Effects of exposure reduction on the accuracy of an intraoral photostimulable-phosphor imaging system in detecting incipient proximal caries

Exposure time reduction of secondary radiographs used in digital subtraction radiography in detecting intrabony change

Objectives

Digital subtraction radiography (DSR) is a suitable technique for detecting incipient bone changes. However, in DSR, one or more follow-up radiographs must be taken. The aim of this study was to assess the possibility of reducing the exposure time for the radiographs that follow the initial one.

Methods

Maxillary premolar and molar radiographic images of a dry skull were taken with a digital radiography system. The initial radiographs, without bone chips, were taken at 0.32 and 0.16 s. Then, five bone chips (weight range 7–15 mg) were placed on the maxillary molar buccal side of the dry skull. Secondary radiographs were taken at 0.32-, 0.16-, 0.08-, 0.04-, and 0.02-s exposure times. For each bone chip, radiographs were taken three times. The secondary and initial images were subtracted to yield subtraction images. Four observers were asked to evaluate bone change visibility in the subtraction images. The Friedman test was used for statistical analysis.

Results

Significant differences were seen at each of the settings for the 0.32-s group (p = 1.24e−030) and 0.16-s group (p = 7.52e−009). By comparing the different groups, observer evaluations indicated that visibility changed when the secondary radiograph was taken at 1/8 of the exposure time of the initial radiograph. In both groups, the visibility of the 0.02-s subtraction image was significantly lower than that of the other subtraction images.

Conclusion

In DSR, the exposure time of the secondary radiograph can be reduced to 1/4 of the exposure time of the initial radiograph.

Comparison of digital systems and conventional dental film for the detection of approximal enamel caries

OBJECTIVES

The aims of this study were (1) to compare the accuracy of the detection of approximal enamel caries lesions using three intraoral storage phosphor plate digital systems and one conventional film-based radiographic system; and (2) to determine whether there is a correlation between the histological and radiographic measurements of enamel caries.

METHODS

160 approximal surfaces were radiographed under standardized conditions using three storage phosphor stimulable systems (DenOptix and Digora FMX with white and blue plates), and one film system (Insight film). 17 observers scored the images for the presence and depth of caries using a 4-point scale. The presence of caries was validated histologically (gold standard). Two-way analysis of variance was used to test the differences in sensitivity, specificity and overall accuracy (TP + TN). The data from the radiographic and histological measurements were statistically analysed by Spearman's rank correlation coefficient.

RESULTS

Two-way analysis of variance and the post hoc t-test demonstrated that Digora (white plate) had higher specificity and overall accuracy values than DenOptix (P = 0.021); there was no statistically significant difference among the other imaging modalities (P > 0.05). There was no significant correlation between the histological depth measurements and the radiographic measurements from Digora (blue plate) (P = 0.43), Digora (white plate) (P = 0.15), DenOptix (P = 0.17) and Insight film (P = 0.06).

CONCLUSIONS

The results suggest that (1) the performance of the three storage phosphor image plate systems was similar to that of the Insight film for detection of approximal enamel caries, and (2) the increase in histological depth of enamel caries was not significantly correlated with radiographic measurements.

A comparison of older and newer versions of intraoral digital radiography systems: diagnosing noncavitated proximal carious lesions

BACKGROUND

The authors conducted a study to compare the accuracy of an older and newer version of two intraoral digital systems in terms of radiographic detection of proximal carious lesions.

METHODS

Under in vitro and standardized conditions, the authors obtained radiographs of 160 noncavitated proximal surfaces using the Digora FMX (Soredex, Tuusula, Finland), the Digora Optime, the Schick CDR (Schick Technologies, Long Island City, N.Y.) and the Schick CDR Wireless (Schick Technologies) systems. Eight observers recorded proximal carious lesions on a five-point confidence scale. The presence of caries was validated histologically.

RESULTS

The new digital systems (Digora Optime and Schick CDR Wireless) had significantly higher sensitivities than their predecessors. The authors found no significant differences in specificity among the Digora FMX, Schick CDR and Schick CDR Wireless systems, all of which had a significantly higher specificity than did the Digora Optime system (P < .02). The positive predictive value for the Digora Optime system was affected by its high sensitivity and low specificity, and it was lower than that for the two CDR systems (P < .02).

CONCLUSIONS

Regarding overall accuracy, the difference between the older and newer versions of the photostimulable storage phosphor and complementary metal oxide semiconductor systems was not statistically significant. However, the authors found more false-positive diagnoses made with the Digora Optime system than with the Digora FMX system.

