Answer to Question #10817 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
I have a General Electric lunar bone density dual-energy x-ray absorptiometry (DEXA) scanner. The AP spine techniques are 76 kVp at 3.0 mA. I am trying to measure kVp (kilovolt peak) noninvasively with a quality assurance device and my measurements read 140 kVp with no filtration in the beam.
My questions are:
- How can I measure kVp noninvasively with DEXA?
- Why am I measuring 140 kVp when the set technique indicates 76 kVp?
There is basically no way to measure kVp noninvasively for a DEXA unit. These are dual energy devices (switching kVps rapidly during the scan) with extremely heavy filtration. In addition, the detectors of the measurement device must be irradiated all of the time during the measurement. Also, the kVp measurement devices expect a "typical" x-ray spectrum and the results are based on this assumption.
The kVp should be within specifications if the results of the DEXA calibration phantom fall within the limits provided with the phantom.
Joel E. Gray, PhD