RESUMEN
PURPOSE: The purpose of this study was to determine the values for noise equivalent quanta, detective quantum efficiency, modulation transfer function, noise power spectrum, and the values for the parameters for automated CDMAM test phantom analyses required to achieve satisfactory quality of digital mammograms. MATERIALS AND METHODS: During the course of tests according to PAS 1054 (8 CR and 12 DR systems), test images were made with a test phantom insertion plate containing two lead edges in nearly horizontal and vertical directions. Only original data were processed with a program that was developed at the Cologne University of Applied Sciences (FH-Köln). All equipment systems complied with the requirements regarding visual recognition of gold-plated mammo detail test objects. CDMAM test images were also evaluated using the CDIC (CUAS) and CDCOM (EUREF) programs. RESULTS: CDMAM test images show comparable values for the parameters, precision, sensitivity and specificity. DR systems require about half the dose used for CR systems for similar results. The NEQ values achieved with the dose used for the CDMAM test images show larger scatter ranges. The MTF of the different equipment system types differ significantly from each other. CONCLUSION: Visual evaluation of CDMAM test images can be replaced by automated evaluation. Limiting values were determined for each parameter. Automated evaluation of CDMAM test phantom images should be used to determine the physical parameter NEQQC. This method is much more sensitive to noise and sharpness influences and has a higher validity than diagnostic methods. Automated evaluation objectivizes testing.
Asunto(s)
Algoritmos , Mamografía/instrumentación , Mamografía/métodos , Intensificación de Imagen Radiográfica/instrumentación , Intensificación de Imagen Radiográfica/métodos , Programas Informáticos , Diseño de Equipo , Análisis de Falla de Equipo , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , Relación Señal-RuidoRESUMEN
PURPOSE: The study aims at investigating how far image quality (MTF and NPS) differs in between CT, CBCT and DVT units and how far the geometrical 3 D accuracy and the HU calibration differ in respect to surgical or radio therapeutic planning. MATERIALS AND METHODS: X ray image stacks have been made using a new designed test device which contains structures for measuring MTF, NPS, the 3 D accuracy and the Hounsfield calibration (jaw or skull program). The image stacks of the transversal images were analyzed with a dedicated computer program. RESULTS: The MTF values are correlated with the physical resolution (CT and DVT) and are influenced by the used Kernel (CT). The NPS values are limited to an intra system comparison due to the insufficient HU accuracy. The 3 D accuracy is comparable in between the system types. CONCLUSIONS: The values of image quality are not yet correlated with dose values: NPS. Investigations to an appropriate dosimetry are ongoing to establish the ratio between dose and image quality (ALARA principle). No fundamental difference between the systems can be stated in respect radio therapeutic planning: improper HU calibration accuracy in CBCT and DVT units. The geometric 3 D accuracy of high performance DVT systems is greater than that of CT Systems.
Asunto(s)
Tomografía Computarizada de Haz Cónico/normas , Aumento de la Imagen/normas , Procesamiento de Imagen Asistido por Computador/normas , Imagenología Tridimensional/normas , Garantía de la Calidad de Atención de Salud/normas , Tomografía Computarizada por Rayos X/normas , Artefactos , Calibración , Tomografía Computarizada de Haz Cónico/instrumentación , Análisis de Fourier , Humanos , Aumento de la Imagen/instrumentación , Procesamiento de Imagen Asistido por Computador/instrumentación , Imagenología Tridimensional/instrumentación , Fantasmas de Imagen , Dosis de Radiación , Planificación de la Radioterapia Asistida por Computador/instrumentación , Planificación de la Radioterapia Asistida por Computador/normas , Radioterapia Asistida por Computador/instrumentación , Radioterapia Asistida por Computador/normas , Cirugía Asistida por Computador/instrumentación , Cirugía Asistida por Computador/normas , Tomografía Computarizada por Rayos X/instrumentaciónRESUMEN
AIM: To test whether image processing methods are suitable for detecting differences in the image quality of digital mammography units and whether the methods are more sensitive than visual test methods like the evaluation of CDMAM test images. METHODS: Test images according to PAS 1054 were acquired with CR and DR systems and analyzed automatically. Only parameters were used that are obligatory for calculating the detective quantum efficiency (DQE), the noise power spectrum (NPS), the spatial resolution (MTF, modulation transfer function), and the averaged glandular dose (AGD). The derived value, the NEQ index, is linked to the noise equivalent quanta (NEQ). Additionally CDMAM test images were acquired and evaluated at one CR and one DR system. RESULTS: The accuracy of the evaluated values is in the range below of 2 %. The accuracy requirements are fulfilled to establish values for detecting changes in image quality related to changes in dose no greater than one exposure value. If a visual evaluation of test images is used, a significant difference in image quality can only be detected when the dose is doubled. CONCLUSION: A method is proposed for establishing dose-correlated tolerances for values used in constancy and acceptance tests independently of the type of mammography unit (CR and DR systems). A method which abstains from visual tests for establishing the performance of digital mammography units could be used in acceptance tests.
