Principle One: X-rays should be emitted from the smallest source of radiation as possible.
As electrons strike the focal spot, x-rays are emitted. The smaller the focal spot inside the tubehead, the greater the detail on the resultant image. Manufacturers govern the size of the focal spot, and it cannot be changed by the operator. However, the focal spot can become enlarged over time due to continuous use. When focal spot enlargement does occur, the resultant radiographic image becomes less sharp. The focal spot must be monitored through a quality assurance program. Resolution test devices will determine any change in the focal spot size.