ABSTRACT
The speed and average gradient of a conventional screen-film system was measured at four European laboratories. This is the first interlaboratory comparison in which the measurement conditions described in ISO 9236-1 were applied. The four laboratories used calibrated measurement equipment. The values obtained by the four laboratories were within a range of 14% for the speed and within a range of 8% for the average gradient. These variations are consistent with the expected measurement uncertainty.
Subject(s)
X-Ray Film/standards , Calibration , Europe , Laboratories/standards , Quality Control , Reproducibility of ResultsABSTRACT
In radiological acceptance tests, the film processing settings are verified by means of light sensitometry. The preliminary standard DIN 6868-55 probably published in August 1996 standardizes this procedure. This standard, its legal relevance and the sensitometer specifications are discussed. An outlook to the future development of the procedure as regards both the necessary technical progress and the establishment of a hierarchical metrological structure is included.
Subject(s)
Quality Assurance, Health Care/legislation & jurisprudence , Radiography/instrumentation , Technology, Radiologic/instrumentation , Germany , Humans , Reference Standards , Technology, Radiologic/legislation & jurisprudenceABSTRACT
The modulation transfer function (MTF) of a screen-film system can be measured by two methods, i.e., a slit method with Fourier transform on the line spread function and a square-wave response function (SWRF) method. However, it is still uncertain whether MTFs obtained by the two methods are identical. In this study, MTFs of relatively sharp and unsharp screen-film systems were measured by using the two methods. The slit method provided slightly greater MTF for the relatively sharp system than the SWRF method. However, MTFs of the unsharp system obtained with the two methods were comparable. Generally, the slit method tends to provide reliable results for unsharp systems, whereas the SWRF method is favorable for sharp systems. Accuracy and consistency of these measurements were examined by comparison of experimental and theoretical edge responses derived from the measured MTFs. However, the difference in edge responses obtained by the two methods was relatively small compared with the variation of the measured edge responses, and thus results were considered inconclusive as to whether either of the methods can provide more accurate MTFs. International interlaboratory comparison indicated that the variation in the measured MTFs at six different institutions was relatively large for both methods. However, the MTFs of two screen-film systems measured by the slit method appear to agree with those by the SWRF method within the variation expected from the interlaboratory comparison.
Subject(s)
Models, Theoretical , Radiography/standards , X-Ray Film , Fourier Analysis , Humans , Laboratories/standards , Mathematics , Quality Control , Radiography/methods , Reproducibility of ResultsABSTRACT
The visual observer performance for detecting low-contrast patterns by employing both the receiver operating characteristic (ROC) and the 9-alternative forced choice (9-AFC) method is investigated. For each observer and each experimental technique, the results were reproducible with respect to a repeated observation. When the results of different observers for each method are compared, a strong variation of values is found. From the ROC data obtained, the expected percentages of correct detection in a 9-AFC experiment is calculated and compared with the corresponding values of the actual 9-AFC experiment. For some observers, the latter values were significantly higher than the computed ones, whereas for others the results showed good agreement with predictions from theory.
Subject(s)
Decision Making , Epidemiologic Methods , ROC Curve , Visual AcuityABSTRACT
The image quality in radiology is to a large extent determined by three measurable parameters of screen-film systems: the H-D curve, the modulation transfer function and the Wiener spectrum. Measuring methods of the three parameters are described and results are presented. It turns out that the modulation transfer function is correlated to the visual sharpness and the Wiener spectrum is correlated to the visual impression of graininess. The combination of the three parameters to a single image quality criterion in the form of the detective quantum efficiency (DQE) demonstrates that the DQE is not a generally valid quality criterion for high sharpness and low graininess.
Subject(s)
Radiographic Image Enhancement/instrumentation , X-Ray Intensifying Screens/standards , Humans , Technology, RadiologicABSTRACT
Radiographic noise of screen-film combinations used in medical diagnostics can be described quantitatively by means of a power spectrum (Wiener spectrum) by which the quantum mottle can be mathematically expressed. The authors present a measurement method for power spectra and the results obtained with several screen-film combinations. The influence of various parameters on the spectra is discussed, such as sensitivity, transfermodulation film-function, and noise.
Subject(s)
Radiographic Image Enhancement , X-Ray Intensifying Screens , Humans , Information Theory , Radiographic Image Enhancement/instrumentationABSTRACT
A lead bar pattern, with continuously varying frequencies, has been used for measurement of modulation transfer functions of screen-film combinations. Although the highest usable frequency of the grid is only 3.4 mm-1, evaluation of the first as well the third harmonic permits the expansion of the frequency range up to 10.2 mm-1. Automatic evaluation of the images of the bar pattern gives reproducible results. These are presented.