ABSOLUTE MEASURES OF IMAGE QUALITY FOR THE SENS-A-RAY DIRECT DIGITAL INTRAORAL RADIOGRAPHY SYSTEM

To study the noise characteristics of the Sens-A-Ray (Regam Medical Sy stems AB, Sundsvall, Sweden) system, 20 radiographs were obtained at e ach of three different exposure levels at 70 and 90 kVp with a homogen eous x-ray field. Exposures were measured with an ionization chamber. Noise power spectra were calculated over three areas within each radio graph, and ensemble averages were subsequently found from 60 data file s at each exposure level. Noise equivalent quanta were calculated with the noise power spectra acid modulation transfer function data from p revious studies. Finally, the detective quantum efficiency was calcula ted by dividing the noise equivalent quanta by The estimated incident photon fluence at the different exposures. The system has a maximum de tective quantum efficiency of approximately 0.030 at 70 kVp and 0.025 at 90 kVp. A broad maximum exists at approximately 2 cycles/mm, indica ting that the signal-to-noise ratio is most favorable at this spatial frequency.