RESOLUTION OF THE IMAGING SYSTEM
This is covered in more detail in other chapters of the book (see pp. 141, 154). However, it should be noted that the fastest film-screen combination or exposure index compatible with diagnostic quality should be used. When determining the quality required in an image the practitioner must be aware of what structures need to be defined. An image to determine the position of bones in a plaster cast following an orthopaedic reduction needs less resolution than the original image to diagnose the fracture. Ideally the smaller of the foci of the X-ray tube should be used (fine focus) but if this does not enable a short exposure time to be used on a patient likely to move then the practitioner may need to use a broad focus. This is another example of where the practitioner needs to make a decision that is a compromise between the ideal conditions and getting a diagnostic image.
