[Measurement of focal spot in X-ray tube using imaging plate]

Comparisons of focal-spot size measurements with a direct-exposure X-ray film, screen-film (S/F) system, and imaging plate (IP) were carried out for slit and star resolution pattern camera techniques. The focal-spot measurements of X-ray units with the nominal size of 0.1-1 mm were performed, and measurement using the computed radiography (CR) system was investigated. Compared with the direct-exposure X-ray film method, the measurements of focal-spot size by the S/F system were slightly small for all focal spots. The measurements obtained with IP were slightly large for large and small focal spots, although the measurement of micro focal-spot size was overestimated, extending the tolerance level owing to the sampling. With the star pattern camera technique, differences between the three kinds of detectors were minimal. Therefore, it was thought that measurement of focal-spot size using the CR system would be practical for both large and small focal spots if this method were used for quality control in medical facilities.