Evaluation of CRT images of digitized film angiographs

X-ray sheet film images of the test chart, the vascular phantom and angiography were digitized at sampling pitch of 0.2 mm and 0.15 mm using film digitizer TFR-01 (Toshiba) and transferred to a device for image storage and display system with 1635-line display monitor (TDF-500AS, Toshiba). Comparison of image qualities between film- and CRT-images was performed in fundamental and clinical studies. Resolution of the test chart image of conventional radiography was worse on CRT than on the original film, although it was improved when film image was digitized at resolution of 0.15 mm/pixel in comparison with that at resolution of 0.2 mm/pixel. Moiré stripes which occurred due to interference were found on CRT images taken using a grid technique. On CRT images of X-ray sheet film using direct magnification technique moiré stripes were not produced because of non grid technique, and the resolution approached that of the original film. In the study using vascular phantom, the optimal image on CRT could be obtained by various image processing procedures, and image quality on CRT with resolution of 0.15 mm approached that of original film. In case of direct magnification CRT images were superior to film images. Subtraction image of the vascular phantom at resolution of 0.2 mm/pixel was obtained on CRT and compared with film subtraction image. On conventional subtraction CRT image moiré stripes impaired the image quality in comparison with the film subtraction. However, magnification subtraction image of the vascular phantom on CRT was superior to the film subtraction. The results obtained in the test chart studies and phantom studies were also confirmed in clinical studies using various kind of angiograms. In addition, ROC study using clinical angiograms showed no significant statistical differences between the original film and CRT image even with 0.2 mm matrix size. Angiographic image on CRT at resolution of 0.15 mm/pixel or less is available for clinical use in place of conventional film image.     

Film-screen magnification versus electronic magnification and enhancement of digitized contact mammograms in the assessment of subtle microcalcifications.

RATIONALE AND OBJECTIVES: To compare information drawn from magnification mammography with that extracted from electronic magnification, processing, and display of the digitized contact images. METHODS: Contact and magnification images of a mammographic statistical phantom were obtained. The magnification films versus the computer-enhanced, digitized images of the corresponding contact mammograms were separately presented to three observers. Receiver operating characteristic analysis was used to compare lesion detectability. The contact and magnification mammograms of 86 patients with subtle microcalcifications were also studied. The breast imaging reporting and data system (BI-RADS) scheme was used to compare the magnification patient films versus the corresponding digitized contact images. Differences in mammographic assessment were evaluated by using the kappa statistic. The dose to breast tissue from contact and magnification mammography was measured to evaluate dose reduction in instances where magnification mammography was to be avoided. RESULTS: Lesion detectability was found to be similar when either the digitized film image or the magnification hard-copy film was inspected. Interpretation of patient images by inspection of the contact and magnification screen-film mammograms on a view-box was in excellent agreement with that yielded by inspection of the contact image on a view-box and the computer-enhanced, digitized contact image on a display monitor. CONCLUSIONS: Electronic magnification and processing of the digitized contact image may provide valuable information concerning subtle microcalcifications, rendering magnification mammography unnecessary for many patients with such lesions.     

Effect of a digital imaging network on physician behavior in an intensive care unit

This study examined the effect of a medical image management network on the behavior of physicians working in a medial intensive care unit (MICU). For 1 year, 8-week periods during which chest radiographs were digitized and made available to MICU physicians on a digital display console were alternated with 8-week periods during which only film images were available. Clinical efficacy during the periods was compared by measuring the time between completion of imaging examinations and initiation of specific clinical actions such as placement and positioning of tubes. Results indicate that the time required to take some clinical actions decreased with the immediate availability of images on the digital display console. Established procedures for obtaining radiologic information were altered by the digital imaging network. The time at which physicians viewed images changed, and consultations between MICU staff and radiologists decreased. These results indicate that behavior patterns are altered when a new technology replaces an existing one. Optimal use of this technology may require changes in the logistics of clinical practice.     

