X-ray Phase Contrast
X-rays can visualize much more than just the shadows of bones. A Talbot-Lau interferometer images absorption, phase, and small-angle scatter all in a single scanning protocol. Our group investigates the information recovery and enhancement from such interferometers together with Prof. Gisela Anton’s group at ECAP. Particular research topics are
- Setup design optimization
- Image-based acquisition correction
- X-ray dark-field tomography
Scientific Reports 2019: A 3-D Projection Model for X-ray Dark-field Imaging
X-ray dark-field is a function of the material, the relative orientation of the sample, the X-ray beam direction, and the direction of the interferometer sensitivity. This property is very interesting for tomographic reconstruction of structures below the imaging resolution. However, tomographic reconstruction itself is a substantial challenge. A key step of the reconstruction algorithm is the inversion of a forward projection model. In this work, we propose a very general 3-D projection model. We derive the projection model under the assumption that the observed scatter distribution has a Gaussian shape. We theoretically show the consistency of our model with existing, more constrained 2-D models.
IJCARS 2019: Simulation Study on X-ray Phase Contrast Imaging with Dual-Phase Gratings
Two phase gratings in an X-ray grating interferometers can solve several technical challenges for clinical use of X-ray phase contrast. In this work, we adapt and evaluate this setup design to clinical X-ray sources and detectors in a simulation study.
Medical Physics 2017: Talbot-Lau X-ray Phase Contrast for Tiling-based Acquisitions without Reference Scanning
Grating-based Talbot-Lau interferometers are a popular choice for phase-contrast X-ray acquisitions. Here, an air reference scan has to be acquired prior to an object scan. This particularly complicates acquisition of large objects: large objects are tiled into multiple scans due to the small field of view of current gratings. However, phase reference drifts occurring between these scans may require to repeatedly move the object in and out of the X-ray beam to update the reference information. We propose an image processing technique that completely removes the need for phase reference scans in tiled acquisitions. We estimate the reference from object scans using a tailored iterated robust regression, using a novel efficient optimizer.
SPIE Journal of Medical Imaging 2017: Improved Reconstruction of Phase-stepping Data for Talbot-Lau X-ray Imaging
The standard acquisition method for Talbot-Lau interferometers is phase stepping. In this paper, we review the implicit assumptions in phase stepping reconstruction. We find the assumptions of perfectly known grating positions and homoscedastic noise variance are violated in some scenarios. Additionally, we investigate a recently reported estimation bias in the visibility and dark-field signal. In order to adapt the phase stepping reconstruction to these findings, we propose three improvements to the reconstruction. These improvements are a) to use prior knowledge to compute more accurate grating positions to reduce Moire artifacts, b) to utilize noise variance information to reduce dark-field and phase noise in high visibility acquisitions, and c) to perform correction of an estimation bias in the interferometer visibility, leading to more quantitative dark-field imaging in acquisitions with a low signal to noise ratio.