Comparison of Lung T2* During Free-Breathing at 1.5 T and 3.0 T with Ultrashort Echo Time Imaging

Assessment of lung effective transverse relaxation time (T-2*) may play an important role in the detection of structural and functional changes caused by lung diseases such as emphysema and chronic bronchitis. While T-2* measurements have been conducted in both animals and humans at 1.5 T, studies on human lung at 3.0 T have not yet been reported. In this work, ultrashort echo time imaging technique was applied for the measurement and comparison of T-2* values in normal human lungs at 1.5 T and 3.0 T. A 2D ultrashort echo time pulse sequence was implemented and evaluated in phantom experiments, in which an eraser served as a homogeneous short T-2* sample. For the in vivo study, five normal human subjects were imaged at both field strengths and the results compared. The average T-2* values measured during free-breathing were 2.11(+/- 0.27) ms at 1.5 T and 0.74(+/- 0.1) ms at 3.0 T, respectively, resulting in a 3.0 T/1.5 T ratio of 2.9. Furthermore, comparison of the relaxation values at end-expiration and end-inspiration, accomplished through self-gating, showed that during normal breathing, differences in T-2* between the two phases may be negligible. Magn Reson Med 66:248-254, 2011. (C) 2011 Wiley-Liss, Inc.