Does a flat panel detector reduce the patient radiation dose in interventional cardiology?

An internal audit has been performed to evaluate the patient radiation dose in the clinical use of X-ray cardiac flat panel detector (FPD) systems. Fluoroscopy and image acquisition (cine mode) programs are optimised for low-dose settings. The diagnostic and therapeutic interventional cardiac procedures are performed at 6 pulse s(-1) for fluoroscopy and 15 frames s(-1) for image acquisition. The FPD entrance dose is configured for 29 nGy pulse(-1) in the fluoroscopy mode and 0.10 microGy frame(-1) in the cine mode. From the data collected, the following local reference levels for coronary angiography and angioplasty have been obtained: kerma-area products 23 and 44 Gy cm(2), cumulative doses 376 and 776 mGy, fluoroscopy times 5 and 15.5 min and cine images 617 and 1163 images.

Neuroradiologic applications with routine C-arm flat panel detector CT: evaluation of patient dose measurements

BACKGROUND AND PURPOSE

Since the introduction of flat panel detector-equipped C-arms, the use of flat panel detector CT (FPCT) in the neuroradiologic angiography suite has become more frequent. This examination implicates its own specific radiation exposure. We used the CT dose index (CTDI) concept and adapted it to the special FPCT geometry to provide a consistent comparison with multisection head CT (cCT).

MATERIALS AND METHODS

Exposure data obtained for routine scanning during a period of 1 year were used to assess a specific dose of a total of 217 rotational scans performed in 105 patients. One hundred seventy-two scans were 3D digital subtraction angiography (DSA) scans. There were 45 scans that were performed to achieve high-quality, soft-tissue resolution. Dose measurements in cylindrical polymethylmethacrylate (PMMA) phantoms were used to determine the CTDI value and to compare it with the reference values for cCT. In addition, the dose-area product (DAP) was registered and correlated with the CTDI and corresponding dose-length product (DLP) values. Exposure data and dose values were compared with cCT.

RESULTS

Mean-weighted CTDI value of 3D-DSA was approximately 9 mGy per scan. High-quality, soft-tissue resolution FPCT scans, comparable with cCT, revealed a mean dose value of 75 mGy (reference value for cCT, CTDI(w) approximately 60 mGy).

CONCLUSION

The high-speed scans used for 3D-DSA revealed a significantly lower CTDI(w) and DLP compared with clinical CT. The high-quality FPCT protocol resulted in a higher dose and should therefore be limited to acute cases, when patient transfer to a CT scanner is considered to be a disadvantage for patient management.

Imaging the neonate in the incubator: an investigation of the technical, radiological and nursing issues

Modern neonatal incubators incorporate an X-ray tray device into the mattress support structure to facilitate patient examination with minimal disturbance and distress. However, the usual method of examination is to place the image plate directly underneath the baby. Users often cite radiological reasons for not using X-ray trays but modern quantitative evidence is lacking. This work looks at the technical and clinical aspects of imaging neonates in incubators and the impact that these may have in determining the imaging protocol. A number of hospitals were surveyed to determine their current method of examination and the reasons for their preference. Experimental measurements of the radiological impact of using (or not using) the X-ray tray were performed for a range of neonatal incubators. The average dose to the image plate was 5.9 microGy (range 5.4-6.4 microGy) for the "plate on mattress" method and 3.0 microGy (2.0-3.8 microGy) when using the tray--a 49% reduction owing to the mattress support materials. However, when using a computed radiography (CR) imaging system, the image quality differences were marginal. Survey results indicated that nurses preferred to use the tray but that radiographers were reluctant. We conclude that incubator manufacturers could do much to improve the radiological performance of their equipment and we offer recommendations. We also conclude that, with appropriate nurse and radiographer training and the advent of CR imaging systems, use of X-ray tray facilities may optimize imaging of the neonate in the incubator.

[Elastic stable intramedullary nailing (ESIN) in pediatric forearm shaft fractures: intraoperative image intensifier times]

AIM

Elastic stable intramedullary nailing (ESIN)is the therapy of choice in pediatric forearm shaft fractures. It requires increased intraoperative image intensifier times and radiation load.

METHOD

We performed a retrospective analysis of 78 operative procedures from a five-year period. In 16 cases the image intensifier times of the distinct steps of the operation were investigated prospectively.

RESULTS

Average duration of the surgical procedure was 36.9 (18-144) minutes. Average radiation time was 59.5 (8-222) seconds. In educational operations, the duration of surgery was significantly longer than in procedures performed by experienced surgeons, but radiation times only were increased tendentially. In those procedures investigated prospectively, 53.1% of the image intensifier time was used for fracture passage.

CONCLUSION

In ESIN of forearm shaft fractures,intraoperative image intensifier times of less than 2 minutes can be expected. Low intraoperative radiation times are a mark of quality. They serve for radiation protection of the patients, surgeons and OT staff.

Transition from screen-film to digital radiography: evolution of patient radiation doses at projection radiography

PURPOSE

To retrospectively evaluate patient radiation doses in projection radiography after the transition to computed radiography (CR) in the authors' hospital.

MATERIALS AND METHODS

The hospital's ethical committee approved the study and waived informed consent. In 2001, a dose reduction initiative was implemented, which involved collecting radiographic parameters, calculating patient entrance doses, and monitoring changes with an online computer, and a training program for radiographers was conducted. A database with 204 660 patient dose values was used to compute changes in patient doses over time. Sample sizes ranged from 1800 to 23 000 examinations. Doses were compared with European and American reference values. Kruskal-Wallis and Mann-Whitney tests were used for statistical analysis.

RESULTS

Median values for patient entrance doses increased 40%-103% after implementation of CR. Initial increases were corrected during the 1st year, and additional dose decreases were achieved after the dose reduction initiative was launched. At present, doses range between 15% and 38% of the European diagnostic reference levels established for screen-film radiography and between 28% and 41% of the reference values recommended by the American Association of Physicists in Medicine, representing an effective 20%-50% reduction in the initial values for CR.

CONCLUSION

Though patient doses can increase considerably during the transition from conventional screen-film radiography to CR, dose management programs, including specific training of radiographers and patient dose audits, allow for reductions of the previous values.

Strahlenexposition bei der digitalen Vollfeldmammographie mit einem Selen-Flachdetektor

PURPOSE

Calculation of the average glandular dose for mammography on a full-field digital mammography system using a selenium flat-panel detector.

