Sens-A-Ray. A new system for direct digital intraoral radiography

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.

The way we were (and how we got here): fifty years of technology changes in dental and maxillofacial radiology

The history of the last 50 years (1970-2020) of technological changes and progresses for equipment and procedures in dental and maxillofacial radiology is related from the insider perspective of an industrial physicist and technologist who has been instrumental at innovating and developing medical equipment in different parts of the world. The onset and improvement of all major categories of dental and maxillofacial radiographic equipment is presented, from the standpoint of their practical acceptance and impact among common dentists and maxillofacial radiologists: X-ray sources and detectors for intraoral radiography, and panoramic systems, both film-based and digital (including photo-stimulated phosphor plates); and cone beam CT.

Comparison of Efficiency and Image Quality of Photostimulable Phosphor Plate and Charge-Coupled Device Receptors in Dental Radiography

The photostimulable phosphor (PSP) plate and charge-coupled device (CCD) are receptors commonly used for intraoral radiography in U.S. dental schools. However, it is unclear which receptor is more beneficial for radiology education and patient care in an academic setting. The aim of this study was to compare the time efficiency, image quality, and operator performance for student-operated PSP plate and CCD receptors. At one U.S. dental school in 2018, 20 dental hygiene and dental students (n=10 each) were recruited as operators. They each exposed anterior and posterior periapical and bitewing radiographs on dental radiograph teaching and training replica using the PSP plate and CCD as receptors. The time taken to expose the radiographs was recorded. Image sharpness/definition, brightness/contrast, and technical errors, including placement, angulation, and cone cut errors, were evaluated on a three-point scale with 0=non-diagnostic, 1=diagnostic acceptable with minor errors, and 2=perfect diagnostic quality. The results showed that it was generally faster for the students to expose intraoral radiographs with CCDs than with PSP plates, although the difference was not significant (p>0.05). Image quality and technical accuracy, especially angulation, were significantly superior for PSP relative to CCD (p<0.05). This study found that PSP imaging was of higher quality and accuracy than CCD, whereas CCD was more efficient. Dental and dental hygiene students would benefit from being trained on both receptors to be able to adapt to a diversified workplace.

Direct digital radiography versus conventional radiography - assessment of visibility of file length placed in the root canal: An in vitro study

AIM AND OBJECTIVE

To compare conventional and direct digital radiography (DDR) in working length measurement of the root canal and to assess the significance of the different enhancement modes provided by the software to visualize the file length.

MATERIALS AND METHODS

Access cavities were prepared in 30 extracted maxillary central incisors. Size 15 k-file was introduced into the canal till it was flush with the apical foramen. The working length was calculated as 0.5 mm less than the vernier caliper measured length of each file. The files were then sealed with resin at their respective lengths. Intraoral periapical radiographs and direct digital radiographs were taken. Vernier caliper was used to measure the file length in the periapical radiographs, and standard, positive conversion, and colorize modes were used with the CDR system. A multiple regression analysis was conducted to give an accurate analysis between the actual file length and the different groups.

RESULTS

There was no statistical significance between the different groups tested. The multiple regression analysis test showed that the positive and colorize modes more accurately corresponded to the actual file length.

CONCLUSION

Both conventional radiography and DDR can be reliably used for working length determination. The positive and colorize modes enhancement features of DDR greatly improve the visual perception, leading to more accurate measurements.

Digital radiographic evaluation of optical density of porcelains used for fabrication of inlay/onlay prosthesis

The purpose of this article was to compare the mean value of optical density of four porcelains commonly used for fabrication of inlay/onlay prostheses using direct digital radiograph. The sample consisted of 20 2-mm thick porcelain specimens (measured by digital pachymeter): Empress (Ivoclair), Simbios (Degussa), Vita Omega 900 and Vitadur Alpha (Vita Zahnfabrik). The values of optical density of the specimens were expressed in millimeters aluminum equivalent (mm eq Al). The samples were X-rayed using two charge coupled devices (CCD) - RVG (Trophy) - Visualix (Gendex) and a phosphor plate system - Digora (Soredex). The optical density reading was performed with Image Tool 1.28 in a total of 110 measurements. Statistical analysis showed that there were statistically significant differences in all materials studied (p < 0.05) regardless of the radiographic system used. The highest optical density value was found for Omega 900 (1.8988 mmeqAl - Visualix - Gendex) and the lowest for Vitadur Alpha (0.8647 - Visualix - Gendex). Thus, the material presenting the highest degree of optical density was Omega 900, Empress and Simbios presented intermediate optical density values, Vitadur Alpha presented the lowest value, and the optical density of porcelains was not influenced by the digital radiography systems.

