Evaluation of the quality of image for various breast composition and exposure conditions in digital mammography
Breast density has a close relationship with breast cancer risk. The exposure parameters must be appropriately chosen for
each breast. However, the optimal exposure conditions for digital mammography are uncertain in clinical. The exposure
parameters in digital mammography must be optimized with maximization of image quality and minimization of
radiation dose. We evaluated image quality under different exposure conditions to investigate the most advantageous
tube voltage. For different compressed breast phantom thicknesses and compositions, we measured the Wiener spectrum
(WS), noise-equivalent number of quanta (NEQ), and detective quantum efficiency (DQE). In this study, the
signal-to-noise ratios were derived from a perceived statistical decision theory model with the internal noise of eye-brain
system (SNRi), contrived and studied by Loo et al.1 and Ishida et al.2 These were calculated under a fixed average
glandular dose. The WS values were obtained with a fixed image contrast. For 4-cm-thick and 50% glandular breast
phantoms, the NEQ showed that high voltages gave a superior noise property of images, especially for thick breasts, but
the improvement in the NEQ by tube voltage was not so remarkable. On the other hand, the SNRi value with a Mo filter
was larger than that with a Rh filter. The SNRi increased when the tube voltage decreased. The result differed from those
of WS and NEQ. In this study, the SNRi depended on the contrast of signal. Accuracy should be high with an intense,
low-contrast object.