Asunto(s)
Neoplasias de la Mama/diagnóstico por imagen , Interpretación de Imagen Asistida por Computador/instrumentación , Mamografía/instrumentación , Intensificación de Imagen Radiográfica/instrumentación , Algoritmos , Artefactos , Relación Dosis-Respuesta en la Radiación , Diseño de Equipo , Femenino , Humanos , Fantasmas de Imagen , Radiometría/instrumentación , Sensibilidad y EspecificidadRESUMEN
PURPOSE: To test the sensitivity of automatic methods for evaluating CDMAM test images with respect to noise. MATERIALS AND METHODS: CDMAM test images were analyzed with two computer programs. The images were made with different tube loads [mAs]. The other exposure conditions remained constant. They were analyzed with the CDCOM program, which is offered by the EUREF as a free download, and with the CDMAM Image Checker (CDIC), which was developed by the authors. RESULTS: The determination of the sensitivity in one image always delivers the same result when the same type of computer program is used. This means that the precision of both programs is sufficient. The dose sensitivity of CDIC is two times higher than the sensitivity of CDCOM. However, the required entrance dose (ESAK) for a faultless evaluation with the CDIC program is in the range of 10 mGy. The nominal sensitivity values for the CDCOM program attain a higher level. Differences in dose of more than 5 % should be detectable by both programs. CONCLUSION: Methods that dispense with visual inspections to determine the performance of X-ray units for mammography can be applied in the acceptance test or the yearly constancy tests according to the German X-ray directive ( section sign 16). The CDCOM program cannot be characterized fully because the data is not complete. Finally the detection methods are not clear. Therefore, the CDCOM program can be called a black box method, while the CDIC has to be called an open source method (general public license).
Asunto(s)
Aumento de la Imagen/métodos , Procesamiento de Imagen Asistido por Computador/métodos , Mamografía/métodos , Fantasmas de Imagen , Garantía de la Calidad de Atención de Salud/métodos , Programas Informáticos , Benchmarking/normas , Alemania , Humanos , Aumento de la Imagen/normas , Procesamiento de Imagen Asistido por Computador/normas , Fantasmas de Imagen/normas , Garantía de la Calidad de Atención de Salud/normas , Dosis de Radiación , Sensibilidad y Especificidad , Programas Informáticos/normasRESUMEN
PURPOSE: To find out whether the quality requirements in daily, weekly or monthly tests of the "European protocol for the quality control of the physical and technical aspects of mammographic screening (EPQC)" can be maintained when screening the population of a large area. Furthermore, to check the specific tolerances of different test positions given by the EPQC for redundancy and statistical correlation. MATERIALS AND METHODS: Daily test images were obtained with an additional exposition of a sensitometric step wedge according DIN 6868 - 2. Weekly densitometry and visual inspection were performed at the University of Applied Sciences, Cologne. RESULTS: All units were able to maintain basic requirements on image quality as long as films of the same batch number were used. Some tolerance requirements of the EPQC are inconsistent and redundant. CONCLUSION: The occasionally considerable fluctuations of film processing require a daily check on the processing conditions. Daily test images of the units are only obligatory in the first 4 to 5 weeks of a new operation. All test results should be analyzed retrospectively in an independent test laboratory with emphasis on the statistical behavior of the unit. The tolerances prescribed by the EPQC are not always consistent and should be adapted to today's scientific standard when applied in mammography screening centers.
Asunto(s)
Mamografía/métodos , Mamografía/normas , Femenino , Alemania , Humanos , Laboratorios/normas , Tamizaje Masivo , Control de Calidad , Reproducibilidad de los Resultados , Estudios Retrospectivos , Factores de TiempoRESUMEN
The point of time, in which archived X-ray films were processed, can be proved with the determination of the remaining content of thiosulphate. The methylene blue method of DIN 19069 (equivalent to ISO 18917) was adapted to X-ray films. The range of time is in about two and a half year,in which the remaining content of thiosulphate is correlatable to the point of time in processing. This range of time covers the range, in which "radiological bodies" control the results of constancy testing. This method brings the "radiological bodies" in a better position to decide wether the recommended time of processing is true or not, when test images according DIN 6868-3 and/or the sensitometric step wedges according DIN 6868-2 are checked.
