Definition, classification and retrospective analysis of photostimulable phosphor image artefacts and errors in intraoral dental radiography

Can Digital Enhancement Restore the Image Quality of Phosphor Plate-Based Radiographs Partially Damaged by Ambient Light?

To assess the effect of digital enhancement on the image quality of radiographs obtained with photostimulable phosphor (PSP) plates partially damaged by ambient light. Radiographs of an aluminum step wedge were obtained using the VistaScan and Express systems. Half of the PSP plates was exposed to ambient light for 0, 10, 30, 60, or 90 s before being scanned. The resulting radiographs were exported with and without digital enhancement. Metrics for brightness, contrast, and contrast-to-noise ratio (CNR) were derived, and the ratio of each metric between the exposed-to-light and non-exposed-to-light halves of the radiographs was calculated. The resulting ratios of the radiographs with digital enhancement were subtracted from those without digital enhancement and compared among each other. For the VistaScan system, digital enhancement partially restored brightness, contrast, and CNR. For the Express system, digital enhancement only restored CNR and not the impact of ambient light on brightness and contrast. Specifically, digital enhancement restored 23.48% of brightness for the VistaScan, while percentages below 1% were observed for the Express. Digital enhancement restored 53.25% of image contrast for the VistaScan and 5.79% for the Express; 40.71% of CNR was restored for the VistaScan, and 35% for the Express. Digital enhancement can partially restore the damage caused by ambient light on the brightness and contrast of PSP-based radiographs obtained with the VistaScan, as well as on CNR for the VistaScan and Express systems. The exposure of PSP plates to light can lead to unnecessary retakes and increased patient exposure to X-rays.

Ambient light exposure of photostimulable phosphor plates: is there a safe limit for acceptable image quality?

OBJECTIVES

To subjectively assess radiographs obtained with photostimulable phosphor (PSP) plates exposed to clinical levels of ambient light prior to read-out to potentially set a safe limit for acceptable image quality.

METHODS AND MATERIALS

Six dental regions of a dry human skull were X-rayed using PSP plates from VistaScan and Express under four exposure times: 0.1, 0.2, 0.32, and 0.4 s. Before read-out, the PSP plates were exposed to ambient light for 0, 5, 10, 30, 60, and 90 s. Six observers were asked to classify the 288 resulting radiographs as acceptable or unacceptable based on the identification of anatomical structures and global image quality. The number of answers classifying radiographs as unacceptable was used to calculate a rejection rate; a pairwise comparison for better image quality was further conducted among radiographs considered acceptable. Reproducibility was tested by having 25% of all experimental groups reassessed.

RESULTS

Intra- and interobserver agreement ranged from 0.87 to 1.00 and from 0.81 to 0.92, respectively. Exposure of PSP plates to ambient light increased rejection rates mostly as of 10 s. In the pairwise comparison, subtle differences were observed between radiographs obtained with PSP plates not exposed and those exposed to ambient light for 5 s.

CONCLUSIONS

Ambient light exposure of PSP plates impairs the image quality of radiographs. A safe limit of ambient light exposure of 5 s for VistaScan and Express should be considered. Ambient light exposure of PSP plates within safe limits can avoid retakes and reduce unnecessary patient exposure to X-rays.

Reduction of scratch or dirt artifacts on intraoral radiographs using dual imaging plates in image processing

OBJECTIVES

Artifacts including scratches and dirt artifacts on the digital intraoral radiographs finally contribute to making inaccurate diagnoses. The aim of this study was to reduce the incidence of artifacts using dual imaging plates (DIPs) in imaging processing.

METHODS

Conventional X-rays were taken of a porcine mandible embedded in acrylic resin using a DIP which consists of a front IP (FIP) and a back IP (BIP) with some scratches and dirt. The two images of the FIP and BIP were then synthesized and averaged to obtain a conventional DIP image. The following image processing method was used to make a DIP with artifact reduction (DIP+AR) image. A subtraction image of the FIP and BIP was constructed and the standard deviation (SD) was calculated. If the pixel value was over 3SD on the subtraction images, the pixel value of the DIP was swapped with the value on the opposite side of the non-artifact pixel. The conventional and DIP+AR images were also subjectively evaluated.

