Optimizing maternal fat suppression with constrained image-based shimming in fetal MR

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Medical Physics
• Radiology

Background:

• Echo planar imaging (EPI) is crucial for fetal functional and diffusion MRI.
• Large field-of-view requirements in fetal MRI cause prolonged EPI readouts, increasing susceptibility artifacts and water-fat shift.
• Gradient performance limitations due to safety concerns further exacerbate EPI distortions.

Purpose of the Study:

• To reduce artifacts and enhance the stability of EPI in fetal brain imaging.
• To balance local field homogeneity within the fetal brain with broader variations for maternal fat suppression.
• To optimize EPI sequences for improved fetal neuroimaging.

Main Methods:

• Optimized Spectral Pre-saturation with Inversion-Recovery (SPIR) fat suppression by tuning SPIR pulse frequency offsets.
• Acquired fetal brain EPI data from 6 pregnant women using image-based (IB) shimming.
• Implemented localized IB shimming for fetal brain B0 homogeneity and fat-constrained IB shimming for maternal fat B0 variation.

Main Results:

• Determined the optimal SPIR pulse offset at 3 Tesla to be 550 Hz.
• Both shimming methods achieved comparable B0 homogeneity within the fetal brain.
• Fat-constrained IB shimming demonstrated superior fat suppression efficiency compared to localized IB shimming.

Conclusions:

• Combining optimized SPIR fat suppression with fat-constrained IB shimming effectively minimizes EPI distortions in fetal brain imaging.
• This approach enhances maternal fat suppression while maintaining fetal brain image quality.
• The study provides a method to improve the diagnostic utility of fetal brain MRI.