MATERIALS AND METHODS

Mammographic examinations were carried out using the Selenia digital mammographic system from Lorad/Hologic. 1992 mammographies of 500 patients in cranio-caudal and medio-lateral projections were evaluated. Based on the recorded exposure conditions (tube voltage, tube loading, filtration, compressed breast thickness), the entrance surface air kerma was calculated by multiplying the tube loading by the measured tube output and was corrected according to the inverse square law. The average glandular dose was determined for each exposure by multiplying the entrance surface air kerma value by the relevant conversion factor for a breast composition of 50 % adipose tissue and 50 % glandular tissue by weight.

RESULTS

The mean values for patient age and compressed breast thickness were 61 years and 58 mm, respectively. The average glandular dose was 1.57 mGy for a single view (1.46 mGy for cranio-caudal view images and 1.68 mGy for medio-lateral view images).

CONCLUSION

Full-field digital mammography with a selenium flat-panel detector requires a dose similar to that of units with a flat-panel detector based on amorphous silicon and a dose approximately 20 % lower than that of conventional screen/film mammography.

Diagnostic accuracy of two software modalities for detection of caries lesions in digital radiographs from four dental systems

OBJECTIVE

To compare the caries diagnostic accuracy of two software modalities used in the assessment of digital radiographs obtained with four different dental systems, and to evaluate whether the software used for image assessment influenced the mutual comparison of those four dental systems relating to their caries diagnostic accuracy.

METHODS

Under in vitro and standardized conditions 122 teeth (with 228 unrestored approximal and 99 occlusal surfaces) were radiographed in blocks of 3 test teeth and 2 non-test teeth using two storage phosphor plate systems: Digora (Soredex, Helsinki, Finland) and DenOptix (Gendex, Dentsply, Milan, Italy) and two charge coupled device (CCD)-based sensor systems: Dixi (Planmeca, Helsinki, Finland) and Sidexis (Sirona, Bensheim, Germany). The images were displayed and examined in two software modalities: their own dedicated software and a general software. Three observers examined all images for the presence of approximal enamel and dentine and occlusal dentine caries lesions using a 5-point confidence scale. The true presence of caries was validated by ground section histology. The diagnostic accuracy of the software modalities was expressed as ROC curve areas (A(z)) and differences between modalities were tested by paired t-test. Comparison of systems was analysed by post hoc t-test.

RESULTS

Results of approximal and occlusal surfaces assessed together revealed nearly identical mean A(z) with the two software modalities on images obtained with the Digora (A(z)=0.71) and DenOptix (A(z)=0.72) systems. On Dixi images the mean A(z) was 0.75 using the system's own software and 0.73 using the general software. On Sidexis images the corresponding mean A(z)s were 0.79 and 0.75. None of those differences were significant.

CONCLUSION

No significant difference in caries diagnostic accuracy was found between two software modalities used for examination of digital radiographs obtained with four different digital systems, and the software modality did not influence the mutual rank of the four systems relating to their diagnostic accuracy.

Comparison of screen-film and full-field digital mammography in Japanese population-based screening

PURPOSE

To investigate how the greater contrast of full-field digital mammography (FFDM) affects the detection of suspicious lesions in Japanese population-based screening.

MATERIALS AND METHODS

Screen-film mammography (SFM) and FFDM were performed in 480 women aged 50 years or more. A set of mediolateral oblique views was obtained with each modality. All mammograms were independently double-read. The five-scale category assessment and type of finding using the Breast Imaging Reporting and Data system (BI-RADS) nomenclature were given. Intraobserver variance, recall rates, and positive predictive value were calculated.

RESULTS

The findings between the two modalities were discordant. kappa-values for each reader were 0.619 and 0.385, respectively. Almost half of the microcalcifications were called with both modalities. The detection of masses was less concordant between the readers (27%). The masses were detected more frequently with FFDM (73%). Other findings were only detected with one modality. The recall rate was not significantly different (2.9% with SFM vs. 4.2% with FFDM; p=0.253). The positive predictive value was not significantly different (14% with SFM vs. 10% with FFDM; p=0.69), either. Two patients with breast cancer were detected with both modalities.

CONCLUSION

Recall rates and positive predictive value were not significantly different between SFM and FFDM. Cancers were detected with both modalities.

Evaluation of soft copy distribution of diagnostic studies before soft copy interpretation

To meet the imaging needs of an expanding clinical campus and clinical volume, a web-based image distribution system (Stentor, San Francisco, CA) was implemented before the implementation of soft copy interpretation. This study sought to assess system utilization as a metric of system's capability to meet demand for enterprise image review. Study period included all examinations stored on the system and subsequently viewed from June 1, 2001 to August 8, 2001. Server log files were analyzed for study storage and subsequent study retrieval. A total of 24,887 studies were stored on the server and available for immediate retrieval, and, of these, 12,458 studies (50%) subsequently were reviewed. Modality-specific study review included 65% for computed radiography, 46% for digital radiography, 56% magnetic resonance, 54% for computed tomography, and 18% for ultrasound scan. Enterprise image distribution before the implementation of picture archiving communication system is a viable operational decision and can be implemented successfully before implementation of soft copy interpretation. System utilization indicates a great value in the electronic availability of image studies.

Precise image-receptor calibration and monitoring of beam quality with a step wedge

OBJECTIVE

To describe an extended bootstrap calibration procedure that uses a step-wedge absorber and minimal equipment for rapid, accurate calibration of image receptors and simultaneous monitoring of beam quality.

METHODS

Multiple radiographs of a step wedge are made at different exposures, with a precision dosimeter as a reference. An iterative least-squares minimization procedure is used to fit the data with a single calibration function. The calibration range can be extended by varying two exposure parameters in addition to stepwedge thickness. Small variations in beam quality and other experimental artifacts can be detected by testing redundant data for self-consistency. As a demonstration, two photostimulable phosphor (PSP) systems were calibrated, one with a well-regulated X-ray source and the other with a poorly regulated source.

RESULTS

The first PSP system was calibrated over a range of 3.2 orders of magnitude with a relative standard deviation of the estimate of only 0.36%. The slope of the calibration curve agreed with the nominal, factory-set value within 0.8% (on a logarithmic scale). The second PSP system had a nearly linear response with a relative standard deviation of the estimate of 0.44% over the upper 97% of its range. Both X-ray sources showed easily detectable variations in tube potential.

CONCLUSIONS

The new calibration method eliminates many of the sources of error of previous techniques such as inverse-square sensitometry. If a suitably precise X-ray source is available, the relative accuracy is limited only by the precision of the receptor system.

