[The radiological exam of the chest in the elderly. Technical and methodological considerations]

PURPOSE

We investigated the capabilities of chest radiography in the elderly considering that the examination must meet the main clinical indications of this population and that it is necessary in the elderly because the correct clinical assessment is often difficult or impossible.

MATERIALS AND METHODS

We reviewed the chest radiographs of 756 consecutive elderly patients admitted to our hospital from September 1 to October 31, 1996. If possible, chest radiographs were performed with the AMBER technique (156 patients, 20.7%); 240 patients (31.7%) underwent conventional radiography and the others frontal projections only (360 patients, 47.6%). T-MAT G RA Kodak high contrast films with Kodak Lanex green transmitting intensifying screens were used in all cases. The AMBER examinations of 48/156 patients with hemodynamic clinical indications were repeated with conventional frontal projections. Radiographic reports were made separately by different radiologists who considered especially the diagnostic accuracy of every examination in determining the venous overload of pulmonary circulation.

RESULTS

Hemodynamic studies are the most frequent clinical indication of chest radiography in elderly patients (228/756 patients in our series, 30.2%); moreover, even if careful cardiac and pulmonary circulation studies are very important in these patients, only 52.4% of all radiographs could be made in two orthogonal projections. The blurred appearance of vascular landmarks indicating increased extravascular fluid is better depicted by conventional radiography (59.7% of cases) than by AMBER (40.3%).

CONCLUSIONS

We conclude that the reduced pulmonary contrast obtained with the so-called "hard X-ray" technique poorly depicts the blurred appearance of pulmonary vessels in pulmonary venous overload. Moreover, "hard X-ray" techniques can be only sporadically used because elderly patients are often in very critical conditions, which prevents this type of examination.

X-ray imaging with amorphous selenium: theoretical feasibility of the liquid crystal light valve for radiography

A novel radiographic imaging system based on a liquid crystal light valve is described. A liquid crystal light valve is a photon addressed spatial light modulator that consists of a high resolution, solid-state electrostatic detector (photoconductor) and an electro-optic light modulator (liquid crystal cell) physically coupled in a sandwich structure. We propose a light valve with a thick, x-ray sensitive photoconductive layer and call the system under study the x-ray light valve (XLV). The image formation in the XLV is based on x-ray exposure controlled modulation of light from an external source; the XLV is essentially an x-ray image intensifier that allows the image brightness to be adjusted independently from the x-ray exposure. Thus the XLV may be coupled to an optical imager, such as a charge coupled device (CCD), for image digitization without a secondary quantum sink. A model of the XLV operation is developed to investigate its sensitivity, speed, noise, and resolution. The imaging properties of the XLV are found to be time dependent, which leads to an unusual transmission versus exposure characteristic. The feasibility of clinical use of the XLV based on amorphous selenium (a-Se) photoconductor and a twisted nematic liquid crystal cell is analyzed, and the device is shown to be adaptable to a variety of radiographic imaging tasks.

[Can digital selenium-based radiography in thoracic diagnosis replace the analog x-ray imaging technic?]

PURPOSE

To find out the diagnostic value of digital selenium radiography, we compared the image quality of chest x-ray images from 50 patients who had been examined via conventional chest x-ray and digital selenium radiography of the chest.

METHOD

50 patients with a malignant melanoma underwent chest x-ray within 3 months in conventional technique and with digital selenium radiography (Thoravision: Philips Medical Systems, Hamburg, Germany). In this period none of the patients showed a difference in respect of clinical status or radiological diagnosis. Simultaneous examinations on the same day were not performed to avoid unnecessary exposure to x-rays. The digital and conventional images were compared by 4 radiologists with regard to image quality by the detection of defined anatomic structures.

RESULTS

Image quality of digital selenium radiography was considered superior to that of conventional chest x-rays in the mediastinum, the retrocardiac and retrodiaphragmatic areas, the superior and inferior lobes of the lung especially near the parietal pleura, and the chest wall.

CONCLUSIONS

Compared to analogous techniques there is no loss of image information when employing digital selenium radiography in chest x-rays. On the contrary, new assessment criteria may be gained. We conclude that digital selenium radiography offers diagnostic advantages in chest x-ray examination.