Film-screen digital radiography

The anticipated benefits of digitized projection radiographic data to medical imaging has generated much interest and activity. Numerous methods for capturing the radiographic image data prior to digitization are being evaluated. In this paper the excellent performance of the film-screen system as a receptor for projection radiographic data is discussed. An experimental system for obtaining high quality digital radiographic data by laser scanning radiographic films is described. This system is being used to evaluate the clinical utility of various digital image processing algorithms. Future plans include an investigation of quantitative analysis of projection radiographic data. Digital data obtained by film scanning can be used with digital image archiving and communications systems.     

Histogram-directed processing of digital chest images

One of the potential advantages of digital chest imaging is the ability to process these images. However, such processing, when uniformly applied to the entire image, is often unsatisfactory due to the different processing requirements of lung field and mediastinum. Therefore, a method to selectively process these regions based upon the histogram of the original image has been developed. Thirteen conventional chest films were digitized with a laser film scanner. Analysis of individual lung field and mediastinum histograms showed that the chest image histogram is essentially bimodal with significant lung field-mediastinum histogram peak separation; overlap between these peaks is small (9% of the total histogram) and insensitive to minor pathologic change or radiographic technique. Using these histograms, a gray level threshold distinguishing mediastinum from lung field was selected and used to direct the regionally-selective processing of several chest images. This technique may prove especially useful for digital enhancement of the underexposed mediastinum often encountered on conventional chest radiographs.     

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.     

Radiological laser film scanner sampling artifact

Artifacts seen on laser digitized radiographs are analyzed and mathematically explained based on the concept of image contrast. Our investigation considered the following determinants: (a) laser spot size, (b) signal processing components, (c) image characteristics, and (d) observer performance. A functional relationship between the sampling interval, laser spot size, and the contrast of the artifact seen on the digitized image is derived. This relationship is verified experimentally using a variable spot size laser source and sampling at interval of 175.0 microns. The problem of digitizing artifact seen on film images obtained with anti-scatter grids is discussed.     

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.     

Linear and logarithmic subtraction for detecting enamel subsurface demineralization

OBJECTIVE: To compare the diagnostic performance of linear and logarithmically contrast-enhanced subtraction images, acquired with digital and digitized radiographs, in detecting approximal enamel subsurface demineralization. METHODS: Fifty caries-free human third molars were immersed in a demineralizing solution for 60, 75, 90, and 120 days, in order to induce artificial enamel subsurface demineralization. The teeth were coated with nail varnish, leaving only a circular window of approximately 7 mm2 in one of the approximal surfaces, allowing contact with the solution. Standardized radiographs of the teeth were taken prior to and after the demineralization period with three digital systems, CygnusRay MPS, DenOptix and DIGORA, and InSight film. Conventional, digital and digitized radiographs were assessed by three experienced radiologists. Linear and logarithmically contrast-enhanced subtraction images were acquired and then examined by a fourth independent radiologist. For the validation of the radiographic diagnosis, the enamel test areas were submitted to Knoop microhardness profiling. Radiographic interpretation data was evaluated using ROC analysis. The areas under the ROC curves (Az) were compared by the chi-squared test. The level of significance was set at P=0.05. RESULTS: No significant differences were found between linear and logarithmically contrast- enhanced subtraction images, acquired with the four studied modalities: CygnusRay MPSlinear (Az=0.95), CygnusRay MPSlog (Az=0.98), DenOptixlinear (Az=0.97), DenOptixlog (Az=0.99), DIGORAlinear (Az=0.98), DIGORAlog (Az=0.98), digitized radiographylinear (Az=0.99), digitized radiographylog (Az=0.99). CONCLUSION: Linear and logarithmically contrast-enhanced subtraction images, acquired with digital and digitized radiographs, were diagnostically comparable for assessing enamel subsurface demineralization.     

