Pilot Study on the Digital Regulation for Bright/Dark Tone-difference of Radiograph using HA Phantom

Abstract

In dental radiographs, the effects of digital regulation on the conversion from the irregular tone of excessively bright or excessively dark to the standard tone was investigated with seven stages of hydroxyapatite phantom (HA phantom) made of 20 mL of polyvinyl silicone (PS) containing 15 g of hydroxyapatite crystal powder (HA) (HA 750 mg/PS mL).
Three kinds of HA phantom radiographs; standard (ST), excessively bright (EB), and excessively dark (ED) were used, and three images were made by scanning the radiographs of ST, EB and ED with a GT-500 scanner (SEIKO-EPSON) at 720 dpi. Also, two images that were regulated from EB and ED to the standard by digital regulation of TCD (tone curve dialogue) were prepared. A total of five scanned images were used to evaluate the accuracy of the digital regulation of TCD with gray scale values and hydroxyapatite contents (GSV/HA mg). The error range of the digital regulation compared with HA mg of theoretical value was narrow as follows; average -18.8 mg and standard deviation 30.5 mg in the regulated EB. Average -5 mg and standard deviation 61.5 mg in the regulated ED. From these findings, the digital regulation by TCD for irregular tones of dental radiographs is reliable for tracing the chronological change of the mineral content in alveolar bone.