Evaluation of a new ultraviolet-emitting rare-earth film-screen combination

The performance of a 400 speed class DuPont Ultra Vision Rapid (UVR) film-screen combination has been evaluated and compared with that of DuPont Quanta Fast Detail screens with Cronex 10L film (QFD-200 speed class). The speed was calculated from the constructed characteristic curves (H&D) at different energies. Image quality was derived objectively using the Leeds test object TOR (CDR). An anthropomorphic phantom was then employed to determine image quality subjectively by means of radiologist appraisal. Lumbar spine and chest radiography of patients were performed to evaluate the potential for dose reduction in clinical conditions by measuring skin entrance doses with thermoluminescent dosimeters (TLDs). UVR provided better resolution (9 lp mm-1 as opposed to 8 lp mm-1) and contrast response than QFD. UVR has accommodated a wider exposure latitude than might be expected with conventional 400 speed class film-screen combinations. Use of UVR resulted in better image quality than use of QFD over a wide range of exposure factors. The use of UVR can result in a dose reduction of 50% with no loss in image quality.

Digital chest imaging using a selenium detector. The impact of hard copy size on observer performance: a computed tomography-controlled study

RATIONALE AND OBJECTIVES

The authors compare radiologist detection performance under clinical conditions for assessment of the effect of size reduction on the diagnostic performance of digital chest images obtained with a selenium detector.

METHODS

Sixty-five patients were examined with the digital system. The images were acquired without an antiscatter grid. Sixty-five posteroanterior life-size images (35 x 43 cm) and sixty-five posteroanterior minified images (56% of life size) were analyzed by three observers for detection of pulmonary, mediastinal, and pleural pathology, using computed tomography as the reference standard. The diagnostic value of life-size and minified images for the detection of these chest abnormalities was analyzed with receiver operating characteristic (ROC) methods.

RESULTS

For the detection of the various abnormalities by all radiologists, the areas under the ROC curves with life-size images versus minified images, respectively, were as follows: pulmonary opacities, 0.78 versus 0.78; interstitial disease, 0.74 versus 0.75; mediastinal disease, 0.70 versus 0.72; and pleural abnormalities 0.72 versus 0.67.

CONCLUSIONS

There was no statistically significant difference between the radiologists' performance in detecting pulmonary, mediastinal, and pleural pathology with life-size versus that with minified (56% of life size) digital selenium chest radiography.

Memory artifact related to selenium-based digital radiography systems

Digital images acquired on radiography systems with amorphous selenium detectors are susceptible to "memory artifacts" from prior x-ray exposures. In routine clinical use and in a laboratory experiment, artifacts appeared in chest radiographs until the selenium recovered from initial exposure. Memory artifacts were eliminated when 3 minutes or more elapsed between acquisition of a lateral chest radiograph and acquisition of the next radiograph.

Improved Bayesian image estimation for digital chest radiography

PURPOSE

Previously, we have shown that Spatially Varying Bayesian Image Estimation (SVBIE) can be used to reduce scatter and improve contrast-to-noise ratios (CNR) in digital chest radiographs with no degradation of image resolution. This previous algorithm used a model for scatter compensation that was derived for emission tomography. Here, we develop and evaluate a new iterative SVBIE technique that incorporates a scatter model derived for projection radiography.

MATERIALS AND METHODS

Portable digital radiographs of an anthropomorphic chest phantom were obtained along with quantitative scatter measurements using a calibrated photostimulable phosphor system. The new iterative SVBIE technique was applied to the phantom image to reduce scatter. Scatter fraction reduction, CNR improvement, and resolution degradation were evaluated.

RESULTS

Residual scatter fractions were reduced to less than 2% in the lungs and 30% in the mediastinum at 14 iterations. CNR was improved by approximately 50% in the lung region and 187% in the mediastinum. Resolution was not degraded.

CONCLUSIONS

The new SVBIE technique can reduce scatter to levels far below those provided by an antiscatter grid and can increase CNR without loss of resolution. The new technique outperforms the previous Bayesian techniques.

