SENSITOMETRIC RESPONSE OF THE SENS-A-RAY, A CHARGE-COUPLED IMAGING DEVICE, TO CHANGES IN-BEAM ENERGY

Objectives. To evaluate image density (pixel values) and image contras t due to variations in beam energy (kVp) for the Sens-A-Ray intra-oral radiographic sensor. Method. Images of an aluminium step wedge were m ade at 50, 70 and 90 kVp. Mean pixel values (with standard deviations) for representative attenuator thicknesses were measured using region- of-interest histogram analysis. Corresponding entrance doses were meas ured using a beryllium-windowed ionization chamber. Results. The steep est response slopes were found with the lowest kVp settings; hence the CCD results mimic the behaviour of standard radiographic film, with t he high contrast being found with low kVp. The entrance dose resulting in pixel saturation was less with low kVp than high kVp. It is sugges ted that this is due to the CCD receptor being most sensitive to X-ray photons of relatively low keV. Conclusion. While the kVp needs to be selected in relation to both tissue and receptor characteristics, it i s possible to use low kVp techniques with the Sens-A-Ray without incre asing the entrance dosage.