Artifacts in computed radiography

Impact of enhancement filters of a CMOS system on halo artifact expression at the bone-to-implant interface

OBJECTIVE

To assess the impact of enhancement filters on the formation of halo artifacts in radiographs of dental implants obtained with a complementary metal oxide semiconductor (CMOS) system.

METHODS

Digital radiographs of dental implants placed in dry human mandibles were processed with the Noise Reduction smoothing filter, as well as the Sharpen 1, Sharpen 4, and Sharpen UM high-pass filters available in the CLINIVIEW™ software (Instrumentarium Dental, Tuusula, Finland). Subjective analysis involved evaluating the left, right, and apical surfaces of each implant for the presence of much, few, or no halo. The objective analysis involved measurement of the halo area using the Trainable Weka Segmentation plugin (ImageJ, National Institutes of Health, Bethesda, MD, USA). Data were analyzed using Friedman's test (subjective analysis) and ANOVA (objective analysis) (α = 5%).

RESULTS

In the subjective evaluation, the Sharpen 4 filter produced more radiographs with much halo present, and in the objective evaluation, a bigger halo area when compared to the original images and the Noise Reduction filter for all surfaces (p < 0.05).

CONCLUSIONS

When evaluating dental implants, priority should be given to original images and those enhanced with smoothing filters since they exhibit fewer halo artifacts.

CLINICAL RELEVANCE

Post-processing tools, such as enhancement filters, may improve the image quality and assist some diagnostic tasks. However, little is known regarding the impact of enhancement filters in halo formation on CMOS systems, which have been increasingly used in dental offices.

Accuracy of various imaging methods for detecting misfit at the tooth-restoration interface in posterior teeth

Purpose

The present study aimed to evaluate which of the following imaging methods best assessed misfit at the tooth-restoration interface: (1) bitewing radiographs, both conventional and digital, performed using a photostimulable phosphor plate (PSP) and a charge-coupled device (CCD) system; (2) panoramic radiographs, both conventional and digital; and (3) cone-beam computed tomography (CBCT).

Materials and Methods

Forty healthy human molars with class I cavities were selected and divided into 4 groups according to the restoration that was applied: composite resin, composite resin with liner material to simulate misfit, dental amalgam, and dental amalgam with liner material to simulate misfit. Radiography and tomography were performed using the various imaging methods, and the resulting images were analyzed by 2 calibrated radiologists. The true presence or absence of misfit corresponding to an area of radiolucency in regions subjacent to the esthetic and metal restorations was validated with microscopy. The data were analyzed using a receiver operating characteristic (ROC) curve, and the scores were compared using the Cohen kappa coefficient.

Results

For bitewing images, the digital systems (CCD and PSP) showed a higher area under the ROC curve (AUROC) for the evaluation of resin restorations, while the conventional images exhibited a larger AUROC for the evaluation of amalgam restorations. Conventional and digital panoramic radiographs did not yield good results for the evaluation of resin and amalgam restorations (P<.05). CBCT images exhibited good results for resin restorations (P>.05), but showed no discriminatory ability for amalgam restorations (P<.05).

Conclusion

Bitewing radiographs (conventional or digital) should be the method of choice when assessing dental restoration misfit.

Artifacts in Computed Radiography

Computed radiography offers many advantages over the conventional radiography. With new technological breakthroughs and the development of systems that are more cost-effective, there has been an increase in its use in the recent years. However, like all imaging modalities, one must be aware of the various artifacts that are likely to lead to misdiagnosis. In this article, we illustrate the potential hardware and software artifacts that are associated with its use.

Radiolucency in stemless shoulder arthroplasty is associated with an imaging phenomenon

Stemless humeral implants show comparable midterm clinical results compared to stemmed components. Recently, radiolucencies around the metaphyseal seating of humeral stemless implants were reported on postoperative radiographs. It is controversial whether they are attributable to bone resorption. We hypothesized these radiolucencies result from imaging artifacts. Seven cadaveric specimens (three male and four female) were first radiographed and then scanned with CT. A stemless humeral component of current design was implanted in each specimen. After implantation, all specimens were radiographed with different exposure settings. The implant was removed, and the specimens were scanned with CT again. Pre- and post-implantation radiographs and CT scans were compared. The mean Hounsfield units (HU) at the humeral resection plane from the pre-implantation CT were correlated with the diameter of the radiolucent halo on the post-implantation radiographs. A symmetric radiolucent halo of variable diameters occurred on all radiographs after implantation when an automatic exposure control was used. The halo disappeared in all specimens when the tube voltage was reduced. Lower CT-values (HU) before the implantation resulted in greater halos on the radiograph after implantation. Symmetric radiolucent halos can result from imaging artifacts, which is most likely due to radiation scatter. The halos can be minimized by reducing the tube voltage. The halo effect appears to be pronounced in bones with decreased density. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2040-2050, 2017.

