Influence of room lighting on grey-scale perception with a CRT-and a TFT monitor display

Grey value contrast sensitivity of dental practitioners in function of luminance and age

OBJECTIVES

Grey value perception is important in viewing and interpreting X-ray images. It is possible that ageing decreases the number of gray values that a person can distinguish. This hypothesis was tested in a group of dental practitioners from students to experienced dentists using a 12-bit grey scale.

METHODS AND MATERIALS

A custom-made computer software was used based on the principle of the "just noticeable difference" (JND). Observers were shown a picture of an outer square with increasing grey value in which a smaller square of different grey value popped up in changing positions. As soon as the observers could see the difference, they clicked the inner square. The grey values were shown with a 12-bit depth in batches of 400 grey value steps. 59 dentists of 3 age groups (20-24, 25-45 and 46-70 years) participated in the study. A subgroup of 20 practitioners performed a validation test with test-retest and test in reversed grey value sequence (white to black). JND was calculated and plotted against grey value using a third-order polynomial function. These curves were compared statistically.

RESULTS

Test-retest, also in reversed order did not yield different curves (p values between 0.79 and 0.97). Curves between different age groups showed significant differences, with older practitioners needing more contrast to accomplish the task. Contrast sensitivity showed an optimum in the darker third of the grey scale (values around 1200).

CONCLUSION

Age and grey value played a significant role in grey value perception by dental practitioners.

Comparison of occlusal caries detection using the ICDAS criteria on extracted teeth or their photographs

BACKGROUND

Using photographs of occlusal surfaces instead of extracted teeth for the detection of caries can be useful in multicenter studies or education. Using a panel of observers, ICDAS scores on teeth or photographs were evaluated against the histological gold standard. The hypothesis was that both outcomes were equivalent.

METHODS

Four examiners with different experience in ICDAS scored photographs of occlusal surfaces of 100 extracted teeth on a monitor using ICDAS criteria. Two of the examiners had previously scored extracted teeth prior to photography. Digital images of histological sections of the teeth were observed by all examiners and consensus scores were given for each investigation site (gold standard). Kappa statistics and Spearman correlation coefficients as well as repeated measure ANOVA were performed. ROC curves were constructed for each examiner and the areas under the ROC-curves (AUC) of both scoring techniques (extracted teeth, digital images) were compared (α = 0.05).

RESULTS

Intra- and inter-rater kappa for ICDAS on teeth were 0.81-0.94 and on photographs 0.54-0.88, respectively. Correlation with histology was 0.58- 0.61 for the teeth and 0.50-0.62 for the photographs. AUC of ICDAS scores of extracted teeth (mean 0.89) were slightly higher than those for photographs (mean 0.84). However, both AUC values were not statistically significant (p = 0.38).

CONCLUSION

Using photographs to assess occlusal surfaces with the ICDAS criteria was not statistically different from scoring the extracted teeth.

A Subjective Assessment of Perceived Clarity of Indirect Digital Images and Processed Digital Images with Conventional Intra-oral Periapical Radiographs

OBJECTIVES

To compare and analyze the perceived clarity and diagnostic value of Conventional periapical Radiographs (CRs) with those of their Digitized Periapical Images (DIs) and Processed Digitized Periapical Images (PDIs) counterparts.

MATERIAL AND METHODS

Forty two intraoral periapical radiographs of patients with clinically suspected periapical pathosis were made to constitute the group of CRs. These were photographed by using a Canon Power Shot SD500 (7.1 Megapixel) digital camera and the unaltered images were transferred to a computer laptop, to form the group of DIs. Subsequently, the contrast and brightness of these images were modified to represent the group of PDIs. Two experienced oral radiologists independently evaluated 5 specific apical and periapical region parameters of all the 42 CRs, DIs and PDIs for perceived image quality and diagnostic value and graded them on a three point grading scale. Conventional radiographs served as the control. Data were analyzed by using paired t-test and Kappa analysis.

RESULTS

The clarity and diagnostic quality of the PDIs were statistically significant as compared to those of their conventional counterparts. In comparison, the DIs group fared badly, with deterioration of the image quality. The interobserver agreement was good and all the results were statistically significant.

CONCLUSION

Indirectly digitizing the radiographs by employing a digital camera and further digitally processing the images resulted in an improvement in their perceived clarity and they enhanced their diagnostic properties.

