LORAD AFFINITY Series, Руководство по обслуживанию

Страница: 84 / 214

4-28 P/N 9-500-0255
Service Manual
Chapter 4: Calibrations and Performance Checks
Automatic Exposure Control System Calibration
2. Set the unit for an Auto-Time exposure at 26 kV, Large focus, Mo filter. Set the Film data
field to the screen-film combination loaded in the cassette.
3. Place 4.0 cm of BR-12 or PMMA acrylic on the 18 x 24 cm Bucky, centered laterally
over the AEC detectors. Lower the compression device onto the BR-12.
4. Take an exposure, develop the film, then measure the optical density (OD). Write the
mA and OD in the place provided on the Large Bucky Factor Worksheet (Table 4-11) for
the 18 x 24 cm Bucky.
5. Remove the 18 x 24 cm Bucky.
6. Place a 24 x 30 cm Bucky on the system and set the unit for an Auto-Time exposure at
26 kV, Large focus, Mo filter. Set the Film data field to the screen-film combination
loaded in the cassette.
7. Place 4.0 cm of BR-12 or PMMA acrylic on the 24 x 30 cm Bucky, centered laterally
over the AEC detectors. Lower the compression device onto the BR-12.
8. Take an exposure, develop the film, then measure the optical density (OD). Write the
mA and OD in the place provided on the Large Bucky Factor Worksheet (Table 4-11) for
the 24 x 30 cm Bucky.
9. Divide the 18 x 24 cm Bucky mAs by the 24 x 30 cm Bucky mAs (as shown in Table 4-
11). This is the Large Bucky Factor.
10. On Calibration Screen #2, select LgBky FACTOR and adjust as necessary to match the
calculated Large Bucky Factor.
11. Take an exposure with the 24 x 30 cm Bucky and develop the film. Measure the OD.
Adjust the Large Bucky Factor until the large Bucky OD is within 0.10 of the small Bucky
OD.
Table 4-11: Large Bucky Factor Worksheet
5.18 Compression Thickness Threshold Adjustment
Note… For this adjustment the unit must be in 100 mA mode. Ensure that the
Compression Thickness Threshold is 1.0 cm at the start of this procedure.
1. For units with no HTC Bucky, go to Step 3, for units with HTC Bucky, go to Step 2.
12. Set unit to Calibration Screen #3, set the HTC C-THK threshold for 1.0 cm.
13. Set unit to Calibration Screen #2.
14. Install the 18 x 24 cm Bucky onto the IRSD and insert a loaded cassette. Always use the
same cassette and Bucky for all calibration steps.
15. Set the unit for an Auto-Time exposure at 25 kV, Large focus, Mo filter. Set the Film data
field to the screen-film combination loaded in the cassette.
16. Place the amount of BR-12 or PMMA acrylic that was used in the final 25 kV, low atten-
uation exposure from Table 4-6 on the Bucky, centered laterally and extending 1.0 cm
over the chest wall edge. Use motorized compression to lower the compression paddle
onto the phantom material.
18 x 24 cm Bucky 24 x 30 cm Bucky
Thickness mAs OD Thickness mAs OD
4.0 cm 4.0 cm
Final Large Bucky Factor _________