Fast Volumetric Imaging of Bone Using a Three-Dimensional Short TR Adiabatic Inversion Recovery Ultrashort Echo Time (STAIR-UTE) Sequence.

Bone is invisible with conventional MRI sequences. It is highly desirable to develop novel MRI sequences to image bone, providing a radiation-free modality for skeletal imaging. We compared the morphological and quantitative strength of three-dimensional (3D) ultrashort echo time (UTE), zero echo time (ZTE), and short TR adiabatic inversion recovery UTE (STAIR-UTE) MRI techniques for bone imaging in various skeletal anatomical regions, including the forearm, wrist, lower leg, upper leg, and skull. Five healthy volunteers (four male and one female) were subject to four MRI sequences, including 3D UTE with 2° and 7° flip angles (FAs), 3D ZTE with 2° FA, and 3D STAIR-UTE with 14° FA. Regions of interest (ROIs) were drawn in cortical bone, marrow cavity, and muscle to measure their signal intensities. An artifact-free ROI was also placed in the image background to measure the standard deviation (SD) of noise. The signal-to-noise ratio of bone (SNRBone) and contrast-to-noise ratios (CNRs) between bone and marrow (CNRBone-Marrow) and bone and muscle (CNRBone-Muscle) were measured in different anatomical regions. These SNR and CNRs were divided by the square root of acquisition time. In addition, bone volume renderings were generated from 3D STAIR-UTE images. The averages and SDs of SNRBone, CNRBone-Marrow, and CNRBone-Muscle were calculated for different anatomical regions. UTE with 7° FA has the highest positive SNR and negative CNR. UTE and ZTE sequences with the same FAs of 2° have similar SNR and CNR values. The STAIR-UTE sequence with 14° FA has the lowest SNR but is the only sequence providing positive CNR for bone at all investigated body regions, which can be used for direct bone volume rendering. The STAIR-UTE technique provides high contrast volumetric imaging of skeletal anatomies, which enables us to generate direct bone surface-rendered images in clinically acceptable scan time.