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Related Concept Videos

NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences01:17

NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences

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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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Upsampling01:22

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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Reconstruction of Signal using Interpolation01:10

Reconstruction of Signal using Interpolation

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Signal processing techniques are essential for accurately converting continuous signals to digital formats and vice versa. When a continuous signal is sampled with a period T, the resulting sampled signal exhibits replicas of the original spectrum in the frequency domain, spaced at intervals equal to the sampling frequency. To handle this sampled signal, a zero-order hold method can be applied, which creates a piecewise constant signal by retaining each sample's value until the next...
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Bandpass Sampling01:17

Bandpass Sampling

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In signal processing, bandpass sampling is an effective technique for sampling signals that have most of their energy concentrated within a narrow frequency band. This type of signal is known as a bandpass signal. The key principle of bandpass sampling involves sampling the signal at a rate that is greater than twice the signal's bandwidth to prevent aliasing.
A bandpass signal has a spectrum with a lower frequency limit, denoted as ω1, and an upper frequency limit, denoted as ω2....
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Aliasing01:18

Aliasing

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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.
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Frequency-Domain Interpretation of PD Control01:24

Frequency-Domain Interpretation of PD Control

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Proportional-Derivative (PD) controllers are widely used in fan control systems to improve stability and performance. A fan control system can be effectively represented using a Bode plot to illustrate the impact of a PD controller through its transfer function. The Bode plot visually conveys how PD control modifies the fan's response across various frequencies, providing a frequency domain interpretation of the controller's behavior.
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Generation and Coherent Control of Pulsed Quantum Frequency Combs
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Improved design of frequency-swept pulse sequences.

Jean-Baptiste Verstraete1, Mohammadali Foroozandeh1

  • 1Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, OX1 3TA Oxford, UK.

Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|February 10, 2022
PubMed
Summary

This study introduces a simple method for designing complex magnetic resonance pulse sequences. New sequences like CHORUS-CPMG and PROCHORUS improve performance and reduce scan times by up to 40%.

Keywords:
-tolerant pulsesBroadband pulsesCHORUSCPMGChirped pulsesFrequency-swept pulsesHS pulsesJ-modulationPROCHORUSPerfect echoPulse superposition

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Area of Science:

  • Magnetic Resonance Spectroscopy
  • Quantum Control

Background:

  • Frequency-swept pulses are crucial for spin manipulation in magnetic resonance (MR) spectroscopy, especially under B1 field variations.
  • Designing complex pulse sequences with multiple frequency-swept pulses is often challenging due to timing and parameter sensitivity.

Purpose of the Study:

  • To present a simple and general approach for constructing advanced frequency-swept pulse sequences.
  • To introduce novel pulse sequences for enhanced performance in MR spectroscopy.

Main Methods:

  • Development of a general strategy for designing frequency-swept pulse sequences.
  • Implementation of pulse superposition for sequence compression.
  • Mathematical modeling, experimental validation, and computational simulations.

Main Results:

  • Introduction of CHORUS-CPMG for broadband B1-tolerant Carr-Purcell-Meiboom-Gill experiments.
  • Development of PROCHORUS for broadband chirped excitation with suppressed homonuclear J-modulation.
  • Demonstration of 25-40% reduction in pulse sequence durations through pulse superposition.

Conclusions:

  • The proposed general approach simplifies the design of sophisticated frequency-swept pulse sequences.
  • The new sequences offer improved robustness and efficiency for magnetic resonance applications.
  • Pulse superposition is an effective strategy for compressing pulse sequence durations.