[Digital radiography of the thorax]

Digital radiography of the thorax can, now be substituted to conventional chest radiography. Computed radiography with phosphor plates and the new selenium detector are emphasized. The major image processing are explained. Successively the main other methods of digital radiography are described: scanning equalization radiography, laser-digitized radiography and multiwire proportional chambers. Then the advantages and the drawbacks of chest computed radiography are extensively reviewed.

[Digital chest x-rays with a selenium detector: a prospective comparison with a conventional film-screen combination]

PURPOSE

To compare a new digital chest radiography system that uses amorphous selenium as the x-ray detector, with conventional radiography for the detection of pathological alterations of the chest.

MATERIAL AND METHODS

Two observers analysed pairs of posteroanterior and lateral chest radiographs of 95 patients. One pair of radiographs was obtained with the digital selenium chest radiography system, and the other with conventional film-screen technique. 9 criteria were rated using a 4 point scale. Technical parameters were standardised. Radiation dose was measured in both techniques and compared.

RESULTS

A total of 855 criteria were rated. 740 findings were diagnosed in accordance on both techniques (740/855 = 87%). 115 criteria (115/855 = 13%) showed deviations. The mean radiation dose for the selenium detector was 0.02 cGy and for the conventional system 0.11 cGy.

CONCLUSION

The exposure of radiation is lower using a selenium x-ray detector compared to conventional film-screen technique in chest radiography. The digital selenium system performs well in a clinical setting, providing visualisation of pathological findings as good as a standard screen-film system.

Technical trends in functional radiology of the lung

In functional radiology of the lung, the depiction of subtle details of circulatory and bronchial anatomy, is very important. At present, the evolution of the radiographic techniques allows to overcome the difficulty in imaging, essentially related to the marked difference in density of chest structures, producing radiographs optimized to the concomitant representation of the parenchyma and higher absorption structures. Main quality factors related to radiation beam optimization on one hand and to imaging systems on the other hand, are considered with an analysis of the evolution of methods and techniques of thoracic radiology.

Stimulable phosphor plates in chest radiology

The stimulable phosphor plate technique has revolutionised radiology with portable equipment. The image quality permits diagnosis under difficult control conditions (ICUs). In order to achieve a signal-to-noise ratio, and therefore a contrast resolution similar to the commonly used film/screen systems, a higher radiation dose is needed. However, overall, with this technique a radiation dose reduction may be achieved as a result of the elimination of the need for retakes. The available stimulable phosphor plate systems, with adequate image processing are reliable, and at least as good as conventional film/screen systems for diagnosis in chest radiography. There are, however, other aspects that make the stimulable phosphor plate technique particularly appealing. Firstly, its reproducibility, which particularly in chest radiography allows images to be obtained with the same grey scale and darkness. Secondly, as this technique permits digital archiving and visualisation of images on screen, images can be rapidly distributed over a network making them available when and where they are needed.

Chest radiograph and functional radiology

In the course of the years the concept of functional radiology has gradually been developed. It represents the integration of chest radiography with some basic concepts of respiratory pathophysiology. The correlation between the higher vascularization at the bases of lung as compared to the apex with the gravitation factor was the initial reference. From this data, combined with physiologic parameters, over the years, relatively simple but diagnostically significant semeiotic findings were achieved. The different combinations of acquired "morphofunctional" signs allow the differential diagnosis in a number of organic and hemodynamic alterations, adding to conventional "morphologic" radiology. New contributions to the functional radiology of the lung might come from procedures as high resolution computed tomography (HRCT) which with the dynamic study supplies morphologic and densitometric information to be correlated with changes in pulmonary flow and ventilation/perfusion ratio.

Storage phosphor radiography

Storage phosphor radiography is a digital technique that uses photo-stimulable, phosphor screens to substitute for conventional screen-film combinations. While the technique is more than 15 years old, it is only recently that technological and economic aspects of these systems have become favourable enough to envisage a more widespread clinical application.

