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B1 inhomogeneity-corrected T1 mapping and quantitative magnetization transfer imaging via simultaneously estimating
Albert Jang1,2, Paul K Han2,3, Chao Ma2,3
1Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts, USA.
Magnetic Resonance in Medicine
|July 10, 2023
Summary
A new method, Bloch-Siegert shift and magnetization Transfer Simultaneously (BTS), accurately measures spin-bath parameters by compensating for magnetic field inhomogeneity and macromolecular effects. This robust technique improves accuracy in complex biological environments.
Area of Science:
- Magnetic Resonance Imaging
- Biophysics
- Quantitative MRI
Background:
- Accurate measurement of spin-bath model parameters is crucial for understanding tissue properties.
- Existing methods can be biased by transmit field (B1) inhomogeneity and magnetization transfer (MT) effects.
- Macromolecular environments pose challenges for precise parameter estimation.
Purpose of the Study:
- Introduce a novel method, Bloch-Siegert shift and magnetization Transfer Simultaneously (BTS).
- Utilize BTS for accurate measurement of binary spin-bath model parameters.
- Quantify free pool spin-lattice relaxation, macromolecular fraction, exchange rate, and local transmit field.
Main Methods:
- Simultaneously induce Bloch-Siegert shift and magnetization transfer using off-resonance irradiation.
- Derive and validate an analytical signal equation using the binary spin-bath model.
- Employ Bloch simulations and Monte Carlo simulations for performance analysis.
- Conduct ex vivo and in vivo experiments for parameter estimation with B1 compensation.
Main Results:
- Simulations reveal significant bias in existing methods due to B1 heterogeneity and MT effects.
- Phantom experiments demonstrate increased bias with higher macromolecular proton fraction.
- In vivo brain study yields multi-parameter fit results consistent with prior literature.
- BTS proves robust in macromolecule-rich environments despite B1 inhomogeneity.
Conclusions:
- Developed and validated a method for estimating Bloch-Siegert shift and magnetization transfer effects.
- BTS accurately estimates spin-bath parameters (T1, MMF, k) free from B1 bias.
- BTS offers a reliable approach for quantitative MRI in complex biological tissues.
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