Christopher C. Scott BSC, Presenter: Research Grant, Teledyne Technologies Incorporated

Shiva Abbaszadeh, Abstract Co-Author: Research Grant, Teledyne Technologies Incorporated

Sina Ghanbarzadeh, Abstract Co-Author: Nothing to Disclose

Gary Allan PhD, Abstract Co-Author: Employee, Teledyne Technologies Incorporated

Michael Farrier, Abstract Co-Author: Contract, Teledyne Technologies Incorporated

Ian A. Cunningham PhD, Abstract Co-Author: Founder, DQE Instruments Inc

Karim S. Karim PhD, Abstract Co-Author: Research Grant, Teledyne Technologies Incorporated

We believe this detector stands as one of the highest spatial resolution x-ray detectors reported to date for diagnostic x-ray energies and shows promise for high DQE, low dose imaging.

The high inherent spatial resolution of amorphous selenium (a-Se) makes it naturally suited for modalities such as mammography, micro-angiography, and micro-CT where the feature sizes of significance are small. However, the resolution of commercial a-Se detectors is limited entirely by pixel size (e.g. 70-85 micron) and not by the fundamental material limit. The real challenge with smaller pixel sizes is lower signal-to-noise ratio where image quality is at risk of being limited by the noisy amorphous silicon backplane used in all commercially available a-Se detectors. We have developed a high resolution detector by integrating a-Se with a complementary metal-oxide-semiconductor (CMOS) backplane. CMOS technology allows for detector operation with much lower electronic noise, facilitating a reduction in pixel size to 25 micron for an increase in resolution without degradation of signal-to-noise performance.

To predict detector performance both the modulation transfer function (MTF) and detective quantum efficiency (DQE) were modeled. Images for the performance evaluation were captured using a tungsten x-ray source operated at 40 kV. The MTF was calculated from the measured edge-spread function. DQE is a work in progress, although estimates are made based on measured MTF and a predicted noise power spectrum.

The detector MTF was measured to be 0.93, 0.75, 0.57 and 0.41 at 5, 10, 15, and 20 lp/mm respectively. These values are consistent with our predictions and indicate very high resolution. Our 92 micron a-Se layer has non-optimal absorption efficiency for a 40 kV spectrum. However, the DQE modeled at 28 mR exposure is relatively high over a large frequency range with values of 0.50, 0.43 and 0.22 at 0, 10 and 20 lp/mm. When the model is evaluated for a scenario representative of standard mammography (30 kV Mo, 200 micron a-Se layer, 12 mR exposure) the DQE is 0.81, 0.65, and 0.33 at 0, 10 and 20 lp/mm. These results represent a significant improvement over current a-Se technology.

Scott, C, Abbaszadeh, S, Ghanbarzadeh, S, Allan, G, Farrier, M, Cunningham, I, Karim, K, Direct Conversion X-ray Imager with 25 Micron Pixel Resolution for Medical Imaging Applications.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14011696.html