Comparative investigation of subjective image quality of digital intraoral radiographs processed with 3 image-processing algorithms

Revisiting dynamic range and image enhancement ability of contemporary digital radiographic systems

OBJECTIVES

To assess the dynamic range and enhancement ability of radiographs acquired with contemporary digital systems.

METHODS

Five repeated periapical radiographs of human mandibles with an aluminium step-wedge were acquired using two sensor-based and three photostimulable phosphor plate-based systems and an X-ray unit at ten exposure times 0.020, 0.032, 0.063, 0.080, 0.100, 0.200, 0.320, 0.400, 0.500, and 0.630 s. All images had their brightness and contrast enhanced by two experienced oral and maxillofacial radiologists in consensus and were exported as both the original and enhanced file formats. Mean grey values were obtained from the aluminium steps and tabulated with their corresponding thicknesses for each exposure time, digital radiographic system, and file format. Images with saturated steps were excluded and the mean grey values from the remaining images were averaged to assess image brightness and the angular coefficient of the linear trendlines was generated from the relationship between mean grey values and their corresponding aluminium thicknesses to assess image contrast. Brightness and contrast values were compared using two-way ANOVA with post-hoc Tukey (α = 0.05).

RESULTS

Photostimulable phosphor plate-based digital radiographic systems had a broader dynamic range. Longer exposure times produced original images with lower brightness and variable contrast (p < 0.05). Subjective enhancement significantly increased or reduced brightness and/or contrast in some systems (p < 0.05).

CONCLUSIONS

Contemporary digital radiographic systems present different dynamic ranges and exposure-related brightness and contrast. Image enhancement may be a valuable tool at slightly suboptimal exposure times.

Postprocessing of all-zirconia restorations in digital dental radiographs: a quality assurance predicament

OBJECTIVES

The aim of this study was to describe a quality assurance issue, that is, the production of nondiagnostic high-contrast radiographs when imaging teeth restored with all-zirconia crowns on bitewing radiographs.

STUDY DESIGN

All-zirconia crowns were imaged with DIGORA Optime photostimulable phosphor (PSP) plates (Soredex/Orion Corp., Helsinki, Finland). To assess the differences in software processing, the PSP plates were scanned into third-party software as well as directly into the twain and native software provided by the manufacturer. Gamma correction, histogram stretch, and scanner resolution settings were adjusted. Vertical bitewings were acquired to increase anatomic coverage.

RESULTS

Scanning into third-party software or directly into the twain and native software did not improve contrast. Shifting the lower limit of the histogram stretch to 3 with a gamma correction of 2 resolved the problem. Neither scanner resolution setting nor vertical bitewings improved contrast.

CONCLUSIONS

The nondiagnostic high-contrast radiographs result from imaging software not effectively displaying the available gray scale. The software processing error appears to be initiated by the high-attenuation characteristics of zirconia. Consequently, radiographs with a high ratio of zirconia crown to normal anatomy are particularly susceptible.

Influence of VistaScan image enhancement filters on diagnosis of simulated periapical lesions on intraoral radiographs

OBJECTIVE:

To evaluate whether image enhancement filters of VistaScan system improve the diagnostic accuracy of simulated periapical lesions.

METHODS:

10 sockets were prepared on bovine ribs to fit a bovine tooth. Bone defects were created and successively enlarged providing four groups (n = 10): Group 0, absence of lesions; Group 1, periapical lesions with 1.6  mm in diameter; Group 2, with 1.8  mm in diameter; and Group 3, with 2.1  mm in diameter. Periapical radiographs were taken using a photostimulable storage phosphor plate and DBSWIN software. VistaScan filters were applied and the images were allocated into seven groups: Nonfiltered, Fine, Caries 1, Caries 2, Endodontic, Periodontal and Noise Reduction. All the 280 images were assessed about the presence or absence of periapical lesions. Pixel intensities standard deviation were compared between nonfiltered and filtered images. Two-Way Analysis of Variance and the post hoc Tukey's test were used to compare area under the ROC curve, sensitivity and specificity.

RESULTS:

VistaScan filters showed no significant difference for area under receiver operating characteristic curve (p = 0.124), sensitivity (p = 0.835) and specificity (p = 0.832). Area under receiver operating characteristic curve (p = 0.000) and sensitivity (p = 0.000) in 2.1  mm lesions size were significantly higher than in 1.6  mm and 1.8  mm lesions size. Pixel intensities standard deviation was significantly changed in the filtered images compared to nonfiltered ones (p < 0.01), except for Fine in the bone region (p > 0.05).

CONCLUSION:

VistaScan enhancement filters do not influence the diagnostic accuracy of simulated periapical lesions. On the other hand, larger lesions were more frequently detected. The filters change the pixel intensities reducing or intensifying the differences between similar regions.

Effect of digital noise reduction on the accuracy of endodontic file length determination

PURPOSE

The aim of the present study was to evaluate the measurement accuracy of endodontic file length on periapical digital radiography after application of noise reduction digital enhancement.

