Full Field Digital Mammography (FFDM) is increasingly replacing screen-film systems for screening and diagnosis of
breast abnormalities. All FFDM systems are equipped with an Automatic Exposure Control (AEC) which automatically
selects technique factors to optimize dose and image quality. It is therefore crucial that AEC performance is properly
adjusted and optimized to different breast thicknesses.
In this work, we studied the AEC performance of three widely used FFDM systems using the CDMAM and QUART
mam/digi phantoms. We used the CDMAM phantom to generate
Contrast-Detail (C-D) curves for each AEC mode available
in the FFDM systems under study for phantoms with equivalent X-Ray attenuation properties as 3.2 cm, 6 cm and
7.5 cm thick breasts. Generated C-D curves were compared with ideal C-D curves constructed using a metric referred
to as the k-factor which is the product of the thickness and the diameter of the smallest correctly identified disks in the
CDMAM phantom. Previous observer studies have indicated that
k-factor values of 60 to 80 μm2 are particularly useful
in demonstrating the threshold for object detectability for detectors used in digital mammography systems. The QUART
mam/digi phantom was used to calculate contrast-to-noise ratio (CNR) values at different phantom thicknesses. The results
of the C-D analysis and CNR measurements were used to determine limiting CNR values intended to provide a threshold
for proper image quality assessment.
The results of the Contrast-Detail analysis show that for two of the three evaluated FFDM systems, at higher phantom
thicknesses, low contrast signal detectability gets worse. This agrees with the results obtained with the QUART mam/digi
phantom, where CNR decreases below determined limiting CNR values.