Linear response theory for detectors consisting of discrete arrays

The optical transfer function (OTF) and the noise power or Wiener spectrum are defined for detectors consisting of a lattice of discrete elements with the assumptions of linear response, Gaussian statistics, and stationarity under the discrete group of translations which leave the lattice fixed. For the idealized classification task of determining the presence or absence of a signal under signal known exactly/background known exactly (SKE/BKE) conditions, the Wiener spectrum, the OTF, along with an analog of the gray-scale transfer characteristic, determine the signal-to-noise ratio (SNR), which quantifies the ability of an ideal observer to perform this task. While this result is similar to the established result for continuous detectors, such as screen-film systems, the theory of discrete lattices of detectors must take into account the fact that the lattice only supports a bounded but (in the limit of a detector of arbitrarily great extent) continuous range of frequencies. Incident signals with higher spatial frequencies appear in the data at lower aliased frequencies, and there are pairs of signals which are not distinguishable by the detector (the SNR vanishes for the task of distinguishing such signals). Further, the SNR will in general change if the signal is spatially displaced by a fraction of the lattice spacing, although this change will be small for objects larger than a single pixel. Some of the trade-offs involved in detectors of this sort, particularly in dealing with signal frequencies above those supported by the lattice, are studied in a simple model.

[The resolving capacity of systems for the reproduction of x-ray images]

At digital and film X-ray studies, the geometry of a survey exerts a varying effect on the system's resolution. This may lead to the better quality of digital X-ray image when actual magnification is performed.

[A number of x-rage image intensifiers of the URI-612 series]

The paper presents data on 9-, 12-, and 16-inch X-ray optical transducer X-ray image intensifiers commercially produced, their functional and consumers' capacities, as well as their advantages and technical data.

[An experimental study of the film parameters for general roentgenography]

The paper deals with methods for determining the technical data of a film for general X-ray study, presents basic sensitometric parameters of the films used in Russia, defines their parameters when used in as part of a kit also containing the intensifying screens made in the country, and provides recommendations on their use.

[A comparative study of analog and digital intraoral x-ray image detector systems]

The object of this investigation was to compare different intraoral, analog and digital X-ray image detector systems with respect to the diagnostic performance and to the relation of dose and image quality.

METHODS

Three different intraoral film types and one digital system were compared. The same basic image quality-related technical parameters were measured, Contrast detail diagrams and images of pig teeth were captured and evaluated by visual inspection.

RESULTS

The digital system has a speed that is at twice as high as least of the most sensitive analog system. Compared to the analog system, the digital system visualizes better low contrast structures such as carious defects, but shows problems in visualisation of high dynamic ranges such as crown margins or fillings: insufficient suitable dynamic range. Larger objects such as incisors could not be imaged in one exposure due to the small area of the digital detector (24.3 x 18.2 mm). Retakes may be required due to the small dynamic range and detector area.

CONCLUSIONS

The complete imaging of a tooth with crown and apical region, as required in the "radiological guidelines" is in doubt with digital systems having small active areas. The image quality of digital systems differs significantly from that of analog systems, nevertheless, the achievable image quality fulfills the requirements of intraoral dental radiology.

[ROC analysis comparing screen film mammography and digital mammography]

PURPOSE

To compare the diagnosis performances of radiologists on screen film versus digital mammography.

MATERIAL

and methods: Two sets of 123 mammograms, screen film mammography and storage phosphor digital mammography, are studied comparatively with ROC analysis.

RESULTS

Phantom study show that conventional method give better scores for usual tension but the detectability of smaller microcalcification is equivalent. To obtain with digital technic the same conventional score you have to increase the radiation dose. Roc Curves, simulated "detection" mode showed that radiologists performed with higher accuracy with conventional system but this difference is weekly statistically significant. ROC Curves, simulated "diagnostic" mode showed the same results wit no statistically significant difference but when the decision to go to the biopsy is the gold standard, ROC Curves were essentially equivalent for both film screen and digital mammography system. The readers consistently considered the digital mammograms to be less suspicious for cancer findings. The agreement study as proposed by the FDA indicate that probability of a positive digital mammograms given a positive screen film is 75% (threshold value 90%) and the probability of a negative digital mammograms given a negative analog film is 85% (threshold value 85%).

CONCLUSION

Analysis of specific discrepancies indicate that spatial resolution is an essential limiting factor for digital method but high resolution phosphor plate are interesting in imaging treated breast, radioluscent lesion, fatty benign tumor, hamartoma, intramammary lymph node, breast with prosthesis.

Computed radiography versus screen-film radiography: detection of pulmonary edema in a rabbit model that simulates neonatal pulmonary infiltrates

PURPOSE

To determine if computed radiography is equivalent to screen-film radiography in depicting pulmonary edema and to determine if radiation exposure can be reduced with computed radiography while maintaining equivalent diagnostic accuracy for pulmonary edema.

MATERIALS AND METHODS

Oleic acid was intravenously injected into three rabbits at each of four doses: 0, 0.02, 0.04, and 0.06 mL/kg. Two hours later, chest computed radiographs and screen-film radiographs were obtained at 60 kVp and 1.1 mAs. Additional computed radiographs were obtained after reducing milliampere seconds or by reducing milliampere seconds and increasing the kilovolt peak, which reduced bone marrow exposure by up to 20%. The presence of pulmonary opacities, "truth," was established by the wet-dry weight ratio and by chest computed tomography (CT). The radiographs were masked and randomized. Four observers rated the images for the presence of parenchymal opacities with a dichotomous score and judged the quality of the radiographs on a scale from 1 (worst) to 6 (best). Cochran Q tests and McNemar tests were used to analyze the differences in paired comparisons. Image quality was evaluated with logistic regression analysis.

RESULTS

There was no significant difference between truth and observer ability to detect opacity for either modality or for any exposure (P > .05). There was no significant difference between computed radiography and screen-film radiography for image quality (P > .05).

CONCLUSION

Computed radiography is equivalent to screen-film radiography in the detection of pulmonary edema. Radiation exposure reduction of 20% can be achieved without affecting pulmonary edema detection or image quality.

