The modulation transfer functions of x-ray focal spots

Abstract

A method is presented for the experimental determination of the modulation transfer functions of x-ray focal spots. The apparatus described is sufficiently flexible to permit the measurement of these functions under various conditions of x-ray tube operation and at various positions and directions in a plane perpendicular to the direction of the x-ray beam. The results of measurements on four tubes used in the United States are discussed. Data on two tubes are given in detail with the theoretical functions expected from a focal spot having uniform emission and the dimensions specified by the manufacturer. Phase transfer functions are calculated from the measurements and their significance in radiography is discussed.