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Robust 3D Bloch-Siegert based B1+ mapping using multi-echo general linear modeling.

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Interleaving radiofrequency pulses for Bloch-Siegert shift (BSS) based transmit field (B1+) estimation introduces bias. A new general linear model approach using multi-echo acquisition corrects this bias, improving B1+ mapping accuracy.

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Bloch-Siegert shiftGLMRF spoilinginterleaved acquisitionmulti-echo readout

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Area of Science:

  • Magnetic Resonance Imaging (MRI)
  • Quantitative MRI
  • Biophysics

Background:

  • Accurate quantitative MRI, like T1 mapping, requires precise transmit field (B1+) estimation.
  • Bloch-Siegert shift (BSS) based methods offer a potential solution by using phase differences from opposite off-resonance pulses.
  • Interleaving these pulses enhances motion and drift robustness but introduces estimation bias.

Purpose of the Study:

  • To demonstrate the bias introduced by interleaved pulse sequences in BSS-based B1+ estimation.
  • To present a novel method for accurate BSS-based B1+ estimation.
  • To validate the new method against simulations and experimental data.

Main Methods:

  • Simulations and phantom/in vivo experiments were conducted.
  • A multi-echo acquisition sequence was employed.
  • A general linear model was utilized to estimate the Bloch-Siegert shift-induced phase, correcting for bias.

Main Results:

  • The interleaved pulse acquisition was shown to introduce bias in B1+ estimates.
  • The bias amplitude was dependent on pulse sequence parameters and tissue properties (T1, T2).
  • The general linear model-based method successfully removed the dependency on tissue properties and sequence settings, aligning with simulations.

Conclusions:

  • The novel general linear model-based approach provides accurate BSS-induced phase estimation.
  • This method overcomes the limitations of previous interleaved pulse techniques.
  • The general linear model-based method is recommended for improved B1+ mapping in quantitative MRI.