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Related Concept Videos

NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

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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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NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences01:17

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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.
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Upsampling

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Managing signal sampling rates is essential in digital signal processing to maintain signal integrity. A decimated signal, characterized by a reduced frequency range due to its lower sampling rate, can be upsampled by inserting zeros between each sample. This upsampling process expands the original spectrum and introduces repeated spectral replicas at intervals dictated by the new Nyquist frequency. To refine this zero-inserted sequence, it is passed through a lowpass filter with a cutoff...
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Double Resonance Techniques: Overview01:12

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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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Downsampling

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When considering a sampled sequence with zero values between sampling instants, one can replace it by taking every N-th value of the sequence. At these integer multiples of N, the original and sampled sequences coincide. This process, known as decimation, involves extracting every N-th sample from a sequence, thereby creating a more efficient sequence.
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Mitigating undersampling errors in MR fingerprinting by sequence optimization.

David G J Heesterbeek1,2, Kirsten Koolstra3, Matthias J P van Osch4

  • 1Department of Imaging Physics, Delft University of Technology, Delft, The Netherlands.

Magnetic Resonance in Medicine
|December 2, 2022
PubMed
Summary

This study optimized Magnetic Resonance Fingerprinting (MRF) sequences to reduce undersampling artifacts. The new method significantly lowers errors in parameter mapping, improving MRF scan robustness.

Keywords:
MR fingerprintingoptimal experiment designquantitative MRIundersampling

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Area of Science:

  • Magnetic Resonance Imaging (MRI)
  • Medical Physics
  • Biomedical Engineering

Background:

  • Magnetic Resonance Fingerprinting (MRF) enables rapid quantitative MRI.
  • Undersampling in MRF introduces artifacts, limiting accuracy.
  • Optimizing MRF sequences is crucial for robust parameter mapping.

Purpose of the Study:

  • To develop an MRF sequence optimization method accounting for undersampling patterns and reference maps.
  • To enhance robustness against undersampling artifacts in MRF.

Main Methods:

  • Utilized a predictive model based on perturbation theory to optimize MRF flip angle sequences.
  • Incorporated realistic reference maps from prior MRF scans.
  • Compared optimized sequences against conventional and Cramér-Rao lower bound (CRB)-based patterns using simulations and in vivo data.

Main Results:

  • Flip angle optimization significantly suppressed undersampling errors in MRF.
  • An optimized sequence (400-length train) showed substantially lower median absolute errors compared to conventional and CRB-based sequences.
  • In vivo results confirmed the effectiveness of the proposed optimization method.

Conclusions:

  • The developed method effectively optimizes MRF flip angle patterns.
  • Significant mitigation of artifacts caused by strong k-space undersampling in MRF was achieved.
  • This approach enhances the reliability of MRF for quantitative imaging.