Conventional radiographs vs digitized radiographs: image quality assessment

OBJECTIVES: The aim of this study was to compare image quality characteristics of conventional radiographs and their digital counterparts. METHODS: 100 conventional radiographs (E-speed) were used for the evaluation of density and contrast. The radiographs were made using a range of exposures under standardized conditions and were compared with digital images that resulted from scanning the above radiographs with a commercially available scanner. Resolution was evaluated with an experiment using 50 film packets and a resolution target exposed with different exposure times, using both the original radiographs and their scanned equivalents. RESULTS: The digitized radiographs appeared to be of higher density than the conventional ones. Moreover, they demonstrated a narrower density range. Resolution was similar for both types of images. CONCLUSIONS: Although there is an agreement with the literature that the digitized radiographs are of higher density, further investigation is required to detect the various factors that may have an effect on the quality of the digitized images.     

Radiography of the wrist. A new device for standardized radiographs

A number of methods exist for determination of carpal bone angles on lateral wrist radiographs. However, there is no general or precise definition of the angles measured. In this study the positioning of the wrist is emphasized and a device used to obtain standardized radiographs is presented. An analysis of variance of two series of patients revealed no radiological difference between the contralateral wrists in the same person. We conclude that the asymptomatic wrist can be used as normal reference in the assessment of carpal bone angles in the pathological wrist and a difference between the carpal bone angles in the two wrists in the same person exceeding 5 degrees can be considered significant.     

Comparison of 2048-line digital display formats and conventional radiographs: an ROC study

Observer performance tests were conducted to compare the effects on diagnostic accuracy of digital hard copy and video display formats versus conventional radiographic film. Digital images were obtained by digitizing conventional chest radiographs to a 2048 x 2048 matrix with a laser film scanner. Three digital display formats were used: laser-printed digital film, a 2048-line video monitor without user interaction, and a 2048-line video monitor with user interaction. Thirty-one posteroanterior chest radiographs, determined by consensus of four thoracic radiologists to contain septal lines (n = 11), parenchymal nodules (n = 7), nodules and septal lines (n = 7), or neither abnormality (n = 6), were used for the study. Images were interpreted by four radiologists in four separate viewing sessions. Diagnostic accuracy was determined by receiver-operating characteristic analysis for each observer with each viewing technique. No statistical differences in diagnostic accuracy, determined by the area under the receiver-operating-characteristic curve, were found between the analog film, the digital film, and the two video digital display formats. This preliminary study suggests that 2048-line digital displays may be an acceptable alternative to the traditional lightbox viewing method for the perception of these two abnormalities commonly seen on chest radiographs.     

Imaging assessment of the postoperative arthritic wrist

Wrist arthritis is a common disease entity that can result in severe pain, swelling, and decreased wrist motion, leading to the impairment of daily activities and vocational functions. Nonsurgical treatment for wrist arthritis can improve function and provide pain relief in some cases. With disease progression, however, conservative therapy may become ineffective, and surgical treatment may be required. The three main surgical options for wrist arthritis are arthrodesis, carpectomy, and arthroplasty. Because of the high prevalence of wrist arthritis, radiologists will commonly encounter images that were obtained in patients who have undergone one or more of these surgical options. All three options are common in contemporary orthopedic practice and have evolved in recent years, making it imperative that radiologists understand current procedures and stay abreast of advances in techniques and hardware. In addition, familiarity with both normal and abnormal postoperative imaging findings can aid in the assessment of complications and early failure.     

Precision in assessment of osteoporosis from spine radiographs

Inter- and intra-observer variation in spine radiographs of 100 osteoporotic women and longitudinal change in roentgenologic status after 1 year of antiosteoporotic treatment were assessed. The method applied was naked eye inspection, and a score system estimating severity of fractures - vertebral deformation score (VDS). Agreement was assessed by the Kappa coefficient corrected for agreement by change. The results showed a satisfactory inter- and intraobserver agreement for wedge (Kappa = 0.72 and 0.90) and compression fractures (Kappa = 0.60 and 0.92). The method proved less reliable for endplate fractures (Kappa = 0.39 and 0.73). We think that the method of investigation is well suited for monitoring treatment effects in longitudinal studies.     