Detecting film-screen artifacts in mammography using a model-based approach

Microcalcifications can be one of the earliest signs of breast cancer. Unfortunately, their appearance in mammograms can be mimicked by dust and dirt entering the imaging process and this has been shown previously to lead to false positives. We use a model of the imaging process and, in particular, the blurring functions inherent within it to detect the film-screen artifacts caused by dust and dirt and, thus, reduce false-positives. A crucial facet of the work is the choice of the correct image representation upon which to perform the image processing. After extensive testing, our algorithm has identified no microcalcifications as being artifacts and has an artifact detection rate of approaching 96%.

[The economic expediency of digital fluorography]

The paper shows the advantages of digital versus routine film fluorography, which allows a user to make a choice of the type of an apparatus for fluorographic examination. The expenses of a fluorographic room on developing equipment and expendable materials for different types of the room's equipment. It gives the cost and specific features of the use of current film and digital fluorographs and the data on the cost of an examination using film and digital fluorography in case of the most cost-effective fluorographic systems.

Super-global distortion correction for a rotational C-arm x-ray image intensifier

Image intensifier (II) distortion changes as a function of C-arm rotation angle because of changes in the orientation of the II with the earth's or other stray magnetic fields. For cone-beam computed tomography (CT), distortion correction for all angles is essential. The new super-global distortion correction consists of a model to continuously correct II distortion not only at each location in the image but for every rotational angle of the C arm. Calibration bead images were acquired with a standard C arm in 9 in. II mode. The super-global (SG) model is obtained from the single-plane global correction of the selected calibration images with given sampling angle interval. The fifth-order single-plane global corrections yielded a residual rms error of 0.20 pixels, while the SG model yielded a rms error of 0.21 pixels, a negligibly small difference. We evaluated the accuracy dependence of the SG model on various factors, such as the single-plane global fitting order, SG order, and angular sampling interval. We found that a good SG model can be obtained using a sixth-order SG polynomial fit based on the fifth-order single-plane global correction, and that a 10 degrees sampling interval was sufficient. Thus, the SG model saves processing resources and storage space. The residual errors from the mechanical errors of the x-ray system were also investigated, and found comparable with the SG residual error. Additionally, a single-plane global correction was done in the cylindrical coordinate system, and physical information about pincushion distortion and S distortion were observed and analyzed; however, this method is not recommended due to a lack of calculational efficiency. In conclusion, the SG model provides an accurate, fast, and simple correction for rotational C-arm images, which may be used for cone-beam CT.

[Image quality and radiation exposure in digital mammography with storage phosphor screens in a magnification technic]

PURPOSE

Comparison of image quality between digital phosphor storage plate mammography in magnification technique and a conventional film screen system regarding the special aspect of radiation exposure.

MATERIALS AND METHODS

Radiograms of a RMI-mammography phantom were acquired using a conventional film screen system and two digital storage plate systems. Additionally, the radiograms of one digital system were post-processed emphasizing contrast and included in the comparison.

RESULTS

The detectability of details in storage plate mammographies with magnification technique is almost equal to that of film screen mammographies. Thereby, lower radiation exposures were necessary using the digital systems.

CONCLUSIONS

Based on these results, storage plate mammography in magnification technique is used in clinical routine at our institution. The correct parameters in image postprocessing are of elementary importance for detail detectability. Future studies must show, whether the lower radiation exposure in digital radiograms of the breast, revealing much higher background noise, will allow the same detail detectability as film screen mammographies.

[The reduction of the radiation dosage by means of storage phosphor-film radiography compared to a conventional film-screen system with a grid cassette on a skull phantom]

PURPOSE

How much can the radiation dose be reduced for skull radiography by using digital luminescence radiography (DLR) compared to a conventional screen film system with a grid cassette?

METHODS AND MATERIALS

A skull phantom (3M) was x-rayed in anterior-posterior orientation using both a conventional screen film system with grid cassette and DLR (ADC-70, Agfa). The tube current time product (mAs) was diminished gradually while keeping the voltage constant. The surface entrance dose was measured by a sensor of Dosimax (Wellhöfer). Five investigators evaluated the images by characteristic and critical features, spatial resolution and contrast.

RESULTS

The surface entrance dose at 73 kV/22 mAs was 0.432 mGy in conventional screen film system and 0.435 mGy in DLR. The images could be evaluated very well down to an average dose of 71% (0.308 mGy; SD 0.050); sufficient images were obtained down to an average dose of 31% (0.136 mGy; SD 0.065). The resolution of the line pairs were reduced down to 2 levels depending on the investigator. Contrast was assessed as being very good to sufficient. The acceptance of the postprocessed images (MUSICA-software) was individually different and resulted in an improvement of the assessment of bone structures and contrast in higher dose ranges only.

CONCLUSION

For the sufficient assessment of a possible fracture/of paranasal sinuses/of measurement of the skull the dose can be reduced to at least 56% (phi 31%; SD 14.9%)/40% (phi 27%; SD 9.3%)/18% (phi 14%; SD 4.4%). Digital radiography allows question-referred exposure parameters with clearly reduced dose, so e.g. for fracture exclusion 73 kV/12.5 mAs and to skull measurement 73 kV/4 mAs.

Proportionality between Wiener spectra of quantum mottle and the squares of modulation transfer functions

Rossmann proposed that the Wiener spectra of the quantum mottle of radiographs made using screen-film systems were proportional to the squares of the modulation transfer functions (MTFs) of the screen-film systems. On the other hand, Lubberts theoretically pointed out that the shape of the Wiener spectrum of the quantum mottle depended on the sum of the squares of the MTFs for different depths in the screen phosphor layer, rather than the square of the sum of the MTFs for the different depths, i.e. the square of the MTF of the screen-film systems. The purpose of this study is to experimentally investigate the proportionality between the Wiener spectra of the quantum mottle and the squares of the MTFs of screen-film systems using two screen-film systems having different screen thicknesses. For this purpose, we determined correction factors for the square of the MTF of the screen-film system in the Wiener spectrum of the quantum mottle at each spatial frequency when the Wiener spectral values of the screen mottle were separated into those of the quantum mottle and structure mottle. The correction factor is the ratio of the normalized Wiener spectrum of the quantum mottle to the square of the MTF of the screen-film system. As a result, for a thin screen, the correction factors were unity for all spatial frequencies; on the contrary, for a thick screen, the factor increased with spatial frequency. By calculating the theoretical correction factors using the models for the MTF and Wiener spectrum of the quantum mottle of Nishikawa and Yaffe based on Lubberts' theory, we verified that our experimental results agreed with Lubberts' theory. Furthermore, by obtaining the screen thickness dependence of the theoretical correction factors for the two screens, we showed that, for screens thinner than 0.02 mm, Rossmann's theory can be applied to the relationship between the Wiener spectrum of the quantum mottle and the MTF of the screen-film system, whereas for screens thicker than 0.02 mm, Lubberts' theory should be applied.

