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British Journal of Radiology (2006) 79, 425-431
© 2006 British Institute of Radiology
doi: 10.1259/bjr/28579947
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Optical density variations in CT films and their effect on image quality

I A Tsalafoutas, PhD1, G V Papoutsis, RT2, P N Maniatis, MD3 and K A Gogos, MSc4

1 Medical Physics Unit, 'Konstantopoulio - Agia Olga' Hospital, 3-5 Agias Olgas, Nea Ionia, 142 33, Athens, 2 Field Service Engineering Department, General Electric Medical Systems, 156 Cyprou Avenue and 91 Konstantinoupoleos Str, Argyroupolis, 164 51, Athens, 3 Computed Tomography Department, 'Konstantopoulio - Agia Olga' Hospital, 3-5 Agias Olgas, Nea Ionia, 142 33, Athens, 4 Nuclear Medicine Department, 'Hygeia' Hospital, 4 Erythrou Stavrou, 151 23, Maroussi, Athens, Greece


Figure 1
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  		Figure 1. The SMPTE test pattern.

 

Figure 2
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  		Figure 2. The variation of the contrast index(CI), speed index (SI) and maximum optical density (ODmax) values with frame numbers for tests 1.1 (Agfa film), 1.2 (Ferrania film), 1.3 and 1.4 (Konica film) performed on different days with the same laser printer (Scopix LR3300, Agfa) at the same CT installation. The frames have been numbered starting from the upper left corner, and vertical lines indicate the start of each of the 5 rows with 4 frames each.

 

Figure 3
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  		Figure 3. The variation of the contrast index(CI), speed index (SI) and maximum optical density (ODmax) values with frame numbers for tests performed at different CT installations which all had the same laser printer model (Scopix LR3300, Agfa) and used the same film (LT 2B daylight, Agfa).

 

Figure 4
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  		Figure 4. The variation of the contrast index(CI), speed index (SI) and maximum optical density (ODmax) values with frame numbers for tests performed at different CT installations, using three laser printer models (3: Scopix LR3300-Agfa; 7.1: Scopix LR5200-Agfa; 8.1: Ektascan 2180-Kodak).

 

Figure 5
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  		Figure 5. The variation of the contrast index(CI), speed index (SI) and maximum optical density (ODmax) values with frame numbers for tests performed at different CT installations, using different dry printer models (9,10,11: DryView 8100-Kodak; 12: DryView 8700-Kodak; 13: Drystar 3000-Agfa).

 

Figure 6
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  		Figure 6. The variation of the contrast index(CI), speed index (SI) and maximum optical density (ODmax) values for the laser and dry printers that exhibited the largest frame-to-frame variations (3: Scopix LR3300-Agfa; 9: DryView 8100-Kodak).

 

Figure 7
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  		Figure 7. The sensitometric curves used for updating the look-up tables before acquiring the SMPTE films (tests 1.1 to 1.4). The dashed line is the sensitometric curve that resulted when the film changed from Agfa to Ferrania before updating the look-up tables. The latter curve is included in the graph to demonstrate the influence of look-up tables on the sensitometric characteristics of CT films.

 




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