Optimizing SNR for multi-metabolite hyperpolarized carbon-13 MRI using a hybrid flip-angle scheme

Area of Science:

• Magnetic Resonance Imaging
• Medical Physics
• Biomedical Engineering

Background:

• Hyperpolarized carbon-13 (¹³C) MRI offers metabolic insights but faces challenges with signal-to-noise ratio (SNR).
• Optimizing radiofrequency (RF) pulse excitation is crucial for maximizing SNR in dynamic imaging experiments.

Purpose of the Study:

• To develop and evaluate a multispectral variable flip angle (msVFA) scheme for improving SNR in hyperpolarized ¹³C MRI of [1-¹³C]pyruvate.
• To dynamically adjust spectral profiles and flip angles during image acquisition to enhance SNR.

Main Methods:

• Implemented a novel msVFA scheme with spectrally varying RF pulse shapes for each acquisition.
• Optimized flip angles for pyruvate and its metabolites to maximize SNR across dynamic scans.
• Compared msVFA against a constant flip-angle excitation model using simulations and in vivo experiments in pregnant guinea pigs.

Main Results:

• In vivo experiments demonstrated significant SNR increases with msVFA compared to constant flip angle methods.
• Observed SNR improvements reached up to 250% for multiple metabolites in targeted organs.
• The msVFA technique proved effective across various organs, including placentae, maternal liver, and kidneys.

Conclusions:

• The msVFA excitation technique substantially improves SNR in hyperpolarized ¹³C MRI.
• This method enhances SNR for all observed metabolites in key organs, advancing diagnostic capabilities.