Brain short T₂ component imaging using double adiabatic inversion recovery prepared ultrashort Echo time (DIR-UTE)...

Area of Science:

• Biomedical Imaging
• Neuroscience
• Radiology

Background:

• Short T2 components in the brain are crucial indicators of myelin structure.
• Direct magnetic resonance imaging (MRI) of these components is challenging due to their short T2 values and low proton density.
• Existing MRI techniques struggle to selectively visualize these short T2 signals amidst dominant long T2 water signals.

Purpose of the Study:

• To introduce and validate a novel 3D double adiabatic inversion recovery-prepared ultrashort echo time (DIR-UTE) sequence.
• To achieve selective whole-brain imaging of brain's short T2 components, which are associated with myelin.
• To assess the potential of short T2 proton fraction (SPF) as a biomarker for demyelinating diseases like multiple sclerosis (MS).

Main Methods:

• Development of a 3D DIR-UTE sequence utilizing adiabatic inversion pulses to suppress long T2 signals.
• Acquisition of rapidly decaying signals using an ultrashort echo time (UTE) 3D sequence.
• Evaluation of the sequence in phantoms, six healthy volunteers, and five MS patients using a 3T MRI scanner.

Main Results:

• Phantom studies confirmed effective suppression of long T2 signals across a range of T1 values.
• The DIR-UTE sequence successfully captured short T2 signals in healthy volunteers, with estimated T2* of 0.21±0.01 ms in white matter.
• Significantly lower short T2 proton fraction (SPF) was observed in normal-appearing white matter and MS lesions compared to normal white matter, and lower average SPF in MS patients versus controls.

Conclusions:

• The novel 3D DIR-UTE sequence effectively suppresses long T2 signals and selectively images short T2 components in the brain.
• Measured SPF differences in white matter, gray matter, and MS lesions indicate reduced myelin content in disease states.
• SPF derived from the DIR-UTE sequence shows promise as a quantitative imaging biomarker for demyelinating diseases such as MS.