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

Abstract

Short T₂ components in the brain are uniquely associated with myelin structure, but direct MR imaging is challenging due to their relatively short T₂ values and low proton density compared to long T₂ water. This study introduces a novel 3D double adiabatic inversion recovery-prepared ultrashort echo time (DIR-UTE) sequence for selective whole-brain imaging of short T₂ components. The sequence employs two identical adiabatic inversion pulses with optimized inversion times (TIs) to suppress long T₂ signals, followed by a 3D UTE acquisition to capture rapidly decaying signals. Technical feasibility was evaluated using phantoms, six healthy volunteers, and five patients with multiple sclerosis (MS) on a 3T MRI scanner. Short T₂ proton fraction (SPF) was measured in white matter, gray matter, MS lesions, and across the whole brain to assess differences in myelin content. Phantom studies confirmed effective suppression of long T₂ signals over a wide range of T₁ values. In healthy volunteers, DIR-UTE selectively captured short T₂ signals, with an estimated T₂* of 0.21±0.01 ms in white matter. SPF in normal white matter (5.12±0.57 %) was significantly higher than in normal-appearing white matter (4.06±0.61 %, P < 0.0001) and MS lesions (2.76±0.78 %, P < 0.0001). Similar trends were observed in gray matter. Whole-brain analysis also showed lower average SPF in MS patients (3.42±0.38 %) compared to healthy controls (4.01±0.35 %, P < 0.0001). These results demonstrate the DIR-UTE sequence's ability to suppress long T₂ signals and selectively image short T₂ components, with SPF emerging as a potential biomarker for demyelinating diseases like MS.

Keywords: Double adiabatic inversion recovery; Myelin; Short T2; Ultrashort echo time.