Digital mammographic imaging using microlens focusing: estimation of light collection and x-ray utilization

Routine mammographic screening has proven to be the only reliable diagnostic method for early detection of breast cancers. The introduction of digital mammographic imaging to clinical practice should provide significant improvement in image quality and lead to better detection sensitivity. One limitation of some recently developed indirect digital imagers is a small fill factor in the photodetector. A small fill factor reduces the amount of light collected from individual x-ray interactions in the screen and can lead to an overall reduction in the number of x-ray quanta detected. At the SPIE meeting last year, we suggested using a focused microlens array between the florescent screen and photodetector as a method for improving x-ray utilization in indirect digital mammographic imaging systems. This year we have conducted a Monte Carlo simulation of a uniform field x-ray source and a digital imager. We have used this simulation tool to compare the proposed imager, which employed microlens focusing, with more standard imager configurations. The evaluation included light collection efficiency and x-ray utilization performance measure. The results indicate that including microlens focusing between the scintillation screen and the photodetector can improve light collection and increase the number of x-ray quanta detected.