American Journal of Biomedical Engineering. 2011; 1(1): 41-43 DOI: 10.5923/j.ajbe.20110101.07 Design of a Microcontroller Based and X-Ray Waveform Independent kVp-Meter Y. Ülgen * , M. Tümer Boğaziçi University, Institute of Biomedical Engineering, 34682, Çengelköy-Istanbul, Turkey Abstract The kVp setting is one of the major factors affecting the image quality in X-ray imaging and should be an- nually measured and calibrated if necessary. In this work, a kVp-meter is designed around the ATmega16 (Atmel) micro- controller, based on the physical principle that the linear attenuation coefficient of materials, namely copper has a smooth dependence on the energy level of the X-ray photons. Based on the logarithm of the ratio of the radiation intensities through 0.5mm and 1mm thick copper filters, a look-up table is generated in the range 60-120kVp. Logarithmic operation increased the precision at higher kVp values. Since sampling is performed over the exposure period in a continuous manner, the measurement is not affected by the X-ray waveform. A prototype unit was built and the performance was tested in terms of accuracy, precision and reliability. Keywords kVp Meter, Linear Attenuation Coefficient, X-ray Imaging 1. Introduction The kVp control of the X-ray device is a measure for the energy level of the emitted X-rays and corresponds to the penetrating power of the beam. To increase the contrast on the radiographic image, the kVp should be adjusted accord- ing to the type of the tissue. The kVp affects not only the intensity reaching the image receptor but also the subject contrast of the image. An uncalibrated X-ray machine leads to unnecessary exposure of the patients. For this reason, the kVp adjusting circuit of the X-ray machines should be con- trolled on regular basis. There are various ways to measure the kVp like direct measuring method (with high-voltage divider), X-ray spectroscopy or the Wisconsin kVp test cassettes. Electronic kVp-meters provide a measurement based on the change in X-ray transmission through varying thick- nesses of filtration. kVp-meters in general do not measure the true peak voltage; but rather an effective kV value by integrating the detector's outputs over exposure time and then taking their ratio. The instrument then corrects this value, usually according to a switch set by the user to indi- cate what type of X-ray machine (1Φ or 3Φ or DC) is being measured, to give an effective kVp by knowing the amount of ripple in the waveform. The method employed in this article relays on the same principle, namely the dependence of the linear attenuation coefficient µ of copper on the energy level of the X-ray pho * Corresponding author: ulgeny@boun.edu.tr (Y. Ülgen) Published online at http://journal.sapub.org/ajbe Copyright © 2011 Scientific & Academic Publishing. All Rights Reserved tons: if µ can be measured, then the energy level of the photons, hence the kVp can be determined. Copper material is used since its µ exhibits a smooth behaviour within the energy range of X-ray imaging[1,2] as can be seen from Figure 1. Figure 1. The relation between the linear attenuation coefficient of cop- per and the incident photon energy. However this behaviour is valid only for monochromatic X-ray beam. In practice, the energy spectrum generated at a certain kVp exhibits a continuous behaviour called Brehmss trahlung continuum up to the largest possible keV level which is in fact the kVp, with a few peaks called characte- ristic X-rays. Filtration eliminates the relatively lower energy photons and the effective peak level is shifted to the right, where the overall intensity, namely the number of photons decreases. Therefore it is important to have a µ-kVp relationship rather than µ-photon energy. 2. Method and Measurement 0 5 10 15 20 25 30 20 40 60 80 100 120 µ Cu (mm -1 ) Photon Energy (keV)