Exposure Comparison – D7 Film versus Digital Radiography (DR)
The aim of this project is to examine the saturation level of Vidisco DDA panels (in this case the RayzorX/RayzorXPro, which is representative of all Vidisco flat panels) to dose in comparison to D7 film, when using various thicknesses of steel (Fe).
Every effort was made to ensure that the parameters of comparison were identical. The Vidisco set up included the use of the Eresco 200 MFR 3.1 X-ray source. It is probable that any other CP source will produce similar or identical results.
In this test, no comparison was made between DR and D7 film from the aspect of Signal-to-Noise Ratio (SNR)
The Source Detector Distance (SDD) in Vidisco’s test was 70cm (700mm), which is identical to the declared SFD in the film testing. In its tests, General Electric noted that fast Film D7 was used and the density level was 2. A density reading of 2.0 is the result of only one percent of the incident light making it through the film.
Vidisco introduced a parallel parameter in DR: The saturation level was set at 99%. In terms of Grey Levels in relationship to the panel, this corresponds to 16,220 Grey Levels, while the panel itself has a capacity of 16,384 Grey Levels or 14 bit. Thus Vidisco ensured that the parameters used in its testing were indeed the same as those set in the General Electric film testing.
The criteria being tested were the relative dose and penetration when using different energy levels. To achieve this data, Vidisco used various energy levels, starting at 80 kV up to 200 kV, at 20 kV intervals.
Two stainless steel step wedges were used for the tests. Each of them started from 1/8 of an inch up to one inch. In order to achieve 1 1/8 of an inch up to 2 inch thickness, the first one-inch step wedge was placed on top of the other, thus adding up to 2 inches. Lead masking was applied around the step wedges in order to increase the contrast by preventing blooming.
The tests indicated that the Grey Level received with the Vidisco DR systems for a given energy is 30 -60 times higher than in film. Or, in other words, the exposure time needed to achieve 99% saturation is 30 -60 times shorter when using DR than with film D7.
The Amount of Dose Required to Reach D=2 in Film and to 99% Saturation in DR for Various Steel Thicknesses, 5-30mm, and Various Energies 80-200kV
The Steel thickness that Can be Penetrated (D=2 in Film, 99% Saturation in DR) When Using One Dose (mA X min.) with Various Energies (80-200kV)