Dual-Echo EPI sequence for integrated distortion correction in 3D time-resolved hyperpolarized ¹³ C MRI

Area of Science:

• Magnetic Resonance Imaging
• Metabolic Imaging
• Medical Physics

Background:

• Hyperpolarized 13C metabolic imaging offers insights into cellular metabolism.
• Off-resonance effects in echo-planar imaging (EPI) cause geometric distortions and spatial misregistration.
• Accurate spatial localization is crucial for correlating metabolic signals with anatomy.

Purpose of the Study:

• To develop and validate a novel dual-echo 3D EPI sequence for integrated off-resonance correction in hyperpolarized 13C metabolic imaging.
• To improve the accuracy and reliability of time-resolved volumetric metabolic mapping.
• To overcome limitations of existing EPI sequences in hyperpolarized 13C imaging.

Main Methods:

• Implementation of a dual-echo 3D EPI sequence with a spectral-spatial pulse for excitation.
• Acquisition of multi-echo 1H EPI reference scans to encode EPI distortions.
• Combination of phase maps and frequency offset encoding for geometric distortion correction and spatial registration.
• Validation using phantom studies and in vivo rat imaging with [1-13C]pyruvate and [1-13C]lactate.

Main Results:

• Phantom studies demonstrated improved spatial registration in off-resonance corrected images.
• In vivo rat imaging showed close agreement between kidney metabolic signals and underlying anatomy.
• The dual-echo acquisition provided an approximate twofold increase in signal-to-noise ratio compared to single-echo acquisition.

Conclusions:

• A novel dual-echo 3D EPI sequence enables integrated off-resonance correction for hyperpolarized 13C imaging.
• The proposed sequence offers significant advantages over flyback EPI for time-resolved metabolic mapping.
• This method enhances the accuracy and utility of hyperpolarized 13C metabolic imaging.