Comparison of lung T 2 * 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, 2011. © 2011 Wiley‐Liss, Inc.