Enhanced Sensitivity and Resolution in Biomolecular CEST NMR Experiments Using the Extended Hadamard Encoding Scheme

Area of Science:

• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Chemical Exchange Saturation Transfer (CEST) Imaging

Background:

• Hadamard Transform (HT) enables faster Nuclear Magnetic Resonance (NMR) experiments by simplifying spectral information extraction.
• However, complex interactions like spin-spin couplings and chemical exchange can disrupt the direct link between spectral peak intensity and frequency, leading to artifacts in NMR experiments.

Purpose of the Study:

• To identify and explain the origin of artifacts in NMR Chemical Exchange Saturation Transfer (CEST) experiments when using frequency-domain Hadamard encodings.
• To propose and validate an extended Hadamard Transform (eHT) scheme to eliminate these artifacts while retaining the benefits of HT.

Main Methods:

• Investigated artifacts arising from classical frequency-domain Hadamard encodings in NMR CEST experiments.
• Developed and implemented an extended Hadamard Transform (eHT) scheme.
• Performed and processed CEST NMR experiments using the eHT scheme.

Main Results:

• Demonstrated that classical frequency-domain Hadamard encodings introduce significant artifacts in NMR CEST experiments due to chemical exchange.
• The proposed eHT scheme successfully eliminated these artifacts in CEST NMR experiments.
• eHT-processed CEST NMR experiments showed improved performance compared to standard implementations and other accelerated methods for protein CEST.

Conclusions:

• The extended Hadamard Transform (eHT) effectively removes artifacts in NMR CEST experiments caused by classical Hadamard encodings.
• eHT preserves the sensitivity and speed advantages of the Hadamard Transform for accelerated CEST NMR.
• This advancement offers a more robust and accurate approach for advanced protein CEST NMR studies.