Digital tomosynthesis: technique for electronic reconstructive tomography

A technique is described for obtaining tomographic images through retrospective reconstruction of digital data. The apparatus used for this technique, called digital tomosynthesis consists of a linear tomographic x-ray machine that has been modified by the addition of a fluoroscope and TV system, a video disk recorder, an analog-to-digital converter, and a small computer for data processing and manipulation. Video frames are collected and stored during a single tomographic sweep. The stored data are then digitized and retrospectively processed in the computer for reconstruction of any desired tomographic plane within the body. The major advantages of DTS include short patient study time, low radiation dose compared with conventional tomography, the ability to enhance the digitized image through manipulation of window and level display, and the applicability of this technique to dynamic studies such as angiotomography. Phantom studies show good diagnostic quality of the resulting images, and preliminary vascular studies in dogs indicate the clinical potential of this technique for use in digital subtraction angiotomography.     

颈动脉和椎基底动脉16层螺旋CT减影成像的应用价值

目的:探讨颈动脉和椎基底动脉CTA减影技术的临床应用价值。方法:对43例患者行颈动脉和椎基底动脉CTA检查,原始数据在工作站进行减影和三维图像后处理。图像由2名观察者对颈动脉和椎基底动脉的显影情况进行评分,数据应用SPSS11.0进行统计学分析。结果:减影和非减影的颈动脉和椎基底动脉图像的观察评分有显著性差异。CTA减影血管重建后的图像质量优良,在显示颈动脉和椎基底动脉的完整性方面明显优于常规CTA血管重建。减影图像对于显示管壁钙化效果欠佳,需结合平扫和非减影图像进行钙化斑块评估。结论:CTA减影成像技术改善了对颈动脉和椎基底动脉复杂解剖及异常管壁结构的显示,结合非减影图像,可为临床提供更加丰富的诊断信息。     

Computer-aided diagnosis and artificial intelligence in clinical imaging

Computer-aided diagnosis (CAD) is rapidly entering the radiology mainstream. It has already become a part of the routine clinical work for the detection of breast cancer with mammograms. The computer output is used as a "second opinion" in assisting radiologists' image interpretations. The computer algorithm generally consists of several steps that may include image processing, image feature analysis, and data classification via the use of tools such as artificial neural networks (ANN). In this article, we will explore these and other current processes that have come to be referred to as "artificial intelligence." One element of CAD, temporal subtraction, has been applied for enhancing interval changes and for suppressing unchanged structures (eg, normal structures) between 2 successive radiologic images. To reduce misregistration artifacts on the temporal subtraction images, a nonlinear image warping technique for matching the previous image to the current one has been developed. Development of the temporal subtraction method originated with chest radiographs, with the method subsequently being applied to chest computed tomography (CT) and nuclear medicine bone scans. The usefulness of the temporal subtraction method for bone scans was demonstrated by an observer study in which reading times and diagnostic accuracy improved significantly. An additional prospective clinical study verified that the temporal subtraction image could be used as a "second opinion" by radiologists with negligible detrimental effects. ANN was first used in 1990 for computerized differential diagnosis of interstitial lung diseases in CAD. Since then, ANN has been widely used in CAD schemes for the detection and diagnosis of various diseases in different imaging modalities, including the differential diagnosis of lung nodules and interstitial lung diseases in chest radiography, CT, and position emission tomography/CT. It is likely that CAD will be integrated into picture archiving and communication systems and will become a standard of care for diagnostic examinations in daily clinical work.     

Comparing the performance of mammographic enhancement algorithms: a preference study

OBJECTIVE: The objective of this study was to compare the performance of four image enhancement algorithms on secondarily digitized (i.e., digitized from film) mammograms containing masses and microcalcifications of known pathology in a clinical soft-copy display setting. MATERIALS AND METHODS: Four different image processing algorithms (adaptive unsharp masking, contrast-limited adaptive histogram equalization, adaptive neighborhood contrast enhancement, and wavelet-based enhancement) were applied to one image of secondarily digitized mammograms of forty cases (10 each of benign and malignant masses and 10 each of benign and malignant microcalcifications). The four enhanced images and the one unenhanced image were displayed randomly across three high-resolution monitors. Four expert mammographers ranked the unenhanced and the four enhanced images from 1 (best) to 5 (worst). RESULTS: For microcalcifications, the adaptive neighborhood contrast enhancement algorithm was the most preferred in 49% of the interpretations, the wavelet-based enhancement in 28%, and the unenhanced image in 13%. For masses, the unenhanced image was the most preferred in 58% of cases, followed by the unsharp masking algorithm (28%). CONCLUSION: Appropriate image enhancement improves the visibility of microcalcifications. Among the different algorithms, the adaptive neighborhood contrast enhancement algorithm was preferred most often. For masses, no significant improvement was observed with any of these image processing approaches compared with the unenhanced image. Different image processing approaches may need to be used, depending on the type of lesion. This study has implications for the practice of digital mammography.     