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

OBJECTIVES

To detect and determine image error and artefact types in intraoral radiographs obtained with photostimulable phosphor (PSP) technology, place them in an appropriate classification and retrospectively analyze the PSP-specific image errors and artefacts. The causes and solutions of PSP-specific errors and artefacts have also been discussed.

METHODS

The radiographic database of Ondokuz Mayis University, Faculty of Dentistry, Department of Dentomaxillofacial Radiology, was used for this study. Different types of image errors and artefacts observed on intraoral radiographs during 2014-15 were detected and defined. A total of 2100 intraoral radiographs were individually evaluated for the distribution of PSP-specific image artefacts.

RESULTS

There were 34 image error and artefact types detected and classified into 4 groups according to the causative factors. The most common PSP-specific image artefacts were found in fading with a ratio of 44.1% for the ambient light-related group, peeling of the plate borders with a ratio of 53.4% for the PSP plate-related group and straight line with a ratio of 42.2% for the scanner-related group.

CONCLUSIONS

The determination and definition of the image errors and artefacts with clarification of their causes and solutions are important for the improvement of radiographic quality and the reduction of the retake ratio.

Computed radiography image artifacts revisited

OBJECTIVE

Computed radiography (CR) has provided a ready cost-effective transition from screen film to digital radiography and a convenient entrance to PACS. This article revisits artifacts encountered in CR systems. These artifacts may obscure abnormalities, mimic a clinical entity, or hamper image quality.

CONCLUSION

With the new-generation CR systems, software- and hardware-related artifacts have decreased, making operator errors more evident. The purpose of this study is to establish the current trend of CR artifacts and the new facets in identifying and resolving problems quickly that will help prevent future occurrences. This article also brings to light the importance of constant review required of this extensively studied topic to avoid diagnostic misadventures.

Durability of imaging plates in clinical use

In many X-ray clinics, the traditional photographic film has been replaced by an imaging plate (IP). The IP is re-usable and the purpose of this study was to test if image deterioration occurred after successive uses of the IP. The emphasis is placed on the efficiency of image formation and on image uniformity. In a cross-sectional study, 21 clinically used IPs were exposed with a standardized phantom imaging protocol. These IPs were in clinical use between one month and two years and the IPs were exposed between 191 and 3787 times. After digitizing, the mean pixel value (MPV) in a predefined image area was determined. The relation between MPV and IP uses was assessed. In a second experiment, image uniformity of 30 other clinically used IPs was visually inspected for artifacts on a diagnostic monitor. These IPs were in clinical use between one week and two years and exposed between 76 and 5373 times. The first experiment showed that no significant deterioration of the MPV with increasing usage count of the IP was present (p = 0.15). The second experiment showed the appearance of clinically relevant artifacts on the IP before 3000 uses. It was concluded that the efficiency of the image formation process does not significantly deteriorate after successive use of IPs and is therefore not expected to limit their life span. Mechanical handling in the digitizer of the used system seems to set a limit to IP durability. Uniformity should therefore be checked regularly in clinical quality control.

Artifacts found during quality assurance testing of computed radiography and digital radiography detectors

A series of artifact images, obtained over 5 years of performance testing, of both computed radiography (CR) and integrated digital radiographic X-ray imaging detectors are presented. The images presented are all either flat field or test object images and show artifacts previously either undescribed in the existing literature or meriting further comment. The artifacts described are caused by incorrect flat field corrections, a failing amplifier, damaged detector lines affecting their neighbors, lost information between neighboring detector tiles, image retention, delamination of a detector, poor setup of mechanical movements in CR, suckers damaging a CR plate, inappropriate use of grid suppression software, inappropriate use of a low pass spatial frequency filter, and unsharp masking filters. The causes and significance of the artifacts are explained and categorized as software or hardware related. Actions taken to correct the artifacts are described and explained. This work will help physicists, radiographers, and radiologists identify various image quality problems and shows that quality assurance is useful in identifying artifacts.

