X線撮影系のレスポンス関数
(II) X線管焦点
1965 年 34 巻 3 号 p. 190-196
詳細
1965 年 34 巻 3 号 p. 190-196
It is shown that the optical transfer function of a focal spot of an X-ray tube can be defined and treated in quite the same way as other blurring elements. Optical transfer functions of the, focal spots are measured photoelectrically with an X-ray fluorescent screen. The line spread func-n tion of the focal spot in X-ray intensity distributions is reproduced on the fluorescent screen in. the form of light emissions when a metal slit is placed between the focal spot and the fluorescent: screen as an object, and the light image on the fluorescent screen is Fourier-transformed optically by an area type masking method with a direct scanning apparatus described in a previous paper6). Optical transfer functions of the focal spot which have negative components along some directions: correspond to photographs of a Siemens' star which shows spurious resolutions. The line spread function calculated from optical transfer function data agrees with the one obtained by the photographic method within experimental errors. Field characteristics of the focal spot due to the geometry of the X-ray tube are obtained theoretically and experimentally, and good agreement between the results by these two treatments shows that field characteristics can be determined by simple calculations in some specified fields. It is suggested that field characteristics can be effectively applied to practical radiographic techniques for clinical purposes.
