Baba-Hamed, Tewfik; (1990) Application of dual energy techniques for tissue characterization in conventional diagnostic radiology. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The aim of this thesis has been to investigate the use of detectors suitable for single projection dual energy tissue characterization during a single exposure. The advantage of these systems is that the collection and analysis of data are in real time and their size permits their use in conventional fluoroscopic procedures. In the detectors developed in this work energy discrimination was based on two methods, beam filtration (split detector) and pulse height analysis (PHA). A narrow beam geometry computer model was used to select the optimum combination of detectors and x-ray tube energies for use in dual energy analysis. The thesis describes the construction and experimental evaluation of the optimised dual energy probes. They were used for tissue characterization and it was found that unique values of a particular dual energy coefficient exist up to Z=22 with a precision of 8% for the split detector method, and up to Z=29 with a precision of 3.5% for the semiconductor PHA method independently of patient and tissue thicknesses. The errors associated with the experimental measurements imposed a requirement on the tissue thickness of at least 1 mm for characterization. The effect of scattered radiation on the dual energy systems was studied theoretically using a Monte Carlo model. The coherent scatter was considered and recent data on molecular atomic form factors for liquid water was used. The results from both the Monte Carlo computer model and the experimental measurements showed that scatter affects the recorded dual energy signal. The dual energy probes were used for in vitro gallstone analysis. It was found that these probes were capable of differentiating between cholesterol and pigment stones, a significant factor in deciding upon the course of treatment for gallstone disease.

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