M. Perhomaa et al., CT lung densitometry in assessing intralobular air content - An experimental and clinical study, ACT RADIOL, 41(3), 2000, pp. 242-248
Purpose. To introduce a parameter called "intralobular air content percenta
ge" to replace the CT number of the lung and to establish a proper protocol
for its assessment.
Material and Methods. We calibrated the HU (Hounsfield unit) scale for low
densities with foam and evaluated the influence of certain acquisition and
reconstruction parameters on the accuracy of CT densitometry of the lungs.
The reproducibility of the results obtained in human experiments and the in
tralobular air content percentage of normal and diseased lung tissue were a
ssessed.
Results: Air content could be reliably derived from the calibrated CT numbe
r of an area within a secondary lobulus. The mean intralobular air content
of normal lungs varied from 77.8% to 88.0% in full inspiration. Helical or
axial recording with a 10-mm slice thickness, a standard or soft algorithm
and high tube currents and voltage settings, was suitable for the measureme
nts.
Conclusion. Before absolute lung density measurements (as a HU number or an
air content percentage), the CT equipment has to be calibrated for low den
sities. The intralobular air content percentages of cooperative patients we
re reliably reproducible.