LORAD AFFINITY Series, Service Manual

Page: 80 / 214

4-24 P/N 9-500-0255
Service Manual
Chapter 4: Calibrations and Performance Checks
Automatic Exposure Control System Calibration
ments (6 - 14 mAs), it may be necessary to increase or decrease the amount of BR-12 or
PMMA used.
6. Make another exposure, develop the film, then measure the Optical Density.
7. Repeat Steps 5 and 6 as necessary, to obtain the mean OD requirement (±0.15 OD).
8. Replace the 2.0 cm absorber with the 5.0 cm absorber. Using the same techniques as in
Steps 5 and 6, make an exposure, develop the film, then measure the Optical Density.
9. Make Offset adjustments to calibrate the Optical Density to the value requested by the
customer. Increase the Offset value if the density is too high. To maintain mAs require-
ments (65 - 130 mAs), it may be necessary to increase or decrease the amount of BR-12
or PMMA used.
10. Make another exposure, develop the film, then measure the Optical Density.
11. Repeat Steps 9 and 10 as necessary, to obtain the mean OD requirement (±0.15 OD).
12. Replace the 5.0 cm absorber with the 2.0 cm absorber, make an exposure, develop the
film, then measure the Optical Density. Ensure the Optical Density reading is within
±0.15 OD of the exposure at 5.0 cm. If necessary, repeat the entire procedure to bring
both the 2.0 cm and the 5.0 cm exposures within the specified requirements.
13. Change the Gain, Offset and M-Density (if required) values for each of the remaining
small focal spot kV stations to the Gain, Offset, and M-Density values obtained in this
procedure.
5.11 kV Tracking - Small Focal Spot (Mo)
This procedure ensures that the automatic exposure control system will produce proper OD
films at intermediate kV levels, small focus, with 4.0 cm of attenuation.
1. Place 4.0 cm of BR-12 on the Magnification Table - centered laterally - positioned 1.0
cm over the chest wall edge.
2. Set the unit for an Auto-Time exposure, Small focal spot, Mo filter.
3. Make exposures at 25 through 30 kV. Check the optical density tracking each film.
4. If necessary, adjust Gain and Offset at each kV station to maintain OD within ±0.15 OD
of the mean optical density value.
5.12 Initial Calibration—Small Focal Spot (Rh)
This procedure will make gain and offset adjustments to the automatic exposure control
system for small focal spot exposures. Exposures used to adjust the offset must be taken
between 65 mAs and 130 mAs, and exposures used to adjust the gain must be taken
between 6 mAs and 14 mAs. Always take sample exposures, then adjust the amount of
attenuation to achieve the proper mAs before making gain or offset adjustments.
Note… Before starting this procedure, select the small focus, then set the Gain and
Offset values to the values used at 26 kV for the Large Focal spot.
1. Set the unit for an exposure at 28 kV, Small focal spot, Rh filter, Mag Auto-Time.
2. Place 2.5 cm of BR-12 or PMMA on the breast platform, centered laterally, and extend-
ing 1.0 cm over the chest wall edge. Place the AEC detector in the position closest to the
chest wall.
3. Place the AEC detector in the position closest to the chest wall. Take an exposure,
develop the film, then measure the optical density (OD).