AbstractID: 9185 Title: Implementation of the Ideal Observer SNR for X-ray Technique Optimization in
CR Mammography
The ideal observer SNR model (SNRIO) was implemented in an experimental x-ray
technique optimization study for a CR mammography system. The x-ray tube had a Mo
anode and Mo and Rh filters. A peak potential range of 22-35 kVp was used. BR-12
phantoms with thickness 2-8 cm were imaged to simulate the x-ray attenuation and
scatter properties of a patient. The x-ray mAs was adjusted to provide an equal mean
glandular dose (MGD) for each phantom thickness, filter type, and kVp. The contrast
and scatter properties of the phantom were measured using Bucky and table-top imaging
techniques. The system glare was measured and removed from the x-ray scatter to
primary ratio measurements. The modulation transfer function included the effects of CR
system blur, focal spot magnification blur, and contrast reduction attributable to scatter.
The noise power spectrum included the effects of CR system noise and the quantum noise
of the primary and scattered x-rays. A frequency task function was derived assuming a
0.25 mm radius spherical lesion. For each imaging condition, the SNRIO was divided by
the MGD, and this value (SNRIO/MGD) was used as the figure of merit. The
SNRIO/MGD decreased by 10x from the 2 to 8 cm phantom. For each phantom
thickness, the SNRIO/MGD had a maximum value in the kVp range investigated.
Optimum kVp values ranged from 27 to 31 for the 2 - 8 cm phantoms. The SNRIO/MGD
improvement for the Bucky vs. table-top technique was 8 to 60 % for the 2-8 cm
phantoms.