Photon-counting radiography with the gas microstrip detector.

We have built a proof of-concept photon-counting x-ray imaging system using a Xe:CH4 gas microstrip detector (GMD) as the image receptor, and have used this system to demonstrate several advantages of photon counting over energy integration. Our experiments spanned x-ray spectra from 10 to 50 kVp and Xe:CH4 pressures from 1 to 4 atm. When photon counting is done, the energy deposited in the detector by each incident photon can be measured on adjacent anode strips and a centroid calculation can be used to provide spatial resolution significantly better than the anode strip pitch. We measured > 11 lp mm(-1) at 13 kVp with our 200 microm pitch detector, and 8.2 lp mm(-1) at 50 kVp. The energy resolution of our GMD is 5.2% at 59.6 keV, and the space-charge limited counting rate is >2 x 10(6) mm(-2) s(-1) at 3 atm for a 30 kVp beam.