Comparison of complementary metal oxide semiconductor and charge-coupled device intraoral X-ray detectors using subjective image quality

OBJECTIVE

To compare the subjective image quality of the newer generation Schick CDR detector employing complementary metal oxide semiconductor (CMOS) technology with images using the earlier generation charge-coupled device (CCD) Schick CDR detector.

METHODS

All radiographic images were made using the same formalin-fixed adult cadaver maxilla with surrounding natural soft tissues in place. The X-ray generator used was a Villa Sistemi Medicali Diamatic srl AP/Explor X operated at 70 kVp and 8 mA. The source-to-detector distance was set at 38 cm and an optical bench was used to ensure reproducible beam geometry. A range of exposures was applied for both detectors. A panel of nine dentists independently observed and evaluated images made at each exposure. For both detectors, the three images ranked highest were randomized for re-evaluation in panels of six images. Each image was repeated randomly a total of 10 times. Features chosen as observation points were: (1) proximal dental caries; (2) gingival soft tissues; (3) cortical bone; (4) root canal space; (5) root apices; (6) periodontal ligament space; and (7) endodontic instrument tip clarity. Comparisons were made by use of odds ratio analysis applying a 95% confidence level. Interrater and intrarater reliabilities were computed to assess consistency in observer ratings.

RESULTS

The CMOS sensor was rated as outperforming its CCD predecessor for depiction of cortical bone and root apices; the CCD detector was only rated superior for depiction of root canal space. No significant difference was found between the two detectors in perceived depiction of proximal dental caries, gingival soft tissues, periodontal ligament space or endodontic instruments. Combining rating scores from each of the tasks, CMOS and CCD detectors had a similar proportion of image ratings of excellent, acceptable and poor.

CONCLUSIONS

Regarding subjective image quality, the Schick CMOS and CCD detectors were perceived to produce radiographic images of similar overall quality.

Two decades of computerized information technologies in dental radiography

The author describes her experiences in developing a radiology department utilizing digital radiography in dentistry.

Canal length evaluation of curved canals by direct digital or conventional radiography

OBJECTIVES

The purpose of this study was to compare the accuracy of a digital radiograph imaging system (DDR) with conventional radiography for the purpose of estimating endodontic file lengths in curved canals of mandibular molars.

STUDY DESIGN

Sixty extracted human mandibular molars with root curvatures ranging from 5 degrees to 52 degrees were mounted in plastic blocks. Canal length was estimated by using on-screen DDR with both 2- and 3-click measurement and from conventional E-speed radiographs by using a millimeter ruler and x2 magnification. Two operators familiar with both radiographic methods performed the estimates.

RESULTS

One-way analysis of variance and Newman-Keuls tests revealed no significant differences between the groups. Although both conventional and DDR methods of analysis overestimated the true canal length, the DDR accuracy improved as the curvature severity increased.

CONCLUSIONS

The image quality of DDR systems has improved to the point that they can now be used for estimating canal lengths, even for curved canals, with accuracy comparable to that of conventional radiographs. However, further work remains to be done to optimize image quality.

[Clinical and comparative study of the image quality of 3 digital radiographic systems, E-speed film and digitalized film]]

The aim of this study was to evaluate, subjectively, the image quality of two CCD digital systems, a digital storage phosphor system, a digitized film and an E-speed film. Five objects were radiographed with 50, 60 and 70 kVp, with exposure times of 0.08, 0.13, 0.2, 0.4 and 0.8 s. In order to maximize the fidelity of the results, the dental X-ray unit employed was submitted to an evaluation so that the relation between exposure time and dose could be established. A good reproducibility was obtained. Six evaluators analyzed 375 images, using a scoring scale which ranged from 0 to 4. The results revealed different responses, indicating that the storage phosphor system had the best performance, in the various exposures employed. However, it was possible to conclude that all systems studied, except for the Sens-A-Ray, can offer images in ideal conditions for the diagnosis, as long as their latitudes are respected.

Digital imaging modalities for dental practice

The introduction of the computed tomograph in the 1970s revolutionized medical diagnosis by initiating the transition from analogue to digital imaging. During this period, more specialized equipment for image processing was developed, such as cathode-ray tubes for image display, special sensors for image acquisition, and storage devices for image archiving. Digital imaging systems designed exclusively for use in dentistry were developed in the latter half of the 1980s. Some are now being clinically applied under conditions of close scrutiny to determine diagnostic accuracy, image quality, and radiation exposure to patients. This article reviews the enabling technologies of digital systems used in dentistry, and focuses upon intraoral digital imaging systems, concepts for digital image acquisition, and variations in radiation dose and their effects on diagnostic accuracy of caries detection.

