Affiliations: Department of Radiology, Emory University School of
Medicine, Atlanta, GA 30322, USA
Note: [] Corresponding author: Andrew Karellas, Ph.D., Professor of
Radiology, Director, Medical Physics, Emory University School of Medicine, 1364
Clifton Road NE, Atlanta, GA 30322, USA. Tel.: +1 404 712 2411; Fax: +1 404 712
5813; E-mail: akarell@emory.edu
Abstract: Spatially coherent fiberoptic plates are important components of
some charge-coupled device (CCD)-based x-ray imaging systems. These plates
efficiently transmit scintillations from the phosphor, and also filter out
x-rays not absorbed by the phosphor, thus protecting the CCD from direct x-ray
interaction. The thickness of the fiberoptic plate and the CCD package present
a significant challenge in the design of a digital x-ray cassette capable of
insertion into the existing film-screen cassette holders of digital mammography
systems. This study was performed with an aim to optimize fiberoptic plate
thickness. Attenuation measurements were performed on nine fiberoptic plates
varying in material composition that exhibit desirable optical characteristics
such as good coupling efficiency. Mammographic spectra from a clinical
mammographic system and an Americium-241 (Am-241) source (59.54 KeV) were used.
The spectra were recorded with a high-resolution cadmium zinc telluride
(CZT)-based spectrometer and corrected for dead time and pile-up. The linear
attenuation coefficients varied by a factor of 3 in the set of tested
fiberoptic plates at both mammographic energies and 59.54 keV. Our results
suggest that a 3-mm thick high-absorption plate might provide adequate for
shielding at mammographic energies. A thickness of 2-mm is feasible for
mammographic applications with further optimization of the fiberoptic plate
composition by incorporating non-scintillating, high-atomic number material.
This would allow more space for cooling components of the cassette and for a
more compact device, which is critical for clinical implementation of the
technology.