Contrast improvement in a new radiotherapy imaging system

PURPOSE

The aim of this paper is to compare the EC-L Kodak system for radiation therapy beam localization with a conventional one that could be daily employed in a radiotherapy department.

BACKGROUND

The main purpose of portal images is to verify the treatment volume in actual clinical conditions. Low contrast is the main constraint affecting portal film image.

METHODS

Kodak proposes a new imaging system (film and cassette) characterized by contrast enhancement as imaging standard for radiotherapy. The evaluation of system contrast was carried out by using a step-wedge consisting in 4 60 x 60 mm plexiglas steps and an anthropomorphic phantom. Portal films were exposed to a 6 MV photon beam by a linear accelerator (Varian Clinac 1800) with a 250 x 340 mm field size at the 1000 mm source film distance. The 2 imaging system performances were evaluated analyzing the image optical density.

RESULTS

The use of the Kodak system results in a real contrast improvement, so it is satisfactory to describe the field placement as to the region of interest.

CONCLUSIONS

The most critical characteristic attaining this method regards low contrast, i. e. the small optical density difference existing between different anatomical regions on the film. Since radiographic techniques can significantly influence quality of portal films, the adequate choice of film and screen combination, as well as the exposure technique is particularly useful in a radiotherapy quality assurance program.

Characteristics of the Orthopantomograph OP 100

OBJECTIVE

To investigate empirically the imaging characteristics of the Orthopantomograph OP 100 and compare them to the average form of the dental arch.

METHODS

Repeatable radiographs were taken of a lead resolution grid positioned at 1 mm increments along known angular intervals of the projected X-ray beam. Focal trough thickness was determined by visibility of the 1.5 lp mm-1 resolution limits. The path of the effective rotation center was determined using a film positioned at right angles to the slit beam. The vertical magnification and horizontal magnification and distortion index, corrected for the position of the tomographic layer, were calculated using a reference object placed at various resolution limits of the focal trough. The beam projection angle was calculated with respect to the central plane of the focal trough and the average dental arch shape compared with the average proximal contact angle.

RESULTS

The maximum resolution observed at the central plane of the focal trough was 5 lp mm-1. The width of the focal trough varied from 17 mm in the anterior region to 44 mm in the posterior region. The path of the effective rotation center was found to translate between three fixed centers of rotation, with the effective anterior projection radius of 24 mm. The vertical magnification factor within the focal trough showed a linear increase along the beam path from 1.24-1.37 and the horizontal magnification varied from 1.01-1.63. The distortion index varied from 0.84-1.24. The beam projection angle increased from 90 degrees anteriorly to 115 degrees in the premolar area with respect to the central plane of the focal trough and from 90 degrees anteriorly to 110 degrees in the premolar area compared with the average dental arch.

CONCLUSIONS

The OP 100 provides a focal trough conforming well to the overall geometry of the dental arch and provides adequate spatial resolution.

Simultaneous multilayer arthrotomography of the temporomandibular joint using photostimulable phosphor computed radiography

OBJECTIVE

To compare the image quality of photostimulable phosphor computed radiography (CR) with that of a conventional screen-film system for simultaneous multilayer arthrotomography of the temporomandibular joint (TMJ).

METHODS

X-ray attenuation, resolution and granularity was compared. Simultaneous multilayer tomography of TMJ was performed using a skull phantom and diagnostic quality of bone structures estimated. The clinical outcome is demonstrated in two typical cases.

RESULTS

X-ray attenuation was larger with CR. Granularity was more prominent in edge-enhanced CR images and was associated with inferior diagnostic quality. However, it was improved by using a higher tube voltage. Clinical CR without edge enhancement showed a similar resolution to the conventional system but this decreased with enhancement. In an enhanced arthrotomogram, the boundary between contrast medium, bone and soft tissue were clearly defined and a fibrous adhesion also easily seen.

CONCLUSION

Photostimulable phosphor CR is an acceptable alternative for simultaneous multilayer arthrotomography of the TMJ.

[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.

Radiation doses and image information in digital pelvimetry with a phosphorous screen

PURPOSE

The aim of the investigation was to determine the patient dose in digital pelvimetry by means of a phosphorous screen as compared to a screen-film combination of very high sensitivity.

MATERIAL AND METHODS

Entrance dose measurements and absorbed dose determinations in a series of patient exposures were made. In the first series the exposure reduction was achieved by reducing the mAs (tube current x exposure time) for the lateral and the a.p. views as compared with those used for the screen-film system. In the second series the tube potential, kV, was increased for both projections in order to increase the penetration capacity of the radiation.

RESULTS AND CONCLUSION

The imaging plate technique can be used in pelvimetry with a dose reduction (and a corresponding reduction of the radiation risk to the foetus) to less than 50% of that achieved with a screen-film system of the very highest sensitivity.

K-characteristic photon absorption from intensifying screens and other materials: theoretical calculations and measurements

When an extended object is irradiated with primary x rays, K-characteristic radiation is produced throughout the object. At a given location, the ratio of the K-characteristic radiation received to the primary radiation is not well understood. Knowledge of this ratio is important in the consideration of image detector design, as K-characteristic radiation generated within or proximal to the imaging detector may be considered as secondary radiation and as a specialized form of scatter to primary ratio, will reduce image contrast. This article models the production of K-characteristic radiation and calculates the K-characteristic to primary exposure and absorbed energy ratios for a number of sample materials, geometries, and detector types. Calculations have been experimentally verified for tin and gadolinium oxysulphide sample materials in some geometries using an ionization chamber detector. It was found from calculation that the magnitude of the K/p exposure and absorbed energy ratio were closely related to the ratio of the field size to the detector-to-sample distance when the detector-to-sample distances are small compared to the source-to-detector distance. It was also found that the K/p exposure and absorbed energy ratios were maximal and constant when the field size to detector-to-sample ratio was greater than 20:1 for an intensifying screen detector and greater than 100:1 for ionization chamber measurements. Calculation, also confirmed experimentally, indicated that significant ratios of K/p absorbed energy could be detected using intensifying screens proximal to fluorescing sample material.

