T₂* relaxometry of fetal brain structures using low-field (0.55T) MRI

Area of Science:

• Neuroimaging
• Developmental neuroscience
• Biomedical engineering

Background:

• Fetal brain development involves complex structural and functional changes during gestation.
• Structural Magnetic Resonance Imaging (MRI) is established, but functional imaging tools for fetal brains are limited.
• Low-field MRI presents a promising modality to bridge this gap in functional brain imaging.

Purpose of the Study:

• To investigate regional brain T2* quantification in the fetal brain during the second half of gestation using low-field 0.55T MRI.
• To assess the feasibility of low-field MRI for detailed T2* analysis in specific fetal brain structures.
• To establish normative T2* values for different fetal brain regions throughout gestation.

Main Methods:

• Dynamic multi-echo gradient-echo sequences were acquired at 0.55T in 135 fetuses between 20 and 40 weeks' gestation.
• Automated high-resolution reconstruction and segmentation tools were developed to extract T2* values from seven anatomical brain structures.
• Regional T2* values were analyzed across gestational ages to identify trends and variations.

Main Results:

• All regional fetal brain T2* values demonstrated a significant decrease throughout gestation (p < 0.01).
• Cerebellum and white matter exhibited the highest T2* values (350-400 ms around 20 weeks), while brainstem and deep gray matter showed the lowest (around 250 ms early in gestation).
• Observed volumetric growth patterns for brain structures aligned with existing literature.

Conclusions:

• Low-field MRI enables detailed, regional T2* quantification of the developing fetal brain.
• The findings support the potential of low-field MRI for comprehensive fetal brain analysis.
• Wider bore systems may facilitate the development of more inclusive normative data for fetal brain development.