Purpose: Inversion recovery-based UTE (IR-UTE) sequences have been proposed to directly image myelin with extremely short (~0.3 ms). In this study, we demonstrate the feasibility of complex echo subtraction to improve 3D IR-UTE imaging of myelin in white matter of the brain in vivo.
Methods: In IR-UTE imaging, long T2 components in white matter (i.e., water) are suppressed using an adiabatic inversion recovery preparation pulse. Dual echo UTE data acquisition and magnitude echo subtraction are used to suppress the residual white matter and gray matter signals, providing high myelin contrast. Complex echo subtraction may further improve the myelin contrast by reducing the residual long T2 water signal contamination caused by regional T1 variations. To verify the efficacy of the complex subtraction technique, in vivo experiments were performed with 5 non-symptomatic healthy volunteers and 5 multiple sclerosis patients on a 3T clinical MR system. Signal enhancement between the complex subtraction and the magnitude subtraction was introduced to evaluate the improvement.
Results: The complex subtraction improved myelin contrast over the magnitude subtraction in both healthy and patient groups, with more fine myelin structures being revealed. The foci of the demyelinated lesion were more clearly detected by complex subtraction. An average signal enhancement of up to 135.9% was achieved with the complex subtraction over the magnitude subtraction.
Conclusion: The complex echo subtraction improves 3D IR-UTE morphologic imaging of myelin in white matter of the brain.
Keywords: UTE; complex subtraction; inversion recovery; magnitude subtraction; multiple sclerosis; myelin.
© 2019 International Society for Magnetic Resonance in Medicine.