CLINICAL IMPLICATIONS

Though the difference in specificities was statistically significant, the authors question whether the difference between the Digora Optime and the other systems is clinically relevant. Therefore, dentists can purchase any of these systems after considering factors other than those evaluated in this study.

Assessment of enamel demineralization using conventional, digital, and digitized radiography

This experimental research aimed at evaluating the accuracy of enamel demineralization detection using conventional, digital, and digitized radiographs, as well as to compare radiographs and logarithmically contrast-enhanced subtraction images. Enamel subsurface demineralization was induced on one of the approximal surfaces of 49 sound third molars. Standardized radiographs of the teeth were taken prior to and after the demineralization phase with three digital systems - CygnusRay MPS®, DenOptix® and DIGORA® - and InSight® film. Three radiologists interpreted the pairs of conventional, digital, and digitized radiographs in two different occasions. Logarithmically contrast-enhanced subtraction images were examined by a fourth radiologist only once. Radiographic diagnosis was validated by cross-sectional microhardness profiling in the test areas of the approximal surfaces. Accuracy was estimated by Receiver Operating Characteristic (ROC) analysis. Chi-square test, at a significance level of 5%, was used to compare the areas under the ROC curves (Az) calculated for the different imaging modalities. Concerning the radiographs, the DenOptix® system (Az = 0.91) and conventional radiographs (Az = 0.90) presented the highest accuracy values compared with the other three radiographic modalities. However, logarithmically contrast-enhanced subtraction images (Az = 0.98) were significantly more accurate than conventional, digital, and digitized radiographs (p = 0.0000). It can be concluded that the DenOptix® system and conventional radiographs provide better performance for diagnosing enamel subsurface demineralization. Logarithmic subtraction significantly improves radiographic detection.

Accuracy of Digora system in detecting artificial peri-implant bone defects

This study was done to compare the diagnostic accuracy in detecting simulated intrabony defects around fixtures using Digora (DIG; Sordex Orion Corporation, Helsinki, Finland) compared with Ektaspeed Plus film (PLS; Eastman Kodak Co., Rochester, NY). Three titanium implant fixtures were placed in molar areas of three cadavers. Bone defects were created in the interproximal alveolar crest. Exposure time was adjusted to a PLS film and reduced to 1/5 only for DIG (1/5 DIG). The results of four observers were assessed. Sensitivity, specificity, accuracy, and under the receiver operator characteristic curve (ROC) area were evaluated. Statistical analyses were performed by using Friedman test and one-way ANOVA test. Mean sensitivity/specificity were 0.60/0.85 (DIG), 0.54/0.81 (1/5 DIG), and 0.64/0.58 (PLS). There were no statistically significant differences in the diagnostic accuracies. Digora had an equivalent performance to radiographic film in detecting intrabony defects adjacent to the implants, notwithstanding the amount of 1/5 of the exposure time.

Effect of noise on the compressibility and diagnostic accuracy for caries detection of digital bitewing radiographs

OBJECTIVES

To determine the effect of noise on the compressibility and the diagnostic accuracy for caries detection of digital bitewing radiographs.

METHODS

Bitewing radiographs of patients were obtained with a storage phosphor (Digora, Soredex, Helsinki, Finland) and compressed at different JPEG compression levels (2, 27, 53 and 128). A just noticeable difference study was performed to select a compression level to study the added noise effect. Gaussian noise was added at low, medium, and high levels to both the original and compressed images. Seven observers examined the selected approximal surfaces to identify the caries depth. ROC analysis was performed together with ANOVA at P = 0.05.

RESULTS

The compressibility of the images decreased as the noise level increased. ROC analysis revealed no significant difference between the original and compressed images within the same noise level (P > 0.06). With added noise compressed/decompressed images had a higher Az than the corresponding original images.

CONCLUSIONS

JPEG compression at level 27 can be used without a significant deterioration in diagnostic accuracy. Compression at this level seemed to reduce the effect of noise to some extent.

Intraoral radiographic storage phosphor image mean pixel values and signal-to-noise ratio: effects of calibration

OBJECTIVE

The DIGORA intraoral radiographic storage phosphor system needs to be calibrated before images are made. Calibration involves inputting of the maximum exposure to be used. This investigation studied the effects of different maximum exposure calibration settings on the mean pixel value for selected regions of interest and the signal-to-noise ratio for images of a test phantom.