Asunto(s)
Sistemas de Información Radiológica , Película para Rayos X/normas , Archivos , Humanos , Humedad , Modelos Teóricos , Tiosulfatos/análisis , Factores de TiempoRESUMEN
It was tested with 5 different types of mammography films in which manner the values of "Lightspeed" (LS) and "Lightcontrast" (LC), according DIN V 6868-55 will be changed, when preexposed film strips are used, stored at different climates and spaces of time in comparison to strips, which are exposed immediately before processing. It was proved, that the value LS of preexposed film strips in general will be lowered with increasing storage time compared to freshly exposed film strips, when both strips are processed simultaneously. This drift will be enhanced with increasing rel.humidity levels during storage. The value of LC increases in general with longer storage time and higher rel.humidity levels. The tested film types have all individual drifts in LS and LC. The precision of a single measurement using preexposed film strips was established over all different types of films at in about: Delta LS=0.06 and Delta LC (%)=16% [in the borders of 2 sigma (sigma)]. This uncertainty includes solely the precision of sensitometer, densitometer, the method to establish sensitometric values and unavoidable statistical fluctuations. Even when the systematic drift of the used film type is well established, the required precision, restricted to the listed items and prescribed in DIN V 6868-55, table D.1 to determine the values of LS with Delta LS=0.039 and the values of LC with Delta LC=7.2% is overstepped in so far, that it is impossible to draw a precise conclusion from the measured values to the performance of the subsystem film and processing. If any exceeding of the dose in image receptor plane is monitored, there is no tracking possible to a misadjustment of the subsystem film and processing.
Asunto(s)
Mamografía/normas , Película para Rayos X/normas , Clima , Densitometría , Estudios de Evaluación como Asunto , Humanos , Mamografía/instrumentación , Control de Calidad , Factores de TiempoRESUMEN
The requirements for the target value of the mean optical density (o.d.) including proper tolerances of mammograms are determined in the "European Protocol for the Quality of the Physical and Technical Aspects of Mammography Screening (EPMS)". These requirements are not only applicable to screening mammography. 22 mammography devices were tested with exposures of test phantoms using different kV and thickness of PMMA and with sensitometric step wedges to check the processing conditions. Only five of 22 devices fulfill all requirements of EPMS to the opt. density. These results are caused by three reasons: first, wrong locking of optical density under standard exposure conditions; second, wrong compensation of the optical density by the automatic exposure control due to varing tube voltage (kV) and PMMA thickness and third, an inadequate back coupling to the processing conditions. All tested devices are not conspicuous in respect to the results of constancy tests according DIN 6868-2 [2] and DIN 6868-7 [3]. It is obvious, that the claimed devices are not properly adjusted in the acceptance test according DIN 6868-52 (1990-12) [4]. Respectively the tolerances, used do not fulfill the requirements to proper density in mammograms.
Asunto(s)
Mamografía/instrumentación , Tamizaje Masivo/instrumentación , Fantasmas de Imagen , Diseño de Equipo , Femenino , Humanos , Sensibilidad y EspecificidadRESUMEN
The effects of different film processing conditions on light and x-ray sensitometric responses were compared for a variety of double-emulsion x-ray films. The processing conditions were altered by changes of the developer temperature. Three different exposure variants were applied: x-ray sensitometry using two stepped neutral density attenuators between film and screens, simultaneous double-sided light sensitometry, and single-sided light sensitometry. 13 different types of double-emulsion x-ray films were investigated, among them three asymmetric films. In the special case of exposing the asymmetric films with the single-sided light sensitometer, a method was investigated where each side of the film is exposed at different locations and the sum effect is analyzed. From each sensitometric curve shape two parameters, the logarithmic speed (logS) and the average gradient (G), were evaluated. The results of this study can be summarized as follows: (1) Single-sided and double-sided light sensitometers revealed almost equal changes of logS when the processing conditions are altered. Thus, single-sided light sensitometers can serve as a substitute for double-sided light sensitometers provided that suited exposure methods are used and appropriate sensitometric parameters are evaluated. (2) Light sensitometry quantitatively indicated changes of the film processing that affect the x-ray speed. Hence, light sensitometry is a useful method to monitor changes in film processing.
Asunto(s)
Luz , Película para Rayos X , Rayos X , Fenómenos Biofísicos , Biofisica , Tecnología Radiológica , Temperatura , Pantallas Intensificadoras de Rayos XRESUMEN
UNLABELLED: 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.
