Measurement of the effective size of the input phosphor of an x-ray image intensifier.

A technique is described, using a mobile radiographic x-ray unit, for determining the effective size of the input phosphor of an image intensifier (I.I.), in particular for a unit with over-table x-ray tube, under-table II, and with the I.I. physically inaccessible. The techniques described also enable (1) locating the central axis of the I.I.; (2) the ratio, R, of the dimensions of the radiological image incident upon the front of the I.I. to the dimensions of the image on the monitor screen; and (3) the distance between the input phosphor and the table top, which is needed to determine the distance from focal spot to input phosphor.