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Magnetization transfer using inversion recovery during off-resonance irradiation.

Silvia Mangia1, Federico De Martino, Timo Liimatainen

  • 1Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota School of Medicine, Minneapolis, MN 55455, USA. mangia@umn.edu

Magnetic Resonance Imaging
|May 24, 2011
PubMed
Summary

This study introduces a novel method for estimating magnetization transfer (MT) parameters in vivo. By sampling steady-state formation from both -z and +z axes, it overcomes radiofrequency (RF) safety limits, improving tissue specificity.

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Area of Science:

  • Magnetic Resonance Imaging
  • Biophysics
  • Medical Physics

Background:

  • In vivo estimation of magnetization transfer (MT) parameters is often limited by radiofrequency (RF) safety constraints, specifically tissue heating and specific absorption rate (SAR).
  • These limitations prevent achieving a full steady state magnetization, compromising the accuracy of MT parameter estimation.
  • Current standard MT acquisitions typically initialize magnetization along the +z axis only.

Purpose of the Study:

  • To develop a novel approach for estimating MT parameters in vivo that circumvents radiofrequency (RF) safety limitations (SAR).
  • To improve the accuracy and tissue specificity of MT parameter mapping.
  • To enhance the fitting procedure for MT parameter estimation.

Main Methods:

  • Proposed a new method involving sampling the formation of the steady state from both -z and +z initial magnetization states.
  • Implemented an on-resonance inversion pulse prior to off-resonance irradiation for the -z axis measurement.
  • Conducted human brain imaging to validate the proposed method and compare it with standard MT acquisition.

Main Results:

  • The proposed method successfully circumvents SAR limitations by sampling steady-state formation in separate measurements.
  • The new approach significantly benefits the fitting procedure for estimating MT parameters.
  • Parametric maps generated using this method exhibit notably increased tissue specificity compared to standard MT acquisition.

Conclusions:

  • The novel method of sampling steady-state formation from both -z and +z initial magnetization states offers a significant advancement in in vivo MT imaging.
  • This technique overcomes radiofrequency (RF) safety limitations, leading to more accurate and specific MT parameter estimation.
  • The enhanced tissue specificity demonstrated in human brain imaging highlights the clinical potential of this improved MT acquisition strategy.