Title

Exploration of in-vivo phase-contrast micro-computed tomography with a laser plasma-based x-ray source

Date of Award

2010

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Advisor(s)

Edward Lipson

Second Advisor

Andrzej Krol

Keywords

Phase contrast imaging, X-ray holography, Ultrafast lasers

Subject Categories

Physics

Abstract

X-ray micro-computed tomography (micro-CT) is used for in-vivo tumor imaging in small-animal models of human disease for the purpose of assessing the effectiveness of experimental drugs and/or treatments. We have been constructing, developing, as well as investigating the imaging performance experimentally, of an in-vivo , in-line holography, x-ray phase-contrast, cone-beam, micro-CT system with an ultrafast laser plasma-based x-ray source (ULX).

Projection images of various PMMA step wedge, silicon step wedge, and nylon fiber phantoms, obtained using ULX with Mo and Ta targets and a Be filter, were acquired in the Fresnel diffraction regime. Absorption contrast, phase contrast, and the edge enhancement index were estimated. Line profiles obtained for images of nylon fibers were compared to theoretical simulations. Projection images obtained using ULX exhibited strong diffraction fringes. We found phase contrast to exceed absorption contrast by a factor of three in step-wedge images.

Absorption CT projection sets of phantoms were acquired at various distances, using ULX with Mo target and Be filter. An ex-vivo tomosynthesis projection set (27 projections over 26° trajectory) of a mouse was acquired using ULX. A novel cone-beam CT alignment method using small attenuating spheres to determine the system geometry was implemented. Software was developed and applied for raw image pre-processing. Reconstructed images were compared to images obtained using a commercial micro-CT scanner. We established that our ULX micro-CT system is capable of phase-contrast projection imaging and CT projection set acquisition. However, laser and x-ray target chamber problems limited the quantity and quality of the images we obtained. Reconstructed images of the cylindrical phantom and ex-vivo mouse, acquired with ULX, are not yet superior to those acquired with a conventional micro-CT scanner.

In conclusion, we demonstrated that a ULX source can be applied to in-vivo micro-CT imaging and phase-contrast imaging provided that sufficient average power and temporal stability is achieved. Such a ULX source would allow obtaining information on the real part of the x-ray refracting index distribution in live small animals. Such information cannot be obtained by using a conventional micro-CT scanner.

Keywords: in-vivo micro-CT, x-ray phase-contrast imaging, in-line x-ray holography, ultrafast laser plasma-based x-ray source

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