Robust dual-angle T 1 measurement in magnetization transfer spectroscopy by time-optimal control.

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Spectroscopy
• Biophysics

Background:

• Magnetization transfer (MT) spectroscopy requires accurate T1 relaxation time measurements for metabolic exchange analysis.
• Surface RF coils and broad X-nucleus resonances complicate T1 mapping, especially with fast methods like dual-angle.
• Existing methods struggle with accuracy and precision in T1 mapping for MT spectroscopy.

Purpose of the Study:

• To develop novel resonance offset and T1-robust excitation RF pulses for 7T ³¹P MT spectroscopy.
• To enhance the accuracy and precision of metabolic exchange rate measurements.
• To address challenges posed by RF inhomogeneity and broad resonance bands in fast T1 mapping.

Main Methods:

• Ensemble-based time-optimal control was used to design RF pulses.
• A cost functional incorporating Bloch equations as constraints was introduced.
• Symmetric operator splitting techniques were employed to solve the Bloch equations.

Main Results:

• The designed RF pulses demonstrated improved accuracy and phase properties.
• Reduced RF power requirements were observed compared to conventional methods.
• Enhanced precision in exchange-rate measurements was achieved using dual-angle T1 mapping.
• Successful preclinical in vivo demonstration in quantifying brain creatine kinase activity.

Conclusions:

• The developed RF pulses significantly improve T1 mapping robustness for ³¹P MT spectroscopy at 7T.
• This advancement enhances the precision of metabolic exchange rate quantification.
• The method shows promise for preclinical and potentially clinical applications in metabolic research.