A Programmable Liquid Collimator for Both Coded Aperture Adaptive Imaging and Multiplexed Compton Scatter Tomography

Publication Year:
2012
Usage 3
Abstract Views 3
Repository URL:
https://scholar.afit.edu/etd/1026
Author(s):
FitzGerald, Jack G. M.
Tags:
adaptive imaging; Chancellor's Award; Nuclear Engineering
thesis / dissertation description
A novel, fully reconfigurable collimator device for gamma-ray and X-ray imaging was built and tested as a coded aperture. The device consisted of 10x10, 5x5x5 mm3 chambers. Each chamber either was filled with an attenuating liquid, stopping photons, or evacuated of the attenuating liquid, allowing the photons to pass through. As the pattern of on and off chambers was manipulated, different, semi-independent views of the gamma-ray source were found. Noise in reconstructed images decreased in all tests. Image reconstruction was performed with correlation methods and Maximum Likelihood Expectation Maximization (ML-EM). Using 10 mask patterns, the signal-to-noise ratio (SNR) in images of a Co-57 point source increased by a factor of 4.3 using correlation methods and by a factor of at least 50 using ML-EM. SNR in images of a Cd-109 source with high background increased by a factor of 3.0 using correlation methods and by a factor of 1.8 using ML-EM. Two extended sources were imaged, and the images improved when more masks were used. The Multiplexed Compton Scatter Tomography (MCST) forward problem using a PHDs Co high purity germanium (HPGe) detector was tested and evaluated. Potential applications are discussed in detail.