RESULTS

Image processing to create a DIP+AR image was able to reduce the number of artifacts. Medians of number of artifacts evaluated were 2.00 [interquartile range (IQR), 2.50] in DIP images and 0.67 (IQR, 1.29) in DIP+AR images, indicating a significant reduction of number of artifacts in DIP+AR images.

CONCLUSIONS

DIP+AR image processing can reduce the incidence of artifacts caused by scratches and dirt, and could extend the lifespan of the IP and contribute accurate diagnosis in oral radiology.

Evaluation of histogram equalization and contrast limited adaptive histogram equalization effect on image quality and fractal dimensions of digital periapical radiographs

OBJECTIVES

This study aims to evaluate the effects of histogram equalization (HE) and contrast limited adaptive histogram equalization (CLAHE) on periapical images and fractal dimensions in the periapical region.

METHODS

In this cross-sectional study, digital periapical images were selected from the archive of Dentistry School of Isfahan University of Medical Sciences. The radiographs were taken from mandibular and maxillary anterior single root teeth with healthy root and periodontium. After applying HE and CLAHE algorithms to images, two radiologists evaluated the quality of apex detection from using a 5-point Likert scale (from 5 for very good image quality to 1 for very bad image quality). Afterward, all the images were imported to the ImageJ application, and the region of interest (ROI) was specified as the region between the two central incisors. The fractal box-counting method was used to determine fractal dimensions (FD) values. Nonparametric Wilcoxon-Friedman test, Intraclass Correlation Coefficient test, T-test, and Pair T-test were performed as statistical analysis (α = 0.05).

RESULTS

Fifty-three radiographs were analyzed and the image quality assessments were significantly different between raw images and images after performing HE, CLAHE (p value < 0.001), and using CLAHE algorithm significantly increases image quality assessments more than HE (p value = 0.009). There was a significant difference in FD values for images after applying CLAHE and HE compared to raw images (p value < 0.001), and HE decreased the FD value significantly more than CLAHE (p value = 0.019).

CONCLUSIONS

Employing CLAHE and HE algorithm via OpenCV python library improves the periapical image quality, which is more significant using the CLAHE algorithm. Moreover, applying CLAHE and HE reduces trabecular bone structure detection and FD values in periapical images, especially in HE.

Analysis of image defects in digital intraoral radiography based on photostimulable phosphor plates

OBJECTIVES

In digital intraoral radiography (DIR), images with defects caused by the digital process are sometimes produced. Hence, we analyzed DIR images with defects taken using the photostimulable phosphor (PSP) plate method and then classified these images based on the causes of the defect. The aim of this study was to classify defects in DIR using the PSP plate system, and to discuss the causes of each type of defect and the methods that can prevent their occurrence.

METHODS

Images with defects due to the two PSP plate systems (Arcana and Arcana Mira) were selected and classified according to the defect. Image defects caused by geometrical techniques that occur in both the film and PSP plate methods were excluded from this study. Moreover, changes in the rate of occurrence of images with defects over time were analyzed in this study.

RESULTS

The defects in images obtained by the PSP plate system were classified into six types, which were further divided into those caused by machine error or human error. Both types of error could influence the diagnostic performance. Machine error accidentally and rarely occurred; thus, the prevention of such errors is difficult. However, human error, especially errors caused by photo-induced discharge, could be prevented using appropriate measures.

CONCLUSIONS

In DIR systems using the PSP plate method, human error should be prevented by education and training to improve operation.