Five methods of calcium hydroxide intracanal placement: an in vitro evaluation

OBJECTIVE

The purpose of this study was to evaluate root canal dressing with calcium hydroxide paste using 5 techniques of placement.

STUDY DESIGN

After endodontic preparation, each of 50 single-rooted premolars was filled with calcium hydroxide paste through use of one of the following techniques: Gutta-Condensor, MecaShaper, K-type ultrasonic file, Lentulo, and Pastinject. Radiographs of all 3 third root zones were made after cleaning and shaping and obturation. Density measurements (in pixels) were registered by means of an image analyzer and then compared through use of analysis of variance and Newman-Keuls multiple means tests.

RESULTS

With respect to average filling density, the techniques ranked as follows, in ascending order: Gutta-Condensor, MecaShaper, K-type ultrasonic file, Lentulo, and Pastinject. There was a significant difference (P <.0009) between the Gutta-Condensor and Pastinject techniques, between the MecaShaper and Pastinject techniques, and between the ultrasonic file and Pastinject techniques; all favored the Pastinject. There were no significant differences between the Gutta-Condensor, MecaShaper, ultrasonic file, and Lentulo techniques or between the Lentulo and Pastinject techniques.

CONCLUSIONS

The use of a specially designed paste carrier (the Pastinject) improved calcium hydroxide placement in root canals.

Comparison of digital dental X-ray systems with self-developing film and manual processing for endodontic file length determination

Human skulls were sectioned into 15 sextants. Teeth were then removed and 45 canals were instrumented to their apical foramina. Endodontic files were glued in place at random distances from the apical foramina. Image geometry was maintained by a custom mounting jig. Images were captured with self-developing film, manually processed D-speed film, and a digital radiographic system (Dexis). Digital images were read on a conventional color monitor (cathode ray tube) and a laptop screen (active-matrix liquid crystal display). Fifteen dentists measured the distance from the file tip to the apical foramen of the tooth. Results showed that the measurement error was significantly less for the digital images than for the film-based images. It is likely that these statistical differences may not be of great clinical significance because the digital images could be measured in increments < 0.25 mm.

Image plate systems differ in physical performance

OBJECTIVE

The purpose of this study was to compare 2 storage phosphor image plate systems, the Digora and the DenOptix, with respect to physical performance.

STUDY DESIGN

The 2 systems were tested both with and without use of their default settings through physical and psychophysical measurements. A homogeneous 10-mm-thick aluminum block, a 10-mm-thick aluminum block with a pattern of holes varying in diameter and depth, and a resolving power target were used as test phantoms. The image plates were exposed at 50 kV and 8 mA with a focus-sensor distance of 30 cm and exposure times ranging from 10 to 3,200 ms. Measurements of large area transfer function, gray level variations, perceptibility, contrast resolution, exposure range, and modulation transfer function were performed.

RESULTS

When the two systems were used at their default settings, the DenOptix had a better dose response, a higher contrast index, and a higher modulation transfer function (MTF) than the Digora; however, the DenOptix also had higher noise than the Digora at lower exposures.

CONCLUSIONS

When image enhancement algorithms were applied with the Digora system, performance similar to that of the DenOptix could be obtained.

Assessments of the physical performance of 2 generations of 2 direct digital intraoral sensors

OBJECTIVE

To evaluate the performance of 4 intraoral direct digital sensors regarding their fundamental physical characteristics. The sensors are made by Schick Technologies Inc (Long Island City, NY) and Gendex Dental Systems (Milan, Italy).

STUDY DESIGN

The sensors were exposed by using a Prostyle dental x-ray machine (Planmeca Oy, Helsinki, Finland) operating at 50 kV, 8 mA and various exposure times. Three test phantoms were used: a homogeneous 10-mm thick aluminum block, an aluminum block with a pattern of holes of varying sizes, and a resolving power target. Digital images were transferred as 8 bit TIFF files and analyzed by using a personal computer.

RESULTS AND CONCLUSIONS

Some improvements could be observed in the physical performance of the new generation of direct digital radiographic sensors when compared with the earlier generation. Smaller pixels and higher quantum efficiency have improved sensor performance.