Digital radiography artifacts

Radiographic artifacts may mimic a clinical feature, impair image quality, or obscure abnormalities. With the development of digital radiography (DR), a new set of artifacts is introduced. Regardless of the technology, the classic technical errors that occur with film screen radiography still occur using DR. Artifacts created using computed radiography, DR, and incorrect image processing are discussed. Methods for correction of the artifacts are presented.

Practical guidelines for radiographers to improve computed radiography image quality

Computed Radiography (CR) has become a major digital imaging modality in a modern radiological department. CR system changes workflow from the conventional way of using film/screen by employing photostimulable phosphor plate technology. This results in the changing perspectives of technical, artefacts and quality control issues in radiology departments. Guidelines for better image quality in digital medical enterprise include professional guidelines for users and the quality control programme specifically designed to serve the best quality of clinical images. Radiographers who understand technological shift of the CR from conventional method can employ optimization of CR images. Proper anatomic collimation and exposure techniques for each radiographic projection are crucial steps in producing quality digital images. Matching image processing with specific anatomy is also important factor that radiographers should realise. Successful shift from conventional to fully digitised radiology department requires skilful radiographers who utilise the technology and a successful quality control program from teamwork in the department.

The physics of computed radiography

Cassette-based computed radiography (CR) systems have continued to evolve in parallel with integrated, instant readout digital radiography (DR) systems. The image quality of present day CR systems is approaching its theoretical limits but is significantly inferior to DR. Further improvements in CR image quality require improved concepts. The aim of this review is to identify the fundamental limitations in CR performance. This will provide a background for the development of new approaches to improve photostimulable phosphor CR systems. It will also guide research in designing better CR systems to possibly compete with DR systems in terms of image quality parameters such as detective quantum efficiency and yet maintain CR convenience in being portable and more economical.

Artefacts found in computed radiography

Artefacts on radiographic images are distracting and may compromise accurate diagnosis. Although most artefacts that occur in conventional radiography have become familiar, computed radiography (CR) systems produce artefacts that differ from those found in conventional radiography. We have encountered a variety of artefacts in CR images that were produced from four different models plate reader. These artefacts have been identified and traced to the imaging plate, plate reader, image processing software or laser printer or to operator error. Understanding the potential sources of CR artefacts will aid in identifying and resolving problems quickly and help prevent future occurrences.

Synthetic hair braid extension artifacts in panoramic radiographs

The authors present two case reports that illustrate synthetic hair braid extension artifacts in panoramic radiographs. They found that hairstyles using synthetic hair braid extensions created radiopaque patterns that varied according to hairstyles. They discuss how these hair extensions may affect panoramic radiographs and the importance of determining whether patients are wearing synthetic hair braid extensions.

Evaluation of an automatic-mode image processing method in chest computed radiography

RATIONALE AND OBJECTIVES

The automatic image processing mode of the storage phosphor computed radiography system was evaluated.

MATERIALS AND METHODS

A dedicated chest unit designed for erect view was used to examine a chest phantom. Lucite plates 1, 2, and 3 cm thick that conformed to the shape of the lung were attached to the phantom, and images were obtained in automatic and manual image processing modes. The changes in the optical density of the lung, rib, and heart and the changes in contrast were measured. The degree of diffuse opacity due to the plates and the visibility of superimposed simulated nodular and honeycomb opacities were evaluated.

RESULTS

The decrease in optical density and contrast caused by increasing thickness of the Lucite plates was less pronounced in the automatic mode compared with the manual mode. When plates were placed only on the right lung, the optical density and the contrast on the contralateral side either increased or remained unchanged with the automatic mode. The degree of diffuse opacity was rated higher in the manual mode, and the visibility of superimposed simulated opacities was considered relatively constant in the automatic mode.

CONCLUSION

The automatic image reading mode used in the computed radiography chest system may mask the detection of abnormalities such as diffuse homogeneous lung opacity.

Reduction of patient exposure in pediatric radiology

RATIONALE AND OBJECTIVES

The authors determined whether presently used exposure levels in pediatric imaging can be reduced without loss of information or a decrease in diagnostic accuracy.

