title: Measuring lung water: ex vivo validation of multi-image gradient echo MRI.
abstract: OBJECTIVE
  To validate a fast gradient echo sequence for rapid (9 s) quantitative imaging of lung water.
  
  
  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 H(2) O), an intervention that alters T(2) *, 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 T(2) * and water content, and compared with gravimetric measurements of total water.
  
  
  RESULTS
  T(2) * averaged 1.08 ± 0.02 ms at 5 cm H(2) O and 1.02 ± 0.02 ms at 15 cm H(2) O (P < 0.05). The measure was reliable (R(2) = 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 (R(2) = 0.94), and y = 1.04x + 4 (R(2) = 0.96), for 5 and 15 cm H(2) O inflation pressure respectively. Y-intercepts were not statistically different from zero (P = 0.86).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Medicine, Division of Physiology, University of California, San Diego, La Jolla, California 92093-0852, USA. sholverda@ucsd.edu
authors.forename: Sebastiaan
authors.initials: S
authors.lastname: Holverda
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Theilmann
authors.forename: Rui C
authors.initials: RC
authors.lastname: Sá
authors.forename: Tatsuya J
authors.initials: TJ
authors.lastname: Arai
authors.forename: Evan T
authors.initials: ET
authors.lastname: Hall
authors.forename: David J
authors.initials: DJ
authors.lastname: Dubowitz
authors.forename: G Kim
authors.initials: GK
authors.lastname: Prisk
authors.forename: Susan R
authors.initials: SR
authors.lastname: Hopkins
mesh_terms: D000818:Animals; D002623:Chemistry Techniques, Analytical / Q000379:methods; D017352:Echo-Planar Imaging / Q000379:methods; D008168:Lung / Q000502:physiology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009929:Organ Size; D015203:Reproducibility of Results; D013552:Swine; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water