Quantitative ultrashort TE imaging of the short-T2 components in skeletal muscle using an extended echo-subtraction method

Abstract

Purpose: To introduce an ultrashort echo time (UTE) based method for quantitative mapping of short-T2 signals in skeletal muscle (SKM) in the presence of fat, with the aim of monitoring SKM fibrosis. Methods: From a set of at least five UTE images of the same slice, a long- T*2 map, a fat-fraction map, and a map of short-T2-signal fraction are extracted. The method was validated by numerical simulations and in vitro studies on collagen solutions. Finaly, the method was applied to image the short-T2 signals in the leg of eight healthy volunteers. Results: The imaged short-T2-signal fractions in the collagen solutions correlated with their respective collagen concentrations (R=0.999, P=0.009). Short-T2 tissues such as cortical bone and fasciae were highlighted in the resulting short-T2 fraction maps. A significant fraction of short-T2 signal was systematically observed in the skeletal muscle of all of the subjects (4.5±1.2%). Conclusion: The proposed method allows the quantitative imaging of short-T2 components in tissues containing fat. By also having the fat-fraction and T*2 maps as outcomes, long-T2 suppression is accomplished without requiring modifications to the basic UTE sequence. Although the hypersignal observed in the fasciae suggests that the short-T2 signal observed in SKM might arise from interstitial connective tissue, further investigation is necessary to confirm this statement. Magn Reson Med 78:997–1008, 2017. © 2016 International Society for Magnetic Resonance in Medicine.