How Does Ambient Light Affect the Image Quality of Phosphor Plate Digital Radiography? A Quantitative Analysis Using Contemporary Digital Radiographic Systems

The aim of this study is to quantitatively evaluate the influence of the duration of ambient light exposure on the image quality of digital radiographs obtained with contemporary phosphor plate (PSP)-based systems. Radiographs of an aluminum step-wedge were obtained using VistaScan and Express systems at five X-ray exposure times: 0.10, 0.20, 0.32, 0.40, and 0.50 s; the resulting dose-area products were, respectively, 21.93, 43.87, 70.19, 87.75, and 109.6 mGycm². Before PSP read-out, half of the sensitive surface of the PSP plates was exposed to ambient light for 5, 10, 30, 60, and 90 s. The effect of light exposure on brightness, contrast, contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR), and image saturation was compared using ANOVA with the Tukey test (α = 0.05). Ambient light exposure increased brightness and contrast and reduced CNR and SNR in PSP-based radiographs of contemporary digital systems. At the longest X-ray exposure times, ambient light exposure reduced the dark saturation (mean gray values ≤ 1) observed in Express. In conclusion, the negative effects of ambient light observed on the image quality of PSP-based radiographs are directly proportional to the duration of exposure. Clinicians should be aware of such harmful effects when handling and scanning PSP plates in bright environments.

Integrating Image Analysis and Dental Radiography for Periodontal and Peri-Implant Diagnosis

The recent change in classification of periodontal and peri-implant diseases includes objective evaluation of intra-oral radiographs and quantification of bone loss for disease staging and grading. Assessment of the progression of periodontal disease requires deduction of bone loss longitudinally, and its interpretation as (1) a percentage in relation to tooth root and (2) as a function of the patient's age. Similarly, bone loss around dental implants, after accounting for initial remodeling, is central for determining diagnosis, severity, and progression of peri-implantitis. Bone gain secondary to periodontal regeneration can be measured using standardized dental radiographs and compared to baseline morphology to determine treatment success. Computational image analysis, including machine learning (ML), has the potential to develop and automate quantitative measures of tooth, implant, bone volumes, and predict disease progression. The developed algorithms need to be standardized while considering pre-analytic, analytic, and post-analytic factors for successful translation to clinic. This review will introduce image analysis and machine learning in the context of dental radiography, and expand on the potential for integration of image analysis for assisted diagnosis of periodontitis and peri-implantitis.

Effect of enveloping and disinfection methods on artefact formation on enveloped PSP plate images

Objectives

To investigate the artefacts caused by different disinfection and protection methods that can be used for infection control of photostimulable phosphor (PSP) plates.

Methods

The plates that were enveloped with single or double envelopes were sprayed with an alcohol-containing solution or wiped with an alcohol-containing tissue. Four PSP groups with two plates in each group were formed (A = wiping single envelope, B = wiping double envelopes, C = spraying onto single envelope, and D = spraying onto double envelopes). Any artefacts (1 = no artefact, 2 = presence of artefact less than 0.5 cm wide, and 3 = presence of artefact larger than 0.5 cm wide) on the 12 acquired images were evaluated.

Results

Artefacts (score-3) occurred on the images of Group C-2 PSP plate after the 3rd exposure. According to the Kruskal–Wallis test the difference between the artefact score of the four methods was found significant. Post-hoc comparisons showed the Group C artefact scores were higher than the others and the difference was significant. The total time of enveloping and disinfection processes for groups was; A = 6.30 min, B = 7.58 min, C = 5.48 min, and D = 7.14 min.

Conclusions

Regardless of the number of envelopes, wiping with a tissue was less likely to cause artefacts, while spraying was reliable only when double envelopes were used. However, using a tissue and double envelopes, which are less risky in terms of artefact, causes time loss, difficulty in manipulation, environmental pollution and high cost.

Analysis of photostimulable phosphor image plate artifacts and their prevalence

BACKGROUND

Digital radiography has recently been used in dentistry as a substitute for conventional film radiography worldwide. Digital imaging has many advantages and provides new possibilities for recording and interpreting radiographic data. This system uses different types of digital receptors.

AIM

To detect the frequency, type, and reasons behind the appearance of intraoral image artifacts acquired by photostimulable phosphor plates (PSP).

