Assessment of image quality in dental radiography, part 1 - Phantom validity

Objective. The purpose of this study was to describe and validate an image- quality phantom to be used in dental radiography for comparison of film and digitally acquired images. Study design. An aluminum block of 12 steps, with 7 holes in each step, was covered by acrylic blocks. This phantom was radiographed with Kodak Ultra- speed and Ektaspeed Plus films at 70, 65, and 60 kVp with the whole exposur e range available. All together, 50 dental films were randomly sequenced an d presented to 7 observers. The average number of perceptible holes from al l steps was plotted against exposure for each tube voltage and film type, g enerating a modified perceptibility curve. The tentative optimum exposure r evel was determined from perceptibility curves in each experimental conditi on and compared with that determined by means of the standard aluminum step -wedge and the preset time of the x-ray machine. The density range of this phantom at the optimum exposure was compared with that of clinical dental r adiographs. Validity of the phantom was evaluated according to the optimum exposure level from the modified perceptibility curves and the overall dens ity range. Finally, the average maximum numbers of perceptible holes at the tentative optimum exposure level were compared for each tube voltage and f ilm type. The statistical test used was a 2-way factorial analysis of varia nce. Results, The exposure at the perceptibility curve peak approximated that ob tained by means of the standard aluminum step-wedge and the time preset by the manufacturer. The overall density range at the perceptibility curve pea k covered the clinical density range for each tube voltage and film type. T here were no statistically significant differences between firm types or am ong tube voltages. Conclusions. The x-ray attenuation range for this phantom seemed to approxi mate clinical conditions. In addition, differences in image quality could b e quantitatively evaluated by means of the number of the holes seen in the phantom.