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Radiografía Dental Digital/instrumentación , Radiografía Dental/instrumentación , Animales , Artefactos , Fantasmas de Imagen , Control de Calidad , Radiografía Dental/métodos , Radiografía Dental/normas , Radiografía Dental/estadística & datos numéricos , Radiografía Dental Digital/métodos , Radiografía Dental Digital/normas , Radiografía Dental Digital/estadística & datos numéricos , Análisis de Regresión , Porcinos , Diente/diagnóstico por imagen , Película para Rayos X/estadística & datos numéricos , Pantallas Intensificadoras de Rayos X/normas , Pantallas Intensificadoras de Rayos X/estadística & datos numéricosRESUMEN
The German standard series DIN 6868 does not include a separate requirement for deviations in the sensitivity of different emulsion numbers or, respectively, the relative contribution of the film to sensitivity S of a screen film system (SFS) whose sensitivity is determined according to DIN 6867-1 [1]. The inclusion and interpretation of these contributions in the test body exposure according to DIN 6868-3 [2] has not proved to be of value since an unambiguous error recognition is only possible with considerable experimental experience (additional exposure of a sensitometer strip and interpretation of the resulting consequences). The investigations reported here demonstrate that the correlation of sensitometric parameters obtained from sensitometer strips generated with sensiometer exposure and X-ray exposure is so large that differences in sensitivity of different emulsion numbers of a screenfilm larger than delta log H > or = 0.015 or delta H > or = 4% can be surely detected on exact observance of the experimental limiting conditions. Thus, the statements by the manufacturers in "ZVEI information Nr. 7 of the X-ray Regulation" [3] with regard to the claimed scattering width of screenfilms can be tested and evaluated at least tendencially when the systemic fluctuations and measurement uncertainties, see in particular DIN 6868-55 Appendix E of Sept. 1996 (4), are correctly taken into consideration. In general a deviation in the sensitivity exceeding the manufacturers claimed maximal scattering range of delta log H = 0.06, i.e. delta H = 15% can be detected with certainty.
Asunto(s)
Radiografía/instrumentación , Película para Rayos X/normas , Garantía de la Calidad de Atención de Salud , Película para Rayos X/clasificaciónRESUMEN
A new test procedure is presented to check the correspondence between various screen-film systems (SFS) with the specification of the manufacturer in respect to the speed S according to DIN 6867-1 or rather which dose K is required for the SFS in dependence on the X-ray tube voltage (kV) to give the net density Dn = 1.00, it is based on measurements of dose and density using on X-ray equipment with water as an absorber and scatter test tool. The characteristic curves of the automatic exposure control (AEC) can be recorded and compared with those of SFS, i.e., how is the dose K in the image-receptor-plane regulated by the AEC in dependence on different radiation qualities. It is also possible to check the modes of operation of SFS and AEC with sufficient accuracy but lower time and energy requirements. The consequences of finding the right values to test the X-ray equipment under DIN 6868-50/-3 and for constancy-testing according to DIN 6868-3 are discussed.
Asunto(s)
Tecnología Radiológica/instrumentación , Pantallas Intensificadoras de Rayos X , Calibración , Diseño de Equipo , Humanos , Dosis de Radiación , Dispersión de RadiaciónRESUMEN
AIM: To evaluate the image quality of an asymmetric film-screen combination (a-FSC), a conventional screen-film combination (FSC) at speed class 200, a lung filter, and digital luminescence radiograms in detecting pulmonary nodules. METHODS: Detail perception studies were carried out with an anthropomorphic phantom. The image systems were exposed under standardised conditions with 125 kVp. The systems' perception efficiency was evaluated on the basis of 12.240 single observations with ROC analysis. RESULTS: In the overall evaluation the a-FSC and the filter achieved equally high assessments of 0.878 +/- 0.018 and 0.860 +/- 0.21 respectively (p > 0.05). The 200 speed FSC and the storage phosphor screen radiograms did not differ significantly. In the mediastinum all the tested systems were clearly superior to the 200 speed FSC (p < 0.05). In the lung fields on the other hand the 200 speed system was given a higher assessment of 0.866 +/- 0.026. The a-FSC had slight advantages over the lung filter and the digital imagining modes (p > 0.05). CONCLUSIONS: The a-FSC and digital luminescence radiograms provide significantly more diagnostic information in the mediastinum, together with high detail detectability in the lung fields and without requiring additional dosage.
