The previous article dealt mostly with the basic principles of radiography – this part will cover the methods of ensuring that a radiograph is of an acceptable quality and capable of showing relevant imperfections. As mentioned in the previous article the quality of a radiograph is assessed using three factors: density, contrast and definition or sharpness of the image. Density and contrast have already been covered but there also has to be some method by which the sensitivity (the ability to reveal imperfections) can be measured. To do this devices known as image quality indicators (IQI’s), formerly called, are used. These can be of several forms as illustrated in Fig.1