Frequency correction method for improved spatial correlation of hyperpolarized 13C metabolites and anatomy

Area of Science:

• Medical Imaging
• Metabolic Imaging
• Magnetic Resonance Imaging

Background:

• Spatial shifts in (13)C metabolic imaging arise from bulk frequency offsets.
• Accurate spatial registration is crucial for correlating metabolic and anatomical images.
• Echo-planar imaging (EPI) is susceptible to these shifts due to long readouts.

Purpose of the Study:

• To investigate blip-reversed EPI for measuring and correcting spatial shifts in (13)C metabolic imaging.
• To assess the accuracy of frequency offset detection and correction.
• To evaluate the impact of correction on image quality and signal-to-noise ratio (SNR).

Main Methods:

• Implemented blip-reversed EPI by alternating k-space trajectories to reverse spatial shift direction.
• Utilized mutual information to align images and quantify frequency offsets.
• Acquired time-resolved 3D (13)C metabolic images (pyruvate/lactate/urea) in rats with induced frequency offsets.

Main Results:

• The method accurately measured frequency offsets, with a 35 Hz offset causing a 5.9 ± 0.6 mm shift.
• Correction accuracy was determined to be 4 Hz, aligning with theoretical predictions.
• Spatially corrected images demonstrated an SNR improvement factor of 2 or greater compared to single frames.

Conclusions:

• Blip-reversed EPI is an effective technique for correcting frequency-offset-induced spatial shifts in (13)C metabolic imaging.
• The method ensures precise spatial registration between metabolic and anatomical images.
• This approach enhances image quality and facilitates more reliable metabolic analysis in vivo.