The role of direct intraoral sensors in the provision of endodontic services

The recent commercial success of intraoral sensor systems largely reflects the quest to improve the quality assurances for endodontic services. The many advantages of these systems include reduced radiation exposures, real-time images, resolution improvements after initial image capture and archival benefits, although their diagnostic benefits over conventional film based radiographs remain a concern. For instance, the images from either charge-coupled device or storage phosphor sensors have yet to exceed the potential 50 microns spatial and 12-bit contrast resolutions obtained from the 1.75-6.40 microns silver grain emulsions of conventional films or the potential improvements derived from smaller (1 micron) grains. Intraoral sensor systems alone are therefore unlikely to improve the quality assurances for endodontic services.

Effects of dose reduction on the detectability of standardized radiolucent lesions in digital panoramic radiography

Dose reduction in digital panoramic radiography was studied. Intentional underexposure was performed with the Orthophos DS while six different human mandibles were radiographed. Exposure settings were 69 kV/15 mA (standard), 64 kV/16 mA, and 60 kV/16 mA. Standardized spherical defects, each either 1 or 1.25 mm in diameter, were simulated in 288 of 432 images, and seven observers decided whether defects were present or not. Areas under the receiver operating characteristics curves were calculated. They showed no significant differences in the detectability of the 1-mm defect at 69, 64, or 60 kV. For the 1.25-mm defect, no difference was found between the 69 and 60 kV images, but a statistically significant different detectability was found for 64 kV images in comparison with both 69 and 60 kV images. A dose reduction of up to 43% was ascertained with a Pedo-RT-Humanoid phantom when panoramic radiography was performed at 60 kV/16 mA. The conclusion is that with the Orthophos DS, it seems possible to reduce the dose rate of x-rays without loss of diagnostic quality in the case of radiolucent changes.

Film and digital radiography for detection of simulated root resorption cavities

OBJECTIVES

The purpose of this study was to evaluate observers' ability to detect simulated root resorption cavities in conventional radiographs and digital radiographs from a charge-coupled device system and a storage phosphor system and to determine whether the detectability was influenced by resorption size and exposure.

STUDY DESIGN

In teeth from dry mandibular jaw specimens, resorptive defects 1.2 mm in diameter and two different depths (0.6 and 0.9 mm) were prepared in the buccal root surface. Each tooth was radiographed at a number of different exposure settings. Observers were asked to rate their confidence that a resorption was or was not present using a five-graded confidence scale. Receiver operating characteristic analysis was used to evaluate the results.

RESULTS AND CONCLUSION

Given optimal exposures, all systems reached what might be considered clinically acceptable Az values (> 0.75). The storage phosphor system reached this value at considerably lower exposures than those required for both the film and charge-coupled device systems. There was a tendency to better detect the deeper lesions and to identify them at lower exposures.

Interpretation of periapical lesions comparing conventional, direct digital, and telephonically transmitted radiographic images

The purpose of this study was to evaluate direct digital radiography (DDR) and telephonically transmitted images versus conventional radiography in the interpretation of artificial periapical bone lesions. Five teeth were chosen from four cadaver jaw specimens. Three types of DDR images were evaluated: DDR stored images, DDR transmitted images, and DDR reversed images. A total of 150 DDR computer monitor images and 56 D-speed film images were evaluated by three endodontists and one endodontic graduate student. The Wilcoxon signed-ranks test was used for statistical analyses of the results. DDR reversed images were statistically inferior to DDR stored images, DDR transmitted images, and conventional radiography images (p < 0.0001). There were no statistically significant differences between DDR stored images, DDR transmitted images, and conventional film images in the ability of the evaluator to identify artificial periapical bone lesions (p > 0.05).

Charge-coupled device panoramic radiography: effect of beam energy on radiation exposure

OBJECTIVE

To determine the consequences for entrance exposure of varying the beam energy and operating current for panoramic radiography using a charge-coupled device receptor.

MATERIAL AND METHODS

Images were made of a RANDO average man phantom (Alderson Research Laboratories, Stamford, CT) at kVcp settings of 60, 66, 70 and 80 and an mA of 2.0, 3.2, 6.4 and 10.0. The exposure cycle was set as recommended by the manufacturer at 17.6 s. Diagnostic image quality was rated by a panel of two oral and maxillofacial radiologists and one oral and maxillofacial pathologist. Entrance exposures were assessed using a 3 cc ionization chamber placed at the beam entry points while imaging the molar, premolar, and anterior teeth both using the DigiPan (Trophy Radiologie, Vincennes, France) CCD receptor and conventional T-Mat G film/Lanex Regular screens (Eastman Kodak, Rochester, NY, USA).

