Letter: Ardran/Crooks penetrameter cassette - necessity for re-calibration.
We have frequently been asked if the penetrameter cassette described by us (1968) requires frequent re-calibration. When this cassette was first designed it was our opinion that calcium tungstate intensifying screens did not alter in speed with time or use unless obviously worn, abraided, stained or dirty; we still hold this view.
Checking diagnostic x-ray beam quality.
Abstract A radiographic method is described for comparing the effective kilovoltage and inherent nitration of diagnostic X-ray machines. The apparatus consists of a modified Xray cassette covered by a sheet of lead perforated with two rows of holes; one row is associated with a strip of slow intensifying screen and provides a reference exposure, the other row has a strip of fast intensifying screen and a copper step wedge. The thickness of copper needed to give a film density which matches that of the reference exposure is called the copper reference number and provides an index of the beam quality. The device is calibrated against a constant potential generator for which the kV values are accurately known. For determining the effective kV of machine the beam is attenuated and hardened at source by means of a filter of 1·5 mm of Cu, corresponding approximately to the filtration (of the primary beam) provided by an abdomen plus Bucky grid, plus table top. The method is relatively independent of processing,...
Radiation safety evaluation of fluoroscopes.
The problems of estimating patient exposure and the scattered radiation exposure to the operator during fluoroscopy are made difficult by the nature of fluoroscopic procedures. Field size and position change widely and rapidly and, for a given examination, the extent of exposure will depend to a large extent on the technic of the fluoroscopist. In each case the exposure to both patient and operator is related to the exposure dose rate, the quality of the radiation produced by the machine, and the scatter from the machine. These factors may be called the inherent radiation characteristics of the machine, since they depend on the x-ray unit itself and not on the manner of its use. During the past ten years we frequently have had the opportunity to examine fluoroscopes with regard to inherent radiation safety factors. While it is not possible to determine the safety of a particular unit according to an absolute scale, it is possible, by comparison, to discover whether a given machine measures up to a good st...