<prompt> A step-wedge phantom is used to assess the qualityassurance of:Dark roomTimer of the X-ray machineChemicals used for processingRadiation leakage from X-ray unit  <response>: 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 Pharoahs Oral Radiology Principles and Interpretation 7th edition page no 251 