Dr. Thomas Weber Profile

Dr. Thomas Weber

at Siemens Healthineers

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Publications (6)

Proceedings Article | 1 April 2024 Poster + Paper

Investigation of correction and decomposition algorithms in bedside x-ray imaging simulating a multi-layer flat panel detector

Jamin Schaefer, Stephen Liu, Steffen Kappler, Ferdinand Lueck, Ludwig Ritschl, Thomas Weber, Wojciech Zbijewski, Georg Rose

Proceedings Volume 12925, 1292536 (2024) https://doi.org/10.1117/12.3006758

KEYWORDS: Bone, Monte Carlo methods, Adipose tissue, Sensors, Detection and tracking algorithms, Computer simulations, Attenuation, X-ray imaging, Computed tomography, X-rays

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Proceedings Article | 18 October 2022 Open Access

Dual-energy cone-beam CT with three-material decomposition for bone marrow edema imaging

Stephen Liu, Magdalena Herbst, Thomas Weber, Sebastian Vogt, Ludwig Ritschl, Steffen Kappler, Jeffrey Siewerdsen, Wojciech Zbijewski

Proceedings Volume 12304, 123040Z (2022) https://doi.org/10.1117/12.2646391

KEYWORDS: Medical image reconstruction, Bone, X-ray computed tomography, Sensors, X-rays, Medical imaging, Aluminum, Physics, Photons, Signal attenuation, Monte Carlo methods

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Proceedings Article | 4 April 2022 Presentation + Paper

Feasibility of dual-energy cone-beam CT of bone marrow edema using dual-layer flat panel detectors

Stephen Liu, Chumin Zhao, Magdalena Herbst, Thomas Weber, Sebastian Vogt, Ludwig Ritschl, Steffen Kappler, Jeffrey Siewerdsen, Wojciech Zbijewski

Proceedings Volume 12031, 120311J (2022) https://doi.org/10.1117/12.2613211

KEYWORDS: Bone, Collimation, Sensors, Copper, X-ray computed tomography, Medical imaging, Error analysis, Spectral calibration, Physics, Monte Carlo methods

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Purpose: We investigated the feasibility of detection and quantification of bone marrow edema (BME) using dual-energy (DE) Cone-Beam CT (CBCT) with a dual-layer flat panel detector (FPD) and three-material decomposition. Methods: A realistic CBCT system simulator was applied to study the impact of detector quantization, scatter, and spectral calibration errors on the accuracy of fat-water-bone decompositions of dual-layer projections. The CBCT system featured 975 mm source-axis distance, 1,362 mm source-detector distance and a 430 × 430 mm² dual-layer FPD (top layer: 0.20 mm CsI:Tl, bottom layer: 0.55 mm CsI:Tl; a 1 mm Cu filter between the layers to improve spectral separation). Tube settings were 120 kV (+2 mm Al, +0.2 mm Cu) and 10 mAs per exposure. The digital phantom consisted of a 160 mm water cylinder with inserts containing mixtures of water (volume fraction ranging 0.18 to 0.46) - fat (0.5 to 0.7) - Ca (0.04 to 0.12); decreasing fractions of fat indicated increasing degrees of BME. A two-stage three-material DE decomposition was applied to DE CBCT projections: first, projection-domain decomposition (PDD) into fat-aluminum basis, followed by CBCT reconstruction of intermediate base images, followed by image-domain change of basis into fat, water and bone. Sensitivity to scatter was evaluated by i) adjusting source collimation (12 to 400 mm width) and ii) subtracting various fractions of the true scatter from the projections at 400 mm collimation. The impact of spectral calibration was studied by shifting the effective beam energy (± 2 keV) when creating the PDD lookup table. We further simulated a realistic BME imaging framework, where the scatter was estimated using a fast Monte Carlo (MC) simulation from a preliminary decomposition of the object; the object was a realistic wrist phantom with an 0.85 mL BME stimulus in the radius. Results: The decomposition is sensitive to scatter: approx. <20 mm collimation width or <10% error of scatter correction in a full field-of-view setting is needed to resolve BME. A mismatch in PDD decomposition calibration of ± 1 keV results in ~25% error in fat fraction estimates. In the wrist phantom study with MC scatter corrections, we were able to achieve ~0.79 mL true positive and ~0.06 mL false positive BME detection (compared to 0.85 mL true BME volume). Conclusions: Detection of BME using DE CBCT with dual-layer FPD is feasible, but requires scatter mitigation, accurate scatter estimation, and robust spectral calibration.

