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在作X线摄影时,中心射线必须射经所投照部位的某一点达于胶片中心,有些X线机光阑上附有小灯,对瞄准部位及控制照射野都很方便(如西门子PLEOPHOS250毫安诊断机),但大多数机器上缺乏此种装备,在作垂直投照时大都用一端系有重物的垂线或长尺来瞄准部位,或是把管球拉低对准部位后再提高一定胶片焦点距离投照。在作有角度投照时,大都根据三角函数降低管球一定高度,同时将片夹前移一定距离来保持胶片焦点距离不变。若前移胶片不当或摆患者体位时胶片稍一移动都会
In X-ray photography, the center of the ray must shoot through a certain point of the projected position up to the center of the film, and some X-ray machine diaphragm attached to a small light on the aiming site and control the irradiation field are very convenient (such as Siemens PLEOPHOS250 Ma machine diagnostic), but most of the lack of such equipment on the machine, when used for vertical projection mostly with one end of the weight of the vertical or long aiming point to the site, or the tube down to align the site Then increase the focus of a certain film projection. When making an angle of projection, most of them reduce the height of the tube according to the trigonometric function, and at the same time move the film clip forward a certain distance to keep the film focus distance unchanged. If the front of the film improperly placed or patient position when the film will move a little