Selenium-based digital radiography of the chest: radiologists' preference compared with film-screen radiographs

OBJECTIVE

A new digital thoracic radiography system (Thoravision; Philips Medical Systems, Hamburg, Germany), which uses selenium as a detector material, was evaluated for observer preference. The system has been shown to have higher detection efficiency than conventional film-screen systems and thus could provide an image with reduced noise. The hypothesis tested in this study was that the selenium-based digital system would provide an image appearance for conventional thoracic imaging that would be equal or superior to that provided by a conventional film-screen system.

MATERIALS AND METHODS

Fifty-three patient volunteers were imaged at 120 kV with both the selenium-based system and a thoracic film-screen combination system (InSight HC; Kodak, Rochester, NY). Posteroanterior and lateral images were acquired with both systems, for a total of 212 images. Both imaging systems included a stationary 12:1 antiscatter grid. Exposures were the same for both imaging systems, and the digital images were printed to film. Images for the same patient were compared by six observers--three specialized chest radiologists and three general radiologists. Images included both normal chest radiographs and radiographs with abnormal findings. Each pair of images was ranked on a scale from 1 to 5 for preference of technique, with a score of 3 indicating no preference. Eleven anatomic features were evaluated in the posteroanterior views, and six features were evaluated in the lateral views. Statistical significance of preference was evaluated with Student's t test.

RESULTS

The chest radiologists had a statistically significant preference for the selenium-based system for all 17 features (p < .001). The general radiologists had a statistically significant preference for the selenium-based system for visualization of 10 of the 17 features (p < .05). Neither group had a statistically significant preference for the conventional images in any category.

CONCLUSION

The selenium-based system provided an image appearance that was significantly preferred by all radiologists, more strongly by those specializing in chest radiography. This study demonstrates that a digital thoracic imaging system can routinely produce images that are perceived as equal or superior to conventional images.

[A bimetal anode with tungsten or rhodium? Comparative studies on image quality and dosage requirement in mammography]

PURPOSE

The impact of different anode materials (tungsten and rhodium) on spatial resolution, image contrast and radiation exposure was studied.

MATERIALS AND METHODS

Two mammographic systems providing bimetal x-ray tubes (Mo/W and Mo/Rh) were compared by imaging a breast radiography phantom with additional acrylic plates from 3 to 8 cm thickness. Spatial resolution was evaluated using a line bar pattern. Image contrast was assessed by measuring the ratio of optical densities in a acrylic step-wedge. The entrance dose was measured with a low energy ionisation chamber.

RESULTS

The spatial resolution was about 13 lp/mm regardless of the beam quality. The image contrast depended substantially on the thickness. A similar image contrast was found with Mo/Mo, Mo/Rh and Rh/Rh for simulated breast thicknesses of 4 to 6 cm and with Rh/Rh and W/Rh for 7 cm. In comparison to Mo/Mo the dose reduction was significant for Mo/Rh (35%), Rh/Rh (50%) and W/Rh (60%).

CONCLUSIONS

Bimetal x-ray tubes provide optimal conditions for screen film mammography of both normal and dense breasts, allowing good contrast and dose reduction by using the adequate anode/filter-combination.

[A comparative study of the imaging quality and picture dosage of a new conventional film-screen system for skeletal x-ray diagnosis]

PURPOSE

This paper compares a new film-screen system (FSS) called INSIGHT Skeletal Imaging System with the previously used Lanex/T-MAT G FSS.

MATERIAL AND METHODS

Using a Bronder phantom, measurements were made of dose, resolution and contrast. 135 skeletal phantom images were assessed in order of quality by six observers.

RESULTS

Comparable high resolution film-screen combinations (FSC) showed similar geometric resolution. Comparing high intensifying screens, the new INSIGHT Skeletal Regular FSS showed better resolution than the Lanex medium FSC. Dose reduction for the INSIGHT Skeletal Imaging FSS was 29-56%. The new FSS showed image quality similar to high resolution screens but was significantly better when using high intensifying screens.

CONCLUSION

The new INSIGHT Skeletal Imaging System can replace the Lanex/T-MAT G FFS by retaining quality but reducing radiation dose by 29-56%. Using the new high intensifying FSC, images showed in addition improved film quality.

[The use of an asymmetric film-screen combination for the imaging of round pulmonary foci]

PURPOSE

To examine the diagnostic advantages of an asymmetric film-screen system (a-FSS) compared to a conventional 200-speed FSS with and without anatomical lung filter.

METHODS

Standard radiographs were obtained from an anthropomorphic chest phantom with simulated pulmonary nodules. The existence or non-existence of nodules was assessed in 7344 individual observations. The results were evaluated using ROC analysis.

RESULTS

In an overall evaluation the a-FSS with an ROC area of 0.873 +/- 0.018 was not significantly superior (p > 0.05) to the lung filter but significantly superior (p < 0.05) to the 200-speed FSS. In the mediastinum the a-FSS and the lung filter were significantly superior (p < 0.05) to the 200-speed FSS. In the lung areas the 200-speed FSS and the a-FSS attained equivalent results (p > 0.05), whereas the lung filter was rated significantly lower (p < 0.05).

CONCLUSIONS

Asymmetric FSS improves chest diagnostics, because it yields significantly more diagnostic information in the mediastinum using equivalent x-ray exposure without reducing the image quality in the lung areas in respect of simulated pulmonary nodules.

[The potentials of digital image-intensifier radiography exemplified by digital spot imaging (DSI)]

PURPOSE

We performed a comparative study of digitally and conventionally acquired images in gastrointestinal examinations.

MATERIAL AND METHODS

Radiation dose and spatial resolution were determined in a water phantom. In 676 examinations with either conventional or digital imaging (system: Diagnost 76, DSI) the number of images and the duration of the fluoroscopy time were compared. 101 examinations with digital as well as conventional documentation were evaluated by using 5 criteria describing the diagnostic performance.

RESULTS

The entrance dose of the DSI is 12% to 36% of the film/screen system and the spatial resolution of the DSI may be better than that of a film/screen system with a speed of 200. The fluoroscopy time shows no significant difference between DSI and the film/screen technique. In 2 of 4 examination modes significantly more images were produced by the DSI. With exception of the criterion of edge sharpness, DSI yields a significantly inferior assessment compared with the film/screen technique.

CONCLUSION

The DSI system was well integrated in the daily routine of gastrointestinal examinations. Low dose imaging, direct availability of images and dynamic studies with a frame rate up to 8 images per second are the advantages of the DSI. The lower spatial resolution in some cases is a diagnostic disadvantage that can reduce the diagnostic information.

