Calibration and use of the Wisconsin kVp test cassette

The Ardran-Crooks kVp test cassette is widely used in diagnostic radiology to provide a rapid, simple, noninvasive measurement of x-ray tube potential. A modified version of this cassette called the Wisconsin kVp Test Cassette was introduced commercially in the U. S. in 1972. Since then, the method of calibration of these cassettes has changed significantly. Wisconsin kVp Test Cassettes calibrated by the manufacturer prior to August 1982 may yield underestimates of kVp measurements, particularly when using the 90-110 and 110-130 kVp regions with single-phase units. In August 1982 significant improvements in the calibration methods were implemented. The resultant change in calibration is demonstrated by data from the Centers for Radiological Physics. Present calibration methods are believed to be accurate within the greater of +/- 2 kVp or 2% of actual peak tube potential. Proper use of the cassette is necessary to achieve this level of accuracy.