RESULTS

Acceptable image quality was attained with combinations of 60 kVcp and 3.2, 6.4 or 10 mA, 70 kVcp and 2.0, 3.2 or 6.4 mA; at 80 kVcp irrespective of the mA it was unacceptable. The maximum reduction in entrance dose was 77%, averaged over the three sites, at 70 kVcp and 2 mA.

CONCLUSION

The DigiPan receptor produces satisfactory images with saving in entry exposure saving of approximately 70% when compared with a conventional film/rare earth screen combination.

Marginal bone level buccal to mandibular molars in digital radiographs from charge-coupled device and storage phosphor systems. An in vitro study

The aim of this in vitro study was to compare bone loss measurements in the furcation area of mandibular molars in digital radiographs from a CCD-(Sens-A-Ray) and a storage phosphor (Digora) system, 10 1st and 7 2nd mandibular molars, with intact lingual but reduced buccal bone with furcation involvements, were used. Radiographs were first taken with lead markers at the most apical part of the buccal bone and at the cemento-enamel junction. These radiographs were used to establish a radiographically true distance between the CEJ and the buccal bone level. The lead marker at the CEJ served as a reference point for the observers' subsequent estimates of the extent of bone removed, which were made in radiographs without lead markers at the bone level. 1 exposure (400 ms) for the CCD- and 5 (160 ms, 200 ms, 250 ms, 320 ms, 400 ms) for the storage phosphor system were used. Measurements were made in unprocessed (original) and processed images (contrast enhanced and/or high pass filtered). The results showed underestimation of bone loss, but smaller than previously reported for film radiographs. No significant difference was found between the 2 systems when compared at the same exposure. Nor were any significant differences found between unprocessed and processed images or between storage phosphor images from different exposures. We conclude that digital radiographs are comparable to film based radiographs for measurement of buccal bone loss but that lower exposures can be used, especially with the storage phosphor system.

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.

Correction of background noise in direct digital dental radiography

OBJECTIVES

To clarify the source of noise in direct digital intra-oral radiography with RVG-S (Trophy Radiologie, Vincennes, France) and to use these to develop a method for correction of background noise.

METHODS

Sensor temperature, image acquisition time and X-ray dose were independently analysed with the IPLab Spectrum (Signal Analytics, Vienna, VA) software.

RESULTS

The decrease in pixel value due to the dark current was linearly related to the image acquisition time. Although a variation in sensitivity was observed when the sensor was exposed to X-rays, the mean pixel value of the entire image was linearly related to the exposure time. The image showing only the signal due to X-ray dose was derived from the original RVG-S image by correcting for the dark current and the pixel-by-pixel sensitivity variation of the CCD sensor.

CONCLUSION

The image formed only by X-ray dose distribution can be derived by correcting for the background noise.

Criteria for the assessment of intrinsic performances of digital radiographic intraoral sensors

RATIONALE AND OBJECTIVES

In sensor-based dental digital radiographic imaging systems, it should be possible to assess the intrinsic performance of the sensor by means of objective criteria, independent of the related electronic hardware and image-treatment software.

METHODS

Six criteria are presented and discussed for the objective assessment and quantification of the intrinsic performance of intraoral sensors for dental digital radiography, independent of the characteristics of the subsequent image-treatment software. The criteria are signal-to-noise ratio, blooming, sensitivity, spatial uniformity, modulation transfer function, and geometric deformations. These criteria have been used to evaluate the Visualix sensor.

RESULTS

For each criterion, a series of numerical data are presented as graphs.

CONCLUSION

A method is proposed for objective assessment of radiographic sensors that makes it possible to compare sensors with each other and with conventional radiographs. The criteria proposed also increase understanding of digital diagnostic images and improve their clinical use.

Diagnostic accuracy of direct digital dental radiography for the detection of periapical bone lesions: overall comparison between conventional and direct digital radiography

OBJECTIVES

The diagnostic accuracy of direct digital radiography for the detection of small, experimentally made, periapical lesions was compared with that of E speed film. The high- and low-contrast resolutions of the imaging systems were also compared.

STUDY DESIGN

The high-contrast resolution was evaluated with a line pair plate. The low-contrast resolution was determined with a contrast-detail plexiglass phantom. To evaluate the diagnostic accuracy, the periapical region of dry human mandibles was examined. Receiver operating characteristic based on the readings of seven observers were generated.

RESULTS

The high-contrast resolution of the digital system was inferior, but the low-contrast resolution was comparable to that of E-speed film. For diagnostic accuracy no significant difference was seen between the areas under the receiver operating characteristic curves.

