In-line Phase-contrast Tomography using Betatron X-rays Produced by a Laser-Plasma Accelerator

University essay from Lunds universitet/Atomfysik; Lunds universitet/Fysiska institutionen

Abstract: X-ray phase-contrast imaging is a powerful technique that allows great resolving power for low absorbing samples, such as biological tissue. This method relies on measuring the phase shift induced by the sample instead of the absorption traditional radiography relies on. This phase shift is measured as an intensity modulation at the detector and by using various algorithms one can obtain information about the sample. This technique can be combined with standard tomography to get a full 3 dimensional reconstruction of the sample. Phase-contrast imaging requires a large transversal coherence, requiring a very small x-ray source size, limiting the choice of source to either microfocus x-ray tubes or a synchrotron facility. Microfocus x-ray tubes have very small source sizes but very limited flux, resulting in long exposure times while the beam time at a synchrotron facility is very expensive and limited. Laser based plasma acceleration could prove to be an alternative source for this purpose and this thesis dwells on this possibility, the source size is very small and the brilliance can be compared with that of a synchrotron. The generated x-ray pulses are also very short, on the femtosecond scale, reducing the exposure time needed for a well resolved image, resulting in faster data acquisition and holds promise for time resolved imaging. During the work presented in this thesis a source size measurement was conducted, showing a source size less than 2.5 microns, well suited for phase-contrast imaging. Experiments were carried out using low-absorbing samples such as mylar wires and a few different biological samples in the form of insects. The acquired phase-contrast images were used to calculate the projected thickness and by doing a tomography scan a full 3D reconstruction was created. In conclusion, this thesis shows laser based plasma accelerators to be a good source for phase-contrast imaging in low absorbing materials. Further, it proved to be able to resolve very small details, on the order of tens of microns and could possibly be improved further.

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