Image Copy Research Articles

Analysis of image quality in digital chest imaging

An evaluation of the image quality of an amorphous silicon flat-panel detector system and a computed radiology system compared with a screen-film system was performed by means of contrast-detail phantom images. Hard and soft copy images were evaluated. Although patient dose at clinical settings was strongly decreased with the amorphous silicon system, the low-contrast visibility with this system was still significantly better than with the screen-film system. For the computed radiology system, low-contrast visibility was comparable to the screen-film system. Best results were obtained by soft copy reading at full resolution with adaptation of contrast and brightness. Changing tube voltage (102-133 kV), or additional filtration, did not significantly affect image quality. However, low-contrast visibility improved significantly with increasing exposure. It was clearly demonstrated that, in chest imaging, the amorphous silicon system has superior imaging characteristics compared to the screen-film and the computed radiology system.

Optimal exposure parameters for digital radiography of the infant skull: A pilot study

To determine optimal exposure parameters when performing digital skull radiographs in infants with suspected non-accidental injury (NAI). Anteroposterior and lateral post-mortem skull radiographs of six consecutive infants with suspected NAI were made at six exposure levels for each projection. Entrance surface doses ranged from 75-351 microGy. Exposures were made with a Fuji 5000R computed radiography system onto a standard resolution imaging plate. In three patients exposures were repeated using a high-resolution imaging plate. Hard copy images with an edge-enhancement factor of 0.5 were produced. Six observers assessed and scored the radiographs from 1=poor to 5=excellent for visualization of five criteria. The criteria scored included outer table of skull vault, inner table of skull vault, suture margins, vascular markings and soft tissues of the scalp. Radiographs were then ranked in order of overall image quality. Film density and sensitivity values were recorded. Local research committee approval was obtained. Current parameters give an average entrance surface dose of 253 microGy and 246 microGy for anteroposterior and lateral radiographs, respectively. The study demonstrated no perceived improvement in image quality above an entrance surface dose of 200 microGy (80% of current dose) or by the use of a high-resolution imaging plate. The potential exists to reduce radiation exposure in infants. A study has commenced to determine the effects of dose reduction on diagnostic accuracy in suspected NAI.

Comparison of a digital flat-panel versus screen–film, photofluorography and storage-phosphor systems by detection of simulated lung adenocarcinoma lesions using hard copy images

The purpose of this study was to compare hard copy images from a flat-panel detector digital radiography system with conventional radiography, photofluorographic radiography and storage phosphor radiography for the detection of simulated lung adenocarcinoma lesions and also for radiation dose. To test the diagnostic performance of these four systems, the authors used 15 types of lung adenocarcinoma phantom according to Noguchi's classification and an anthropomorphic chest phantom. The visual evaluation of tumour detectability by four radiologists and two general thoracic surgeons was examined with a five-level confidence scale. Lung doses were measured with glass dosemeters for the chest radiology systems under the conditions used by each hospital and centre. Our results indicated that flat-panel detector digital radiography and storage phosphor radiography are not necessarily superior to conventional radiography and photofluorographic radiography for detecting lung adenocarcinomas when only hard copy images are used, and this suggests a need to carefully optimize chest radiography.

P05.01: Is the nuchal index increased in fetuses with congenital structural heart defects? A prospective study

Objectives: To determine if the Nuchal Index (NIx) is increased in euploid fetuses diagnosed with an isolated structural congenital heart defect (CHD) on fetal echocardiogram. Methods: A prospective case-control study was conducted from March 2002 to July 2003. All patients between 18 and 24 weeks’ gestation referred for fetal echocardiography were approached for participation. Patients were excluded if other major anomalies or an abnormal karyotype were present. The NIx was calculated as the mean nuchal thickness/mean biparietal diameter ×100. Fetal cardiac axis was calculated from hard copy images in a blinded fashion. Analysis was by standard descriptive tests, 2-tailed t-test, receiver operating characteristic (ROC) curve, univariate analysis and discriminant analysis. Cases were classified as normal or abnormal as per the co-authors diagnosis at the time of the fetal echocardiogram. Results: Of the 607 echocardiograms performed, 314 were eligible. Two hundred and seven (22 abnormals and 185 normals) were recruited for a capture rate of 65.9%. The mean NIx in the abnormal and normal group was 9.3 and 7.8 respectively. This was statistically significant (p = 0.003). Using a cut-off of 10.4 at a 5% false positive rate, the sensitivity was 29% with an ROC of 0.699 [95%CI 0.582, 0.816]. Eleven of the 22 abnormal hearts and 7/185 normals had an abnormal cardiac axis. (OR 0.04 [95%CI 0.01, 0.12, p < 0.00001]). Although NIx and Nth were different between the study groups, discriminant analysis was unable to identify an adequate cut-off to allow adequate prediction of CHD. Conclusions: The NIx and CA were significantly different in fetuses with CHD in a high-risk population. However, an appropriate cutoff value could not be found in our study. Further studies in a low-risk population are warranted.

