Unlike conventional z-shimming methods that apply extra gradients to rephase dephased spins—often at the expense of regions unaffected by susceptibility—this technique simply enlarges the phase-encoding window so that all shifted signal remains in view. That means no additional dephasing compensation is required, and normal tissue signals are preserved. Because it relies on acquisition geometry rather than new gradient pulses, it integrates easily into existing scanners, imposes minimal time penalty, and delivers improved signal recovery and SNR in regions prone to susceptibility artifacts.
Description
This invention relates to a technique reducing the signal void by modifying the conventional gradient EPI pulse sequence. This is accomplished by extending the phase-encoding range outside the range required for the given spatial resolution matrix so that the shifted phase encoded signal can be included in the acquired range of the phase encoding.
Applications
Clinical fMRI brain imaging
Neurosurgical planning MRI
Real-time fMRI neurofeedback
High-field MRI artifact correction
Pharmaceutical fMRI trials
Advantages
Recovers signal voids near susceptibility interfaces by expanding phase‐encoding range
Boosts signal-to-noise ratio proportionally to the extra phase encodings
Integrates seamlessly into existing EPI sequences and uses standard FFT reconstruction for real-time processing
Can be used alone or combined with z-shimming without degrading signals from unaffected regions
Incurs only a modest ~10% increase in slice scan time
