Variation of the practical peak voltage with the sample rate for a mammography waveform generator

The Practical Peak Voltage (PPV) was introduced by the IEC 61676 standard as an electrical parameter strongly related to the image contrast, which is determined from the X-ray tube voltage waveform. This quantity is used in diagnostic radiology reference systems quality control. Measurements have been made using a mammography equipment model Senographe 700T, manufactured by GE (General Electric). This equipment works in the voltage range from 22 to 35 kV and the tube has a molybdenum anode. Its internal voltage divider was used to do the acquisition of the voltage data of the X-ray tube. To acquire the waveforms of the equipment, it has been used an acquisition board model NI 5911 (National Instruments) and a LabVIEW routine that calculates all the voltage parameters associated with the X-ray tube. During the measurements, the sample rate was varied from 100 samples/s to 1 Msamples/s for a 24 kV voltage reference. Results showed a variation less than 0.05 kV for the PPV value. At the same time, it was evaluated the maximum value of the tube waveform (kVp - maximum). The results have shown that the value of kVp (maximum) varies up to 1 kV, for the higher sample rates, and have confirmed the low dependence of PPV with the sample rate of the tube waveform, in comparison with kVp (maximum), in mammography range. (author)