Imaging and T₂ relaxometry of short‐T₂ connective tissues in the knee using ultrashort echo‐time double‐echo steady‐state (UTEDESS)

Purpose To develop a radial, double‐echo steady‐state (DESS) sequence with ultra‐short echo‐time (UTE) capabilities for T 2 measurement of short‐T 2 tissues along with simultaneous rapid, signal‐to‐noise ratio (SNR)‐efficient, and high‐isotropic‐resolution morphological knee imaging. Methods THe 3D radial UTE readouts were incorporated into DESS, termed UTEDESS. Multiple‐echo‐time UTEDESS was used for performing T 2 relaxometry for short‐T 2 tendons, ligaments, and menisci; and for Dixon water‐fat imaging. In vivo T 2 estimate repeatability and SNR efficiency for UTEDESS and Cartesian DESS were compared. The impact of coil combination methods on short‐T 2 measurements was evaluated by means of simulations. UTEDESS T 2 measurements were compared with T 2 measurements from Cartesian DESS, multi‐echo spin‐echo (MESE), and fast spin‐echo (FSE). Results UTEDESS produced isotropic resolution images with high SNR efficiency in all short‐T 2 tissues. Simulations and experiments demonstrated that sum‐of‐squares coil combinations overestimated short‐T 2 measurements. UTEDESS measurements of meniscal T 2 were comparable to DESS, MESE, and FSE measurements while the tendon and ligament measurements were less biased than those from Cartesian DESS. Average UTEDESS T 2 repeatability variation was under 10% in all tissues. Conclusion The T 2 measurements of short‐T 2 tissues and high‐resolution morphological imaging provided by UTEDESS makes it promising for studying the whole knee, both in routine clinical examinations and longitudinal studies. Magn Reson Med 78:2136–2148, 2017.