Using adiabatic inversion pulses for long-T2 suppression in ultrashort echo time (UTE) imaging

Ultrashort echo time (UTE) imaging is a technique that can visualize tissues with sub-millisecond T-2 values that have little or no signal in conventional MRI techniques. The short-T-2 tissues, which include tendons, menisci, calcifications, and cortical bone, are often obscured by long-T-2 tissues. This paper introduces a new method of long-T-2 component suppression based on adiabatic inversion pulses that significantly improves the contrast of short-T-2 tissues. Narrow bandwidth inversion pulses are used to selectively invert only long-T-2 components. These components are then suppressed by combining images prepared with and without inversion pulses. Fat suppression can be incorporated by combining images with the pulses applied on the fat and water resonances. Scaling factors must be used in the combination to compensate for relaxation during the preparation pulses. The suppression is insensitive to RF inhomogeneities because it uses adiabatic inversion pulses. Simulations and phantom experiments demonstrate the adiabatic pulse contrast and how the scaling factors are chosen. In vivo 2D UTE images in the ankle and lower leg show excellent, robust long-T-2 suppression for visualization of cortical boneandtendons.