Abstract: The type of rear protection plate (backplate) has a certain influence on the imaging quality in CR testing. The quality of digital image while changing backplate and tube voltages was compared and the reasons for the differences were then analyzed. It was proposed that while tube voltage being below 90 kV, either applying a rear steel screen or no screen could be adopted, whereas on the other hand, using rear lead plate or steel screen with lead plate should be better with the tube voltage being higher than 100 kV.