Góes E G, Pelá C A, Ghilardi N T
CIDRA-Centro de Instrumentação, Dosimetria e Radioproteção, DFM-FFCLRP-USP, Ribeirão Preto, SP, Brazil.
Phys Med Biol. 1997 Oct;42(10):1939-46. doi: 10.1088/0031-9155/42/10/007.
An x-ray sensitometer is used to measure the characteristic curve of radiographic films exposed with fluorescent intensifying screens. The series of relative exposures, necessary to cover the full density range of the film, can be obtained by either time-scale or intensity-scale sensitometric methods. We have developed a convenient method of exposing film-screen systems for time-scale sensitometry. In this method, during exposure the x-ray kilovoltage, tube current and x-ray intensity remain constant and a geometric series of exposures of the film is modulated by varying the exposure time. This time variation can be obtained when a lead disc with different sector openings is rotated in front of the film system by a stepping motor. The conditions normally used are 70 kVp x-rays, 3.5 mm Al total filtration at the tube, and 2.4 m focal spot-film distance. This exposure latitude gives a complete characteristic curve of film-screen systems.
X射线感光计用于测量用荧光增感屏曝光的射线照相胶片的特性曲线。覆盖胶片全密度范围所需的一系列相对曝光量，可以通过时间刻度或强度刻度感光测量方法获得。我们开发了一种用于时间刻度感光测量的胶片-增感屏系统曝光的便捷方法。在这种方法中，曝光期间X射线管的千伏值、管电流和X射线强度保持恒定，通过改变曝光时间来调制胶片的几何级数曝光量。当一个带有不同扇形开口的铅盘由步进电机在胶片系统前旋转时，就可以实现这种时间变化。通常使用的条件是70 kVp的X射线、管处总滤过为3.5 mm铝以及焦点-胶片距离为2.4 m。这种曝光宽容度给出了胶片-增感屏系统完整的特性曲线。