Spatial resolution requirements for digital chest radiographs: an ROC study of observer performance in selected cases

Thirty-eight selected clinical radiographs were digitized and displayed on a 1,024-line monitor at pixel sizes of 1.6, 0.8, 0.4, and 0.2 mm. Eighteen experienced radiologists assessed the radiographs and digital images, which included 12 examples of abnormal solitary nodular density, ten examples of septal lines, and 16 controls, six of which showed diffuse lung abnormalities. For each level of spatial resolution and for film reading, observers gave their decision confidence on a sliding scale of probability. Receiver operating characteristic curves were generated from these data. It was found that while spatial resolution requirements for solitary nodules were not critical for pixel sizes at or below 0.8 mm, the requirement for septal lines was likely to be 0.4 mm (1.25 line pairs/mm).     

Effects of image processing on nodule detection rates in digitized chest radiographs: ROC study of observer performance

To evaluate the effects of image processing in digitized chest radiographs when high-resolution images are used, an examination was done in which the detection of pulmonary nodules in unprocessed digitized chest radiographs was compared with that in images that had undergone processing with two methods, adaptive filtration and histogram equalization. The processing techniques have been optimized in previous work to selectively enhance the retrocardiac and subdiaphragmatic areas without significant alteration of detail in the lung. Eight observers were shown 150 test radiographs (50 unprocessed, 50 processed with adaptive filtration, 50 processed with histogram equalization) containing 150 nodules. The results indicate a statistically significant (P less than .03) difference, with highest observer performance in the chest radiographs processed with adaptive filtration (median area under ROC curve = 0.78), compared with unprocessed images (median = 0.68) and chest radiographs processed with histogram equalization (median = 0.62). Performance in the lung was not significantly different. Adaptive filtration applied to selectively enhance underexposed areas of film images may improve nodule detection. Histogram equalization provided no improvement in performance.     

Computer-aided diagnosis for the detection and classification of lung cancers on chest radiographs ROC analysis of radiologists' performance

RATIONALE AND OBJECTIVES: The aim of the study is to investigate the effect of a computer-aided diagnostic (CAD) scheme on radiologist performance in the detection of lung cancers on chest radiographs. MATERIALS AND METHODS: We combined two independent CAD schemes for the detection and classification of lung nodules into one new CAD scheme by use of a database of 150 chest images, including 108 cases with solitary pulmonary nodules and 42 cases without nodules. For the observer study, we selected 48 chest images, including 24 lung cancers, 12 benign nodules, and 12 cases without nodules, from the database to investigate radiologist performance in the detection of lung cancers. Nine radiologists participated in a receiver operating characteristic (ROC) study in which cases were interpreted first without and then with computer output, which indicated locations of possible lung nodules, together with a five-color scale illustrating the computer-estimated likelihood of malignancy of the detected nodules. RESULTS: Performance of the CAD scheme indicated that sensitivity in detecting lung nodules was 80.6%, with 1.2 false-positive results per image, and sensitivity and specificity for classification of nodules by use of the same database for training and testing the CAD scheme were 87.7% and 66.7%, respectively. Average area under the ROC curve value for detection of lung cancers improved significantly (P = .008) from without (0.724) to with CAD (0.778). CONCLUSION: This type of CAD scheme, which includes two functions, namely detection and classification, can improve radiologist accuracy in the diagnosis of lung cancer.     

Personal computer versus workstation display: observer performance in detection of wrist fractures on digital radiographs

PURPOSE: To retrospectively compare the accuracy of observer performance with personal computer (PC) compared with that with dedicated picture archiving and communication system (PACS) workstation display in the detection of wrist fractures on computed radiographs. MATERIALS AND METHODS: This study was conducted according to the principles of the Declaration of Helsinki (2002 version) of the World Medical Association. The institutional clinical board approved the study; informed consent was not required. Seven observers independently assessed randomized anonymous digital radiographs of the wrist from 259 subjects; 146 had fractures, and 113 were healthy control subjects (151 male and 108 female subjects; average age, 33 years). Follow-up radiographs and/or computed tomographic scans were used as the reference standard for patients with fractures, and follow-up radiographs and/or clinical history data were used as the reference standard for controls. The PC was a standard hospital machine with a 17-inch (43-cm) color monitor with which Web browser display software was used. The PACS workstation had two portrait 21-inch (53-cm) monochrome monitors that displayed 2300 lines. The observers assigned scores to the radiographs on a scale of 1 (no fracture) to 5 (definite fracture). Receiver operating characteristic (ROC) curves, sensitivity, specificity, and accuracy were compared. RESULTS: The areas under the ROC curves were almost identical for the PC and workstation (0.910 vs 0.918, respectively; difference, 0.008; 95% confidence interval: -0.029, 0.013). The average sensitivity with the PC was almost identical to that with the workstation (85% vs 84%, respectively), as was the average specificity (82% vs 81%, respectively). The average accuracy (83%) was the same for both. CONCLUSION: The results of this study showed that there was no difference in accuracy of observer performance for detection of wrist fractures with a PC compared with that with a PACS workstation.     

