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19 March 2010

Answer to Question #1309 Submitted to "Ask the Experts"

Category: Instrumentation and Measurements — Surveys and Measurements (SM)

The following question was answered by an expert in the appropriate field:

How do I find the dose rate at a particular distance from an x-ray unit for different settings of KVp and mAs theoretically?

The exposure at any distance from an x-ray unit is typically measured with a calibrated, integrating ion chamber that measures the dose or exposure. Often, the same instrument provides the ability to measure the accuracy of the x-ray machine's timer. This unit can also be used in conjunction with certified aluminum filters to determine if the x-ray unit has appropriate filtration incorporated into the tube housing or collimator. By taking measurements at various mAs settings, it can tell how well the mAs is tracking and provide the exposure at given distances for each mAs at the typically used kVp settings. Measurement of the accuracy of the kVp usually requires a separate dedicated instrument. Ken Miller, CHP, CMHP

Answer posted on 30 October 2001. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.