X-ray imaging using amorphous selenium: determination of x-ray sensitivity by pulse height spectroscopy.

There is a renewed interest in the application of photoconductors especially amorphous selenium (a-Se) to x-ray imaging. A new method for evaluating W +/-, the energy absorption necessary to release an electron-hole pair in a-Se is described. All previous methods used for the evaluation of the x-ray sensitivity of a-Se measure a change in surface potential on a charged plate due to irradiation by x rays. This results in a measurement of W +/- and other factors in combination. These factors include the energy absorbed from the spectrum of irradiating x rays and the a-Se layer capacitance. Such indirect methods are prone to error. A direct method for the evaluation of W +/-, which is based on the pulse height spectra resulting from the absorption of individual monoenergetic x-ray photons in a-Se, has been developed.

X-ray imaging using amorphous selenium: a photoinduced discharge readout method for digital mammography.

A new digital image readout method for electrostatic charge images on photoconductive plates is described. The method can be used to read out images on selenium plates similar to those used in xeromammography. The readout method, called the air-gap photoinduced discharge method (PID), discharges the latent image pixel by pixel and measures the charge. The PID readout method, like electrometer methods, is linear. However, the PID method permits much better resolution than scanning electrometers while maintaining quantum limited performance at high radiation exposure levels. Thus the air-gap PID method appears to be uniquely superior for high-resolution digital imaging tasks such as mammography.