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Multi-Vendor Phantom Study of CT Lung Density Metrics: Is a Reproducibility of Less Than 1 HU Achievable?

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H Chen-Mayer

H Chen-Mayer1*, P Judy2 , S Fain3 , B Hoppel4 , D Lynch5 , M Fuld6 , (1) National Institute of Standards & Technology, Gaithersburg, MD, (2) Brigham & Women's Hospital, Boston, MA, (3) University of Wisconsin, Madison, WI, (4) Toshiba Medical Research Institute USA, Inc, Vernon Hills, IL, (5) Nation Jewish Health, Denver, CO, (6)Siemens Medical Solutions USA, Inc.,Baltimore, MD


TH-CD-207B-11 (Thursday, August 4, 2016) 10:00 AM - 12:00 PM Room: 207B

To standardize the calibration procedures of CT lung density measurements using low-density reference foams in a phantom, and to demonstrate a reproducibility of less than 1 HU for lung equivalent foam densities measured across CT vendor platforms and protocols.

A phantom study was conducted on CT scanner models from 4 vendors at 100, 120, and 135/140 kVp and 1.5, 3, and 6 mGy dose settings, using a lung density phantom containing air, water, and 3 reference foams (indirectly calibrated) with discrete densities simulating a 5-cm slice of the human chest. Customized segmentation software was used to analyze the images and generate a mean HU and variance for each of the density for the 22 vendor/protocols. A 3-step calibration process was devised to remove a scanner-dependent parameter using linear regression of the HU value vs the relative electron density. The results were mapped to a single energy (80 keV) for final comparison.

The heterogeneity across vendor platforms for each density assessed by a random effects model was reduced by 50% after re-calibration, while the standard deviation of the mean HU values also improved by about the same amount. The 95% CI of the final HU value was within +/-1 HU for all 3 reference foam densities. For the backing lung foam in the phantom (served as an “unknown”), this CI is +/- 1.6 HU. The kVp and dose settings did not appear to have significant contributions to the variability.

With the proposed calibration procedures, the inter-scanner reproducibility of better than 1 HU is demonstrated in the current phantom study for the reference foam densities, but not yet achieved for a test density. The sources of error are being investigated in the next round of scanning with a certified Standard Reference Material for direct calibration.

Funding Support, Disclosures, and Conflict of Interest: Fain: research funding from GE Healthcare to develop pulmonary MRI techniques. Hoppel: employee of Toshiba Medical Research Institute USA/financial interest with GE Healthcare. M. Fuld: employee of Siemens Healthcare for medical device equipment and software. This project is supported partially by RSNA QIBA Concept Award (Fain), NIH/NIBIB, HHSN268201300071C (Y).

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