METHODS

This retrospective descriptive study was conducted in the oral and maxillofacial radiology unit of the dental clinics of the College of Dentistry, Princess Nourah University (PNU). All intraoral digital radiographs were acquired using (Gendex Expert DC., United States) an intraoral X-ray machine with 7 -mA, 65-kVP using a PSP system (Soredex DIGORA Optime imaging plate) and laser scanners (Soredex DIGORA Optime), which can house all sizes of reusable intraoral PSP sensor plates with image acquisition software (MIPACS Dental Enterprise viewer 3.2.2). A total of 50000 intraoral radiographs were retrieved from the clinical database from April 2018 to April 2020 to evaluate the reason, type, and solutions to these image artifacts.

RESULTS

Overall, 50000 intraoral digital radiographs were acquired in a two-year-period; that is, from April 2018 to April 2020. Of these, 3550 (7.1%) retakes were performed due to the presence of image artifacts. Periapical radiographs were the most common image type of intraoral retakes (80.8%). Imaging artifacts were divided into three categories: operator, plate and scanning errors. Out of 3550 retakes, 5%, 1.37%, and 0.73% were related to operator, plate, and scanning errors, respectively. The cone cut was the most common operator error (988 images), Bite marks were the most common plate error (276 images), and delayed scanning artifacts were the most common scanning errors (145 images). The calculated kappa value for interobserver reliability was 0.99, indicating almost perfect interobserver agreement.

CONCLUSION

Our study discussed intraoral image artifacts that were characteristic of PSP, where the most common artifacts were bitemarks, image size reduction, scratches, and delayed scanning.

Benefits of using a photostimulable phosphor plate protective device

OBJECTIVES

To develop and test a protective device (PD) to increase the resistance of photostimulable storage phosphor (PSP) plate to compressive load, and assess the resulting image quality.

METHODS

Two prototypes, polyvinylchloride sheets of 0.3 mm and 0.7 mm each, were developed for PSP plate size 2. The resistance to compressive load was tested using eight new PSPs divided into four test groups: (1) PSP, (2) PSP and paperboard protector, (3) PSP and 0.3 mm PD, and (4) PSP and 0.7 mm PD. The resulting images were analyzed by three oral radiologists, based on the consensus for image artifacts. Additionally, the objective image quality test was performed with four new PSPs, using an 8-step wedge aluminum scale. The mean gray values and standard deviation were measured in a total of 240 images, and the data were analyzed using analysis of variance with Bonferroni post-hoc test.

RESULTS

Artifacts were seen in the PSP control group starting at 40 n, and at 150 n, 175 n and 300 n in 0.3 mm PD, paperboard protector and 0.7 mm PD, respectively. Although there was no statistical difference among groups, there were differences between exposure times (0.06-0.25 s, 0.06-0.40 s, and 0.10-0.40 s). Scanning resolution of 20 lp/mm showed higher mean gray value than 25 and 40 lp/mm (p < 0.05).

CONCLUSION

The developed PDs improved the PSP resistance to compressive forces, with low interference on the pixel gray values, regardless of exposure time and spatial resolution. Nevertheless, the 0.7 mm PD could withstand the maximum compressive load.

Radiopacity of resin-based CAD/CAM blocks assessed by areal grayscale pixel value measurement

PURPOSE

This study assessed radiopacity of resin-based computer-aided-design/computer-aided-manufacturing (CAD/CAM) materials by areal grayscale pixel value measurement.

METHODS

Radiopacities of six resin-based CAD/CAM block materials and resin composite were evaluated and compared to that of enamel and dentin. Specimens of 1-mm thickness were placed on photostimulable phosphor plate and irradiated with digital x-ray unit. On the radiographic image, regions of interests were determined for each specimen and areal grayscale pixel values were measured. Elemental analysis was performed with energy-dispersive x-ray spectroscopy (EDS) on field emission scanning electron microscope (FESEM) images of the specimens. Data were analyzed statistically (α = 0.05).

RESULTS

Radiopacity values of the restorative materials were significantly different from each other (P < 0.05). Radiopacity values of two resin-based CAD/CAM materials were significantly lower than that of dentin (P < 0.05). All tested restorative materials contain zirconium, three materials contain barium, and only resin composite contains lanthanum.

