Affiliations: Center for Bioengineering and School of Electrical
Engineering, University of Oklahoma, Norman, OK 73019, USA | Department of Physics and Engineering, University of
Central Oklahoma, Edmond, OK 73034, USA | Department of Physics and Astronomy, University of
Oklahoma, Norman, OK 73019, USA
Note: [] Current address: Hangyi Jiang, Department of Radiology, Johns
Hopkins University, Baltimore, Maryland, USA
Note: [] Corresponding author: Hong Liu, PhD, Professor and Smith Chair,
School of Electrical Engineering, University of Oklahoma, Norman, OK 73019,
USA. Tel.: +1 405 325 4286; E-mail: liu@ou.edu
Abstract: Full-field digital mammography imaging systems have been
investigated extensively. However, most investigations focus on the quality
assessment of the entire image. In this article, we present the results of
experimental measurements on the position-dependent image characteristics of a
CCD array-based digital imaging system. Objective image quality parameters such
as noise power spectrum (NPS) and signal-to-noise ratio (SNR), which are also
frequency-dependent, are employed for this investigation. The image detector
uses 12 CCDs arranged in a 4 × 3 array to cover a field
of 18 cm × 24 cm with a single x-ray
exposure. Totally 18 sub-areas were chosen as the regions-of-interest (ROIs)
for each full-field image to study position-dependent characteristics. Our
experimental results indicate that the image quality at different positions of
the full-field image exhibit slightly variance due to the characteristic
diversity of the CCDs and due to the oblique angle of the ROIs to the
x-ray source. The image seams caused by the physical gaps
between adjacent CCDs do not increase the noise components significantly to the
composite full-field image. The x-ray energy-dependence of
NPS and SNR was also studied.
Keywords: noise power spectra, modulation transfer function, image quality, digital radiography, full-field mammography systems, signal-to-noise ratio