MATERIALS AND METHODS

Multiple (stacked) image detectors and filters were used to obtain identical compute radiographic images at different exposure levels of neonates with either no active lung disease or hyaline membrane disease. Physical characteristics of the images were measured. A contrast-detail study and a receiver operating characteristic study were conducted to measure observer performance.

RESULTS

Physical measurements and results of the contrast-detail study revealed that the dose-reduction images were essentially limited by x-ray quantum noise. Results of the receiver operating characteristic study indicated that diagnostic accuracy did not decrease significantly up to about 75% exposure reduction levels, although image quality rating data decreased with each exposure reduction.

CONCLUSION

Decreasing exposure levels to about 75% of current levels may be acceptable in some clinical situations where dose is a concern, such as in pediatric imaging.

Computed radiography X-ray exposure trends

RATIONALE AND OBJECTIVES

Computed radiography provides correct optical density on film, independent of the incident radiation exposure, but it can result in under- or overexposure of the imaging plate. In the current study, we evaluated the radiation exposure trends of computed radiography over a 2-year period for portable chest examinations to determine and compare the radiographic techniques of the computed radiography system relative to conventional screen-film detectors.

METHODS

A Fuji computed radiography system was interfaced to a digital workstation to track system usage and examination demographics, including examination type and sensitivity number. Hard-copy films were used for diagnosis. The sensitivity number, a value inversely related to incident exposure on the imaging plate, was used to determine whether the proper techniques were used by the technologists.

RESULTS

The initial use of the computed radiography system revealed a broad distribution of exposures being used; complaints regarding noisy films (e.g., underexposure) resulted in subsequent overexposure for a significant number of films. A quality-control audit indicating excessive exposure resulted in educational feedback and a tighter distribution of exposures within the optimal range as determined by our radiologists. The average technique was approximately equivalent to a 200-speed system.

CONCLUSION

Computed radiography provides excellent dynamic range and rescaling capabilities for proper film optical density, and thus fewer repeat examinations. However, underexposure results in suboptimal image quality that is related to excessive quantum mottle. Overexposure requires film audits to limit unnecessary radiation exposure. In general, the optimal exposures are achieved with approximately 1.5-2 times the incident detector exposure of a 400-speed rare-earth system. The ability of computed radiography to reduce radiation exposure is unlikely when compared with a typical rare-earth screen-film combination (400 speed) in terms of adequate image quality for the diagnosis of subtle, low-contrast findings. For certain diagnostic procedures (e.g., nasogastric tube placement verification), lower exposures can be tolerated.

Radiation dose reduction in computed skeletal radiography. Effect on image quality

PURPOSE

To evaluate the effect of radiation dose reduction on image ++quality in computed musculoskeletal radiography and determine optimal exposure range.

MATERIAL AND METHODS

In 11 corpses, 1 hand and 1 hip were examined with film-screen radiography, and a series of computed radiographs was obtained using exactly the same technique except for the exposure, which was 100, 50, 25, 12.5, 6.25, and 1.56% of the mAs numbers used for the film-screen images. The computed hip radiographs were processed in 2 different ways, one simulating the film-screen images and one using contrast enhancement. Four radiologists reviewed the images regarding the following parameters: cortical bone, trabecular bone, joint space, and soft tissue, giving each a diagnostic quality rating on a scale from 1 to 5. The median and mean values were found for the pooled results.

RESULTS

For the hands, the computed radiographs were ranked inferior to the film-screen images for all parameters except soft tissue, where the computed radiographs scored higher. The computed images with 50 and 25% exposure were ranked equal to the 100% ones. The quality rating slowly declined with lower exposures. For the hips, the 100 and 50% computed radiographs were generally similar to or slightly better than the film-screen images. The decline was somewhat faster than for the hands. The contrast-enhanced hip images scored less than the nonenhanced images at any given exposure for all parameters except soft tissue, where the contrast-enhanced images scored better at all exposures. The difference between nonenhanced and enhanced images became less at the lower exposures.

CONCLUSION

Lowering the exposure in computed musculoskeletal radioagrphy below the level of film-screen radiography is feasible, especially in the peripheral skeleton. Contrast enhancement seems to be valuable only in the evaluation of soft-tissue structures.