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Related Concept Videos

NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences01:17

NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences

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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Measurement of Tumor T2* Relaxation Times after Iron Oxide Nanoparticle Administration
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T2* mapping with background gradient correction using different excitation pulse shapes.

N M Hirsch1, C Preibisch

  • 1Departments of Neuroradiology, Technische Universität München, Munich, Germany. nuria.hirsch@tum.de

AJNR. American Journal of Neuroradiology
|July 28, 2012
PubMed
Summary
This summary is machine-generated.

Magnetic susceptibility variations near brain cavities cause signal loss in gradient-echo images. A novel correction method restores signal intensity and significantly improves T2* values, enhancing image quality.

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Area of Science:

  • Neuroimaging
  • Magnetic Resonance Imaging (MRI)

Background:

  • Air-filled cavities in the brain create magnetic susceptibility variations.
  • These variations cause significant signal intensity loss and T2* shortening in gradient-echo images.

Purpose of the Study:

  • To develop and evaluate a correction method for signal intensity loss in gradient-echo images caused by magnetic susceptibility variations.
  • To improve T2* quantification in brain regions with air-filled cavities.

Main Methods:

  • Implemented a correction method that restores exponential decay using section-profile-dependent correction factors.
  • Utilized gradient-echo imaging with varying gradient strengths.

Main Results:

  • The correction method successfully recovered parts of the lost signal intensity.
  • Uncorrected T2* values dropped by 20% at a gradient strength of 75 μT/m.
  • With correction and exponential excitation pulses, the T2* drop threshold was extended to 220 μT/m.

Conclusions:

  • The developed correction method effectively mitigates signal loss and T2* shortening caused by magnetic susceptibility variations near brain cavities.
  • This technique significantly enhances the reliability of gradient-echo imaging for studying brain structures with air-filled spaces.