Effects of reduced exposure on computed radiography: comparison of nodule detection accuracy with conventional and asymmetric screen-film radiographs of a chest phantom

OBJECTIVE

Radiographic exposure has been thought to have little impact on the diagnostic quality of chest computed radiography because of automatic digital control of global optical density. The objectives of this study were to compare images obtained with two different exposures in computed radiography with conventional and asymmetric screen-film images of the chest for the detection of simulated lung nodules by use of receiver operating characteristic analysis and to relate differences in observer performance to parameters of image noise measured for each receptor condition.

MATERIALS AND METHODS

At 110 kVp (fixed), exposures for the two screen-film systems were those necessary to achieve adequate optical densities over the lung and mediastinal regions of an anthropomorphic phantom. The two exposures used for the computed radiographs corresponded to the exposure used for the conventional chest screen-film system and an exposure 22% lower. An anthropomorphic phantom constructed of materials matched to the muscle, lung, and bone attenuation of a muscular adult man was used. Soft-tissue-equivalent plastic nodules of various sizes were secured at multiple sites on the phantom to simulate lung nodules. The chest phantom was imaged in 50 configurations with a total of 70 superimposed nodules. The perceptual performances of five radiologists were compared by use of receiver operating characteristic analysis. The signal-to-noise ratio in the mediastinum and the coefficient of variation of noise were measured for all four image conditions by use of a step wedge technique to provide an explanation for differences in diagnostic accuracy.

RESULTS

We found no significant differences in the detection of lung nodules between the two screen-film systems or between the conventional screen-film images and the standard-exposure computed radiographs. However, there was a significant decrease in nodule detection on computed radiographs obtained at a reduced exposure; this result was associated with a 21% decrease in the signal-to-noise ratio.

CONCLUSION

Our results show that underexposure of computed radiographs decreases the detection of low-contrast objects such as lung nodules. Although consistent global optical density on computed radiographs is achieved over a wide range of exposures, the alterations in signal-to-noise ratio that result from underexposure can reduce the diagnostic quality of computed radiographs.

Conventional film-screen versus computed storage phosphor radiography. Simulated miliary lung disease in an anthropomorphic phantom

RATIONALE AND OBJECTIVES

In this experimental study, the authors examined whether laser printed hardcopies from digital storage phosphor radiographs yield diagnostic performance equal to conventional film-screen radiographs in the detection of simulated miliary disease, using a standardized object.

METHODS

A commercially available anthropomorphic chest phantom was used for radiographic evaluation. Miliary disease was simulated by superimposing one to four sheets of millet seeds on the lungs, resembling a miliary disease pattern with varying degrees of detectability. An observer study (receiver-operating characteristic) with eight radiologists was conducted to compare the reader performance using hardcopies of computed storage phosphor radiography versus the conventional film-screen system, optimized for chest x-rays. The digitally generated images were presented as a double-image hardcopy, with a conventionally adopted version and an edge enhanced image version.

RESULTS

When analyzed separately, one out of the eight observers performed slightly better using the conventional films. When treated as a group, analysis of the areas under the receiver-operating characteristic curves demonstrated no significant difference in reader performance for each of the systems under investigation (t = 0.286). The Wilcoxon test could not prove a statistical difference.

CONCLUSION

Storage phosphor technology is a method that yields equal diagnostic performance as conventional film in evaluating miliary disease of the chest.

[The monitor findings of digitalized conventional wrist x-rays]

The study aimed at proving the reliability of monitor systems with the matrix of 1024 x 768 for the detection of scaphoid fractures compared to conventional X-ray. Moreover, we were interested in the significance of procedures of digital imaging post processing, depending in particular on the experience of investigators. 5 investigators with different levels of experience analysed 57 X-rays of the wrist. They compared conventional X-rays with images on a high screen monitor system after the digitalisation of these X-rays by a CCD-scanner and analysed untreated and treated images. A 5-point scale ROC analysis was used for evaluation. The analysis covered a total of 1740 evaluations. The untreated images seen on the monitor system proved slightly better than conventional X-rays. Post-processing has no evident advantage over untreated images. Differing levels of experience had no effect whatsoever on the identification of findings.

[The detectability of osteoarticular lesions of the extremities on the television monitor]

The diagnostic accuracy of the light-box reading of conventional (film screen) radiographs of the extremities was compared with that of the same set of images displayed on a 1 k x 1 k interactive monitor after laser digitization. 389 alterations (23 nondisplaced fractures, 129 soft-tissue calcifications and 237 articular bone erosions), identified by two experienced radiologists on 66 conventional radiographs, were the reference standard. ROC statistical analysis was performed on 1,556 observations expressed by four readers. The overall diagnostic performance of the two display modalities were substantially equivalent: no statistically significant differences resulted on the whole, but two individual readers performed better with conventional images. No overall nor individual statistically significant difference was reobserved for the subset of articular erosions either. Light-box reading of conventional radiographs allowed a higher number of calcifications in the soft-tissues and of proximal (carpal) abnormalities to be detected. Although our results indicate the overall high fidelity of monitor-displayed laser-digitized images, major improvements in the performance of digital diagnostic workstations are still required before adopting monitors for routine radiologic activity.

[The value of the InSight HC asymmetric film-screen system in thoracic diagnosis]

The asymmetric film-screen system InSight HC represents a development to optimize chest imaging. The purpose of the study was to compare the exposure range and the image quality of this new system with a conventional film-screen system. The optical density of images in both techniques was measured and the image quality of 100 chest images from 50 intensive-care patients was evaluated. 4 observers graded the image quality of organic, non-organic and pathological structures. Statistical evaluation was performed by interobserver analysis. The asymmetric film-screen system shows a larger exposure range and a superior image quality in the mediastinal field. The image quality in the peripheral field must be judged critically and improved especially because of the poor recognizability of pneumothoraces.

