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Fast quantitative MRI using Controlled Saturation Magnetization Transfer

Research output: Contribution to journalArticle

Original languageEnglish
Pages (from-to)907-920
Number of pages14
JournalMagnetic Resonance in Medicine
Issue number2
Early online date14 Sep 2018
Publication statusPublished - Feb 2019


King's Authors


Purpose: This study demonstrates Magnetisation Transfer (MT) effects directly affect relaxometry measurements and develops a framework which allows single-pool models to be valid in two-pool MT systems.
Methods: A theoretical framework is developed in which a two-pool MT system effectively behaves as a single-pool if the root-mean-squared radiofrequency magnetic field (B1rms) is kept fixed across all measurements. A practical method for achieving “Controlled Saturation Magnetization Transfer” (CSMT) using multiband RF pulses is proposed. Numerical, Phantom and in vivo validations were performed directly comparing steady-state (SS) estimation approaches which under correct single-pool assumptions would be expected to vary in precision but not accuracy.
Results: Numerical simulations predict single-pool estimates obtained from MT model generated data are not consistent for different SS estimation methods and a systematic underestimation of T2 is expected. Neither effect occurs under the proposed CSMT approach. Both phantom and in vivo experiments corroborate the numerical predictions. Experimental data highlights that even when using the same relaxometry method, different estimates are obtained depending on which combination of flip angles (FA) and repeat times (TRs) are employed if the CSMT approach is not used. Using CSMT, stable measurements of both T1 and T2 are obtained. The measured T1 (T1CSMT) depends on B1rms, which is thus an important parameter to specify.
Conclusion: This work demonstrates that conventional single pool relaxometry, which is highly efficient for human studies, results in unreliable parameter estimates in biological tissues due to MT effects. The proposed CSMT framework is shown to allow single-pool assumptions to be valid, enabling reliable and efficient quantitative imaging to be performed.

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