Chest radiography: comparison of high-resolution digital displays with conventional and digital film

This study was performed to compare the performances of observers using three display formats for chest radiography. The display formats were conventional radiographs, digitized radiographs (2,048 X 2,048 X 12 bits) printed on laser film, and digitized radiographs (2,048 X 2,048 X 12 bits) displayed on a high-resolution (2,560 X 2,048 X 12-bit) gray-scale display. The test set for the study consisted of 163 cases. Sixty-four of the cases were normal, whereas the 99 remaining cases demonstrated one or more common radiographic abnormalities. Nine abnormalities were selected for analysis: costophrenic angle blunting, interstitial disease, atelectasis, pneumothorax, parenchymal mass, consolidation, obstructive disease, hilar/mediastinal mass, and apical scarring. Six experienced general radiologists participated in the evaluation. Receiver operating characteristic curves were generated for each abnormality and display format. The results indicate that, while the three display formats are equivalent for the detection of some abnormalities, detectable differences in observer performance may be seen even at 2,048 X 2,048 X 12 bits for the detection of obstructive disease, pneumothorax, interstitial disease, and parenchymal masses.     

Conversion of teaching file cases from film to digital format: a comparison between use of a diagnostic-quality digitizer and use of a flatbed scanner with transparency adapter

RATIONALE AND OBJECTIVES: The authors' institution had decided to convert its radiology teaching files from film to digital media. This study was performed to determine the simplest method for converting the analog film images to digital images without a subsequent loss in diagnostic accuracy. MATERIALS AND METHODS: Twenty chest radiographs that demonstrated interstitial lung disease were randomly selected from the departmental teaching files and matched with 20 control radiographs from healthy adults. Analog film images were converted with both a diagnostic-quality film image digitizer (digitized) and a flatbed scanner equipped with a transparency adapter (scanned). Three radiology faculty members reviewed a mixed set of corresponding analog film, digitized, and scanned images. Reviewers judged whether each image depicted interstitial lung disease, indicated their level of confidence in the diagnosis, and rated each image for quality. Image quality was assessed by each reviewer subjectively at the time of viewing the individual image, without regard to other images. A one-way analysis of variance was performed to determine whether there was a statistically significant difference in diagnostic accuracy between the three image formats. Agreement in diagnosis between corresponding images in the three different formats was evaluated for each reviewer with the McNemar test. RESULTS: There was no statistically significant difference in diagnostic accuracy between analog film and scanned images, but there was such a difference between these two groups and digitized images. Accuracy was 97% for analog film, 94% for scanned, and 89% for digitized images. Results of the McNemar test showed no statistically significant difference in agreement between the analog film images and the scanned images for any of the reviewers (P > .05). CONCLUSION: A high-end flatbed scanner with transparency adapter provided accurate, simple, and inexpensive conversion of analog film teaching files to digital format, with no loss of the ability to detect or diagnose subtle abnormalities such as interstitial lung disease.     

Single-exposure conventional and computed radiography image acquisition

A technique for simultaneously acquiring a conventional film-screen radiographic image and a digital computed radiography (CR) image with a single x-ray exposure is described. Measurements of image contrast, spatial resolution, and signal-to-noise ratios demonstrate that a modified film cassette in which the first intensifier screen has been replaced with a CR imaging plate permits dual-image, single-exposure imaging with only nominal degradation in film and CR image quality relative to the two standard image counterparts. This technique may be used to acquire matched image pairs for research or as a way to provide full-size conventional film images in the clinical environment, while retaining the advantages offered by computed radiography systems.     