P05.02: National database for fetal cardiac anomalies in 2004

Objectives: To determine if the Nuchal Index (NIx) is increased in euploid fetuses diagnosed with an isolated structural congenital heart defect (CHD) on fetal echocardiogram. Methods: A prospective case-control study was conducted from March 2002 to July 2003. All patients between 18 and 24 weeks’ gestation referred for fetal echocardiography were approached for participation. Patients were excluded if other major anomalies or an abnormal karyotype were present. The NIx was calculated as the mean nuchal thickness/mean biparietal diameter ×100. Fetal cardiac axis was calculated from hard copy images in a blinded fashion. Analysis was by standard descriptive tests, 2-tailed t-test, receiver operating characteristic (ROC) curve, univariate analysis and discriminant analysis. Cases were classified as normal or abnormal as per the co-authors diagnosis at the time of the fetal echocardiogram. Results: Of the 607 echocardiograms performed, 314 were eligible. Two hundred and seven (22 abnormals and 185 normals) were recruited for a capture rate of 65.9%. The mean NIx in the abnormal and normal group was 9.3 and 7.8 respectively. This was statistically significant (p = 0.003). Using a cut-off of 10.4 at a 5% false positive rate, the sensitivity was 29% with an ROC of 0.699 [95%CI 0.582, 0.816]. Eleven of the 22 abnormal hearts and 7/185 normals had an abnormal cardiac axis. (OR 0.04 [95%CI 0.01, 0.12, p < 0.00001]). Although NIx and Nth were different between the study groups, discriminant analysis was unable to identify an adequate cut-off to allow adequate prediction of CHD. Conclusions: The NIx and CA were significantly different in fetuses with CHD in a high-risk population. However, an appropriate cutoff value could not be found in our study. Further studies in a low-risk population are warranted.

Focus on Software

Focus on Software

Objective assessment of image quality in conventional and digital mammography taking into account dynamic range

The goal of this work is to develop a method to objectively compare the performance of a digital and a screen-film mammography system in terms of image quality. The method takes into account the dynamic range of the image detector, the detection of high and low contrast structures, the visualisation of the images and the observer response. A test object, designed to represent a compressed breast, was constructed from various tissue equivalent materials ranging from purely adipose to purely glandular composition. Different areas within the test object permitted the evaluation of low and high contrast detection, spatial resolution and image noise. All the images (digital and conventional) were captured using a CCD camera to include the visualisation process in the image quality assessment. A mathematical model observer (non-prewhitening matched filter), that calculates the detectability of high and low contrast structures using spatial resolution, noise and contrast, was used to compare the two technologies. Our results show that for a given patient dose, the detection of high and low contrast structures is significantly better for the digital system than for the conventional screen-film system studied. The method of using a test object with a large tissue composition range combined with a camera to compare conventional and digital imaging modalities can be applied to other radiological imaging techniques. In particular it could be used to optimise the process of radiographic reading of soft copy images.

Use of prior mammograms in the classification of benign and malignant masses

The purpose of this study was to determine the importance of using prior mammograms for classification of benign and malignant masses. Five radiologists and one resident classified mass lesions in 198 mammograms obtained from a population-based screening program. Cases were interpreted twice, once without and once with comparison of previous mammograms, in a sequential reading order using soft copy image display. The radiologists’ performances in classifying benign and malignant masses without and with previous mammograms were evaluated with receiver operating characteristic (ROC) analysis. The statistical significance of the difference in performances was calculated using analysis of variance. The use of prior mammograms improved the classification performance of all participants in the study. The mean area under the ROC curve of the readers increased from 0.763 to 0.796. This difference in performance was statistically significant ( P = 0.008).