[Bedside thoracic radiography: a comparison between 3 different types of grid]

Bedside chest radiography accounts for an increasingly large portion of all chest X-ray examinations. Nevertheless, image quality is often poor mainly because of scattered radiations which decrease image contrast. Moreover, usually no grid is employed because of difficult beam alignment. This work was aimed at comparing different radiologic grids for bedside chest radiography. Fifty patients submitted to two bedside chest radiographs in 24 hours were studied. All the patients underwent the first exam with a Kodak InSight cassette with a newly-designed (columnar type) grid inside, while the second exam was performed with a conventional 8:1 focused lead-strip grid (Gilardoni) in 25 patients and with a 6:1 focused lead-strip grid (Gilardoni) in the extant 25 patients. Both grids were assembled in a Kodak InSight radiographic cassette. Three independent radiologists evaluated film quality, focusing on the depiction of some anatomical structures--e.g., the tracheobronchial tree, the retrocardiac lung, and devices. Seventy-five examinations were obtained for each grid and for each evaluated structure and graded as "good", "acceptable" and "poor". In the 6:1 vs columnar grid test, the highest rate of "good" and "acceptable"--i.e., diagnostic--findings was observed with the columnar grid in evaluating pulmonary vessels (71/75); the highest rate of "poor" findings was obtained with the same grid in evaluating tracheal bifurcation (43/75). In the 8:1 vs columnar grid test, the highest rate of diagnostic findings was shown by the conventional grid in evaluating retrocardiac lung parenchyma and by the columnar grid for pulmonary vessels (69/75); the highest rate of "poor" findings was obtained with the columnar grid in evaluating tracheal bifurcation (40/75). The statistical analysis of the results (Wilcoxon test) was made to compare the two conventional grids with the new columnar one. Statistically significant differences were observed between the 8:1 grid and the columnar grid to evaluate the bronchial tree. No differences were observed between the 8:1 grid and the columnar grid. Furthermore, to determine the effects of different degrees of grid decentering on image quality, a series of exposures was made using a lung-chest phantom. The grids, both the lead-stripe and the columnar one, were comparable. The higher-ratio grid proved better in evaluating tiny details. The columnar grid exhibited better tolerance to X-ray beam and to grid decentering.

Effects of delayed processing on mammographic phantom object detection

OBJECTIVES

Delayed processing of films is a common occurrence in mobile mammography screening programs. The effects of such delayed processing on radiologists' detection of phantom test objects are investigated.

METHODS

Twelve screen-film combinations were exposed using a phantom and developed after delays of 0, 1, 2, 3, 5, and 7 days. Films were scored by three board-certified radiologists specializing in mammography, based on visibility of calcifications, masses, fibrils, and line pairs.

RESULTS

Variance analyses of mean scores indicate that, across screen-film combinations, there are no statistically significant decreases in object detection associated with delayed processing. The analyses do indicate, however, a statistically significant difference in scores unrelated to delay, attributable to the screen-film combination used.

CONCLUSIONS

Delayed processing of mammography film does not lead to a decrease in the visibility of phantom test objects, despite large decreases in overall image optical density.

[X-ray intensifying screens]

The paper provides the technical parameters and data of intensifying X-ray screens made in Russia. They cover both energy properties (sensitivity, spectral characteristics) and the quality of an image (frequency-contrast characteristics, granulation). It is shown in what cases this or that class of screens is preferable to be used.

[Are high-intensifying film-screen combinations suitable for the detection of fine interstitial lung changes? The results of a ROC study with an anthropomorphic thorax phantom]

Exposures of an anthropomorphic thorax phantom in posteroanterior projection were made using a focus-film distance of 200 cm and 125 kV with film-screen combinations in class 200 (Curix RP 1L/MR 200) and class 400 (Curix ST-L/Regular). Pathomorphological structures of the lung parenchyma of fine nodular, linear and reticular types were simulated by suitable materials. A ROC analysis including a t-test showed no significant difference in the evaluation of these structural details (p > 0.05). In order to describe image quality for the two film-screen systems, density curves, sigma D-curves and modulation transfer function (MTF) were determined. The only demonstrable difference was reduced MTF of 10-15% for the higher intensification film-screen combination with a resulting poorer resolution of 3.7 l/mm (for the 400 system) compared with 4.3 l/mm for the 200 system.

Monte Carlo optimization of metal/phosphor screens at megavoltage energies

The physics of imaging with metal/phosphor (Gd2O2S:Tb on brass) screens at megavoltage energies has been investigated using Monte Carlo simulation. It has been found that pair production is a significant contributor to energy deposition for Bremsstrahlung beams with energies greater than 6 MV. The effects of different thicknesses of phosphor and metal have been studied, and it is shown that the metal plays a significant role in establishing electronic equilibrium in the phosphor. The transport of optical photons through the phosphor has been modeled, and was found that only 10% to 20% of the light created in the phosphor escapes from the surface, with much of the loss being due to total internal reflection at the surface. Calculated results have been compared with experimental measurements of screen brightness for different phosphor and metal thicknesses. The SNR of a video electronic portal imaging device (VEPID) has been calculated as a function of x-ray and optical photon detection efficiency. The non-Poisson distribution of energy deposition in the phosphor is an important contributor to the SNR. The results of this paper should serve as a useful guide to the engineering design of future electronic portal imaging systems.

[Nodular lesions simulated on an anthropomorphic thoracic phantom. A comparison between analog and digital images of the thorax]

Aim of this work is to evaluate the diagnostic accuracy of different modalities of digital radiology, compared with conventional radiology, in the detection of lung nodules. Forty images of an anthropomorphic chest phantom, on which simulated nodules had been previously set, were analyzed by 6 radiologists with 4 different viewing modalities: a) conventional radiography; b) photostimulable plates digital radiography; c) photostimulable plates digital image on dedicated monitor; d) conventional radiography digitized with Film Laser Digitizer and viewed on Display Workstation. For each image the radiologists had to transfer on a sketch the site of the detected nodules giving an opinion on their detectability (uncertain-presumable-probable-certain presence) with a 1 to 4 score. The statistical analysis of the results was made using modified ROC curves. No statistically significant difference was found between the areas under a) and c) ROC curves (p = 0.262). A statistically significant difference resulted between the areas under a) and d) ROC curves (p < 0.05) and, particularly, between the a) and b) areas (p < 0.001), in favor of a).

[Interstitial lung diseases. A comparative study between a film-screen combination and a digital storage phosphor technic]

Chest examinations were carried out in 60 individuals using film-screen and digital storage phosphor techniques and identical radiation doses. 29 of these individuals were patients with interstitial pulmonary disease; 31 were normals. Postprocessing of the digital images was carried out with filtering using an unsharp mask and identical parameters for all patients. An ROC analysis using 10 observers showed no significant difference in the evaluation of the interstitial lung disease. Correlation analysis showed a significant positive correlation (p less than 0.001) for the findings in both techniques. Under the present circumstances, film-screen and digital storage phosphor technique are of equal value in the diagnosis of interstitial pulmonary disease.