Proceedings Article | 15 February 2021 Presentation + Paper

Effects of x-ray scatter in quantitative dual-energy imaging using dual-layer flat panel detectors

Chumin Zhao, Stephen Liu, Wenying Wang, Magdalena Herbst, Thomas Weber, Sebastian Vogt, Ludwig Ritschl, Steffen Kappler, J. Webster Stayman, Jeffrey Siewerdsen, Wojciech Zbijewski

Proceedings Volume 11595, 115952A (2021) https://doi.org/10.1117/12.2581822

KEYWORDS: Sensors, X-rays, X-ray imaging, X-ray detectors, Dual energy imaging, Error analysis, Scintillators, Minerals, Copper, Cesium

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Purpose: We compare the effects of scatter on the accuracy of areal bone mineral density (BMD) measurements obtained using two flat-panel detector (FPD) dual-energy (DE) imaging configurations: a dual-kV acquisition and a dual-layer detector. Methods: Simulations of DE projection imaging were performed with realistic models of x-ray spectra, scatter, and detector response for dual-kV and dual-layer configurations. A digital body phantom with 4 cm Ca inserts in place of vertebrae (concentrations 50 - 400 mg/mL) was used. The dual-kV configuration involved an 80 kV low-energy (LE) and a 120 kV high-energy (HE) beam and a single-layer, 43x43 cm FPD with a 650 μm cesium iodide (CsI) scintillator. The dual-layer configuration involved a 120 kV beam and an FPD consisting of a 200 μm CsI layer (LE data), followed by a 1 mm Cu filter, and a 550 μm CsI layer (HE data). We investigated the effects of an anti-scatter grid (13:1 ratio) and scatter correction. For the correction, the sensitivity to scatter estimation error (varied ±10% of true scatter distribution) was evaluated. Areal BMD was estimated from projection-domain DE decomposition. Results: In the gridless dual-kV setup, the scatter-to-primary ratio (SPR) was similar for the LE and HE projections, whereas in the gridless dual layer setup, the SPR was ~26% higher in the LE channel (top CsI layer) than in the HE channel (bottom layer). Because of the resulting bias in LE measurements, the conventional projection-domain DE decomposition could not be directly applied to dual-layer data; this challenge persisted even in the presence of a grid. In contrast, DE decomposition of dual-kV data was possible both without and with the grid; the BMD error of the 400 mg/mL insert was -0.4 g/cm² without the grid and +0.3 g/cm² with the grid. The dual-layer FPD configuration required accurate scatter correction for DE decomposition: a -5% scatter estimation error resulted in -0.1 g/cm² BMD error for the 50 mg/mL insert and a -0.5 g/cm² BMD error for the 400 mg/mL with a grid, compared to <0.1 g/cm² for all inserts in a dual-kV setup with the same scatter estimation error. Conclusion: This comparative study of quantitative performance of dual-layer and dual-kV FPD-based DE imaging indicates the need for accurate scatter correction in the dual-layer setup due to increased susceptibility to scatter errors in the LE channel.

Proceedings Article | 15 February 2021 Presentation + Paper

Image-domain cardiac motion compensation in multidirectional digital chest tomosynthesis

Chumin Zhao, Magdalena Herbst, Thomas Weber, Sebastian Vogt, Ludwig Ritschl, Steffen Kappler, Jeffrey Siewerdsen, Wojciech Zbijewski

Proceedings Volume 11595, 1159525 (2021) https://doi.org/10.1117/12.2581287

KEYWORDS: Chest, Heart, X-rays, X-ray detectors, Sensors, X-ray computed tomography, Visualization, Robotics, Robotic systems

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Proceedings Article | 9 March 2018 Paper

Hairline fracture detection using Talbot-Lau x-ray imaging

C. Hauke, G. Anton, S. Auweter, P. Bartl, J. Freudenberger, K. Hellbach, M. Leghissa, F. Meinel, T. Mertelmeier, R. Nanke, M. Radicke, M. Reiser, L. Ritschl, S. Sellner, S. Sutter, T. Weber, J. Zeidler, T. Geith

Proceedings Volume 10573, 105734F (2018) https://doi.org/10.1117/12.2293504

KEYWORDS: X-ray imaging, X-rays, Bone, Interferometers, Radiography

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