Measurement of the focal spot size of diagnostic x-ray tubes--a comparison of pinhole and resolution methods.

The pinhole camera technique has been compared with resolution and other methods for measuring the focal spot dimensions fo diagnostic X-ray tubes. These comparisons show that the resolution method offers an accurate estimation of the focal spot dimensions without the difficulties normally encountered in pinhole camera techniques. Accuracy and reproducibility of the "star-test" resolution method is examined. The current standard specifications for pinhole camera measurements are also discussed, and in the light of results obtained, changes in these specifications are suggested, particulary with regard to correction factors for non-uniformity of the intensity distribution and manufacturing tolerances.