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Atomic Nuclei: Types of Nuclear Relaxation01:28

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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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Related Experiment Video

Updated: Jun 17, 2025

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Time-division multiplexing (TDM) sequence removes bias in T2 estimation and relaxation-diffusion measurements.

Qiang Liu1,2, Borjan Gagoski3,4, Imam Ahmed Shaik1

  • 1Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.

Magnetic Resonance in Medicine
|August 13, 2024
PubMed
Summary

Time-division multiplexing (TDM) offers accurate accelerated relaxation-diffusion MRI (rdMRI) microstructure measures, outperforming multi-echo (ME) sequences. TDM provides reliable rdMRI data with 2-3x acceleration, unlike ME which shows significant biases.

Keywords:
PulseqdMRIdiffusionmultidimensional MRIrdMRIrelaxometry

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Area of Science:

  • Magnetic Resonance Imaging
  • Biophysics
  • Medical Physics

Background:

  • Accelerated MRI techniques are crucial for reducing scan times in diffusion MRI (dMRI) and relaxation-based imaging.
  • Relaxation-diffusion MRI (rdMRI) combines diffusion and T2 relaxation measurements to probe tissue microstructure.
  • Comparing acquisition sequences is essential for optimizing rdMRI performance and reliability.

Purpose of the Study:

  • To compare multi-echo (ME) and time-division multiplexing (TDM) sequences for accelerated rdMRI.
  • To evaluate the accuracy and reliability of TDM and ME sequences in estimating rdMRI microstructure measures.
  • To assess the impact of acceleration factors on sequence performance.

Main Methods:

  • ME, TDM, and single-echo (SE) sequences were implemented using Pulseq with single-band (SB) and multi-band 2 (MB2) acceleration.
  • Phantom and in-vivo brain scans were performed to compare image intensities and T2 estimates.
  • Microstructure estimation was assessed using relaxation diffusion imaging moment (REDIM) and maximum-entropy relaxation diffusion distribution (MaxEnt-RDD).

Main Results:

  • TDM performance closely matched the gold standard SE acquisition.
  • ME sequences exhibited significantly larger biases (3-4x on phantom, 2x in-vivo) compared to SE.
  • TDM provided comparable diffusion and relaxation parameters to SE, while ME showed substantial biases in R2 maps and relaxation-diffusion covariance.

Conclusions:

  • Time-division multiplexing (TDM) sequences provide accurate and reliable relaxation-diffusion MRI microstructure measurements.
  • TDM enables accelerated rdMRI acquisition with factors of 2-3x without compromising data quality.
  • ME sequences are less reliable for accurate rdMRI microstructure estimation due to higher biases.