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Title: Quantitative contrast enhanced mammography and evaluation of scientific CMOS active pixels sensors for medical imaging
Author: Arvanitis, Costas D.
ISNI:       0000 0004 2670 3193
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2008
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Quantitative contrast enhanced mammography based on a dual energy approach aims to extract quantitative and temporal information of the tumour enhancement after administration of vascular contrast media. This information can be used to indirectly measure the tumour microvessel density and the blood flow of abnormally "leaky" breast tumours. A theoretical framework and optimisation of critical parameters essential for the development of quantitative contrast enhanced mammography is presented here. Using the dual energy approach, measurement of iodine projected thickness can be performed. Temporal variations in the measured thickness can be effectively used to measure the kinetics of the contrast medium using an experimental phantom. For the extraction of the temporal information a limited number of low dose images ( 0.2 mGy) are required in order to keep the patient dose at the same levels as conventional mammography. At the exposure levels currently available, active matrix flat panel imagers (AMFPIs) are limited. A novel active pixel flat panel imager (APFPIs) based on scientific complementary metal oxide semiconductor (CMOS) active pixel sensor (APS) can potentially realise a high performance detector that suits this application. A thorough description of the electro-optical performance of two CMOS APS and the signal and noise properties of these imagers is also presented in this study. The signal and noise properties of the X-ray imagers has been quantified in the mammographic energy range using the modulation transfer function (MTF), the noise power spectra (NPS) and the detective quantum efficiency (DQE). The resulting X-ray imagers offer high sensitivity, low noise, and comparable resolution (MTF=0.1 at 9.5 cycles/mm) with respect to other digital mammographic units. The combined outcome of the above performance resulted in a quantum limited detector at 0.23 uC/kg detector entrance exposure with DQE, at zero frequency equal to 0.5 (DQE (0)=0.50). The development of quantitative contrast enhanced mammography has been experimentally evaluated here, using a currently available amorphous silicon based active matrix flat panel imager (AMFPIs), which was used as a reference detector, and the active pixel flat panel imager (APFPIs) based on CMOS technology, which had the best performance from those evaluated. The quantitative contrast enhanced mammography has been optimised using analytical simulations. The results suggest that active pixel flat panel imagers can be used for the development of quantitative contrast enhanced mammography, although higher pixel sizes and elimination of fixed pattern noise appeared to be very important for the accurate measurement of the projected thickness. The presence of scattered radiation is the only factor that degrades the measurement of the iodine projected thickness and should be removed effectively before any analysis of the energy pair images.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available