Digital enhancement of radiographs for assessment of interproximal dental caries

OBJECTIVES: Evaluation of a particular digital caries image-enhancing mode (filter) for its effect on the validity of measurements of caries lesion depth. METHODS: Standardized radiographs of 44 extracted teeth exhibiting interproximal caries lesions were obtained. Six radiographs were obtained of each tooth and digitized. Four radiographs were made using D-speed film with and without soft tissue scattering equivalent (STSE) at normal exposure time (0.32 s) and underexposed (0.16 s). Two were made using E-speed film with STSE normally (0.16 s) and underexposed (0.08 s). On each of the 264 radiographs, 4 independent examiners measured the central depth (CD) of 1 carious lesion per tooth both on the unchanged radiographic image and after use of the filter. Histometric CD assessments provided a gold standard for comparison with the radiographic measurements (validity). Repeated measures ANOVA was calculated for validity in relation to examiner, lesion type, filter, film type, exposure time and STSE. RESULTS: The lesion type was identified to statistically significantly influence the validity of CD measurements. Examiner in combination with defect type (P<0.001), filter (P = 0.017), exposure (P = 0.027) and film type (P = 0.044) had an additional albeit small effect. CONCLUSIONS: The lesion type significantly influenced the validity of CD measurements: enamel lesions were less underestimated than dentin lesions.     

Mutagenicity and cytotoxicity assessment in patients undergoing orthodontic radiographs

Objectives

The aim of the present study was to evaluate DNA damage (micronucleus) and cellular death (pyknosis, karyolysis and karyorrhexis) in exfoliated buccal mucosa cells from individuals following radiography.

Methods

Lateral and frontal cephalometric X-ray and panoramic dental X-rays were taken of a total of 18 healthy patients (6 male and 12 female) referred for orthodontic therapy. Exfoliated oral mucosa cells were collected immediately before X-ray exposure and after 10 days.

Results

The results revealed no statistically significant difference (P > 0.05) in the frequency micronucleated oral mucosa cells after X-ray exposure. However, X-ray was able to increase other nuclear alterations closely related to cytotoxicity, such as karyorrhexis, pyknosis and karyolysis.

Conclusions

Data indicated that exposure to certain radiography may not be a factor in inducing chromosomal damage, but it does promote cytotoxicity.     

Automatic assessment of the knee alignment angle on full-limb radiographs

In this study a fully automatic assessment of the knee alignment angles in full-limb radiographs was developed and compared to manual standard of reference measurements in a prospective manner.The data consisted of 28 knees which were gathered from total-leg radiographs of 15 patients (12 males and 3 females with a mean age of 29.4 ± 6.9 years) consecutively.For statistical evaluation, a leave-one-out cross-validation was performed. The pattern recognition and consequently the fully automatic assessment were successful in all patients.The automatically measured angles highly correlated with the standard of reference (r = 0.989). The mean absolute difference was 0.578° (95% CI: 0.399-0.757°). 82% of the angles differed less than 1° from the standard of reference, 46% differed less than 0.5° and 31% differed less than 0.2°. The automatic method showed a high agreement between repeated measurements (+0.515° to −0.429°).The automatic assessment of alignment angles in full-limb radiographs were equal to the manual assessment. No measurement related user interaction was necessary to achieve results.     

Computer-aided diagnosis to distinguish benign from malignant solitary pulmonary nodules on radiographs: ROC analysis of radiologists' performance--initial experience

PURPOSE: To evaluate radiologists' performance for determining a distinction between benign and malignant pulmonary nodules on chest radiographs without and with use of a computer-aided diagnosis scheme. MATERIALS AND METHODS: Fifty-three chest radiographs that depicted 31 primary lung cancers and 22 benign nodules were used. The likelihood measure of malignancy for each nodule was determined by using an automated computerized scheme. Sixteen radiologists (nine attending radiologists and seven radiology residents) participated in an observer study in which cases were interpreted first without and then with use of the scheme. The radiologists' performance was evaluated with receiver operating characteristic analysis. RESULTS: The mean area under the best-fit binormal receiver operating characteristic curve plotted in the unit square (Az) values of radiologists who interpreted images without and with the scheme were 0.743 and 0.817, respectively. The performance of radiologists was improved significantly when the scheme was used (P =.002). However, the performance (Az = 0.889) of the computer alone exceeded these results by a substantial margin. The average change in radiologists' confidence level for interpretation without and with the scheme was highly correlated (r = 0.845) with the likelihood measure of malignancy, which was presented as computer output. CONCLUSION: This scheme for computer-aided diagnosis has the potential to improve the accuracy of radiologists' performance in the classification of benign and malignant solitary pulmonary nodules.     

