Analysis of time-density curves of contrast media for improvement of chest dynamic incremental CT

PURPOSE

The goal of this work was to analyze time-density curves (TDCs) of contrast media (CM) in the mediastinal vasculature to optimize chest dynamic incremental CT.

METHOD

Forty-three patients were injected with nonionic CM into the forearm veins with injection rates (ml/s), durations (s), and total amounts (ml) of 2.0, 20, and 40 (protocol 1); 4.0, 20, and 80 (protocol 2); and 2.0, 40, and 80 (protocol 3). TDCs were obtained for the pulmonary trunk (PA) and ascending (AA) and descending (DA) aorta from dynamic scans. Areas under the curves (AUCs) of TDCs for imaginary 30 s scans were evaluated.

RESULTS

AUC peaks were obtained after 10, 17, and 19 s (PA, AA and DA; protocol 1; 9, 16, and 18 s (protocol 2); and 18, 25, and 28 s (protocol 3) delay time.

CONCLUSION

Better chest dynamic incremental CT would be expected with scan midpoints a little after the end of injection of CM.

Comparison of low contrast detectability between a digital amorphous silicon and a screen-film based imaging system for thoracic radiography

Low contrast threshold detectability is investigated theoretically and experimentally for an amorphous silicon (a-Si) x-ray detector designed for digital radiography and for a standard thoracic screen-film combination. A theoretical signal-to-noise ratio is described with a human observer signal detection model. It is calculated using the detective quantum efficiency (DQE) and the modulation transfer function of the imaging system, as well as a spatial response function for the human visual system. Using a four-alternative forced choice observer perception study, the threshold contrasts of disk shaped objects ranging in size from 0.3 to 4.0 mm are determined. Significantly better contrast detectability is obtained from the digital detector, which is attributed to its higher DQE. On average, the disk shaped objects can be detected at 45% less contrast than required for screen-film. With no free parameters the experimental data agree well with those predicted by the observer model. Based upon the data, the model predicts that x-ray exposure for the a-Si detector only needs to be 30% of the exposure required to perform equally well on the contrast-detail detectability task using screen-film.

A time-motion study of digital radiography at implementation

With increasing budgetary restraints on the health system, it is apparent that the main contribution that radiology departments can make to significant cost reduction in hospitals is to decrease the length of time between requesting an X-ray examination and receiving the report (and images). Digital radiography (DR) was introduced into the Radiology Department at the Royal Adelaide Hospital as a pilot project to research the cost-benefits and efficiency of the system, and to determine future directions for planning a digital department. The business plan developed prior to implementation of this pilot project predicted a saving of one bed-day per inpatient when a fully digital department with a picture archiving and communication system (PACS) is installed. This initial study comparing DR and conventional radiography (convR) provides baseline data and shows encouraging results for more rapid transmission of reports to clinicians.

Finding-specific display presets for computed radiography soft-copy reading

Much work has been done to optimize the display of cross-sectional modality imaging examinations for soft-copy reading (i.e., window/level tissue presets, and format presentations such as tile and stack modes, four-on-one, nine-on-one, etc). Less attention has been paid to the display of digital forms of the conventional projection x-ray. The purpose of this study is to assess the utility of providing presets for computed radiography (CR) soft-copy display, based not on the window/level settings, but on processing applied to the image optimized for visualization of specific findings, pathologies, etc (i.e., pneumothorax, tumor, tube location). It is felt that digital display of CR images based on finding-specific processing presets has the potential to: speed reading of digital projection x-ray examinations on soft copy; improve diagnostic efficacy; standardize display across examination type, clinical scenario, important key findings, and significant negatives; facilitate image comparison; and improve confidence in and acceptance of soft-copy reading. Clinical chest images are acquired using an Agfa-Gevaert (Mortsel, Belgium) ADC 70 CR scanner and Fuji (Stamford, CT) 9000 and AC2 CR scanners. Those demonstrating pertinent findings are transferred over the clinical picture archiving and communications system (PACS) network to a research image processing station (Agfa PS5000), where the optimal image-processing settings per finding, pathologic category, etc, are developed in conjunction with a thoracic radiologist, by manipulating the multiscale image contrast amplification (Agfa MUSICA) algorithm parameters. Soft-copy display of images processed with finding-specific settings are compared with the standard default image presentation for 50 cases of each category. Comparison is scored using a 5-point scale with the positive scale denoting the standard presentation is preferred over the finding-specific processing, the negative scale denoting the finding-specific processing is preferred over the standard presentation, and zero denoting no difference. Processing settings have been developed for several findings including pneumothorax and lung nodules, and clinical cases are currently being collected in preparation for formal clinical trials. Preliminary results indicate a preference for the optimized-processing presentation of images over the standard default, particularly by inexperienced radiology residents and referring clinicians.

