Measuring lung water: Ex vivo validation of multi-image gradient echo MRI
Abstract
Purpose:
To validate a fast gradient echo sequence for rapid (9 s) quantitative imaging of lung water.
Materials and Methods:
Eleven excised pig lungs were imaged with a fast GRE sequence in triplicate, in the sagittal plane at 2 levels of inflation pressure (5 and 15 cm H2O), an intervention that alters T2*, but not total lung water. Images were acquired alternating between two closely-spaced echoes and data were fit (voxel-by-voxel) to a single exponential to determine T2* and water content, and compared with gravimetric measurements of total water.
Results:
T2* averaged 1.08 ± 0.02 ms at 5 cm H2O and 1.02 ± 0.02 ms at 15 cm H2O (P < 0.05). The measure was reliable (R2 = 0.99), with an average mean error of 1.8%. There was a significant linear relationship between the two measures of water content: The regression equations for the relationship were y = 0.92x + 19 (R2 = 0.94), and y = 1.04x + 4 (R2 = 0.96), for 5 and 15 cm H2O inflation pressure respectively. Y-intercepts were not statistically different from zero (P = 0.86).
Conclusion:
The multi-echo GRE sequence is a reliable and valid technique to assess water content in the lung. This technique enables rapid assessment of lung water, which is advantageous for in vivo studies. J. Magn. Reson. Imaging 2011;. © 2011 Wiley-Liss, Inc.