ROC analysis of detection of interval changes in interstitial lung diseases on digital chest radiographs using the temporal subtraction technique

PURPOSE: To demonstrate the clinical usefulness of a temporal subtraction technique for the detection of interval changes in various interstitial lung diseases on digital chest radiographs. MATERIALS AND METHODS: One hundred pairs of chest radiographs in 34 patients (63 with and 37 without interval changes) with various interstitial lung diseases were selected. All cases were confirmed by serial chest computed tomography (CT) and ascertained by radiologists. All chest radiographs were obtained with a computed radiography (CR) system, and temporal subtraction images were produced with an iterative image-warping technique. Four radiologists and two thoracic physicians provided confidence levels for interval changes in interstitial lung diseases with and without temporal subtraction. Their performances with and without temporal subtraction were evaluated by means of receiver operating characteristic (ROC) analysis using a sequential test. RESULTS: The area under the ROC curve (Az) values of six observers obtained with and without temporal subtraction were 0.90 and 0.78, respectively. Results showed that the detection of interval changes in interstitial lung diseases was significantly improved by the use of temporal subtraction images compared with CR images alone(P = 0.002). Furthermore, the high detection rate was achieved with temporal subtraction images regardless of the subtlety and location of interval changes. CONCLUSION: Temporal subtraction improved the diagnostic accuracy of radiologists in detecting interval changes in interstitial lung diseases on chest radiographs. It was also useful for cases of multiple interval changes.     

Comparison of peri-implant bone level assessment in digitized conventional radiographs and digital subtraction images

OBJECTIVES: Radiographic assessment of marginal bone height is included in longitudinal control of osseointegrated implants. However, accurate and reproducible results are difficult to obtain. The aim of the present study was to examine the differences between linear measurements in digitized radiographs (DR) and digital subtraction images (DSI) around endosseous implants and the interobserver variability. METHODS: The bone height around 30 implants in 22 patients was assessed by 5 observers. Standardized periapical radiographs were obtained just after the surgery and 4 months later. The radiographs were digitized and manipulated by means of EMAGO software, and linear and logarithmic DSIs were produced. Furthermore, the logarithmic subtraction was enhanced with the use of a filter. The observers had the DRs and three methods of subtraction to assess bone height. ANOVA statistical procedures were applied to analyse differences between the observers in the four assessed images and the Tukey test was used to evaluate the differences between the images. RESULTS: Comparison of the bone height assessments indicated significantly (P<0.05) higher values in the DR than the three methods of DSI. The observers also had a statistically significant variability in this assessment (P=0.00003). CONCLUSIONS: DSI demonstrated lower values of linear measurements of the bone height around endosseous implants, compared with DR. Interobserver variability should be considered when comparing values from follow-up studies.     

Comparison of visual grading and free-response ROC analyses for assessment of image-processing algorithms in digital mammography

Objective

To compare two methods for assessment of image-processing algorithms in digital mammography: free-response receiver operating characteristic (FROC) for the specific task of microcalcification detection and visual grading analysis (VGA).

Methods

The FROC study was conducted prior to the VGA study reported here. 200 raw data files of low breast density (Breast Imaging–Reporting and Data System I–II) mammograms (Novation DR, Siemens, Germany)—100 of which abnormal—were processed by four image-processing algorithms: Raffaello (IMS, Bologna, Italy), Sigmoid (Sectra, Linköping, Sweden), and OpView v. 2 and v. 1 (Siemens, Erlangen, Germany). Four radiologists assessed the mammograms for the detection of microcalcifications. 8 months after the FROC study, a subset (200) of the 800 images was reinterpreted by the same radiologists, using the VGA methodology in a side-by-side approach. The VGA grading was based on noise, saturation, contrast, sharpness and confidence with the image in terms of normal structures. Ordinal logistic regression was applied; OpView v. 1 was the reference processing algorithm.

