Per-pixel Bone Attenuation Contribution Map Generation using Machine Learning for Chest Radiographs
Author Block: T. Dorosti, L. Kaster, M. Lochschmidt, J. B. Thalhammer, S. Peterhansl, F. Schaff, F. Pfeiffer, D. Pfeiffer; Munich/DE
Purpose: We aim to generate attenuation contribution masks for bone structures present in real and synthetic frontal chest radiographs (CXR) on a pixel level using machine learning. Such bone attenuation contribution (BAC) maps will allow for a personalized, per-pixel correction of beam hardening artifacts in novel imaging modalities such as X-ray dark-field (DF) imaging.
Methods or Background: A total of 5959 chest CT scans were retrieved from two publicly available datasets of the Luna16 (n=656) and the RSNA PE challenge (n=5303). Additionally, CXRs from 72 subjects (33 healthy: 20 men, mean age[range]=62.4[34, 80]; 39 with COPD: 25 men, mean age[range]=69.0[47, 91]) were retrospectively selected (10.2018-12.2019) from our in-house dataset. All CT scans and their corresponding 3D binary bone segmentations were forward projected using a simulated X-ray spectrum to generate synthetic CXRs and relative bone thickness projections referred to as BAC maps, respectively. A U-Net model was trained and tested on synthetic radiographs from the public datasets. Model performance was assessed quantitatively for the public synthetic data with the mean absolute percentage error (MAPE), Pearson correlation, and two-sided Student t distribution. For the real in-house CXRs, data was assessed qualitatively, as no reference BAC data is available for real radiographs.
Results or Findings: The predicted BAC maps showed low error rates and strong correlations with the reference. Specifically, for the Luna16 test set (n=131), an MAPE=18.1% and a correlation of 0.81 (P<0.001) were achieved. For the RSNA PE test data (n=1060), an MAPE=12.5% and a correlation of 0.91 (P<0.001) were obtained.
Conclusion: The U-Net successfully generated per-pixel BAC maps for synthetic and real CXRs, demonstrating potential for applications in DF image processing.
Limitations: The sample of real radiographs was restricted to healthy and COPD subjects from a single medical center.
Funding for this study: We acknowledge financial support through the European Research Council (ERC Synergy Grant SmartX, SyG 101167328), and the Free State of Bavaria under the Excellence Strategy of the Federal Government and the States, as well as by the Technical University of Munich – Institute for Advanced Study.
Has your study been approved by an ethics committee? Yes
Ethics committee - additional information: All data was analyzed retrospectively and anonymously. The study was approved by the ethical review committee and was conducted in accordance with the regulations of our institution (approval code: 87/18 S, Institutional Review Board of the Faculty of Medicine,
Technical University of Munich, Germany).