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,...
A penetrameter method for field kV calibration of diagnostic x-ray machines.
Low-kilovoltage studies are useful for detection of objects which normally exhibit low radiographic contrast. For example, in mammography low kilovoltage and inherent filtration permit detection of punctate calcifications and fine soft-tissue structures in fat. Since diagnostic machines are designed primarily for use in the 50 to 150 kV range, their dial calibrations are usually in error at low settings. As an instance, dial settings of 27 pkV typically yield measured values of about 32, and occasionally up to 40 pkV. The problem is complicated by the fact that both contrast and film density depend critically on kilovoltage in this range. While knowledge of the calibration is most important in low-kilovoltage work, it is also useful in more conventional radiography, where it is often convenient to match technics in different x-ray rooms of the same or even different departments. For this reason, we have designed penetrameters for both low kilovoltage and conventional work. Table I summarizes five other fr...