Thesis subjects

Studying physics & astronomy or engineering physics? Please contact Matthieu Boone () if you're interested in a master thesis with us. The subjects below are indicative for the year 2018-2019. We encourage you to contact us for a personal conversation, in which we can discuss the possibilities and think of a subject best suited for you.

Thesis topics (part 1)

Thesis topics (part 2)

You can view the thesis topics in poster format: part 1 and part 2.

No thesis subject has an obligatory internship or mobility, but there are some possibilities for those that we can discuss, possibly in collaboration with our spin-off XRE.

Within the Radiation Physics group, we perform research on

  • Improvement of the micro/nano CT technique
  • Development of new types of CT scanners
  • Development of peripheral equipment for the CT scanners
  • Reconstruction algorithms
  • Phasecontrast imaging
  • 3D analysis of the scan results
  • Combination of CT with XRF to get chemical element information

More information on CT scanning

Application of phase retrieval in iterative reconstruction algorithms

Promotor: Matthieu Boone

Contact:

Number of students: 1

At very high resolutions, X-ray refraction or phase contrast becomes visible along with the traditional contrast due to X-ray attenuation. Although this effect yields a clear visual contrast (by edge-enhancement), it gives rise to unrealistic reconstructions of the 3D volume, which is highly undesirable in quantitative analysis. For highly coherent sources such as synchrotron sources and Inverse Compton Scattering sources such as the Smart*Light source, it is of high importance to correct for and even exploit this effect. However, the processing of the images and extraction of the refractive index is far from trivial, as the measured image is a mixed phase-and-amplitude image, containing both signals simultaneously.

The goal of this master thesis is to investigate the potential of iterative reconstruction algorithms for improving the reconstruction of both the phase and the amplitude signal. In these algorithms a simulation of the physical process of the image formation can be implemented to improve the quality of the reconstructed 3D volume. To achieve this, several approximate models are available, which can be used as initial input, or which can be combined. In order to be practically feasible in image reconstruction, the simulation of the effect needs to be sufficiently correct and fast. Apart from the reconstruction, this simulation approach can also be applied in an in-house developed framework for the simulation of CT scans.

Phase contrast image of a fly
Phase contrast image of a fly
Phase contrast image of a fly's leg
Phase contrast image of a fly's leg

Reconstruction and analysis of raw data frames in hyperspectral detectors

Promotor: Matthieu Boone

Contact:

Number of students: 1

In typical X-ray detector systems, the X-ray energy of all interacting photons is integrated, hence all spectral information is lost. The RP group has access to a novel energy-dispersive full-field detector, of which only a few systems exist worldwide. This detector records a series of 1000 2D images at different energies simultaneously, at an extraordinary energy resolution, allowing to retrieve chemical information from the dataset. To record this spectrum, single frames are acquired very rapidly (at 400Hz), in which single charge clusters generated in the sensor by a single X-ray photon are observed. These charge clusters are analyzed to reconstruct the location of incidence and total energy of the photon. As the creation of these charge clusters is a statistical process, they often overlap, deteriorating the reconstruction.

The goal of this master thesis is to improve the methods to analyze these charge clusters by image analysis and comparison to the simulation of the physical effects that result in these charge clusters. This could reduce the amount of rejected X-rays and reduce artefacts such as pulse pile-up in the measurements, generally improving this imaging modality.

This master thesis subject is in collaboration with Dr. Jan Aelterman of the Image Processing and Interpretation research group, who has experience with similar cluster analysis tasks.

A schematic example of two measured photons with overlapping or neighbouring charge clusters
A schematic example of two measured photons with overlapping or neighbouring charge clusters

A single radiographic hyperspectral image, which is in fact a 3D datacube with the X-ray energy as the 3th dimension
A single radiographic hyperspectral image, which is in fact a 3D datacube with the X-ray energy as the 3th dimension

 

Reconstruction and analysis of hyperspectral datasets

Promotor: Matthieu Boone

Contact:

Number of students: 1

Typically, in X-ray detectors, the X-ray intensity is integrated over all interacting energies. This eliminates all spectral information. The RP group has access to a detector allowing to distinguish between different energies of the interacting photons: an energy-dispersive full-field detector. This is one of the few systems of this type existing worldwide. It has a fantastic energy resolution, with 1000 energies being recorded simultaneously. This yields an immense amount of data, which needs special care to allow for using all information. The spectral information this data contains can be linked to chemical information of the sample.

The goal of this master thesis is to develop methods to exploit the spectral information contained in these datasets. To achieve this, methods from dynamic CT (3 spatial dimensions + time) can be adapted for hyperspectral CT (3 spatial dimensions + energy). These methods can be developed based on simulated data, but real datasets are available for real tests. Additional tests can also be performed during the course of this master thesis.

A single radiographic hyperspectral image, which is in fact a 3D datacube with the X-ray energy as the 3th dimension
A single radiographic hyperspectral image, which is in fact a 3D datacube with the X-ray energy as the 3th dimension
A rendering of an aortic arch in which gold nano-particles are visualized in subfigure c
A rendering of an aortic arch in which gold nano-particles are visualized in subfigure c

 

Analysis of the pitting effect in X-ray imaging

Promotor: Matthieu Boone

Contact:

Number of students: 1

In conventional X-ray tubes, the radiation is created by impinging high-energy electrons on a metal target. Apart from X-rays, a lot of heat is produced in this process, degrading the quality of the target surface. This process of melting the target material is called pitting, as (small) pits are created (see figure), which results in a degradation of the image quality.

The effect of the pitting on the images depends on a large number of factors. It is therefore impossible to virtually reproduce the effect. However, using Monte Carlo simulations of simplified geometries we want to investigate the variation in image quality observed in simulated images, and compare this to real images from both new experiments and the scanning archive.

Scanning Electron Microscope image of the target material in an X-ray tube when the pitting effect has taken its toll. Image courtesy of Felix Mattelaer (WE04).
Scanning Electron Microscope image of the target material in an X-ray tube when the pitting effect has taken its toll. Image courtesy of Felix Mattelaer (WE04).

Optimisation of Dual Energy Computed Tomography (DECT) acquisition parameters

Promotor: Matthieu Boone

Contact:

Number of students: 1

A reconstructed volume in CT usually contains a value in each voxel which represents the linear attenuation coefficient µ. This reconstructed attenuation coefficient is the product of the local mass attenuation coefficient µ/ ρ and the local density ρ of the material. Each element has its own unique energy dependent behaviour for its mass attenuation coefficient with respect to photon energy. This results in the fact that distinction between two elements can be made by using a tuneable monochromatic X-ray energy. However, in laboratory X-ray CT, where the X-ray sources produce polychromatic beams, two materials of different composition can have a very similar linear attenuation coefficient in a reconstructed volume.

In such cases dual-energy CT can offer a solution. The combination of CT scans at different X-ray energies can provide the necessary information to make a distinction between the materials. At UGCT, methods to extract this information are currently being developed and tested. However, these methods are dependent on the choice of the conditions in which both scans are acquired.

At UGCT a tool for optimising single energy scans has been developed. The aim of this master thesis is to expand this tool and develop a method to determine the optimal scanning conditions for both scans when performing a DECT.