Value of CT in the diagnosis and management of gallstone ileus

To retrospectively establish the diagnostic criteria of gallstone ileus on CT, and to prospectively apply these criteria to determine the diagnostic accuracy of CT to confirm or exclude gallstone ileus in patients who presented with acute small bowel obstruction (SBO). Another purpose was to ascertain whether the size of ectopic gallstones would affect treatment strategy. Fourteen CT scans in cases of proved gallstone ileus were evaluated retrospectively by two radiologists for the presence or absence of previously reported CT findings to establish the diagnostic criteria. These criteria were applied in a prospective contrast enhanced CT study of 165 patients with acute SBO, which included those 14 cases of gallstone ileus. The hard copy images of 165 CT studies were reviewed by a different group of two radiologists but without previous knowledge of the patient's final diagnosis. All CT data were further analyzed to determine the diagnostic accuracy of gallstone ileus when using CT in prospective evaluation of acute SBO. The size of ectopic gallstone on CT was correlated with the clinical course. The diagnostic criteria of gallstone ileus on CT were established retrospectively, which included: (1) SBO; (2) ectopic gallstone; either rim-calcified or total-calcified; (3) abnormal gall bladder with complete air collection, presence of air-fluid level, or fluid accumulation with irregular wall. Prospectively, CT confirmed the diagnosis in 13 cases of gallstone ileus with these three criteria. Only one false negative case could be identified. The remaining 151 patients are true negative cases and no false positive case could be disclosed. The overall sensitivity, specificity and accuracy of CT in diagnosing gallstone ileus were 93%, 100%; and 99%, respectively. Surgical exploration was performed in 13 patients of gallstone ileus with ectopic stones sized larger than 3 cm. One patient recovered uneventfully following conservative treatment with an ectopic stone sized 2 cm in the long axis. Contrast enhanced CT imaging offered crucial evidence not only for the diagnosis of gallstone ileus but also for decision making in management strategy.

Image quality of film transparency printer output of digital dental radiographs

The purpose of this study was to evaluate the physical properties of the film transparency output of a printer and its potential use in dental radiography. A color printer (Sony UP-D70XR) was used to produce film transparencies of digital radiographs. A physical evaluation for the image quality was conducted including measurements of the image density reproducibility, the dose response function, the root mean square (RMS) granularity and the modulation transfer function (MTF). The characteristic curve of the hard copy image produced a nonlinear, sigmoid response for pixel value or x-ray absorbed dose. The RMS of the scan parallel direction was greater than that of the scan perpendicular direction in low density areas, but it reversed beyond density 1.3. The MTF of the scan perpendicular direction was superior to that of the scan parallel direction. It was suggested that further examination of the image qualities of this printer is worthwhile.

Digital imaging: Digital Mammography Imaging Screening Trial Project

The Digital Mammography Imaging Screening Trial was formed to determine whether digital mammography could detect breast cancer as well as, or better than, film mammography. Since 2001, 35 facilities helped enrol the 49,528 patients in the US and Canada. Each study participant had a digital mammogram and a film examination. A follow-up mammogram was obtained 1 year after the initial study to determine breast health status. The study completed its accrual in November 2003. One-year follow up mammograms are currently being performed. Over the next 18 months 84 radiologists will interpret soft copy, digital hard copy and film images. Parameters to be analyzed include: diagnostic accuracy of digital monitor images, effect of breast cancer prevalence on the radiologist's interpretation, effect of breast density on diagnostic accuracy of digital and film mammography, and the diagnostic accuracy of different digital and film units. Each facility was required to meet strict quality control standards for both digital and film screen mammography. In addition, each facility was inspected to ensure proper record keeping and documentation. The results from this study should prove beneficial to breast cancer diagnosis and treatment.

Experimental in vitro study to evaluate a flat-panel detector system

To evaluate the contrast-detail performance of a flat-panel detector system, we performed a comparative study of this flat-panel system versus storage phosphor and conventional screen-film systems. Bone models made of human humeri were prepared with foreign bodies, fracture lines and drilled holes to create artificial fractures, osteolyses or metastases. Immersed in a water bath, hard copy images of these models were acquired with the same exposure dose (55 kV; 3.2 mAs) on the flat-panel detector, two state-of-the-art storage phosphor systems (PCR, ADC) and two conventional screen-film systems (Insight, T-Mat). Using a standardized protocol with a 4-point scale for a lesion, 220 different images were analyzed as to their appearance by 5 independent radiologists. The statistical significance of the differences between the used modalities and the observers was determined with a sign test. Especially the drilled holes showed differences between the modalities. The flat-panel detector showed significantly slightly better results locally than the two storage phosphor systems. The same applied to the Insight screen-film systems, but the intraindividual differences between the modalities were not clinically relevant. Under the conditions of the chosen experimental design, the flat-panel detector showed results comparable to the conventional screen-film and the state of the art storage phosphor radiographs. The use in skeletal radiography is possible.

Evaluation and Prediction of Copy Image Using MT (1)

Evaluation and Prediction of Copy Image Using MT (1)

Long line positioning in neonates: does computed radiography improve visibility?

Objectives: To assess the use of soft copy reporting of computed radiography (CR) images in determining intravenous long line tip position in neonates and compare visibility rates with hard copy...

