Hologic DISCOVERY A, Technical Manual

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Discovery QDR Series Technical Manual
4-26
Note: The PosLimitOffset and NegLimitOffset entries in the [ArMotor] section of the
SQDRIVER.INI file determine the motion limits relative to the mechanical stops. If
these entries are not present, or are zero, the motion limits are set to the mechanical
limits, as in the above example.
Note: The last calibration scan data is saved in the file MOTOR_AR.DAT. You can re
analyze the data–e.g., after editing SQDRIVER.INI–by typing the command
CALIBRATE @MOTOR_AR.DAT<Enter>
at the MOTOR$AR> prompt in
SQDRIVER.
4.7 Laser Positioning Offset Adjustment
The laser of the Discovery is used to correctly position the C-Arm over the patient.
Improper adjustment can cause improper detector flattening and may force the operator to
reposition the scan more frequently than necessary.
1. Center the table, turn on the laser, and set the point of a sharp metallic object on
the crosshair
2. At the QDR Main Menu screen, click the
Perform Exam
button, create a test
patient biography, and select
AP Lumbar
as the scan type. (DO NOT use the
spine phantom biography as a patient.) Uncheck the Use Default Scan Mode
check box and click Next. Select Array Mode and click Next.
3. Click the
Start Scan
button.
4. After scan starts and you can see the metallic object, click the
Reposition
Scan
button.
5. Using the mouse, move the image so that the tip of the metallic object is in the
horizontal center of the scan area and touching the bottom edge of the scan area.
6. Click the
Restart Scan
button and let the arm reposition.
7. At the
Start Scan
screen, click the
Cancel
button.
8. Turn on the laser.
9. Locate the 3 laser adjustment screws (small Phillips) under the C-arm. Adjust
these screws to tilt the assembly until the laser crosshair is on the tip of the
pointed object.
10. Run another scan to check your adjustments.
4.8 A/D Gain Control Adjustment
An A/D gain adjustment potentiometer ensures that all systems have the same input to the
A/D converter regardless of slight variations in X-ray flux. The location of the
potentiometer depends on the system configuration:
• On systems with a separate A/D Converter board, the adjustment is the only potenti-
ometer on the A/D Converter board.