A comparative study of a digital radiography system

The present study aimed to examine the efficiency of a new digital radiography system that was installed in the Royal Adelaide Hospital in September 1997, as compared to the existing conventional radiography system. A total of 55 examinations were observed over a 3-week period in January, and these consisted of 18 digital and 10 conventional chest examinations, and 27 conventional orthopaedic examinations. These were combined with 18 digital orthopaedic examinations recorded from a prior study. Total examination time was broken into several components, of which reporting time was of the most interest. The mean reporting times for digital and conventional chest examinations were 17 and 25 min, respectively, a significant (P < 0.1) 8-min difference. The orthopaedic examinations revealed mean reporting times of 8 and 26 min for digital and conventional systems, respectively; a significant (P < 0.001) 18-min difference. These results demonstrate that the digital system is a faster, more efficient system for the reporting of X-rays.

Comparison between a screen-film system and a selenium radiography system. An ROC study using simulated thoracic lesions

RATIONALE AND OBJECTIVES

To evaluate the diagnostic image quality of the hard copies of a commercially available selenium detector-based computed radiography system compared to that of a conventional screen-film system.

METHODS

Ten radiographs of an anthropomorphic chest phantom with simulated nodular and linear-reticular lesions were produced using either system. Each radiograph was subdivided into 15 fields containing zero lesions, one nodular lesion, one linear-reticular lesion, or both lesions. The total of 150 fields for each modality was reviewed by six radiologists, and receiver operating analysis was performed.

RESULTS

The conventional screen-film system performed significantly better for nodular lesions, whereas no statistically significant difference was found between the detection rates of both systems for linear-reticular lesions.

CONCLUSIONS

The better detection of nodules with the dedicated selenium detector can be explained by the higher dynamic range of the system. Detection of linear-reticular lesions was slightly but not significantly better with the screen-film system, but the detection rate of the selenium detector might be further improved with a different image processing technique.

Diagnostic image quality of mobile neonatal chest X-rays and the radiation exposure incurred

A study was undertaken to identify the variation of entrance skin doses (ESDs) in mobile neonatal chest radiography with regard to the European Commission (EC) reference dose and to examine potential relationships with image quality and radiographic techniques. Five sites from the former North West Thames region participated. All mobile neonatal radiographic techniques were surveyed. Dose-area product per examination was directly measured and the ESD calculated. Image quality criteria were developed from those published by the EC. Image quality was graded by two independent observers. Over the five sites, 144 examinations were recorded. Calculated ESDs ranged up to 160 microGy, with an appreciable variation not only between sites but also within sites. A clear relationship between actual rather than nominal speed and dose over all sites was demonstrated (r = -0.95, p = 0.013). No correlation between image quality and dose was noted (r = -0.044, p = 0.665). Neonatal imaging systems at participating sites, within the North Thames region, comply with EC guidelines on patient dose and image quality for mobile chest X-rays. Significant variation in ESDs was encountered between sites with no discernible relationship with image quality or the employed radiographic techniques as described by the EC. The strong inverse relationship between ESDs and actual rather than nominal speed suggests a neglected aspect of radiation protection.

