • Compared receiver coil sensitivity mapping using the reciprocity theorem against bias field correction.

Main Results:

  • Insufficient spoiling of transverse magnetization introduced systematic errors of approximately 3-4 proton units (pu) in absolute proton density.
  • Receiver coil sensitivity mapping based on the reciprocity theorem resulted in erroneous proton density values.
  • Bias field correction provided reliable proton density measurements.

Conclusions:

  • A correction algorithm for insufficient spoiling is proposed to improve quantitative proton density accuracy.
  • Bias field correction is superior to the reciprocity theorem for receiver coil sensitivity mapping in this context.
  • The study provides reliable absolute proton density values in various brain regions, consistent with existing literature.