MATERIALS AND METHODS

Thirty-five human single-rooted permanent teeth with canals measuring 20-24 mm in length were selected. ISO #08 endodontic files were placed in the root canals of the teeth. The file lengths were measured with a digital caliper as the standard value. Standard periapical digital images were obtained using the Digora digital radiographic system and a dental X-ray unit. In order to produce the enhanced images, the noise reduction option was applied. Two blinded radiologists measured the file lengths on the original and enhanced images. The measurements were compared by repeated measures ANOVA and the Bonferroni test (α=0.05).

RESULTS

Both the original and enhanced digital images provided significantly longer measurements compared with the standard value (P<0.05). There were no significant differences between the measurement accuracy of the original and enhanced images (P>0.05).

CONCLUSION

Noise reduction digital enhancement did not influence the measurement accuracy of the length of the thin endodontic files on the digital periapical radiographs despite the fact that noise reduction could result in the elimination of fine details of the images.

Digital radiographic imaging: is the dental practice ready?

BACKGROUND

Digital radiographic imaging is slowly, but surely, replacing film-based imaging. It has many advantages over traditional imaging, but the technology also has some drawbacks. The author presents an overview of the types of digital image receptors available, image enhancement software and the range of costs for the new technology. PRACTICE IMPLICATIONS. The expenses associated with converting to digital radiographic imaging are considerable. The purpose of this article is to provide the clinician with an overview of digital radiographic imaging technology so that he or she can be an informed consumer when evaluating the numerous digital systems in the marketplace.

Marginal bone levels measured in film and digital radiographs corrected for attenuation and visual response: anin vivostudy

OBJECTIVE

To compare the accuracy and precision of measurements on marginal bone levels in differently processed digital radiographs and in film-based radiographs.

METHODS

Twenty-one patients with a diagnosis of chronic periodontitis were included in this study. Periapical radiographs were exposed with the Dixi digital intraoral radiographic system (Planmeca Oy, Helsinki, Finland) and the F-speed Film (Insight, Eastman-Kodak Co., Rochester, NY), respectively. Digital radiographs were subsequently processed into two sets: (a) correction for attenuation and visual response and (b) the same correction but with an additional shift in grey levels. Patients had periodontal surgery immediately after the radiographs were exposed. The vertical distance from cementoenamel junction to the most apical part of the marginal bone was assessed. The measurements were then employed as reference standard and subtracted by the vertical distance from radiographs accordingly. Altogether, 47 sites were evaluated. Seven observers were employed for evaluation under the same viewing conditions. ANOVA was employed for statistical analysis.

RESULTS

No significant differences were found between the absolute differences of the vertical distance obtained from radiographs to their corresponding reference standards when comparing differently processed digital radiographs, but the absolute differences were significantly smaller in digital radiographs than in films. Interobserver variances were not significant.

CONCLUSION

Digital radiographs have a favourable measurement accuracy compared with film radiographs when assessing marginal bone levels.

Subjective image quality of digitally filtered radiographs acquired by the Dürr Vistascan system compared with conventional radiographs

OBJECTIVES

To compare the different digital filters implemented in the Dürr Vistascan system with conventional film and to analyze the filter specificity to anatomic structures.

STUDY DESIGN

Ten panoramic image pairs and 10 periapical image pairs (1 digital and 1 conventional) were obtained from 20 patients conventionally and digitally. The display quality of different anatomic image structures was rated subjectively on a 5-point scale. The responses were evaluated using ANOVA and Tukey-Kramer post hoc tests. The intraobserver reliability was evaluated by Cohen's kappa statistics.

RESULTS

The display quality of anatomic structures was rated higher by using Caries 1 or 2 filters for periapical and Periodontal 1 or 2 filters for panoramic images, whereas nonfiltered and Noise Reduction-filtered images received the lowest scorings compared to all other digital image modalities (P < or = .0097). The superiority of conventional radiographs to the digital ones was statistically significant (P < or = .0039 and P < or = .0152 respectively).

CONCLUSIONS

Depending on the diagnostic task, digital images of the Vistascan system should be filtered before examination. Perfect conventional radiographs still remain the gold standard for image quality.

Sliding window adaptive histogram equalization of intraoral radiographs: effect on image quality

OBJECTIVES

To investigate whether contrast enhancement by non-interactive, sliding window adaptive histogram equalization (SWAHE) can enhance the image quality of intraoral radiographs in the dental clinic.

METHODS

Three dentists read 22 periapical and 12 bitewing storage phosphor (SP) radiographs. For the periapical readings they graded the quality of the examination with regard to visually locating the root apex. For the bitewing readings they registered all occurrences of approximal caries on a confidence scale. Each reading was first done on an unprocessed radiograph ("single-view"), and then re-done with the image processed with SWAHE displayed beside the unprocessed version ("twin-view"). The processing parameters for SWAHE were the same for all the images.

RESULTS

For the periapical examinations, twin-view was judged to raise the image quality for 52% of those cases where the single-view quality was below the maximum. For the bitewing radiographs, there was a change of caries classification (both positive and negative) with twin-view in 19% of the cases, but with only a 3% net increase in the total number of caries registrations. For both examinations interobserver variance was unaffected.

CONCLUSIONS

Non-interactive SWAHE applied to dental SP radiographs produces a supplemental contrast enhanced image which in twin-view reading improves the image quality of periapical examinations. SWAHE also affects caries diagnosis of bitewing images, and further study using a gold standard is warranted.