LORAD AFFINITY Series, Service Manual

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P/N 9-500-0255 4-17
Service Manual
Chapter 4: Calibrations and Performance Checks
Automatic Exposure Control System Calibration
Calibration of the AEC is performed at the factory to assure that the system is capable of
proper calibration and performance. At installation, the AEC must be adjusted to obtain films
of the proper mean optical density (typically 1.6 OD ±0.15 OD depending on the
radiologist’s preference) using the site’s processing equipment. The HTC Factor is set to a
number determined by performing the HTC Factor (Offset) Adjustment prior to leaving the
factory. Do not change the HTC Factor prior to performing AEC Calibration as part of the
initial installation procedures. The AEC Pre-Amp Gain (shown on Calibration Screen #3) is
factory set to 1 and is not selectable or adjustable.
Note… This procedure must be performed for each film type used with the unit.
Before performing the AEC Calibration procedure, be sure to complete the
Tube Voltage Calibration and the Filament Calibration.
AEC system performance is specified at the kV’s that are normally used clinically. The
following chart presents a guideline for typical clinical values for breast composition and
thickness.
Note that 2.0 cm thickness imaging is not appropriate above 26 kV, while 6.0 cm thickness
imaging is not appropriate below 26 kV.
Notes… When calibrating the automatic exposure control system, always use the
same Bucky device and the same cassette to ensure consistent results.
For optimum calibration results use the AEC Worksheets provided at the
end of this procedure (Tables 4-6 through 4-9). Record the AEC
performance values on the worksheets when the AEC system is calibrated.
5.1 AEC Detector Gain Calibration
Any time the AEC Detector Assembly or the X-ray Tube is replaced, the following procedures
must be performed.
Required tools/test equipment:
• 2.0 cm BR-12
• Digital Volt Meter (DVM)
• Standard Issue Tool Set
1. Remove the Gantry’s right side panel (to access the Host Microprocessor board) as per
Chapter 6, Section 2.1.1.
2. Install the 18 x 24 cm Bucky onto the IRSD, insert a loaded cassette, and install a com-
pression paddle.
3. Place 2.0 cm or BR-12 on the Bucky so it covers the AEC detectors.
4. Set the unit for a Manual exposure at 30 kV, 50 mAs.
Table 4-5: Typical kV range versus compressed thickness
Thickness Fatty (kV) 50/50 (kV) Dense (kV)
2.0 cm 23-24 24-25 25-26
4.0 cm 25-26 26-27 27-28
6.0 cm 26-27 27-28 29-30