Conditioning Electrical Impedance Mammography System

• Published in: Measurement : journal of the International Measurement Confederation 2018-02, Vol.116, p.38-48
• Main Authors: Zarafshani, Ali, Bach, Thomas, Chatwin, Chris R., Tang, Shanshan, Xiang, Liangzhong, Zheng, Bin
• Format: Article
• Language: English
• Subjects: And electrical impedance mammography; Bio-impedance current source; Biomedical imaging equipment and instrument; Breast; Breast cancer detection; Capacitance; Ceramic sintering; Circuit boards; Crosstalk; Current conveyors; Current sources; Data acquisition; Design engineering; Electrical impedance; Electrical impedance tomography; Electrical resistivity; Electricity; Ferroelectrics; Image reconstruction; Materials science; Model accuracy; Operational amplifiers; Printed circuits; Screening; Screening and prescreening modality; Systems design
• ISSN: 0263-2241; 1873-412X
• DOI: 10.1016/j.measurement.2017.10.052

A multi-frequency Electrical Impedance Mammography (EIM) system has been developed to evaluate the conductivity and permittivity spectrums of breast tissues, which aims to improve early detection of breast cancer as a non-invasive, relatively low cost and label-free screening (or pre-screening) method. Multi-frequency EIM systems typically employ current excitations and measure differential potentials from the subject under test. Both the output impedance and system performance (SNR and accuracy) depend on the total output resistance, stray and output capacitances, capacitance at the electrode level, crosstalk at the chip and PCB levels. This makes the system design highly complex due to the impact of the unwanted capacitive effects, which substantially reduce the output impedance of stable current sources and bandwidth of the data that can be acquired. To overcome these difficulties, we present new methods to design a high performance, wide bandwidth EIM system using novel second generation current conveyor operational amplifiers based on a gyrator (OCCII-GIC) combination with different current excitation systems to cancel unwanted capacitive effects from the whole system. We reconstructed tomography images using a planar E-phantom consisting of an RSC circuit model with different set of values, which represents the resistance of extra-cellular (R), intra-cellular (S) and membrane capacitance (C) of the breast tissues to validate the performance of the system. The experimental results demonstrated that an EIM system with the new design achieved a high output impedance of 10 MΩ at 1 MHz to at least 3 MΩ at 3 MHz frequency, with an average SNR and modelling accuracy of over 80 dB and 99%, respectively.