Quantitative ultrashort T₂ components imaging in the brain using variable flip angle balanced steady state free...

Area of Science:

• Neuroimaging
• Biophysics
• Medical Physics

Background:

• Myelin integrity is crucial for neurological function.
• Quantitative assessment of myelin in vivo remains challenging.
• Ultrashort T2 (uT2) relaxation times are sensitive to myelin content.

Purpose of the Study:

• Develop a novel method for quantitative measurement of brain ultrashort T2 (uT2) components.
• Enable reliable and high-quality fitting of uT2 fraction, particularly for myelin.
• Generate high-resolution uT2 fraction maps for improved diagnostic capabilities.

Main Methods:

• Employed a modified dual-echo balanced steady-state free precession (bSSFP) ultrashort echo time (UTE) sequence.
• Acquired data at six flip angles from healthy volunteers and multiple sclerosis (MS) patients.
• Analyzed signal differences between two echo times (TE1=50 μs, TE2=2.2 ms) to extract and fit uT2 components.

Main Results:

• Demonstrated clear evidence of a uT2 component matching simulated myelin signals.
• Found significantly higher uT2 fraction in white matter (WM) compared to gray matter (GM) (6-7% vs. 2%).
• Quantified significantly reduced uT2 fraction in MS lesions compared to normal-appearing white matter (4.84% vs. 7.96%).

Conclusions:

• Achieved isotropic sub-millimeter resolution uT2 fraction maps using a simplified fitting model.
• Results correspond to established patterns of myelination and show significant uT2 reduction in MS lesions.
• Verified the repeatability and reliability of the quantification method through consistent repeated scans.