Could standardizing "commercial off-the-shelf" (COTS) monitors to the DICOM part 14: GSDF improve the presentation of dental images? A visual grading characteristics analysis

OBJECTIVES

To investigate whether standardizing commercial off-the-shelf (COTS) display devices to the digital imaging and communications in medicine part 14: greyscale standard display function (DICOM part 14: GSDF) would affect the presentation of dental images.

METHODS

Two COTS display devices from the radiology department of a dental teaching hospital and a laptop computer monitor for reference were calibrated to conform to DICOM part 14: GSDF. Four dental surgeons and two final-year students undertook a relative visual grading analysis of the two devices before and after calibration, under control of the viewing environment.

RESULTS

Calibrating COTS display devices to conform to the DICOM part 14: GSDF and viewing under reduced ambient light result in a consistent, perceived visual sensation for the presented radiological image. The area under the visual grading characteristics curve (AUCVGC) before calibration is 0.62 CI (0.56, 0.68) and AUCVGC after calibration is 0.51 CI (0.45, 0.57).

CONCLUSIONS

Standardizing COTS display devices to the DICOM part 14: GSDF can improve image presentation.

Digital radiography in general dental practice: a field study

OBJECTIVES

The aim of this study was to conduct a field study to survey the performance of digital radiography and how it was used by dentists in general dental practice.

METHODS

19 general dental practitioners were visited at their clinics. Ambient light (illuminance) was measured in the rooms where the monitors were placed. Different technical display parameters were noted. Test images and two phantoms--one low-contrast phantom and one line-pair resolution phantom--were used to evaluate the digital system. How the dentists used the enhancement program was investigated by noting which functions were used.

RESULTS

Average illuminance in the operating room was 668 lux (range 190-1250 lux). On radiographs of the low-contrast phantom taken at the clinic, the ability to observe the holes decreased as illuminance increased. On average, the "light percentage" initially set on the monitor had to be decreased by 17% and contrast by 10% to optimize the display of the test images. The general dental practitioners used the enhancement programs most often to alter brightness and contrast to obtain the subjectively best image. Large differences between the clinics were noted.

CONCLUSION

Knowledge of how to handle digital equipment in general dental practice should be improved. A calibrated monitor of good quality should be a given priority, as should proper ambient light conditions. There is a need to develop standardized quality controls for digital dental radiography.

Effect of room illuminance on monitor black level luminance and monitor calibration

In this article we demonstrate the effect of room illuminance and surrounding monitor black level luminance on image quality for soft copy interpretation. Luminance values of a 10% central target and image quality evaluations and observer performance using a contrast-detail mammography (CDMAM) phantom demonstrate these effects. Our results indicate that high room illuminance has a more damaging effect on image quality when the surrounding monitor luminance is 0% to 5% of the maximum monitor luminance. The effect of room illuminance is less obvious when the surrounding monitor luminance is 20% of the maximum.

Influence of displayed image size on radiographic detection of approximal caries

OBJECTIVES

To evaluate the validity of approximal caries detection on digital bitewing radiographs displayed at different image sizes on either a cathode ray tube (CRT) monitor or a thin film transistor (TFT) monitor.

METHODS

Five observers assessed digital radiographs of a charge-coupled device (CCD)-based sensor system (Sidexis) of 160 unrestored premolars and molars for approximal caries using a six category caries rating scale. Images were displayed at ratios of 1:1, 1:2 and 1:7 on a CRT monitor (Nokia 446 XS) and a TFT display (Panasonic LC 50S). Histological assessments of serial sections were used as the validation standard. Diagnostic accuracy was expressed as area under the receiver operating characteristic (ROC) curve (AUC) and was calculated at two levels of caries penetration: presence of caries (I) and presence of a lesion in the dentine (II). The influence of the factors "monitor type", "image size" and "validation threshold" were analysed with repeated measures analysis of variance.

RESULTS

The ROC curve areas for approximal caries detection at both histological penetration levels were not influenced by the type of monitor display, whereas image size had a significant impact (P<0.01). AUCs for image size 1:7 (I, 0.62; II, 0.65) were smaller compared with ratios of 1:1 and 1:2 (P<0.01). No differences were observed between image size ratios 1:1 (I, 0.69; II, 0.74) and 1:2 (I, 0.68; II, 0.73).

CONCLUSIONS

In this study, the type of monitor did not influence approximal caries detection on digital radiographs. Image sizes with a display ratio of 1:1 and 1:2 resulted in better diagnostic validity than those with a ratio of 1:7.