Standardization of low attenuation area versus total lung area in chest X-ray CT as an indicator of chronic pulmonary emphysema

We examined the methods for measuring the LAA% (100 x low attenuation area/total lung area) on thoracic X-ray CT scans in order to develop a useful indicator of chronic pulmonary emphysema (CPE). First, we modified the method for calculating the LAA% to be applicable by the programming tool installed in a commercially available CT machine in order to minimize manual procedures. This new method proved to be applicable in all CT machines produced after 1987. Second, we examined the difference in the Hounsfield Unit (HU) between different CT machines using two kinds of phantoms. One phantom was composed of Styrofoam, which has a density similar to the low attenuation areas. The other phantom was composed of Styrofoam and water, which has a density similar to the lung. We proved that the difference of LAA% with the correct value was 5% at maximum among four different CT machines. Thus, the phantom developed in the present study may play an important role in the standardization of HU. Finally, the possibility of decreasing the X-ray levels was examined. Twenty-five percent of the standard electrical current provided the same LAA% in cases where the subject was an established CPE patient, whereas the LAA% was overestimated in subjects with a normal LAA% value. However, a correction using a linear regression equation may be possible in the latter cases. It may be concluded that LAA% analysis can easily be performed in many city hospital, without much investment of manual procedures or any corrections to the HU levels between different CT machines. This method may be useful as a routine follow up for CPE patients because of the smaller irradiated dose given when using a CT machine.

[Photostimulation plates or conventional films for bedside chest x-ray in pediatric radiology? A comparative study of quality of image and the dose delivered to patients]

Image quality and patient doses received during chest bedside examinations performed with conventional (film-screen combination) and photostimulable phosphorus plate systems were compared in a study carried out in 1993 in a French pediatric radiology department. Seventy one children (36 males and 35 females) aged between 9 days and 18 years (average: 43 months) were included in the study. Technical performances of all radiological equipment used were permanently checked through a quality control program. One conventional and 3 "photostimulable" films were performed for each patient included (mAs product selected for "photostimulable" system was progressively reduced down to 60% of that of conventional technique). TLD Lithium Fluoride chips were used to measure entrance surface dose during the examination. Image quality of 284 films (213 "photostimulable" + 71 conventional) was assessed by three independent radiologists. Advantages and drawbacks of both studied imaging techniques are discussed in terms of patient dose reduction and image quality.

[Clinical evaluation of single-exposure dual-energy subtraction chest radiography: with FCR 9501 ES]

Using the one-shot energy subtraction method, we took chest radiography of 1,031 outpatients of Kanazawa University Hospital. Chest radiographs were taken with the FCR 9501 ES system, with patients upright. We studied the clinical efficacy of this diagnostic method. The method and usage procedures involved have been sufficiently technologically refined to permit handling of an adequate number of patients in a reasonable time at a permissible exposure dose. However, the system can be further improved technologically in order to obtain fully consistent high-quality images, regardless of the patient's physique. For well-rounded image reading, three kinds of images must be generated simultaneously: an original image; soft tissue (bone subtracted image) and bone (soft tissue subtracted image) Some soft tissue image were helpful for detecting non-calcified parenchymal nodules that overlapped the rib shadow, and some bone image served to precisely diagnose the existence of abnormal ribs, calcified lymph nodes, and calcified nodules. Furthermore, the bone images were helpful for revealing that the fine infiltrative shadows in the lung fields in original images were actually pleural calcifications and that the poorly defined nodular opacities were, in reality, abnormal rib calcifications. In light of the above, we wish to stress the importance of clinical efficacy of not only soft tissue images but bone images derived using the energy subtraction method. The clinical usefulness of this method was confirmed in 66 of 1,031 patients (6.4%) who had initially been scheduled for routine chest radiography. This result indicates how frequently the method encounters applicable cases when applied non-selectively to general patients who require radiographic chest examination. The advantages of this method will become much more evident with an examination protocol that minimizes unnecessary special examinations or optimizes the balance between screening and special examinations.

ROC-analysis of detection performance by analogue and digital plain film systems in chest radiography

PURPOSE

To compare the performances of 4 imaging systems in the diagnostic radiology of the chest: an asymmetric screen-film combination (a-SFC); a conventional screen-film combination of speed class 200 (SFC); a screen-film combination of speed class 200 with an aluminium lung filter; and digital luminescence radiographs (DLR).

MATERIAL AND METHODS

Object detectability studies were carried out using an anthropomorphic chest phantom. The images were obtained under standard exposure conditions at 125 kVp. The detection performance of the various systems was evaluated by receiver operating characteristic (ROC) analysis on the basis of a total of 12,240 observations.