Optimum tube voltage for chest radiographs obtained by psychophysical analysis

Many kinds of x-ray films having various characteristic curves have been developed for chest radiographs. In general, a phototiming device for determination of a mAs value which gives a proper exposure has been used for a chest radiography. For each film, however, the x-ray tube voltage has been determined by the subjective evaluation of radiologists or radiological technologists. In this paper, we propose a new method for determining the optimum tube voltage for chest radiographs using psychophysical analysis. The optimum density and the optimum density range of a screen/film system are obtained from the gradient curve of film and the minimum perceptible contrast delta Dmin [Acta Radiol. Diagnos. 4, 463-476 (1966)]. The optimum tube voltage, by which the lowest density of a mediastinum and the highest density of a lung field just cover the optimum density range, is obtained using the x-ray photon spectrum and sensitivity spectrum of the screen. This objective method does not depend on personal subjective evaluation, therefore it is available for the determination of optimum tube voltage for chest radiographs to be observed by many doctors of various departments.

Design of a PC controlled test device for the study of patient motion in X-ray radiology: first applications and results

Simulation and study of patient motion should be undertaken for different imaging techniques since all new radiological techniques or equipment must pass through evaluation processes to verify their functional capability and assess their performance compared with other equipment. A device to study the effects of motion on X-ray image quality was designed and built. The main goal of the PC controlled device developed by our group is to allow the adaptation of different phantoms and test objects. Preliminary experiments for the evaluation of different thorax screen-film systems were carried out by simulating respiratory motion. It is concluded that moving objects should be included for the comparison of screen-film systems since predictions based only on findings in stationary test conditions could lead to false conclusions.

Automated lung segmentation in digital lateral chest radiographs

We are developing a fully automated computerized scheme for segmenting the lung fields in digital lateral chest radiographs. Existing computer-aided diagnostic (CAD) schemes and automated lung segmentation methods have focused exclusively on the posteroanterior view, despite the diagnostic importance of the lateral view. Information from the lateral radiograph is routinely incorporated by radiologists in their decision-making process, and thus computer analysis of lateral images may potentially add another dimension to current CAD schemes. Automated analysis of the lung fields in lateral images will necessarily require accurate segmentation. Our scheme employs an initial procedure to eliminate external and subcutaneous pixels. Global gray-level histogram analysis then allows for the identification of a range of gray-level thresholds. An iterative gray-level thresholding scheme is implemented using this range of thresholds to construct a series of binary images in which contiguous regions are identified and geometrically analyzed. Regions determined to be outside the lungs are prevented from contributing to binary images at later iterations. Adaptive local gray-level thresholding is applied along the initial contour that results from the global thresholding procedure to extend the contour closer to the true lung borders. This local thresholding method uses regions of interest of various dimensions, depending on the enclosed anatomy. Smoothing and polynomial curve fitting complete the segmentation. A database of 100 normal and 100 abnormal lateral images was analyzed. Quantitative comparison of computer-segmented lung regions with lung regions manually delineated by two radiologists indicated that 83% and 84% of normal and abnormal images, respectively, displayed segmentation contours within three standard deviations of the mean inter-radiologist contour degree-of-overlap value.

[A comparison of the monitor and alternator findings of digital thoracic images with the aid of a computer-supported procedure]

PURPOSE

To compare softcopy and hardcopy reading of chest radiographs a software tool was designed for creating lesions with clearly defined size, location and contrast.

METHOD

An ROC study was performed using a set of chest radiographs with 300 simulated small nodules and linear details displayed on film and on a 1 K monitor. Six observers participated in the study. ROC curves were generated on the basis of 7200 decisions.

RESULTS

There was no significant difference in observer performance overall (AUC = Area under curve). Monitor: 0.84 +/- 0.08 vs. AUC, Film: 0.84 +/- 0.08). Slight, but not statistical significant differences were found in the detection of low-contrast lung nodules and of linear lung details.