CONCLUSION

Four CAD/CAM materials with higher amounts of zirconia or barium (>18%) had radiopacity values significantly higher than the dentin; while two materials with lower amounts of zirconia (<4%) and/or no-barium, had radiopacity values significantly lower than the dentin. EDS analysis suggests materials containing elements with higher atom numbers such as zirconia and barium could exhibit higher radiopacity.

The effects of physical photostimulable phosphor plate artifacts on the radiologic interpretation of periapical inflammatory disease

OBJECTIVE

To evaluate how physical photostimulable phosphor (PSP) plate artifacts, such as those created by scratches, phosphor degradation, and surface peeling, affect the radiologic interpretation of periapical inflammatory disease.

STUDY DESIGN

A novel technique was developed to digitally superimpose 25 real PSP artifact masks over 100 clinical complementary metal oxide semiconductor (CMOS) periapical images with known radiologic interpretations. These images were presented to 25 general dentists, who were asked to state their radiologic interpretations, their confidence in their interpretations, and their opinions on whether the plates should be discarded. Statistical analyses were conducted by using random intercept mixed models for repeated measures and χ² tests of the pooled data.

RESULTS

No statistically significant adverse effect on interpretation was seen, even at severe artifact levels. There was a statistically significant decrease in the clinicians' confidence and an increase in discard proportions when interpreting images with severe PSP plate artifacts (P < .05).

CONCLUSIONS

Although diagnostic efficacy was unaffected, clinicians' confidence decreased and proportionally more clinicians opted to discard sensors when interpreting images with severe artifacts. Future studies on the effects of artifacts on the efficacy of diagnosis of other dental diseases are recommended. Ultimately, these results can guide recommendations for PSP plate quality assurance.

Determination and classification of intraoral phosphor storage plate artifacts and errors

Purpose

The aim of this study was to determine the reasons and solutions for intraoral phosphor storage plate (PSP) image artifacts and errors, and to develop an appropriate classification of the artifacts.

Materials and Methods

This study involved the retrospective examination of 5,000 intraoral images that had been obtained using a phosphor plate system. Image artifacts were examined on the radiographs and classified according to possible causative factors.

Results

Artifacts were observed in 1,822 of the 5,000 images. After examination of the images, the errors were divided into 6 groups based on their causes, as follows: images with operator errors, superposition of undesirable structures, ambient light errors, plate artifacts (physical deformations and contamination), scanner artifacts, and software artifacts. The groups were then re-examined and divided into 45 subheadings.

Conclusion

Identification of image artifacts can help to improve the quality of the radiographic image and control the radiation dose. Knowledge of the basic physics and technology of PSP systems could aid to reduce the need for repeated radiography.

Ex vivo comparison of CBCT and digital periapical radiographs for the quantitative assessment of periodontal defects

OBJECTIVES

Accurate imaging is essential for effective treatment planning in periodontology. The aim of this ex vivo study was to investigate the accuracy of cone beam computed tomography (CBCT) and digital periapical radiographs (PA) in imaging periodontal defects. Hypotheses are: 1. That CBCT is a more accurate method than PA concerning vertical measurements of periodontal bone defects2. That CBCT itself is an accurate method to describe vertical periodontal bone loss MATERIAL AND METHODS: In this study, 117 periodontal defects from 10 human cadavers were investigated radiographically by CBCT and PA by one calibrated observer. Afterwards the vertical bone loss was measured with a periodontal probe by the same calibrated observer. Differences between radiographic and clinical measurements were calculated and analyzed. Bland-Altmann plots including 95% limits of agreement were calculated.

RESULTS

The 95% limits of agreement ranged from 3.29 to -3.27 mm between clinical measurements and measurements in PAs, and from 2.13 to -1.97 mm in CBCTs. The mean difference between clinical and radiographic measurements was 0.0009 mm for PA and 0.0835 mm for CBCT.

CONCLUSIONS

When comparing the clinical measurements, CBCT had a higher agreement and less deviations than PAs, and CBCT seems to be an accurate method to describe vertical periodontal bone loss.

CLINICAL RELEVANCE

Accurate description of defects is helpful for accurate treatment planning.