RESULTS

In the overall evaluation the a-SFC and the SFC plus lung filter received equally high ratings of 0.878+/-0.018 and 0.860+/-0.21, respectively (p>0.05). There was no significant difference between the 200-speed SFC and the storage phosphor radiographs. In the mediastinum all the tested systems were clearly superior to the 200-speed SFC (p<0.05) while in the lung fields the 200-speed SFC received a high rating of 0.866+/-0.026. The a-SFC had slight advantages over the SFC plus lung filter and the 2 digital imaging modes (p>0.05).

CONCLUSION

The a-SFC and the digital luminescence radiographs provide a significant gain in diagnostic information in the mediastinum without diminishing detail detectability in the lung fields and without additional radiation exposure.

[Experiences with a new film-screen system in pediatric thoracic radiography]

PURPOSE

To compare the x-ray images made by the Kodak InSight Pediatric Imaging System (InSight P) with conventional film-screen systems in pediatric chest radiography.

MATERIAL AND METHODS

The comparison involved chest radiographs made using Quanta-Fast-Detail/Cronex 4 (DuPont), Trimax 16/XDA (3 M) and DuPont UVR/UVL systems. The image quality of critical structures and the physical parameters of quantum interference, contrast and resolution were assessed. The energy path of the system was assessed by preparing density curves. Test conditions were in accordance with the latest guidelines of the Bundesärztekammer (German Physician's Association).

RESULTS

The mediastinal area, retrocardiac and paravertebral spaces and the peripheral vessels of the lung were all displayed more distinctly using InSight P. The reason for this seems to be a lower degree of quantum interference associated with this system. With tube voltages between 60 and 80 kV, InSight P displayed a relatively low degree of sensitivity.

CONCLUSION

InSight P can be used to produce predominantly high quality chest radiographs of infants between one and five years of age. However, this system has limited sensitivity in the tube voltage range recommended by the German Physicians' Association.

Selenium radiography versus storage phosphor and conventional radiography in the detection of simulated chest lesions

PURPOSE

To compare selenium detectors with three conventional and digital detector systems for the detection of simulated pulmonary lesions.

MATERIALS AND METHODS

Templates containing nodules, linear structures, and micronodular opacities were superimposed over an anthropomorphic chest phantom. The authors compared lesion detection with use of storage phosphor radiography (250 speed), selenium radiography (250 speed) with an antiscatter grid, selenium radiography (450 speed) without an antiscatter grid, an asymmetric screen-film system (400 speed), and a conventional screen-film system (250 speed). Detection performance of 10 radiologists was compared by using a multireader-multicase receiver operating characteristic analysis of variance.

RESULTS

For the detection of nodules, no statistically significant differences between imaging modes were seen. For the detection of micronodules and linear lesions, both selenium techniques were superior to all other modes (P < .05). In addition, the asymmetric screen-film radiographs were inferior (P < .05) to the conventional screen-film radiographs and to storage phosphor radiographs for the detection of micronodules.

CONCLUSION

The selenium detector improves detection of simulated fine linear and low-contrast micronodular details and appears to be superior to other detector systems for chest radiography.

Chest imaging with a selenium detector versus conventional film radiography: a CT-controlled study

PURPOSE

To compare radiologist detection performance under clinical conditions for assessment of conventional radiographs and digital chest images obtained with a selenium detector.

MATERIALS AND METHODS

One hundred four patients were examined with the digital and conventional systems under near identical technical conditions. The digital images were acquired without an antiscatter grid. Two hundred eight images were analyzed by three radiologists for detection of pulmonary, mediastinal, and pleural abnormalities; computed tomography was used as the reference standard. The diagnostic value of both techniques for the detection of these chest abnormalities was analyzed with receiver operating characteristic (ROC) methods.

RESULTS

For detection of the various abnormalities by all radiologists, the areas under the ROC curves with conventional imaging versus digital imaging, respectively, were as follows: pulmonary opacities, 0.81 versus 0.79; interstitial disease, 0.69 versus 0.73; mediastinal disease, 0.79 versus 0.74; and pleural abnormalities, 0.73 versus 0.68.