CONCLUSION

Soft-copy reading using a high quality 1 K CRT display provides the same accuracy for the detection of subtle computer-simulated lesions as hardcopy reading. A software tool could be used for assigning optimal characteristics of CRT- and hardcopy displays using clearly defined lesions as a gold standard.

[Digital selenium radiography: a comparison of the picture quality of thoracic images in normal and reduced image formats based on the structural anatomical details]

PURPOSE

Is there a loss of information when using selenium radiographic images displayed with reduced image format compared to full format?

METHOD

Digital selenium radiographic chest images in two planes were obtained in 35 patients for medical reasons. The digital data sets of each patient were separately displayed in full format on two different films and were printed in reduced format on one film. The format was reduced to 61% of the full format using an acquisition matrix of 2166 x 2488 pixels, an image display matrix of 4000 x 5000 pixels and a film format of 43 x 49 cm. All images were anonymously evaluated by four independent readers using a questionnaire concerning anatomic structures.

RESULTS

Format reduction did not result in a loss of information in diagnostically relevant anatomic details.

CONCLUSIONS

Displaying digital selenium radiographic data sets of thoracic view in two planes on one film presumably does not lead to a loss of diagnostic information. This procedure may help to reduce film costs.

Thoracic CT findings at hypovolemic shock

PURPOSE

To describe and discuss the thoracic CT features of hypovolemic shock.

MATERIAL AND METHODS

From a group of 18 patients with signs of hypovolemia on contrast-enhanced abdominal CT, 11 were selected for our study as having also undergone a complete chest examination. Pulse rate, blood pressure, trauma score value, Glasgow coma scale value, surgical result, and final outcome were retrospectively evaluated. The CT features analyzed were: decreased cardiac volume, reduced caliber of the thoracic aorta, aortic branches and caval venous system, increased enhancement of the aorta, and increased enhancement of the pulmonary collapses/contusions.

RESULTS

All 11 subjects presented severe injuries and hemodynamic instability; 7 were stable enough to undergo surgery; only 1 of the 11 survived. Two patients showed none of the features of thoracic hypovolemia. All the other patients presented at least two signs: reduced caliber of the thoracic aorta in 7 cases; decreased volume of the cardiac chambers and increased aortic enhancement in 6; decreased caliber of the aortic vessels in 4; decreased caliber of the caval veins in 3; and increased enhancement of the pulmonary collapses/contusions in 3.

CONCLUSIONS

In patients with hypovolemia, CT may show several thoracic findings in addition to abdominal ones. Knowledge of these features is important for distinguishing them from traumatic injuries.

Chest radiographic image quality: comparison of asymmetric screen-film, digital storage phosphor, and digital selenium drum systems--preliminary study

Conventional screen-film radiography does not display all regions of the thorax satisfactorily. Three chest radiographic techniques display both the lung and the mediastinum with good contrast. These techniques are asymmetric screen-film (ASF), digital storage phosphor (DSP), and digital selenium drum (DSD) imaging. ASF systems use two asymmetric screen-film combinations to produce a wide-latitude image of the thorax with good contrast in the lungs. In DSP systems, image data are acquired digitally with a wide dynamic range by using the optical output of a photostimulable phosphor plate; in DSD systems, the wide-range digital image data are acquired by using the electronic charge generated on a drum coated with a thin layer of amorphous selenium. The appearance of a DSP or DSD radiograph is then determined by user-selected image processing operations: tone scaling, spatial frequency processing, and dynamic range compensation. Digital chest radiographs processed with strong regional equalization provide both excellent contrast in the lungs and effective display of the mediastinum and chest wall. At visual comparison, the high lung contrast and good mediastinal, retrocardiac, and subdiaphragmatic detail provided by the DSD method distinguish it from the other two methods.

