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Standardizing CT Lung Density Measure Across Scanner Manufacturers



Huaiyu H. Chen-Mayer, Matthew Fuld, Bernice Hoppel, Phillip Judy, Junfeng Guo, David Lynch, Antonio M. Possolo, Sean B. Fain


Computed Tomography imaging of the lung, reported in Hounsfield Units (HU), can be parameterized as a quantitative image biomarker for the diagnosis and monitoring of lung density changes due to emphysema, a type of chronic obstructive pulmonary disease (COPD). CT lung density metrics are global measurements based on lung CT number histograms, and are typically a quantity specifying either the percentage of voxels with CT numbers below a threshold, or a single CT number below which a fixed relative lung volume, nth percentile, falls. To reduce variability in the density metrics specified by CT attenuation, the Quantitative Imaging Biomarkers Alliance (QIBA) Lung Density Committee has organized efforts to conduct phantom studies in a variety of scanner models to establish a baseline for assessing the variations in patient studies that can be attributed to scanner calibration and measurement uncertainty. We report the results of harmonization analyses of data obtained from phantom study on CT scanners from 4 CT manufacturers with closely matched protocols at various tube potential voltage (kVp) and exposure settings. Free from biological noise, these phantom studies provide an assessment of the accuracy and precision of the density metrics across platforms solely due to machine calibration and uncertainty of the reference materials. Compared to a previous study using the original COPDGene phantom that did not contain reference foams, the COPDGene 2 phantom used in this study has added foam density references in the lung density region, which, after calibration transferred from NIST Standard Reference Materials (SRM) foams, establishes a HU-electron density relationship for each machine. We show that this calibration procedure combined with a simplified physical model enabled the standardization of the CT numbers reported across scanner-protocol, reducing the instrumental reproducibility of the CT density measurement to less than 1 HU.
Medical Physics


computed tomography lung density references, multi-vendor phantom study, harmonization of Hounsfield Unit, Quantitative imaging biomarker.


Chen-Mayer, H. , Fuld, M. , Hoppel, B. , Judy, P. , Guo, J. , Lynch, D. , Possolo, A. and Fain, S. (2017), Standardizing CT Lung Density Measure Across Scanner Manufacturers, Medical Physics, [online], (Accessed April 21, 2024)
Created March 1, 2017, Updated March 12, 2020