An optimal control approach to design entire relaxation dispersion experiments

Area of Science:

• Magnetic Resonance Spectroscopy
• Physical Chemistry
• Biophysics

Background:

• Chemical exchange significantly impacts spin systems, complicating analysis in techniques like Nuclear Magnetic Resonance (NMR).
• Optimizing individual components of relaxation dispersion sequences is complex and may not yield optimal results.

Purpose of the Study:

• To develop a general approach for optimizing relaxation dispersion (RD) sequences in the presence of chemical exchange.
• To enhance the sensitivity and accuracy of spin system analysis by designing entire RD sequences as single shaped pulses.

Main Methods:

• Defined a performance index based on the signal remaining after the RD sequence across various experimental parameters.
• Optimized energy-limited broadband RD sequences, approximating ideal Carr-Purcell-Meiboom-Gill (CPMG) sequences.
• Validated the approach theoretically and experimentally.

Main Results:

• The optimized shaped pulses closely mimic the performance of ideal CPMG sequences.
• Demonstrated significant improvements in signal-to-noise ratio and accuracy compared to standard CPMG sequences.
• The method is effective for energy-limited broadband RD sequences.

Conclusions:

• A unified approach to optimize entire RD sequences as single shaped pulses is effective.
• This method offers substantial improvements over conventional pulse sequence optimization for studying spin systems with chemical exchange.
• The optimized sequences provide a more robust and sensitive tool for NMR analysis.