Normal spectrum of pulmonary parametric response map to differentiate lung collapsibility: distribution of densitometric classifications in healthy adult volunteers
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Pulmonary parametric response map (PRM) was proposed for quantitative densitometric phenotypization of chronic obstructive pulmonary disease. However, little is known about this technique in healthy subjects. The purpose of this study was to describe the normal spectrum of densitometric classification of pulmonary PRM in a group of healthy adults.
15 healthy volunteers underwent spirometrically monitored chest CT at total lung capacity (TLC) and functional residual capacity (FRC). The paired CT scans were analyzed by PRM for voxel-by-voxel characterization of lung parenchyma according to 4 densitometric classifications: normal lung (TLC ≥ -950 HU, FRC ≥ -856 HU); expiratory low attenuation area (LAA) (TLC ≥ -950 HU, FRC < -856 HU); dual LAA (TLC<-950 HU, FRC < -856 HU); uncharacterized (TLC < -950 HU, FRC ≥ -856 HU).
PRM spectrum was 78 % ± 10 % normal lung, 20 % ± 8 % expiratory LAA, and 1 % ± 1 % dual LAA. PRM was similar between genders, there was moderate correlation between dual LAA and spirometrically assessed TLC (R = 0.531; p = 0.042), and between expiratory LAA and VolExp/Insp ratio (R = -0.572; p = 0.026).
PRM reflects the predominance of normal lung parenchyma in a group of healthy volunteers. However, PRM also confirms the presence of physiological expiratory LAA seemingly related to air trapping and a minimal amount of dual LAA likely reflecting emphysema.
• Co-registration of inspiratory and expiratory computed tomography allows dual-phase densitometry.
• Dual-phase co-registered densitometry reflects heterogeneous regional changes in lung function.
• Quantification of lung in healthy subjects is needed to set reference values.
• Expiratory low attenuation areas <30 % could be considered within normal range.
KeywordsLung Healthy subjects Volumetric computed tomography Densitometry Obstructive lung diseases
American Thoracic Society
body mass index
chronic obstructive pulmonary disease
European Respiratory Society
functional residual capacity
low attenuation area
parametric response map
quantitative computed tomography
total lung capacity
- VolExp/Insp ratio
ratio between expiratory and inspiratory lung volume
The scientific guarantor of this publication is Dr Mario Silva. The authors of this manuscript declare relationships with the following companies: A. A. Bankier is consultant for Spiration (Olympus Medical Systems) and has received authorship honoraria from Elsevier. R. Chamberlain is employed at Imbio, LLC (Minneapolis, MN). Imbio received NIH grant for validation of parametric response map (NIH R44HL118837).
The authors state that this work has not received any funding. Professor Dr. Alexander A. Bankier has significant statistical expertise. Institutional Review Board approval was obtained. Written informed consent was waived by the Institutional Review Board. Our study population has been previously reported in “Dufresne V. et al. Effect of systemic inflammation on inspiratory and limb muscle strength and bulk in cystic fibrosis. Am J Respir Crit Care Med 2009” and “Nemec SF et al. Comparison of four software packages for CT lung volumetry in healthy individuals. Eur Radiol 2015”. Methodology: retrospective, experimental, performed at one institution.
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