Can a high-density dental material affect the automatic exposure compensation of digital radiographic images?

Abstract

Objectives: To investigate the influence of high-density dental material on the automatic exposure compensation of digital radiographic imaging systems. Methods: Two radiographic phantoms were custom made to reproduce radiographic densities of the dental tissues: enamel, dentin and pulp chamber. The phantoms were X-rayed using the Digora Toto, Digora Optime and VistaScan systems for 0.063, 0.1 and 0.16 s. Radiographic acquisitions were repeated in the presence of a high-density material equivalent to a titanium implant, in the small and large sizes. Mean grey values of the dental tissue-equivalent regions were obtained with the Image J software, averaged and compared between the absence and presence of the high-density material using ANOVA for multiple comparisons and Tukey's test (α = 0.05). Results: The presence of a high-density material significantly (p ≤ 0.05) decreased grey values of the dental tissue-equivalent images in the Digora Toto and VistaScan, regardless of the exposure time. For the Digora Optime, the high-density material decreased the pulp-equivalent grey values at all exposure times, the dentin-equivalent grey values significantly increased at exposure time of the 0.1 and 0.16 s, and the enamel-equivalent grey values significantly increased at the exposure time of 0.16 s (p ≤ 0.05). In general, the size of the high-density material did not affect the grey values significantly (p ≤ 0.05). conclusions: In general, the presence of a high-density dental material in digital radiographic systems influences the AEC by adjusting dental tissue-equivalent grey values.

Automatic exposure compensation and subjective image enhancement in the radiographic diagnosis of caries

“…Similarly, in another in-vitro study, AEC altered the dental tissue-equivalent gray values in the presence of a material equivalent to a titanium implant. 6 Nevertheless, the present study revealed that the AEC-related gray value variation of the radiographic image was not sufficient to affect the diagnostic accuracy of proximal carious lesions, which may be attributed to the simulation of a clinical condition with much more attenuating structures. The radiographic detection of proximal caries has been studied extensively in the literature; 1,10,11,12,13 however, the objectives addressed have focused mostly on the comparison between analogue and digital systems, 1,10,12,13 and the use of post-processing methods.…”

“…In addition, we believe that the location and amount of high-density material in the radiograph did not influence our results, because the action of the AEC seems to be based mainly on the highest and lowest pixel values of the image, and not on the quantity and location of these pixels. 3,6 Furthermore, because this was an ex-vivo study, it had the relevant limitation of lacking clinical signs (sensitivity and/or pain) in the diagnostic process. Conversely, the present methodology enabled greater control of the variables, standardization of the radiographic acquisitions and comparison of the diagnosis with a reference standard, factors that contributed toward obtaining sounder results.…”

“…3 Importantly, in addition to the energy factors that can be adjusted on the X-ray machine, such as exposure time, milliamperage and kilovoltage, the physical properties of the X-rayed object can also affect the amount of radiation reaching the image receptor. Recent in-vitro studies 2,6 have shown that the presence of high-density materials affect the gray values of digital radiographic images; furthermore, radiographic images of specific digital systems obtained at constant exposure factors tend to be much denser (darker) when the AEC is triggered by metallic materials. From a clinical perspective, dental practitioners should be aware that any factor affecting the final image quality must be tested to determine how well it has performed several different diagnostic tasks, before it can be used in the clinical routine, regardless of the manufacturer's claim that such a tool was developed to improve the diagnosis.…”

Automatic exposure compensation in intraoral digital radiography: effect on the gray values of dental tissues

“…Previous studies have shown that AEC can improve the accuracy of diagnosis of proximal caries in under- and overexposed images [ 4 ]. It was also stated previously that the effect of AEC is influenced by the presence of high-density objects [ 6 , 10 ].…”

“…In some systems, image enhancement is also performed automatically by the software, after image acquisition, but before it is displayed on the monitor, through an image pre-processing tool called Automatic Exposure Compensation (AEC) [ 4 – 6 ]. This tool increases image contrast, modifying pixel values non-linearly, producing high-contrast radiographs [ 7 , 8 ].…”