Results

In the FROC study all algorithms performed better than OpView v. 1. From the current VGA study and for confidence with the image, Sigmoid and Raffaello were significantly worse (p<0.001) than OpView v. 1; OpView v. 2 was significantly better (p=0.01). For the image quality criteria, results were mixed; Raffaello and Sigmoid for example were better than OpView v. 1 for sharpness and contrast (although not always significantly).

Conclusion

VGA and FROC discordant results should be attributed to the different clinical task addressed.

Advances in knowledge

The method to use for image-processing assessment depends on the clinical task tested.Image processing applied in two-dimensional digital mammography has been suggested as a means of improving image quality, especially for patients with dense breast tissue [1-6]. In practice, edge enhancement, histogram equalisation and other greyscale adjustments [3,4] are applied that alter the pixel values of the images in order to enhance the conspicuity of relevant findings like masses and microcalcifications. The algorithms may vary substantially among different vendors and there is no consensus on what processing algorithm is considered optimal among radiologists [4]. The process by which image-processing algorithms and settings are optimised often remains undocumented, and testing of algorithms is neglected in any European acceptance protocol for digital mammography systems [7]. Whether image processing provides improved diagnostic accuracy or simply improves the subjective appearance of images deserves further study.With the advent of new technologies such as digital breast tomosynthesis, manufacturers have been and are introducing even more complex image processing and (iterative) reconstruction. Many researchers are studying the effects of such algorithms on clinical performance [8-13]. In most of these studies image quality has been quantified using physical measurements [8,9,13] (such as noise, signal-to-noise ratio, detective quantum efficiency, modulation transfer function) or psychophysical measurements [10,11] (using, for example, contrast–detail phantoms). Although physical methods are of fundamental importance in describing the image quality, establishing the link between physical image quality measures and clinical utility has been pursued for decades and their relationship is not yet fully understood [14,15].Receiver operating characteristic (ROC) analysis [16] and its location-specific variants [17-19] are currently considered the best methods to quantify and report diagnostic performance: they measure the ability of an observer to detect and correctly interpret pathological structures, such as microcalcifications and masses in a mammogram. Unfortunately, these methods require a large number of patient images and a large number of pathological lesions to reach a sufficient statistical power; moreover, the true health state of the patient must be known to classify an image as normal or abnormal, requiring a follow-up of typically 1 year to confirm benign and normal cases. Further, the cases need to be subtle so that false positives occur during the image interpretation. These requirements make the measurement of clinical performance difficult in practice and very time consuming. ROC analysis is typically performed at the introduction of new imaging modalities; for the evaluation of more subtle updates in a technology, the required effort may be considered excessive.A simpler method has been published by the European Commission (CEC) [20] and is based upon the scoring of image quality by inspecting normal anatomical structures; good visibility of these (normal) structures on a radiograph is considered to define appropriate image quality and accurate diagnosis. The set of anatomical criteria is specific for the given type of examination [20-22], and visual grading analysis (VGA) is typically applied to evaluate them. Images have to be graded with an absolute score by a number of observers or alternatively one can use the side-by-side approach, which involves simultaneous viewing of two images, and the score is meant to express the comparison of the two images. The number of studies using this approach has increased in the past few years [15,23-27].Correlation between VGA experiments and more objective ROC studies has previously been investigated, but the results of the few published studies are contradictory [28-30]. Pilgram et al [28] found a strong correlation between diagnostic performance and the subjective evaluation of image quality on the diagnosis of craniosynostosis. They studied in detail the responses of one observer, who read radiographs having different image quality (obtained with three different methods) for a set of patients with this diagnosis and found that the increase in diagnostic performance resulted primarily from increased specificity, suggesting that, when image quality is being evaluated, specificity and the evaluation of normal structures should be the focus of attention. In the studies of Tingberg et al [29,30], the influence of different characteristic curves on the diagnostic quality of radiographs of the lumbar spine and the chest evaluated with both VGA and free-response forced error (FFE) (an ROC variant) experiments showed mixed results. In the first experiment [29], lumbar spine images were manipulated by adding artificial lesions, and image processing was applied to simulate image appearance from three different screen–film combinations; VGA evaluation and FFE results were in good agreement. In the later paper [30], the authors found that images with greater contrast than the original had significantly improved image quality in the VGA study although this did not affect detectability in the FFE experiment, indicating that VGA has a stronger discriminative power than FFE. These contradictory results suggest that the influence of image processing on image interpretation justifies further research.The aim of this study was to investigate the role of a VGA method in the assessment of image-processing algorithms for digital mammography relative to an earlier applied free-response ROC (FROC) study that investigated the same algorithms but for the specific task of microcalcification detection.