CONCLUSIONS

The quality of the direct digital images is comparable to that of E-speed film for the detection of periapical bone lesions.

Digital enhancement of radiographs: can it improve caries diagnosis?

Unlike traditional radiographs, digital images are electronically alterable and offer the potential for enhancing diagnostic information. The authors conducted a small-scale study to examine differences in clinicians' diagnoses of caries using traditional radiographs and digitized images vs. microscopic diagnosis. Two general dentists and one oral-maxillofacial radiologist scored the images for caries. This study suggests that digital enhancements may aid some clinicians in caries diagnosis.

On the dynamic range of different X-ray photon detectors in intra-oral radiography. A comparison of image quality in film, charge-coupled device and storage phosphor systems

OBJECTIVE

To compare film for intra-oral radiography with two charge-coupled device (CCD) and one storage phosphor system for digital imaging in respect of subjective image quality, detectability of small mass differences and appearance of burn-out effects and blooming phenomena at various exposure times.

METHODS

Dried mandibles with teeth from different areas were radiographed at exposures covering a relative range from 1 to 100. Image quality was subjectively evaluated after image processing, when applicable, using a visual grading scale from 0 to 10. The number of visible holes in an aluminium block was used to measure the detectability of small mass differences. Burn-out effects and blooming were evaluated by measuring widths of roots and of aluminium and plastic cylinders.

RESULTS

Radiographs with the storage phosphor system achieved image quality scores similar to those of film but over a larger exposure range, while CCD images were rated lower and over a smaller range. All holes in the aluminium block were only detected with the storage phosphor system. While the widths of roots were strongly affected by sensor saturation in CCD images and by burn-out in film images, smaller effects were seen with the storage phosphor system. Similar results were obtained with aluminium and plastic cylinders.

CONCLUSIONS

Higher image quality was achieved over a much wider exposure range with the storage phosphor system than with either film or the CCD systems.

Endodontic measurements in digital radiographs acquired by a photostimulable, storage phosphor system

Digora is a newly developed digital system for intraoral radiography utilizing photostimulable storage phosphor image plates. The aim was to test the quality of the system in respect to the visibility of endodontic files and root apices at different exposures. In teeth from five dry mandibular jaw sections, Hedstrom files no. 15 were placed with the file tip at varying distances from the apex. The specimens were covered with soft tissue equivalent material and placed behind a 2-cm thick polymethyl methacrylate cylinder filled with water. Distance from focus to image plate was 30 cm. Exposures were made at 60 kV and 7 mA at 7 timer settings from 16 ms to 1000 ms in 50% increments. All images were viewed from the monitor by each of 8 observers allowed to use available contrast enhancement facilities to obtain subjectively good image quality. Utilizing built-in measurement functions, distances from file tip and root apex, respectively, to a reference line were measured in 0.1 mm. For measurements between file tip and reference line, and root apex and reference line, there was no statistically significant difference between measurements made at the lowest exposure, compared to the second lowest exposure but there was a statistically significant difference compared to the 5 highest. Measurements at the second lowest exposure were not significantly different from those obtained at the 5 highest exposures. Interobserver variability expressed as standard deviation between observers showed the largest value for measurements obtained at the lowest exposure. The mean observed distances between the tip of the file and the root apex were calculated and showed no statistically significant differences between different exposures. We concluded that the Digora intraoral image plate system provided reliable endodontic measurements even at very low exposures.

Observers' use of image enhancement in assessing caries in radiographs taken by four intra-oral digital systems

OBJECTIVES

To evaluate observers' use of image-enhancement facilities and time consumption in assessing caries in radiographs taken with four digital systems.

METHODS

In total, 131 extracted human premolars and molars were mounted three in a line. Radiographs were taken using four digital systems: Digora (DIG), Radio VisioGraphy (RVG), Sens-A-Ray (SAR) and Visualix (VIX), and imported into a programme with routines for adjustment of brightness, contrast and gamma curve. Sixteen images from each digital system were compressed (JPEG, irreversible compression). The 588 images were scored by six observers for approximal and occlusal caries on a five-point confidence scale using enhancement as they pleased. The programme automatically recorded any enhancement made without the observers knowing this.

RESULTS

Some form of digital enhancement was used in almost all images, with the gamma curve being the most frequent. The VIX images were enhanced most followed by SAR, DIG and RVG images. The differences were significant (p < 0.01) except between DIG and SAR images. The compressed images were enhanced significantly more than their uncompressed counterparts (p = 0.02). The average time spent recording one image was 24 s. On average, significantly less time was spent with the DIG images than the other systems (p < 0.01), while there were no significant differences between the CCD-based systems (p > 0.2). There was no relationship between time spent and number of manipulations performed.