STUDY DESIGN

A dental phantom containing a step wedge made of different thicknesses of homogeneously radiopaque bone-equivalent material was imaged at 70 kVp with exposures ranging from 12.8 to 105.2 microC.kg-1. Images were displayed through use of imaging software, and a region of interest was set for each bone-step. The mean pixel values and their standard deviations were measured.

RESULTS

Except for very low exposures (< 10% of the calibrated maximum), there was a linear relationship between exposure and the pixel values within the regions of interest irrespective of the calibrated maximum exposure. Low exposures resulted in underexposed low-contrast images. Low calibrated maximum exposures (< 54.5 microC.kg-1) resulted in low-density images with poor signal-to-noise ratios.

CONCLUSIONS

Because of the very wide image latitude of the DIGORA system, loss of image quality was not observed as a result of adjustments in the calibration setting over the range of exposure commonly used in dental practice. The highest accepted exposure was limited by prior calibration; hence, if diligence is applied, patient exposure can be minimized without detriment to image quality.

Observer agreement in the detection of proximal caries with direct digital intraoral radiography

OBJECTIVE

The aim of this study was to compare several values for consistency obtained by charged-coupled-device-based direct digital intraoral radiography with those obtained by conventional film-based radiography to evaluate observer agreement in determining the depth of proximal caries.

STUDY DESIGN

A total of 93 proximal surfaces on radiologic images that were obtained by both the conventional film-based bite-wing technique and by direct digital intraoral radiography were evaluated by six observers. One of these observers also evaluated the same images six months after the initial evaluation. The kappa value, consistency ratio, agreement ratio, and Kendall's correlation coefficient were calculated for interobserver and intraobserver agreement.

RESULTS

The overall kappa values for interobserver agreement were 0.439 and 0.424 in the direct digital system and the film-based radiography, respectively. The depth-related change of the values showed similar patterns in the two modalities for both interobserver and intraobserver agreement.

CONCLUSION

The digital intraoral system resulted in no deterioration in observer agreement, and it presents no problems for clinical use with respect to the reliability of diagnosis.

In vivo study of approximal caries depth on storage phosphor plate images compared with dental x-ray film

The aim of this in vivo study was to compare approximal caries depth on storage phosphor plate images to conventional film. A Soredex Digora imaging plate was placed in a film bite-wing positioner behind a Kodak Ektaspeed Plus film package without lead foil. The effect of scattered radiation on film without lead foil with a storage phosphor plate at the back was studied in a separate in vitro experiment. Compared with film protected by lead foil, the film showed higher density, but comparable contrast. For the in vivo study, clinical bite-wing exposures were made with the setup described above, with exposure settings for Ektaspeed Plus film. A four-point scale was chosen for approximal caries depth: 0 = no caries; 1 = caries in enamel; 2 = caries reaching dentino-enamel junction; 3 = caries into dentin. The bite-wing film images were shown to a panel of four experts. Sixty surfaces were selected for observer performance, based on identical scorings of the experts consensus classification. Next, six dentists evaluated both film and storage phosphor plate images with the same four point scale. Analysis of variance revealed a significant observer and image modality effect without an interaction effect. In conclusion, caries depth on storage phosphor plate images was underestimated compared with film-based images.

Efficacy of digital intra-oral radiography in clinical dentistry

OBJECTIVES

This article emphasizes the comparison of intra-oral digital imaging to film-based imaging. Additional possibilities of digital imaging that may contribute to system efficacy are discussed as well.

STUDY SELECTION

The main subjects for research in digital imaging are image quality, image acquisition, diagnostic quality, image manipulation, automated analysis, and application software.

DATA SOURCES

Representative articles on these subjects from the international literature are used for this review. Indirect digital imaging still requires film processing, sophisticated film digitizers, and time to digitize film. Although it is not an efficient method for the dental practice, digitization can be very useful for quantitative analysis of radiographs. Direct digital imaging is more efficient than indirect digital imaging. The main advantages are (semi) real time imaging, low X-ray dose requirements, and no need for chemical processing. In spite of a more limited resolution of the images, direct imaging may perform as accurately as film-based imaging. Direct image plate systems can well be used, for instance, for full-mouth series. The main application of direct sensor systems appears to be endodontology and implantology. In summary, direct digital imaging may be as efficient as film-based imaging in clinical dentistry. The computer provides for many additional options in digital imaging, such as the digital storage, compression, and exchange of radiographic information. Image manipulation (e.g. image enhancement, subtraction radiography and image reconstruction) and automated analysis may benefit radiodiagnosis.

CONCLUSION

It can be concluded that digital imaging certainly has great potential, especially with respect to improvement of diagnostic quality and automated image analysis.