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.