Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

increased too much because the number of silver grains present in the emulsion limitsthese 00 values. Overdevelopment therefore primarily affects the low 00 partof the H & 0 curve, where silver halide crystals that were not exposed to lightbecome developed.Underdevelopment occurs if the developer concentration is too low or if the temperatureof the developer is too low. Underdevelopment manifests as a reduction in00 at the high exposure end of the H & 0 curve. In addition to changes in densitythat are seen with overdevelopment or underdevelopment (Fig. 7.5), the slope of theH & 0 curve is reduced and the films will appear flat and lack contrast.1Vtlter spots can occur on the film if the replenishment rates are incorrect, if thesqueegee mechanism that the film passes through after the wash tank is defective, orif the dryer is malfunctioning. Water spots are best seen with reflected light. This andother artifacts are shown conceptually in Fig. 7-6. A slap line is a plus-density line perpendicularto the direction of film travel that occurs near the trailing edge of the film.This is caused by the abrupt release of the back edge of the film as it passes throughthe developer-to-fixer crossover assembly. Pick-off artifacts are small, clear areas of thefilm where emulsion has flecked off from the film base; they can be caused by roughrollers, nonuniform film transport, or a mismatch between the film emulsion andchemicals. Wet pressure marks occur when the pinch rollers apply too much or inconsistentpressure to the film in the developer or in the developer-to-fixer crossover racks.Several types of shoe marks can occur. Shoe marks result when the film rubs againstthe guide shoes during transport. The artifact manifests as a series of evenly spacedlines parallel the direction of film transport. Plus-density shoe marks are caused by thet rollertransportdirectionFIGURE 7-6. Typical artifacts associatedwith film processors are illustrated.