Figure 4. The effect of screen–film speed class on (a) effective dose, (b) optical density (OD) difference of the L3 tranverse process and (c) signal-to-noise ratio (SNR) of the trabecular structure on the L3 vertebra for the anteroposterior projection. The effect of screen–film sensitivity class on (d) effective dose, (e) OD difference of the L3 spinous process and (f) SNR of the trabecular structure at an anterior position on the L5 vertebra for the lateral projection.