A step-wedge phantom is used to assess the quality
assurance of:: (A) Dark room, (B) Timer of the X-ray machine, (C) Chemicals used for processing, (D) Radiation leakage from X-ray unit
Answer is C. How frequently processing solutions are replaced depends primarily on the rate of use of the solutions but also on the size of tanks, whether a cover is used, and the temperature of the solutions. In most offices, the solutions should be changed weekly or every other week. The results of the step-wedge test help determine the proper frequency.
Reference: White and Pharoah's Oral Radiology Principles and Interpretation 7th edition page no 251