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Related Concept Videos

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.
Spin decoupling is usually achieved by...
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...
Parallel Resonance01:23

Parallel Resonance

The parallel RLC circuit is an arrangement where the resistor (R), inductor (L), and capacitor (C) are all connected to the same nodes and, as a result, share the same voltage across them. The parallel RLC circuit is analyzed in terms of admittance (Y), which reflects the ease with which current can flow. The admittance is given by:
Impulse Response01:17

Impulse Response

The impulse response is the system's reaction to an input impulse. In an RC circuit, the voltage source is the input, and the capacitor's voltage is the output. The system's state and output response before and after input excitation are distinctly defined.
Kirchhoff's law forms an input signal equation, with the capacitor's current and voltage providing the output. Substituting the current and dividing by RC yields a differential equation. The output for an impulse input is the impulse...
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
Aliasing01:18

Aliasing

Accurate signal sampling and reconstruction are crucial in various signal-processing applications. A time-domain signal's spectrum can be revealed using its Fourier transform. When this signal is sampled at a specific frequency, it results in multiple scaled replicas of the original spectrum in the frequency domain. The spacing of these replicas is determined by the sampling frequency.
If the sampling frequency is below the Nyquist rate, these replicas overlap, preventing the original signal...

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Related Experiment Video

Updated: May 28, 2026

Three-Dimensional Phase Resolved Functional Lung Magnetic Resonance Imaging
10:44

Three-Dimensional Phase Resolved Functional Lung Magnetic Resonance Imaging

Published on: June 21, 2024

Off-resonance artifacts correction with convolution in k-space (ORACLE).

Wei Lin1, Feng Huang, Enrico Simonotto

  • 1Invivo Corporation, Philips Healthcare, Gainesville, Florida 32608, USA. wei.lin2@philips.com

Magnetic Resonance in Medicine
|October 14, 2011
PubMed
Summary
This summary is machine-generated.

A new k-space convolution method rapidly corrects off-resonance artifacts in MRI. This technique improves echo-planar, radial, and spiral imaging, enhancing image quality and applicability.

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Area of Science:

  • Magnetic Resonance Imaging (MRI)
  • Medical Physics
  • Image Processing

Background:

  • Off-resonance artifacts degrade image quality in echo-planar imaging (EPI) and non-Cartesian MRI (radial, spiral).
  • These artifacts limit the clinical utility and broader application of advanced MRI techniques.
  • Accurate artifact correction is crucial for reliable MRI diagnostics.

Purpose of the Study:

  • To develop a general, rapid, and effective method for correcting off-resonance artifacts in MRI.
  • To improve the applicability of EPI, radial, and spiral MRI sequences.
  • To provide a reusable solution for artifact correction across different MRI contrasts.

Main Methods:

  • A k-space convolution-based method was developed for off-resonance artifact correction.
  • Acquired k-space data is segmented by acquisition time.
  • Off-resonance artifacts are corrected using a convolution kernel derived from a spatial phase modulation term.
  • Field maps are determined via inverse Fourier transform of a calibrated basis kernel.

Main Results:

  • The proposed method successfully corrected off-resonance artifacts in phantom and in vivo studies for radial, spiral, and EPI datasets.
  • For radial acquisitions with alternating view-angle ordering, self-calibration of the field map was achieved.
  • Convolution kernels demonstrated reusability for images acquired with the same sequence but different contrasts.

Conclusions:

  • The k-space convolution method offers a general and rapid solution for off-resonance artifact correction in various MRI sequences.
  • The technique enhances image quality and expands the applicability of advanced MRI methods.
  • The reusability of convolution kernels presents an added efficiency for multi-contrast MRI acquisitions.