The cost-effectiveness of carbon-fibre cassettes in mobile chest radiography

Employment of carbon fibre materials is an effective method of reducing radiation dose, yet the increased associated costs have led to a reluctance in implementation. This study investigates the level of dose reduction achievable, while maintaining image quality, in mobile chest radiography using carbon-fibre cassettes, compared with plastic cassettes, and balances this against increased expense of the cassettes. Dose measurements using thermoluminescent dosimeters were carried out on intensive therapy unit (ITU) patients undergoing an anteroposterior chest X-ray examination. Resultant image quality was assessed using objective Commission of European Communities (CEC) criteria. A retrospective audit recorded number of ITU patients currently having chest X-rays to determine total dose savings over the life of the cassettes. The results show significant reductions (p < 0.0001) of 32 % for entrance surface and effective dose with carbon-fibre cassettes. No deterioration in total image quality was noted. The added expense of </= 2260 per personSievert (calculated from the effective dose reduction) for employing carbon-fibre cassettes is minimal compared with the estimated cost of manSievert exposures reported by other workers.

Technical aspects of twin screen-film chest radiography: cost effective lung and mediastinal imaging

OBJECTIVE

To determine the sensitometry and 'cross-talk' of a twin screen-film cassette and to assess its clinical potential.

MATERIALS AND METHODS

The twin cassette utilises two sets of screens, divided by filter material, to provide an optimised image of the mediastinum and the lungs. The exposure difference for the two images was measured sensitometrically. The contribution to film density of visible light and K-characteristic radiation, from adjacent screens in the absence of a dividing filter, was investigated.

RESULT

Clinical experience indicated that an exposure difference of 3.4 between the front and back screens, was optimal. Visible light and K-characteristic radiation from the front screens, contributed up to 20 and 24% respectively, of the back film exposure and screen absorbed energy respectively. This was reduced to 0 and 6% with the use of the filter.

CONCLUSIONS

The twin screen-film cassette provides extended latitude to enable optimal visualisation of the lung and mediastinal regions. Adjacent screen 'cross-talk' has been overcome to allow standard and portable chest applications.

Clinical evaluation of twin screen-film chest radiography: cost effective lung and mediastinal imaging

OBJECTIVE

A new twin screen-film cassette system optimised for conventional chest radiography was evaluated by four thoracic radiologists.

MATERIALS AND METHODS

The twin screen-film cassette system produces two film images, the front film optimised for the mediastinal region of the chest, the rear for the lung region. Image degradation on either screen-film system due to internal photon scatter has been virtually eliminated due to the use of a dividing filter. Fifty patients were included in a trial that resulted in a set of chest images for each patient, taken on the same inspiration, by both the twin screen-film cassette and the conventional system. The resultant fifty sets of images were evaluated by four chest radiologists who scored 12 radiographic features of the chest and patient pathologies present, using a paired difference technique.

RESULTS

The image quality of the twin screen-film cassette system was judged to be significantly superior to the conventional screen-film system in nine of the 12 radiographic features scored (P < 0.003). In the three other regions and for the patient pathologies, no significant conclusions were drawn.

CONCLUSION

The new twin screen-film system showed improved visualisation of radiographic features, particularly in the mediastinal and retrocardiac lung regions. This new system shows promise in both standard and portable clinical applications.

[Choice of electron equipment for x-ray diagnostic digital scanning system]

The paper deals with the choice of electron equipment for X-ray diagnostic devices with digital image processing which are intended for population-based mass prophylactic examinations of lung. Guidelines for the optimization of the package of electron devices for processing and storing of data and for obtaining hard copies of X-ray films.

Postoperative portable chest radiographs: optimum use in thoracic surgery

PURPOSE

Daily portable chest radiographs are routinely ordered in many institutions after thoracic surgery. Our purpose was to assess the efficacy and cost of this practice and to determine the optimum use of postoperative x-ray studies.

METHODS

A prospective review of all portable chest x-ray films after 100 consecutive elective thoracotomies (DRG 75) was conducted. Each x-ray study initiated a three-part survey. First, the surgeon listed whether the x-ray study was routine and the anticipated management had it not been available. The radiologist then interpreted and scored the x-ray study as follows: negative, expected findings; A, minor findings necessitating no intervention; B, minor findings necessitating intervention; or C, major findings necessitating intervention. Finally, the x-ray film and the interpretation were returned to the surgeon. Any interventions necessitated by the x-ray study were recorded.

