4–20
12/12/94 – 1234563
Size and Resolution
Sizes and Resolutions of Kodak STORAGE PHOSPHOR SCREENS
The 35 cm x 43 cm CASSETTE is new and can be used only in CR 800 Systems.
The PLATE is removed from the CASSETTE in a direction 90 degrees from the
current design, thus it It is not backward compatible with the current CASSETTES
of the same size. The new CASSETTES are easily distinuishable.
The other 3 sizes are interchangeable with currently available products used with
CR 400 Systems and have the same catalog numbers.
Two screen resolutions (types) are supported by the CR 800 System: General
Purpose (GP-25) and High Resolution (HR).
The HR SCREENS, available in 24 cm x 30 cm and 18 cm x 24 cm sizes, are constructed identically to GP SCREENS, but have a thinner phosphor coating. The overall
image sharpness from these SCREENS is superior to the GP; however, due to the thinner phosphor layer, the HD SCREENS require special exposure techniques
(approximately double the X-ray exposure).
The CR 800 adjusts for the difference in light intensity by an adjustment in the pixel pode values in the final processing.
The dynamic range of the photostimulable phosphors is linear over an exposure range of greater than 10,000 to1, as opposed to roughly 40 to 1 for film, making it more
difficult to under or over expose a computed radiograph.
Image Matrix Size
The CR 800 scans the STORAGE PHOSPHOR SCREENS at the resolutions shown in the table below. The scan rate is the same for GP and HR SCREENS of the
same sizes.
Note
The file size of the 24 x 30 cm PLATE is more than the larger 35 x 35 cm PLATE due to the greater sampling rate. The image size in pixels for the 24 x 30 cm PLATE
is the same as for the largest PLATE (35 x 43 cm) because they have the same sampling rate, thus they also have the same file size.
Pixel size is smaller for smaller PHOSPHOR SCREENS. When scanning smaller PLATES, the laser spot size and the digitization rate do not change. However scan
speed is slower. To produce smaller pixels, the sweep rate of the laser beam (fast scan) and the transport speed of the PHOSPHOR SCREEN under the COLLECTOR
(slow scan) decrease. The result is that the pixel size decreases, thereby increasing the limiting resolution of the image. Limiting resolution (LP) is the term used to
define the smallest object in an image that you are able to see. It is prmarily deteremined by the sampling rate (pixel size).
SCREEN Size
GP-25
HR
35 x 43 cm
YES
NO
35 x 35 cm
YES
NO
24 x 30 cm
YES
YES
18 x 24 cm
YES
YES
PLATE size
Image Size
Pixels x Lines
Sampling rate
Pixel Size in
microns
Limiting Resolution
LP = Line Pairs
File Size
35 x 43 cm
2048 x 2500
5.8 pixels / mm
168 +/- 2
2.8 LP/mm
10 MB
35 x 35 cm
2048 x 2048
5.8 pixels / mm
168 +/- 2
2.8 LP/mm
8 MB
24 x 30 cm
2048 x 2500
8.33 pixels / mm
115 +/- 2
3.8 LP/mm
10 MB
24 x 18 cm
2392 x 1792
9.95 pixels / mm
97 +/- 2
4.8 LP/mm
8 MB
