T.O. 33B-1-16-696.7.3.8 FilmLatitude.The film characteristic that is the reverse of contrast or gamma is film latitude. The higher the contrast, the smaller thelatitude and the lower the contrast, the greater the latitude. Latitude is, therefore, the range of radiation intensities thata film is capable of recording.6.7.3.9 Screens.The radiation reaching the film may be in part caused by the use of intensifying screens to reduce the exposure time.The intensification factor for lead or calcium tungstate screens depends on the energy converted to either electrons orlight to which the screen is sensitive. This factor varies with kilovoltage and type of film. The film must be selected toachieve highest efficiency of energy conversion from the screens used. The use of screens is covered more thoroughlyin Section III.6.7.4 TechniqueCharts.The characteristics of X-ray equipment must be known to properly operate the unit and obtain maximum results. Theutilization of X-ray equipment with the least amount of lost time requires a set of technique charts which show theexposure times required for various thicknesses of material under stated conditions. These charts are generallyavailable from the manufactures of X-ray machines. (See Figure 6-34). However, due to the differences betweenindividual machines, it may be necessary or desirable to prepare additional technique charts for the specific purposesand conditions to which the machine will be applied. If published technique charts are available; these charts can beused as a guide in preparing the detailed charts.Figure 6-34. A Typical X-ray Exposure Technique Chart.
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