RESULTS

In 6 months, 99 patients underwent 82 pulmonary resections and 18 other major procedures. In the postoperative period, 769 portable chest x-ray studies were ordered, median five per patient (range 2 to 49). Of these, 731 (95%) were routine and 38 (5%), nonroutine. Severity scores were as follows: negative in 106 (13.8%), A in 558 (72.5%), B in 59 (7.7%), and C in 46 (6.0%). X-ray findings altered management in 43 of 769 studies (5.6%): in 33 routine (4.5%), in 10 nonroutine (26.3%), in 13 A (2.3%), in 22 B (37.3%), and in 8 C (17.4%).

CONCLUSIONS

These results demonstrate that routine daily portable chest x-ray studies have a minimal impact on management. It is, in fact, nonroutine x-ray studies that more often alter management. Had routine portable chest x-ray studies, which cost $114 each in our institution, been limited to one immediately after the operation, only 133 such studies (100 routine and 33 nonroutine) would have been needed in the care of these patients. Elimination of 636 (82.7%) x-ray studies reduces the cost of care by $725 per patient ($286,000 annually). For major thoracic procedures, it is safe, efficacious, and cost effective to eliminate routine postoperative portable chest x-ray studies and order nonroutine portable studies only when clinically indicated.

[The neonatal respiratory insufficiency syndrome: the role of the chest radiogram]

INTRODUCTION

Chest radiography is considered the most reliable diagnostic tool to study the respiratory distress syndrome in newborns and one of the few diagnostic investigations which can be used considering the clinical situation of these patients and the need of a prompt diagnosis.

MATERIALS AND METHODS

We examined 124 newborns (56 males and 68 females) submitted to chest radiography at least once. Two radiologists analyzed the images investigating: a) chest expansion, b) reticulonodular opacities, c) aerial bronchograms, d) parenchymal consolidation, e) atelectasis, f) pneumothorax. The clinical diagnosis was made by neonatologists on the basis of clinical and instrumental data and of the clinical evolution of the patients.

RESULTS

Twenty of 23 clinically negative patients had negative chest radiographs and 3 were false positives. Transient tachypnea was diagnosed in 14 newborns where chest radiography showed reticulonodular opacities. Ten of 62 patients with hyaline membrane disease had a negative chest radiograph, 26 had fine granular opacities, 16 marked hypoexpansion with reticulonodular opacities and aerial bronchogram, and 10 diffuse parenchymal consolidations with aerial bronchogram also in the peripheral lung. Eleven patients had a clinical and radiological diagnosis of segmental or lobar atelectasis; 5 newborns had an aspiration syndrome and radiography showed parenchymal consolidations in 4 and was negative in one. Five patients had pneumothorax, 3 diaphragmatic hernia and 1 infective pneumonia; radiology confirmed the diagnosis in all cases. We had three false positives and 11 false negatives at conventional radiography--i.e., 10 had MMI and one the meconium aspiration syndrome. Diagnostic sensitivity was 89.1%, specificity 86.9% and diagnostic accuracy 88.7%.

CONCLUSIONS

Our results are partially limited by the lack of a reference gold standard. Nevertheless, if we consider the clinical condition and the respiratory distress syndrome evolution as a valid reference, the diagnostic accuracy of radiography is good.

[Potentialities of digital low-dose x-ray apparatus in the diagnosis of heart and lung diseases]

The paper presents experience in clinically testing a digital low-dose X-ray apparatus. X-ray studies were performed in 169 patients: 140 with cardiovascular abnormalities and 19 with lung diseases. The findings show the high quality of images of thoracic aorta and lung structures. The radiation dose received during an examination is many times lower than at routine X-ray study and fluorography, which makes it possible to use the apparatus in mass surveys of contingents at risk for tuberculosis.