Fluke Biomedical 76-025 - Manual (Page 9)

2-3
2.5 kVp Determination by Copper Transmission Method
1. Use the same setup as you did for the HVL determination.
2. Select a technique that gives you exposure readings that are greater than 10 mR with both thicknesses of
copper in the beam (approx. 0.76 mm). The facility's standard technique may be a good place to start.
Make the exposures with the facility's standard technique. If it is not able to produce exposure values greater
than 10mR, then increase the mA and time or mAs settings. Do not change the kVp setting.
The kVp setting should not differ from the facility's
standard technique. Do not round off your exposure
readings.
3. Insert both copper filters in the slot of the phantom cradle. Be sure the filters are centered to the probe, and
make an exposure. Record the total thickness of the copper filters in mm and the output in mR. Record the
average of the three exposures and the respective thicknesses.
4. Decrease the total thickness of copper filtration by removing the 0.25 mm thickness of copper. Make three
exposures. Record the average of the three exposures in mR.
5. Determine the ratio of the two average exposure values for the two different copper filters (0.76 mm Cu:
0.51mm Cu). The answer must have a value less than 1.00.
6. Using a kVp chart, find the copper transmission ratio value along the y-axis. To find the kVp, trace a line
horizontally from the point along the y-axis, and determine where it intersects with the existing line plotted on
the chart. After the intersection has been determined, trace a line straight down to the x-axis to get the
corresponding kVp value.
If the ratio is less than 0.359, indicate the kVp as 54.0. If
the ratio is greater than 0.657, indicate the kVp as 96.0.
The copper transmission ratio method for kVp
determination will not work for kVps outside the range of
55 to 95 kVp.
NOTE
NOTE