Quantitative MRI measurement of lung density must account for the change in T(2) (*) with lung inflation.
OBJECTIVE
To evaluate lung water density at three different levels of lung inflation in normal lungs using a fast gradient echo sequence developed for rapid imaging.


METHODS
Ten healthy volunteers were imaged with a fast gradient echo sequence that collects 12 images alternating between two closely spaced echoes in a single 9-s breathhold. Data were fit to a single exponential to determine lung water density and T(2) (*). Data were evaluated in a single imaging slice at total lung capacity (TLC), functional residual capacity (FRC), and residual volume (RV). Analysis of variance for repeated measures was used to statistically evaluate changes in T(2) (*) and lung water density across lung volumes, imaging plane, and spatial locations in the lung.


RESULTS
In normal subjects (n = 10), T(2) (*) (and [lung density/water density]) was 1.2 +/- 0.1 msec (0.10 +/- 0.02), 1.8 +/- 0.2 ms (0.25 +/- 0.04), and 2.0 +/- 0.2 msec (0.27 +/- 0.03) at TLC, FRC, and RV, respectively. Results also show that there is a considerable intersubject variability in the values of T(2) (*).


CONCLUSIONS
Data show that T(2) (*) in the lung is very short, and varies considerably with lung volume. Thus, if quantitative assessment of lung density within a breathhold is to be measured accurately, then it is necessary to also determine T(2) (*).
Theilmann
Rebecca J
RJ
Department of Radiology, University of California, San Diego, La Jolla, California, USA. rtheilmann@ucsd.edu
Arai
Tatsuya J
TJ
Samiee
Ahsan
A
Dubowitz
David J
DJ
Hopkins
Susan R
SR
Buxton
Richard B
RB
Prisk
G Kim
GK
D000704:Analysis of Variance; D003287:Contrast Media; D005260:Female; D005652:Functional Residual Capacity / Q000502:physiology; D019786:Gadolinium DTPA; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008168:Lung / Q000033:anatomy & histology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D019047:Phantoms, Imaging; D012016:Reference Values; D012115:Residual Volume / Q000502:physiology; D014109:Total Lung Capacity / Q000502:physiology
D003287:Contrast Media; D019786:Gadolinium DTPA