Routine evaluation of focal spots.

The star test pattern is the optimum method for routine quality control investigations of focal spots since its radiographic image patterns are directly related to the resolution capability of the tube. The pinhole image of the focal spot can also be used. The two methods are compared. Both methods were used to study “blooming” from tube current. The extent to which target resolution capability may be degraded by heat was evaluated. Data indicate that the heat which results from operating the tube within approved load conditions causes no detrimental effects on resolution capability; in fact, the focal spot size decreases slightly. No deterioration is produced in serial radiography.