Fluke Biomedical 07-649 - Manual (Page 11)

Operation
Fluoroscopy HVL Data
2
2-5
Place an additional 1 mm of aluminum on the tabletop directly beneath the sensitive volume of the probe.
Take a 15-second exposure and record in mR/min the reading for 2.5 mm of aluminum.
Place an additional 2 mm of aluminum on the tabletop directly beneath the sensitive volume of the probe.
Take a 15-second exposure and record in mR/min the reading for 4.5 mm of aluminum.
Place an additional 2 mm of aluminum on the tabletop directly beneath the sensitive volume of the probe.
Take a 15-second exposure and record in mR/min the reading for 6.5 mm of aluminum.
This step need only be performed if the value obtained with 6.5 mm aluminum is not less than half the 0
mm aluminum value. Record the resulting exposure rate value and the total thickness of aluminum (in
mm).
2.11 HVL for ABC Units that Cannot be Placed in Manual
Mode
The following procedure is to be used only on those units that cannot be switched into the Manual mode
for HVL determination.
It is essential that a fixed amount of attenuating material remain in the beam between the x-ray tube and
the ABC during all measurements. The position of the aluminum filters in the beam will vary during the
procedure.
1. With the phantom and probe properly positioned, adjust the size of the fluoroscopic x-ray beam until
it is slightly larger than the sensitive volume of the probe head.
2. Set the probe selector switch to the Exposure Rate mode.
3. Place 6.5 mm of aluminum on the tabletop directly beneath the probe. This places 6.5 mm of
aluminum between the tube head and the probe. Without making any changes in the standard
patient techniques, make an exposure of at least 15-second duration and note the exposure rate for
6.5 mm of aluminum.
4. Move the 6.5 mm of aluminum to the top of the phantom. Be sure that the aluminum is completely
in the beam and is over the probe. This places 6.5 mm of aluminum between the phantom and the
ABC. Make a 15-second exposure, and note the exposure rate for 0 mm of aluminum.
5. If the exposure rate obtained in the above step for 0 mm of aluminum is more than twice the
reading obtained in the second step for 6.5 mm of aluminum, record the value obtained in the
above step as the 0 mm of aluminum exposure rate and the value obtained in the second step as
the 6.5 mm of aluminum value. Record the console kVp value in the HVL section of the data form.
6. Do this step only if the second step exposure rate value is not less than half of the step 3 exposure.
Add more aluminum and repeat steps 2 and 3 above until you have sufficient aluminum to exceed
the HVL. When you have added sufficient aluminum filtration, record the total amount of aluminum.
Record the value obtained in step 3 for the total aluminum as the 0 mm of aluminum exposure rate.
Record the value obtained in step 2 for the total aluminum exposure rate value. Record the console
kVp value in the HVL section of the data form.
7. Move 1.5 mm of aluminum from the top of the phantom and place on the tabletop beneath the
probe. This will place 1.5 mm of aluminum between the tube head and the probe, leaving the
remainder of the aluminum between the probe and the ABC. Make a 15-second exposure, and
record the exposure rate for 1.5 mm of aluminum.
8. Move an additional 1 mm of aluminum from the top of the phantom to the tabletop beneath the
probe. This will place 2.5 mm of aluminum between the source and the probe, leaving the
remainder of the aluminum between the probe and the ABC. Make a 1-second exposure, and
record in mR/min the reading for 2.5 mm of aluminum.
9. Move an additional 2 mm of aluminum from the top of the phantom to the tabletop beneath the
probe. This will place 4.5 mm of aluminum between the tube head and the probe, leaving the