CONCLUSION

There was no statistically significant difference between the radiologists' performance in detecting pulmonary, mediastinal, and pleural abnormalities with conventional radiography versus that with digital selenium chest radiography.

Basic imaging properties of a new screen-film system for chest radiography

To evaluate the potential clinical usefulness of a new screen-film system (advanced screen-film system; AD system) for chest radiography, its fundamental imaging properties compared with a conventional screen-film system (HR-4/HR-S) were investigated. The basic imaging properties were evaluated by measuring characteristic (H&D) curves, relative speeds, MTFs (modulation transfer functions), WS (Wiener spectra), and x-ray attenuations of screens. The detail visibilities and pathological details of various diseases in chest radiographs of patients were evaluated subjectively. The film gradient of the AD system was slightly lower at low radiographic density, and higher at high density, as compared with a conventional screen-film system. The screen speed of the AD system was 212% greater than that of the conventional system, and the film speed was 53% that of the conventional film. As the result, the total speed of the AD system was slightly higher compared with the conventional system. The spatial resolution of the AD system was comparable to or slightly lower than that of the conventional system. The noise level of the AD system was considerably lower than that of the conventional system at low (D = 0.5) and middle (D = 1.0) radiographic density levels. However, it was high at high radiographic density (D = 1.8). The radiographic densities in the underpenetrated areas with the AD system were greater than those of the conventional system when the lung densities are matched comparable. Improvement in noise level with the AD system at low and middle density levels may be useful for detection of various diseases in chest radiographs.

Effects of dose reduction on digital chest imaging using a selenium detector: a study of detecting simulated diffuse interstitial pulmonary disease

OBJECTIVE

The purpose of this study was to evaluate the effect of dose reduction on the diagnostic performance of a new digital chest imaging system in which amorphous selenium is used as the X-ray detector. Diagnostic performance was assessed for the detection of simulated diffuse interstitial pulmonary disease (DIPD).

MATERIALS AND METHODS

DIPD was simulated by superimposing plastic sheets that contained small radiopaque objects (birdseed) on an anthropomorphic chest phantom. We varied the number of sheets from zero to four to simulate the degree of abnormality. We made 80 images with a standard X-ray dose, 80 images with 55% of the standard dose, and 80 images with 35% of the standard dose. Six observers were asked to indicate the presence of DIPD using a five-level scale of confidence. Two hundred forty chest images were then analyzed using receiver operating characteristic (ROC) curves.

RESULTS

The area under the ROC curve was 87.2 for all readers with standard-dose imaging (95% confidence interval [CI], 83.7-90.7), 91.7 with 55% of the standard dose (95% CI, 88.8-94.6), and 90.0 with the 35% dose (95% CI, 87.1-92.9). The area under the ROC curve for subtle DIPD (one superimposed sheet) was 75.3 for all readers with standard-dose imaging (95% CI, 67.1-83.5), 79.7 with 55% of the standard dose (95% CI, 71.9-87.5), and 70.3 with the 35% dose (95% CI, 61.7-78.9). For each dose, we observed a gradual improvement of the ROC curves with each additional sheet superimposed on the chest phantom (p < .001).

CONCLUSION

We found no significant difference in diagnostic performance among images made with standard X-ray dose, those made with a 55% dose, and those made with a 35% dose (95% CI).

Portable chest radiology in intensive care: a comparison of a new dual characteristic film-screen system (Insight) incorporating a flexible grid with a standard film-screen system

Insight (Insight, Kodak, UK) is a new dual image receptor system which utilizes an asymmetric film screen combination. Conventional radiography was compared with the Insight system, in combination with a cassette incorporating a flexible grid, in fifty patients on the intensive care unit. Radiographs were analysed by intensive care junior medical staff, nursing staff and two groups of radiologists. Insight provided better visualization of lung parenchyma, mediastinal detail and position of endotracheal tubes than conventional radiography. Central venous catheters were generally seen better on conventional radiographs than on Insight. Insight system produces a significant improvement in plain chest radiography in the intensive care unit. In the absence of digital radiography it is a suitable technique for routine radiography in the intensive care unit.