Identifying out-of-voxel echoes in edited MRS with phase cycle inversion

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Spectroscopy
• Signal Processing

Background:

• Out-of-voxel (OOV) signals in MRI can complicate spectral analysis.
• Understanding the origin of OOV signals is crucial for improving data quality.
• Coherence Transfer Pathways (CTP) formalism provides a framework for analyzing signal origins.

Purpose of the Study:

• To identify the origin of OOV signals using the CTP formalism.
• To leverage signal phase information from acquisition phase cycling schemes.
• To enable optimization of crusher gradients for OOV signal suppression.

Main Methods:

• Introduced Phase Cycle Inversion (PCI) to identify OOV signals.
• PCI removes and replaces receiver phases to match unwanted CTPs.
• Validated PCI using MEGA-edited PRESS sequence in simulations, phantom, and in vivo experiments.

Main Results:

• Simulations showed PCI fully separates signals from different CTPs.
• PCI identified the CTP responsible for OOV signals in phantom and in vivo studies.
• Optimized gradient schemes based on PCI led to cleaner spectra in volunteers.

Conclusions:

• PCI is a flexible and generalizable method for diagnosing OOV signal origins.
• The approach aids in optimizing MRI acquisition parameters.
• This technique can be applied across various pulse sequences and voxel locations.