Abstract
Short T(2) components in the brain are uniquely associated with myelin structure, but direct MR imaging is challenging due to their relatively short T(2) values and low proton density compared to long T(2) 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 T(2) components. The sequence employs two identical adiabatic inversion pulses with optimized inversion times (TIs) to suppress long T(2) 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 T(2) 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 T(2) signals over a wide range of T(1) values. In healthy volunteers, DIR-UTE selectively captured short T(2) signals, with an estimated T(2)* 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 T(2) signals and selectively image short T(2) components, with SPF emerging as a potential biomarker for demyelinating diseases like MS.