Determination of the Potency of X-Ray Developer

Abstract

Deterioration of x-ray developer is nearly-proportional to the number of square inches of film developed. A simple method for estimating this deterioration is to keep account of the amount of film developed. Charts to be used in the dark room for this purpose are available and the method is recommended by photographic material manufacturers. R. B. Wilsey (1) recommends a method which makes use of the fact that the time of development bears a definite ratio to the time required for the image to appear after the film is first immersed in the developer. This ratio is known as the Watkins' factor. Pieces of film which have been exposed over part of their surfaces are developed in a tray, measuring the seconds to the first appearance of the image. Multiplication of this appearance time by the Watkins' factor gives proper development. Chamberlain and Newell (2) have worked out and described a method of adjusting for changes in the speed of the film as well as for the weakening of the developer with use. Their method is an exact one but since the test films are made with the aid of an accurately controlled therapy machine, it is not available to many roentgenologists. Thanks to the ingenuity of Dr. Robert S. Stone (3), a method is here described in which the test films are exposed with a radiographic machine, such as most roentgenologists have in their laboratories. Because radiographic apparatus is not equipped with instruments to insure constancy of output from time to time, special precautions are necessary in order that the process of calibrating the developer may be carried over from one test film to the next. Directions for Determining the Potency of the X-Ray Developer with Radiographi-Cally Exposed Film Place a fresh 8 × 10-inch film in an exposure holder (no intensifying screens) under an aluminum step ladder: the ladder we use is made of aluminum sheets 1 mm. thick × 10 inches wide arranged in a staircase running from one to seven thicknesses (Fig. 1). A radiographic tube is placed so that its focal spot is 60 inches above the center of the 8 × 10-inch film. Then, place 2 mm. of aluminum in the filter slots of the tube stand, and expose for 14 seconds at 70 K.V.P., 10 milliamperes. This film holder is opened in the dark room and about an inch is cut off one of the 8-inch ends of the film. Place this strip horizontally in one-day-old developer at 65° F. for five minutes. (Absolutely fresh developer has been found somewhat variable in our experience.) After being fixed, washed, dried, and labeled, this strip is set aside as the “standard strip” with which subsequent calibration strips are to be compared (Fig. 2). From one to three days later, depending upon the size of the tank in relation to the volume of work, another strip, approximately an inch wide, is cut from the film (which in the meantime has been carefully protected from light and x-rays). This is developed for 5 minutes, placed horizontally in the developer.