Asunto(s)
Fantasmas de Imagen , Interpretación de Imagen Radiográfica Asistida por Computador , Nódulo Pulmonar Solitario/diagnóstico por imagen , Pantallas Intensificadoras de Rayos X , Humanos , Sensibilidad y Especificidad , Tecnología RadiológicaRESUMEN
A new method is presented to check several automatic exposure control systems (AEC) for their suitability in radiological image production. It is based on measurements of dose and density with water as an absorbing and scattering medium. The characteristic curves of an AEC can be recorded, i.e., in what way is the dose K in the image receptor plane regulated by the AEC in dependence on the different radiation qualities and the specific water volume. These characteristics can be compared with several screen-film systems (SFS), i.e., which dose K is required by the SFS in dependence on the X ray tube voltage (kV) to get the net density of Dn = 1.00. It is possible to check the way of operating of an AEC with sufficient accuracy but less time and energy are needed. The disparity of the characteristics of AEC and SFS and their results on radiological examination are discussed.
Asunto(s)
Garantía de la Calidad de Atención de Salud , Pantallas Intensificadoras de Rayos X , Humanos , Dosis de Radiación , Valores de Referencia , Dispersión de RadiaciónRESUMEN
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.
Asunto(s)
Intensificación de Imagen Radiográfica , Radiografía Torácica/métodos , Pantallas Intensificadoras de Rayos X , Filtración , Humanos , Enfermedades Pulmonares/diagnóstico por imagen , Fantasmas de Imagen , Curva ROC , Radiografía Torácica/instrumentación , Sensibilidad y EspecificidadRESUMEN
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.
Asunto(s)
Enfermedades Pulmonares/diagnóstico por imagen , Pulmón/diagnóstico por imagen , Pantallas Intensificadoras de Rayos X , Estudios de Evaluación como Asunto , Filtración/instrumentación , Humanos , Análisis Multivariante , Variaciones Dependientes del Observador , Fantasmas de Imagen/estadística & datos numéricos , Curva ROC , Radiografía Torácica/instrumentación , Radiografía Torácica/estadística & datos numéricos , Sensibilidad y Especificidad , Pantallas Intensificadoras de Rayos X/estadística & datos numéricosRESUMEN
The information obtainable from a radiograph depends on the viewing conditions under which the radiograph is viewed. All the viewing conditions can be defined in terms of scattered light. The amount of information taken from a radiograph with S = 1000 (S = speed class) and perfect conditions is the same as that from a radiography with S = 100 viewed under poor conditions. The optimum illuminance for the radiograph viewing room is 50 lx diffuse. The influence of scattered light is small enough to cause only a small loss of information. With the illuminance of 50 lx diffuse in the viewing room and Lo = 2000 cd/m2, the density range should be delta D = 2.85. The scattered light reduces it to delta D = 2.60 when the radiograph is viewed under the above-mentioned circumstances.
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Radiografía , Tecnología RadiológicaRESUMEN
It is shown that the number of contrasts which can be differentiated on a radiograph depends on the detail size, the noise, and the viewing conditions. The minimum signal-to-noise ratio (SNR) for a perception approach is equivalently described by the SGA value. This testing method was first developed by De Belder and Bollen to examine the visibility of low contrast details. The correlation between the SGA and the speed class S of the system can be explained by this method.
Asunto(s)
Radiografía/normas , Pantallas Intensificadoras de Rayos X , Alemania , Humanos , Sensibilidad y EspecificidadRESUMEN
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.
Asunto(s)
Pulmón/diagnóstico por imagen , Modelos Estructurales , Pantallas Intensificadoras de Rayos X , Estudios de Evaluación como Asunto , Humanos , Curva ROC , Radiografía , Sensibilidad y Especificidad , Pantallas Intensificadoras de Rayos X/estadística & datos numéricosRESUMEN
The present article describes the circumstances concerning the use of testing aids such as sensitometers with one-sided exposure. It is shown which phenomena must be considered if radiographic films coated on both sides are exposed with a) standard pocket sensitometers (one-sided exposure), b) lab sensitometers (double-sided exposure to ANSI Ph 2.9 [1964]), c) x-radiation in the cassette, intensifying screen and film system (to DIN 6867 T 1). The effect of the emission spectrum on the resulting contrast factor is described. The importance of different emulsion technologies (e.g. orthochromatic anticross-over films) for the contrast factor with one-sided exposure is described. The cross-over factor (c.o.), the apparent variation in sensitivity of the front and back emulsion with one-sided exposure, is the cause of the reduction in the contrast factor (G average) as against double-sided exposure: delta G(%) = c.o.2 x 10(3)/8.4