RESUMEN
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.
Asunto(s)
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
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