Performances of Multi-Frequency Voltage to Current Converters for Bioimpedance Spectroscopy
Keywords:Voltage-to-current converter, Bioimpedance Spectroscopy, Multi-frequency Impedance
Breast cancer is one of the most common diseases affecting women and the mortality rate is very high in Bangladesh, mainly due to the lack of early diagnosis. X-ray mammography is not available widely in Bangladesh, besides it has an associated biological hazard. Multi-frequency bio-impedance measurement or bio-impedance spectroscopy has a great potential in many biomedical applications including breast cancer screening which involves tissue characterization. In Bio-impedance spectroscopy a range of frequencies of low level current is injected to the human body and corresponding bio-impedance is measured. In a typical bio-impedance measurement system an ac source with a constant current amplitude is an essential part in which the current amplitude should not change with frequency or load, the latter being typically of the order of a few kilo ohms in the human body. The constant current source is usually obtained from a voltage-to-current converter and several standard designs are available, for example a floating current source, a Howland current source and an enhanced Howland current source. The present work was taken up to perform a comparative study of these three types of current sources based on a commonly available low cost operational amplifier, 741. It was found that the enhanced Howland current source gave the best performance, the current being almost constant up to a frequency of about 10kHz for a load of 10k?. This work gives an understanding of this fundamental circuit segment that is essential for the development of a Bioimpedance Spectroscopy system.
Bangladesh Journal of Medical Physics Vol.5 No.1 2012 71-76