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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...
NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences01:17

NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences

A pulse is a short burst of radio waves distributed over a range of frequencies that simultaneously excites all the nuclei in the sample. Upon passing a radio frequency pulse along the x-axis, the nuclei absorb energy corresponding to their Larmor frequencies and achieve resonance. This shifts the net magnetization vector from the z-axis toward the transverse plane. This angle of rotation of the magnetization vector, or the flip angle, is proportional to the duration and intensity of the pulse.
Magnetic Resonance Imaging01:24

Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is a noninvasive medical imaging technique based on a phenomenon of nuclear physics discovered in the 1930s, in which matter exposed to magnetic fields and radio waves was found to emit radio signals. In 1970, a physician and researcher named Raymond Damadian noticed that malignant (cancerous) tissue gave off different signals than normal body tissue. He applied for a patent for the first MRI scanning device in clinical use by the early 1980s. The early MRI...
Atomic Nuclei: Magnetic Resonance01:05

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The number of nuclear spins aligned in the lower energy state is slightly greater than those in the higher energy state. In the presence of an external magnetic field, as the spins precess at the Larmor frequency, the excess population results in a net magnetization oriented along the z axis. When a pulse or a short burst of radio waves at the Larmor frequency is applied along the x axis, the coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the...
Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
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¹³C NMR: ¹H–¹³C Decoupling01:04

¹³C NMR: ¹H–¹³C Decoupling

The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
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Quantitative Magnetic Resonance Imaging of Skeletal Muscle Disease
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Variable bandwidth filtering for magnetic resonance imaging with pure phase encoding.

Juan C García-Naranjo1, Paul M Glover, Florin Marica

  • 1MRI Centre, Department of Physics, P.O. Box 4400, University of New Brunswick, Fredericton, NB, Canada E3B 5A3.

Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|December 9, 2009
PubMed
Summary
This summary is machine-generated.

Optimizing filter bandwidth in pure phase encoding magnetic resonance imaging (MRI) improves signal-to-noise ratio (SNR). This enhancement allows for reduced scan times without compromising image quality.

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Area of Science:

  • Medical Imaging
  • Magnetic Resonance Imaging (MRI)
  • Signal Processing

Background:

  • Pure phase encoding MRI, while advantageous, is typically time-consuming compared to frequency encoding methods.
  • Current practice sets acquisition filter bandwidth to maximum expected values, leading to suboptimal filtering for low k-space points.
  • This suboptimal filtering in single point imaging (SPI) limits signal-to-noise ratio (SNR) and necessitates longer acquisition times.

Purpose of the Study:

  • To present an optimized method for setting the filter bandwidth in pure phase encoding MRI.
  • To improve the inherent signal-to-noise ratio (SNR) by matching filter bandwidth to sampled k-space points.
  • To reduce the number of signal averages required for acceptable SNR, thereby decreasing scan time.

Main Methods:

  • Implementation of a variable bandwidth filter tailored to individual k-space points.
  • Comparison of the variable bandwidth filter's performance against fixed low-pass filtering.
  • Quantitative assessment of SNR gains and potential reductions in averaging time.

Main Results:

  • Theoretical SNR increase of 41% predicted with the variable bandwidth filter.
  • Practical measurements demonstrated a 20% gain in SNR.
  • This SNR improvement translates to a potential 31% reduction in averaging time for image acquisition.

Conclusions:

  • Optimizing filter bandwidth in pure phase encoding MRI significantly enhances SNR.
  • The variable bandwidth approach offers a practical method to reduce scan times without compromising image quality.
  • This technique provides a valuable strategy for improving the efficiency of MRI acquisitions.