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

Use of Digital Diagnostic Aids for Initial Caries Detection: A Review

The advance in digital diagnostic technologies has significantly facilitated the detection of dental caries. Despite the increase in clinically available digital diagnostic aids for dental caries, there is yet to be a comprehensive summary of all available technology. This review aims to provide an overview of digital diagnostic aids for the clinical detection of dental caries, particularly those at an initial stage. Currently available digital diagnostic aids for caries detection can be classified into four categories according to the initial source of energy, including radiation-based aids, light-based aids, ultrasound-based aids, and electric-based aids. Radiation-based aids use ionizing radiation, normally X-ray, to produce images of dental structures. Radiation-based aids encompass digital bitewing radiography and cone beam computed tomography. Light-based aids employ light or laser to induce signals for the detection of the changes in the carious dental hard tissue. Common light-based aids include digital transillumination and light/laser-induced fluorescence. Ultrasound-based aids detect the signal of ultrasound waves to assess the acoustic impedance of the carious teeth. The ultrasound caries detector is an available ultrasound-based aid. Electric-based aids assess the changes in the electric current conductance or impedance of the teeth with caries. Available electric-based aids include electrical conductance measurement and alternating current impedance spectroscopy. Except for these clinically available digital diagnostic aids, many digital diagnostic aids for caries detection are still under development with promising results in laboratory settings.

Automatic exposure compensation of digital radiographic technologies does not affect alveolar bone-level measurement

OBJECTIVE

To evaluate whether the automatic exposure compensation in the presence of high-density materials can affect the measurement of alveolar bone level.

METHODS

Thirty regions of seven dry skulls and six mandibles were radiographed with and without a high-density material, using two digital radiographic technologies: photostimulable phosphor plate (PSP, Digora Optime) and sensor (CMOS, Digora Toto), totaling 120 images. The distances from the cement-enamel junction to the alveolar bone crest were measured using cone-beam computed tomography (CBCT) images to represent the reference standard. The same measurements of alveolar bone level and the average of the pixel values of the image were evaluated on the radiographs. Paired t test compared the average pixel values and alveolar bone-level measurements between images with and without high-density material. One-way analysis of variance compared the difference between radiographic and CBCT measurements (α = 0.05).

RESULTS

The high-density material reduced the pixel values in PSP (p = 0.002) and CMOS (p < 0.001) technologies, demonstrating the AEC functioning in both technologies. There was no difference in bone-level measurements between the images without and with the high-density material for both technologies (p ≥ 0.091), or between the tomographic and radiographic measurements (p ≥ 0.319).

CONCLUSION

In the presence of high-density material, the automatic exposure compensation reduces the average pixel values of the images (i.e., images get darker), but does not influence the radiographic measurements of alveolar bone level.

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

Background

This study aimed to investigate the effect of automatic exposure compensation (AEC) of intraoral radiographic systems on the gray values of dental tissues in images acquired with or without high-density material in the exposed region using different exposure times and kilovoltages. The influence of the distance of the high-density material was also investigated.

Methods

Radiographs from the molar region of two mandibles were obtained using the RVG 6100 and the Express systems, operating at 60 and 70 kV and 0.06, 0.10, and 0.16 s. Subsequently, a titanium implant was inserted in the premolar’s socket and other images were acquired. Using the ImageJ software, two regions of interest were determined on the enamel, coronary dentine, root dentine, and pulp of the first and second molars to obtain their gray values.

Results

In the RVG 6100, the implant did not affect the gray values (p > 0.05); the increase in kV decreased it in all tissues (p < 0.05), and the exposure time affected only the root dentine and pulp. In the Express, only enamel and coronary dentine values changed (p < 0.05), decreasing with the implant presence and/or with the increase in exposure factors. The distance of the implant did not affect the results (p > 0.05).

Conclusions

AEC’s performance varies between the radiographic systems. Its effect on the gray values depends not only on the presence or absence of high-density material but also on the kV and exposure time used.

Radiographic diagnosis of proximal caries is not affected by exposure protocols and presence of high-density material on systems with automatic exposure compensation

OBJECTIVES

To investigate the performance of radiographic systems with automatic exposure compensation (AEC) on the caries diagnosis in images acquired with different exposure parameters and in the presence of high-density material. Also, the image quality was assessed.

METHODS

Forty posterior teeth (80 proximal surfaces) were radiographed using a phosphor plate and a CMOS system. Images were acquired with different exposure times (0.06, 0.10 and 0.16 s) and kilovoltages (60 and 70kVp), in the absence and presence of high-density material in the X-rayed region (control and high-density groups). Five radiologists assessed the caries using a 5-point scale. Diagnostic values were compared using two-way ANOVA.

RESULTS

For both radiographic systems, there were no significant differences in the area under the ROC curve (0.60-0.73), sensitivity (0.79-0.87) and specificity (0.29-0.48) between the control and high-density groups, exposure times or kilovoltages (p > 0.05). For image quality, scores assigned to the control and high-density groups were similar in each exposure protocol in both systems.

CONCLUSIONS

The presence of high-density material, exposure time and kilovoltage did not affect the caries diagnosis in any of the systems tested. It is recommended to use protocols with lower doses to reduce the patient's exposure.

Radiographic modalities for diagnosis of caries in a historical perspective: from film to machine-intelligence supported systems

Radiographic imaging for the diagnosis of caries lesions has been a supplement to clinical examination for approximately a century. Various methods, and particularly X-ray receptors, have been developed over the years, and computer systems have focused on aiding the dentist in the detection of lesions and in estimating lesion depth. The present historical review has sampled accuracy ex vivo studies and clinical studies on radiographic caries diagnosis that have compared two or more receptors for capturing the image. The epochs of film radiography, xeroradiography, digital intraoral radiography, panoramic radiography and other extraoral methods, TACT analysis, cone-beam CT and artificial intelligence systems aiding in decision-making are reviewed. The author of this review (43 years in academia) has been involved in caries research and contributed to the literature in all the mentioned epochs.