T2*and proton density measurement of normal human lung parenchyma using submillisecond echo time gradient echo magnetic resonance imaging

Objective: To obtain T2* and proton density measurements of normal human lu ng parenchyma in vivo using submillisecond echo time (TE) gradient echo (GR E) magnetic resonance (MR) imaging, Materials and methods: Six normal volun teers were scanned using a 1.5-T system equipped with a prototype enhanced gradient (GE Signa, Waukausha, WI). Images were obtained during breath-hold ing with acquisition times of 7-16 s. Multiple TEs ranging from 0.7 to 2.5 ms were tested. Linear regression was performed on the logarithmic plots of signal intensity versus TE, yielding, measurements of T2* and proton densi ty relative to chest wall muscle. Measurements in supine and prone position s were compared, and effects of the level of lung inflation on lung signal were also evaluated. Results: The signal from the lung parenchyma diminishe d exponentially with prolongation of TE. The measured T2* in six normal vol unteers ranged from 0.89 to 2.18 ms (1.43 +/- 0.41 ms, mean +/- S.D.). The measured relative proton density values ranged between 0.21 and 0.45 (0.29 +/- 0.08, mean +/- S.D.). Calculated T2* values of 1.46 +/- 0.50, 1.01 +/- 0.29 and 1.52 +/- 0.18 ms, and calculated relative proton densities of 0.20 +/- 0.03, 0.32 +/- 0.13 and 0.35 +/- 0.10 were obtained from the anterior, middle and posterior portions of the supine right lung, respectively. The anterior-posterior proton density gradient was reversed in the prone positi on. There was a pronounced increase in signal from lung parenchyma at maxim um expiration compared with maximum inspiration. The ultrashort TE GRE tech nique yielded images demonstrating signal from lung parenchyma with minimal motion-induced noise. Conclusion: Quantitative in vivo measurements of lun g T2* and relative proton density in conjunction with high-signal parenchym al images can be obtained using a set of very rapid breath-hold images with a recently developed ultrashort TE GRE sequence. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.