Quantitative chemical exchange sensitive MRI using irradiation with toggling inversion preparation

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biomedical Engineering
• Medical Physics

Background:

• Chemical exchange (CE) sensitive MRI contrast is influenced by longitudinal and transverse relaxation.
• Transverse relaxation often obscures CE contrast, especially in intermediate exchange regimes.
• Separating relaxation effects is crucial for accurate CE quantification in physiological and pathological states.

Purpose of the Study:

• To develop a novel MRI acquisition scheme to isolate pure chemical exchange contrast.
• To simplify the quantification of CE parameters like exchange rate and labile proton concentration.
• To enable accurate CE-mediated relaxation rate determination with reduced hardware and SAR limitations.

Main Methods:

• A toggling inversion pulse is applied before off-resonance irradiation.
• Irradiation images are acquired with and without the inversion pulse at labile proton and reference frequencies.
• Numerical simulations and phantom experiments were used to evaluate the method's signal characteristics.

Main Results:

• The proposed method effectively cancels longitudinal and transverse relaxation contributions.
• Quantification of CE parameters is simplified.
• CE-mediated relaxation rates can be determined rapidly without reaching steady-state.

Conclusions:

• The novel MRI acquisition scheme successfully isolates chemical exchange contrast.
• This method offers a simplified and potentially more robust approach for quantifying CE parameters.
• The technique reduces hardware and specific absorption rate constraints, broadening its applicability.