Ionizing radiation from medical imaging now accounts for over 95% of all man-made radiation exposures and is the
single largest radiation source after natural background radiation. As a result, new techniques are under development for
reducing radiation exposure incurred in diagnostic radiography.
It was the purpose of this study to determine if a transmission X-ray tube and generator system in conjunction with a
flat-panel detector is capable of achieving diagnostic quality radiographic images at reduced radiation doses.
It was found that transmission tube technology, in combination with a flat-detector system, is capable of producing
radiographic images of sufficient quality for diagnostic medical imaging within certain parameters. It is postulated at this
time that when low mAs is required, as in imaging of neonatal and young pediatric patients, the transmission tube may
prove to be very effective in obtaining diagnostic images at reduced radiation dose.
We have designed and built a dual-energy x-ray absorptiometry (DXA) instrument for the measurement of bone density in-vivo using a high-purity germanium detector array. This system uses a fan beam geometry and a strip of 24 2 mm wide detectors to function as a scanned projection quantitative imaging system. The use of photon-counting detectors with a k-edge filtered x-ray spectrum avoids spectral overlap in the dual-energy data, and optimizes dose efficiency. The multielement detector is energy-sensitive and capable of high counting rates (106 counts per second per element). Dual-energy data is acquired in a single short exposure, enabling high-speed scanning. We have examined the temporal stability of the system, and developed strategies for controlling against thermally induced drift. Counting rate nonlinearity due to dead-time losses was modelled, and a correction for this phenomenon was implemented. We measured scattered radiation and investigated scatter removal schemes. The spatial resolution of the system was evaluated, and the entrance skin exposure to the patient was measured using thermoluminescent dosimeters (TLDs). A noise reduction algorithm was incorporated into the scanner which exploits the correlation of the pixel noise in the basis material images, derived from dual-energy data, to improve signal-to-noise without compromising edge sharpness or quantitative accuracy. This instrument shows promise as a research tool for the investigation on new scanning methodologies in bone-mineral densitometry.