CONCLUSIONS

The observers took advantage of the facilities available for enhancement of density and contrast in digital images. The potential of gamma curve manipulation requires further investigation.

Digital radiographic images will benefit endodontic services

Future assurances for endodontic services and assessments of traumatized teeth will depend in part on significant improvements to the quality of dental radiographs. Whereas digital images offer many potential sensor, display and archival advantages over film-based radiographs, the marginal image improvements from intraoral sensors primarily benefit patient education. Precisely digitized conventional radiographs are more likely to yield quantum image resolution improvements, although neither dentists nor patients will benefit until cost-effective digitizing systems have been developed for the dental office.

Measurement accuracy: a comparison of two intra-oral digital radiographic systems, RadioVisiography-S and FlashDent, with analog film

OBJECTIVES

To compare the accuracy of measurement algorithms incorporated into the software provided with two CCD-based digital radiographic systems and compare assessments using intra-oral film.

METHODS

A test object with three radiopaque reference points was imaged using Ektaspeed intra-oral film, both with and without an overlaid 1 mm reference grid, the RVG-S, the measurement software of which overlays a 2 mm grid, and the FlashDent, which uses a mouse-driven cursor to estimate distances. Geometric factors, including source-to-object and receptor-to-object distances, vertical and horizontal cone angulation, and vertical angulation of receptor, were successively altered. Six viewers estimated vertical, horizontal and diagonal distances for each image.

RESULTS

Increased source-to-object distance resulted in a 5-10% reduction in image dimensions, whereas increased receptor-to-object distance produced a magnification of 15-20% with all techniques. Increased vertical and horizontal cone angulation resulted in slight increases in magnification (0-5%) whereas greater receptor angulation resulted in noticeable magnification under all test conditions (10-15%). Estimated values for vertical, horizontal and diagonal measurements were approximately 5-10% higher than the actual dimensions, irrespective of the technique used. The FlashDent mouse-driven cursor system and direct measurement of distances from conventional film were more accurate in horizontal and diagonal dimension estimates than using an overlaid grid. Intra-observer and inter-observer differences were found for specific situations.

CONCLUSION

The mouse-driven computerized measurement cursor and intra-oral film assessment using a ruler provided the most accurate, reliable and consistent dimensional measurements.

Perceptibility of defects in an aluminum test object: a comparison of the RVG-S and first generation VIXA systems with and without added niobium filtration

OBJECTIVE

To compare the first generation VIXA (Gendex, Milan, Italy) and the RVG-S (Trophy Radiologie, Vincennes, France) for detection of defects in an aluminium test object at various exposures both with and without added niobium filtration.

METHODS

Images of a 7 mm aluminium test object with defects ranging from 0.1 to 1.5 mm with standardized projection geometry. Seven dentists acted as observers. Perceptibility curves were developed for both sensors under the various filtration conditions and exposures.

RESULTS

At optimum exposures both the VIXA and the RVG-S permitted the same number of defects to be observed. The optimum exposures were similar for the two systems, but the dynamic range was greater for the RVG-S. Addition of niobium filtration did not appreciably alter the radiation dose required to perceive a given number of defects using either system.

CONCLUSIONS

The two systems performed equally at optimum exposure when the dose is approximately the same irrespective of the presence or absence of niobium filtration. Beyond the optimal level, the RVG-S outperformed the VIXA system.

Video-based teleradiology for intraosseous lesions. A receiver operating characteristic analysis

Immediate access to off-site expert diagnostic consultants regarding unusual radiographic findings or radiographic quality assurance issues could be a current problem for private dental practitioners. Teleradiology, a system for transmitting radiographic images, offers a potential solution to this problem. Although much research has been done to evaluate feasibility and utilization of teleradiology systems in medical imaging, little research on dental applications has been performed. In this investigation 47 panoramic films with an equal distribution of images with intraosseous jaw lesions and no disease were viewed by a panel of observers with teleradiology and conventional viewing methods. The teleradiology system consisted of an analog video-based system simulating remote radiographic consultation between a general dentist and a dental imaging specialist. Conventional viewing consisted of traditional viewbox methods. Observers were asked to identify the presence or absence of 24 intraosseous lesions and to determine their locations. No statistically significant differences in modalities or observers were identified between methods at the 0.05 level. The results indicate that viewing intraosseous lesions of video-based panoramic images is equal to conventional light box viewing.