Evaluation and Prediction of Copy Image Using MT (2)

Evaluation and Prediction of Copy Image Using MT (2)

Focus on Analytical Instruments

Focus on Analytical Instruments

Landsat TM analysis of fracture patterns: a case study from the Coastal Cordillera of northern Chile

Cretaceous rocks on the continental margin of northern Chile record a complex geodynamic evolution. Cycles of transtensional and transpressional deformation and of extrusive and intrusive magmatism are linked to the development of crustal-scale lineaments. The Landsat Thematic Mapper is used here as a tool to define these structural features. Geocorrected data were digitally enhanced and lineaments plotted directly from a hard copy image, thereby excluding artificial or non-geological features that might degrade the subsequent structural analysis. The lineaments were then digitized and analysed using a Weighted Moving Average (WMA) technique to suppress noise and to enhance azimuthal variation. Statistical analysis of the data reveals three lineament populations. The first is a set of NNE-trending lineaments that belong to the margin-parallel, sinistral Atacama Fault System. The second is a series of NW-trending lineaments with a similar orientation to large-scale structures identified across the South American continental plate. The third is a widely spaced set of NE-trending lineaments. The key result of this study is that lineaments identified from remotely sensed data may have orientation patterns that differ considerably from those identified by traditional geological mapping and that full structural analysis of structurally complex crustal regions will likely be incomplete without a comprehensive analysis of remotely sensed data. Although the NW-trending structures are numerically dominant on the Landsat TM image, they are seldom recorded at map scale and are under-represented on published geological maps. Of the 275 faults marked on the published geological map sheets, 89 are N to NNE-trending and only 88 are NW-trending. By contrast, of 841 lineaments identified from the satellite image, 455 are NW-trending and 178 are N- to NNE-trending. The lack of prior recognition of the NW-trending structures means that their importance has been underestimated in reconstructions of the geodynamic evolution of the region. In addition, as major ore deposits in the region are frequently located at intersections between two fracture systems, the recognition here of the NW-trending set of structures should illuminate future mineral exploration programmes.

Content-based image copy detection

Abstract This paper proposes a novel method to detect copied versions of digital images. The proposed copy detection scheme can be used as either an alternative approach or a complementary approach to watermarking. A test image is reduced to an 8×8 sub-image by intensity averaging, and the AC coefficients of its discrete cosine transform (DCT) are used to compute distance from those generated from the query image, of which a user wants to find copies. A challenge is that the replicated image may be processed to elude copy detection or enhance image quality. We show ordinal measure of DCT coefficients, which is based on relative ordering of AC magnitude values and using distance metrics between two rank permutations, is robust to various modifications of the original image. The optimal threshold selection scheme using the maximum a posteriori criterion is also described. The efficacy of the proposed method is extensively tested with both cluster-free and cluster-based detection scheme.

Robustness investigation of DCT digital watermark for printing and scanning

AbstractThis paper reports the effect of printing and scanning on digital watermarks for a hard copy image and investigates the necessary conditions for the watermark to be robust against the printing and scanning process. The effect of the printing and scanning process on the image content is presented first, and that on the Discrete Cosine Transform (DCT) domain is discussed next. Thus, we have necessary conditions for the watermark to be robust and present a sufficient condition to construct robust watermarking. It is realized by decreasing mutual interference between the embedded elements. This will enable us to make image content common to both the electrical nets and the physical nets. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 86(4): 11–19, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.10059

A comparison of conventional film, CR hard copy and PACS soft copy images of the chest: analyses of ROC curves and inter-observer agreement

Study objective: The aim of this study was to determine whether the accuracy of diagnosis of a spectrum of chest pathology was affected by the imaging technique used, and to compare conventional film/screen, hard copy computed (phosphor plate) radiography (CR) and soft copy CR (PACS) images. Materials and methods: For each of 44 patients who had a CT examination of the thorax, PA and lateral chest radiographs were produced using conventional film, hard copy CR and soft copy PACS images. Five radiologists independently scored all images for the presence of abnormalities. The data were analysed in two stages using the result of the CT scan as the reference standard diagnosis: firstly, to investigate differences in abnormality scores between image modalities and observers using ROC analysis; secondly, to investigate the agreement of the diagnoses with the reference standard by the analysis of kappa scores. Results: The ROC analyses and comparison of kappa scores showed no differences between image modalities (P=0.72, P=0.87), but highly significant differences between observers (P<0.001, P=0.003). Conclusion: The detection of chest lesions did not vary between conventional film, CR hard copy and PACS soft copy images. For all three image types, there were statistically significant differences between observers.