LORAD AFFINITY Series, Service Manual

Page: 83 / 214

P/N 9-500-0255 4-27
Service Manual
Chapter 4: Calibrations and Performance Checks
Automatic Exposure Control System Calibration
Table 4-9: AEC Performance Worksheet—Small Focal Spot, Rh Filter
5.16 HTC Factor (Offset) Calibration
This procedure is only applicable for those systems with an HTC Bucky.
1. Set unit to Calibration Screen #3, set the HTC C-THK threshold for 6.0.
2. Set unit to Calibration Screen #2.
3. 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.
4. Place the amount of BR-12 or PMMA acrylic that was used in the final 26 kV, low atten-
uation exposure from Table 4-6 on the Bucky, centered laterally, and extending approxi-
mately 1.0 cm over the chest wall edge.
5. Place the AEC detector in the position closest to the chest wall. Take an exposure,
develop the film, then measure the optical density (OD).
6. On Calibration Screen #2, select HTC FACTOR and adjust as necessary to set OD to
match the OD reading from the 26 kV, low attenuation exposure on Table 4-6 (+0.05
OD). Record final results on Table 4-10.
Table 4-10: HTC Factor Worksheet
5.17 Large Bucky (24 x 30 cm) Factor Calibration
1. Set unit to Calibration Screen #2.
Small Focal Spot
0.025 mm Rhodium Filter
Mag Table/Paddle/BR-
12
KODAK MIN-R-2000
Film/Cassette
Gain - Lower Thickness = 6 to
14 mAs
Offset - Higher Thickness = 65
to 130 mAs
kV mA Recommended
Thickness
mAs OD Gain/Offset Max/-1 cm mAs OD
28 30 2.5 cm G=
5.0 cm
28 30 6.0 cm O=
29 30 3.0 cm G=
5.5 cm
29 30 6.5 cm O=
30 30 3.0 cm G=
5.5 cm
30 30 6.5 cm O=
31 30 3.5 cm G=
6.0 cm
31 30 7.0 cm O=
32 30 3.5 cm G=
6.5 cm
32 30 7.5 cm O=
Note… Adjust thickness as necessary to achieve desired results.
HTC FACTOR
kV Reduced
mA
Thickness mAs OD HTC Factor
26 30