Accuracy of caries diagnosis in digital images from charge-coupled device and storage phosphor systems: an in vitro study

OBJECTIVES

To evaluate the diagnostic accuracy of carries detection with four intra-oral digital radiographic systems in vitro and to investigate the impact of image compression.

METHODS

116 extracted human premolars and molars mounted three in a line with approximal contacts were radiographed with four digital systems (Digora, RVG, Sens-A-Ray, and Visualix) and imported into a Windows-based program. Sixteen images from each system were compressed (JPEG, irreversible compression). The total of 528 images was assessed by six radiologists using a 5-point confidence scale for the detection of approximal and occlusal caries. Caries was validated histologically. The disease threshold was caries in enamel for approximal surfaces and in dentine for occlusal surfaces.

RESULTS

Mean ROC curve areas for approximal surfaces were 0.611 (DIG), 0.572 (RVG), 0.594 (SAR), and 0.596 (VIX), and for occlusal surfaces 0.794 (DIG), 0.819 (RVG), 0.751 (SAR), and 0.761 (VIX). There were no significant differences between the areas under the ROC curves (p > 0.05); nor were there any significant differences between the compressed and uncompressed images (p > 0.05).

CONCLUSIONS

The four digital systems performed almost equally well for detection of caries in vitro, and compressed images were as accurate as uncompressed.

Future trends in dental radiology

Direct digital dental radiographic systems offer the potential to radically change the way dentists diagnose and treat dental pathoses. They offer instantaneous availability of radiographs, markedly lower patient radiation exposure, and the elimination of developing chemicals and developing equipment. The storage of dental radiographs as digital data permits their transmittal over phone lines facilitating phone consultations and may someday allow expedited authorization of treatment plans by dental insurance companies. With the use of digital subtraction radiology the dental practitioner will be able to diagnose periodontal disease progression and dental caries progression long before current techniques can detect a change. With tuned aperture computed tomography, the owner of a filmless digital system can make tomographic radiographs that allow the visualization of slices through areas of interest without having to buy additional hardware. Computer-aided diagnosis will facilitate the detection of proximal dental caries and osteoporosis, and may someday allow automated tracing of cephalometric radiographs.

Absolute measures of image quality for the Sens-A-Ray direct digital intraoral radiography system

To study the noise characteristics of the Sens-A-Ray (Regam Medical Systems AB, Sundsvall, Sweden) system, 20 radiographs were obtained at each of three different exposure levels at 70 and 90 kVp with a homogeneous x-ray field. Exposures were measured with an ionization chamber. Noise power spectra were calculated over three areas within each radiograph, and ensemble averages were subsequently found from 60 data files at each exposure level. Noise equivalent quanta were calculated with the noise power spectra and modulation transfer function data from previous studies. Finally, the detective quantum efficiency was calculated by dividing the noise equivalent quanta by the estimated incident photon fluence at the different exposures. The system has a maximum detective quantum efficiency of approximately 0.030 at 70 kVp and 0.025 at 90 kVp. A broad maximum exists at approximately 2 cycles/mm, indicating that the signal-to-noise ratio is most favorable at this spatial frequency.

Sens-A-Ray characteristics with variations in beam quality

This study examined the relationship between x-ray beam quality and image characteristics with the use of the Sens-A-Ray (Regam Medical Systems, Sundsvall, Sweden). To evaluate the x-ray response, properties of the image sensor, dark current and statistical noise, sensitivity, and contrast resolution were measured. Tube voltage, tube current, and exposure time were varied. Exposures were determined with the use of an ionization chamber. Pixel values beneath a lead strip were used to calculate dark current effects. Contrast was measured with pixel values from the images of a step-wedge. Dark current noise increased in proportion to exposure time. Although the sensitivity at each tube voltage was linear and proportional to the exposure, the gradient was inversely proportional to increased tube voltage. After subtraction of the dark current and statistical noise, the gradient of the sensitivity at low tube voltage remained steeper than at high tube voltages. Hence, sensitivity decreased with increased tube voltage. Sensitivity gradients at each different tube current were similar. Irrespective of exposure, contrast resolution between adjoining step-wedge steps > or = 9 mm were too small to distinguish at 50 kVp. The gray levels for each step below 12 mm in thickness were distinguishable with 90 kVp. Increased dark current noise consequent to long exposure times narrowed the available gray scale range. Lower tube voltage resulted in higher sensitivity with larger gradients than higher tube voltages.