THEORY GUIDE Imaging Sequence
10DEC05
TG4825-1
Page
82 of 120
2 The MCPU BOARD A2, through the DIGITIZER BOARD A3, sets up the GALVO BOARD
A4 and PMT/DAS BOARD A5 with the following information recorded during calibration of
the CR 825/850 SYSTEM:
• offset and amplitude of the GALVO
• gain of the PMTs
• high voltage of the PMTs
• number of pixels/line
• number of lines to scan
• offset for start of fast scan
Note
The number of lines scanned includes the lines scanned for the image and also the
“throwaway lines”. “Throwaway” lines at the beginning of the scanning are lines that are
scanned but are not part of the image.
On GP and HR plates, the start and stop of the fast scan is approximately 10 pixels in from
the edge of the PHOSPHOR. The actual distance will vary from approximately 1 mm for small
CASSETTES to approximately 5 mm for larger CASSETTES, because the pixel size is
smaller on the small CASSETTES. This START/STOP OFFSET is determined at the
calibration of the CASSETTE.
EHR MAMMOGRAPHY and LLI CASSETTES perform an overscan which shows the edge of
the screen.
3 When the MSC BOARD A1 is ready, it sends a message to the MCPU BOARD A2,
which sends messages to:
• MSC BOARD A1 to start the slow scan
• DIGITIZER BOARD A3 to start moving the GALVO
• PMT/DAS BOARD A5 to start the collection of data
4 The GALVO starts and provides the deflection of the laser beam onto the SCREEN. The
laser beam moves horizontally across the SCREEN. This horizontal motion is the fast
scan direction. See “GALVO.”
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