Radiation response of amorphous silicon imaging arrays at diagnostic energies

The first diagnostic X-ray signal measurements for two-dimensional amorphous silicon imaging arrays are presented. Data were acquired for a variety of phosphor screens, for energies ranging from 70 to 120 kVp, both in the presence and in the absence of a phantom simulating the attenuation of a human chest. Results are reported in terms of pixel charge per unit exposure at the array. Also, linearity of pixel response with exposure as a function of sensor bias, pixel response as a function of sensor bias, and the first data quantifying the degree of reciprocity of the pixel response are reported. Significant results include: (a) pixel response remained linear to within 1% for ~70% of the signal range at 0.5 volts and ~95% at 3.0 volts; (b) from a partial response at 0 volts, pixel response is observed to increase rapidly up to ~1 volt after which more gradual increases in response are observed; and (c) for exposure rates varying by a factor of ~5, pixel response was approximately consistent with reciprocal behavior although evidence of limited (~6%) reciprocity failure is suggested