Considerations on the measurement of practical peak voltage in diagnostic radiology.

An evaluation of the non-invasive measurement of the practical peak voltage (PPV) in the quality control of X-ray units used in diagnostic radiology was carried out. Two instruments were employed: the PTW Diavolt Universal Tester with readings in PPV and the Waveform Tester for X-rays (WATEX) prototype proposed here, which uses a PIN structure (P-type diffusion, Intrinsic region, N-type diffusion) photodiode as a sensor. The reference for the measurements was the voltage signal obtained in an oscilloscope from an invasive high voltage divider in order to verify the accuracy and precision of the measurements. The readings of the PPV in the Diavolt show a systematic error between 1% and 8%, always being less than the real value. An explanation for this difference is proposed, based on the relation between the effect of the X-rays in the film and the response of the sensor to the product of the applied voltage to the X-ray tube (peak voltage kVp), and the anode current. This explanation was confirmed using the WATEX waveform tester.