K-edge digital subtraction arthrography of the painful hip prosthesis: a feasibility study

K-edge energy subtraction radiography is a method for detecting the presence of iodinated contrast material by subtracting two digital radiographs produced by X-ray beams with energies above and below the iodine K edge. We performed a feasibility study on the application of K-edge energy digital subtraction arthrography (KEDSA) to painful hip prostheses. During arthrography, loosening of the prosthesis is implied if contrast material is seen dissecting around the prosthesis, an often difficult detection task because of adjacent prosthesis metal or cement. In conventional arthrography a preliminary mask image is thus used from which films obtained after injection of iodinated contrast material are subtracted. Movement by the patient during this process may preclude subsequent subtraction. With KEDSA, since multiple image pairs may be obtained after the injection of contrast material, the problem of patient motion is virtually eliminated. A conventional X-ray tube operating between 55 and 65 kVp was alternately filtered by iodine and cerium filters to produce the KEDSA images. The apparatus was capable of producing a subtracted image within 3 sec. The technique was applied to phantoms and to six patients immediately after hip arthrography that had been positive for prosthesis loosening. Although of lower spatial resolution, the KEDSA images were, in all cases, positive for loosening in a pattern consistent with the conventional arthrographic images. KEDSA was shown to be successful in detecting extraarticular contrast material. During a single study, subtraction in various imaging planes as well as postexercise subtraction imaging can be accomplished-techniques not heretofore possible in routine subtraction arthrography.     

Digitizing and consolidating mammograms and other images for teaching applications

RATIONALE AND OBJECTIVES: Most mammograms are obtained using screen-film technique and must be digitized for teaching purposes. Digitizing mammograms poses special problems because of high contrast and multiple views. We describe the equipment and process for digitizing and consolidating mammograms for teaching purposes. These techniques can be applied to any type of images where consolidation may be helpful. MATERIALS AND METHODS: Mammograms are digitized using a high optical density scanner. After the window and levels are adjusted, a four-view mammogram may be consolidated into a single image if desired. RESULTS: The high contrast of film screen mammograms is managed by using a high optical density scanner. Consolidation of image sets, such as a four-view mammogram, allows images to be easily inserted into text, slide, or poster documents. CONCLUSIONS: Digitizing mammograms for teaching purposes is facilitated by use of a high optical density scanner and consolidation of image sets into single images. The techniques described are also useful for other areas of radiology in which display of multiple images or modalities is desirable.     

Digital radiography in urography

The clinical utility was evaluated of a computed radiographic system in urography. The system (FCR 101, Philips Medical Systems, Inc., Shelton, CT) is based on a photo-stimulatable phosphor screen (imaging plate) for X-ray image detection and storage. The X-ray information recorded on the imaging plate is converted into digital from and processed by means of a computer. After processing is completed, the digitized image is reversed back to analogic signals, which modulate the intensity of a laser beam scanning the image on a single-emulsion film (Fuji CR 633). Two hundred IVP's were obtained in four groups, of 50 patients each, with normal azotemic values by rapid infusion of a low osmolality contrast medium (iopamidol 150 mgI/ml). While conventional radiographs were performed on the first group of patients with the injection of 0.6 gI/kg body weight of contrast medium, digital examinations were carried out, in the remaining three groups, with the injection of 0.6, 0.3 and 0.12 gI/kg, respectively. The digital images were processed with the "Abdomen-routine" program. A specific algorithm was implemented in order to reduce the excessive contrast resolution of the bladder, which is due to the characteristics of the nonionic contrast medium and enhanced by the reading program. The image details were evaluated by two observers and then statistically analyzed with nonparametric tests. Statistical analysis did not show any difference in the quality of digital and screen-film images. Image processing improved some inadequate images, by reducing the contrast resolution of the bladder, and allowed a better detection of some details. Low doses (0.3 gI/kg) of a low osmolality (150 mgI/kg) contrast medium were enough to obtain good images. Another biological advantage was obtained by a consistent radiation dose reduction (about 40%).