Abstract
BackgroundMalignant breast tumor tissue has a significantly different electrical impedance spectrum than surrounding normal tissues. This has led to the development of impedance imaging as a supplementary or alternative method to X-ray mammography for screening and assessment of breast cancers. However low spatial resolution and poor signal to noise ratio has limited the clinical application.MethodsIn order to improve spatial resolution we developed a trans-admittance mammography (TAM) system including an array of 60×60 current sensing electrodes. We adopted a similar setup to X-ray mammography where the breast is situated between two holding plates. The top plate is a large solid metal electrode for applying a sinusoidal voltage over a range of frequencies from 50 Hz to 500 kHz. The bottom plate has 3600 current sensing electrodes that are kept at the ground potential. Currents are generated from the top voltage-applying electrode and spread throughout the breast, entering the TAM system through the array of current sensing electrodes on the bottom plate. The TAM system measures the exit currents through 6 switching modules connected to 600 electrodes each. Each switching module is connected to 12 ammeter channels which are switched sequentially to 50 of the 600 electrodes each measurement time. Each ammeter channel is comprised of a current-to-voltage converter, a gain amplifier, filters, an analog to digital converter, and a digital phase sensitive demodulator.ResultsWe found an average noise level of 38 nA, amplitude stability of less than 0.2%, crosstalk of better than -60 dB and 70 dB signal to noise ratio over all channels and operating frequencies. Images were obtained in time difference and frequency difference modes in a saline phantom.ConclusionWe describe the design, construction, and calibration of a high density TAM system in detail. Successful high resolution time and frequency difference images showed regions of interest with the expected admittivity changes in the frequency spectrum.
Highlights
Malignant breast tumor tissue has a significantly different electrical impedance spectrum than surrounding normal tissues
We describe a new design of the trans-admittance scanner for the mammography setup (TAM) with better spatial resolution
Basic performance We developed a high density trans-admittance mammography (TAM) system capable of producing trans-admittance projection images of conductive objects
Summary
Malignant breast tumor tissue has a significantly different electrical impedance spectrum than surrounding normal tissues. This has led to the development of impedance imaging as a supplementary or alternative method to X-ray mammography for screening and assessment of breast cancers. The idea of using a handheld probe with a planar array of electrodes was first suggested by Kao et al (2006) who used two radiolucent plates of planar electrode arrays with the breast situated between them [13,14] This design allows a dual-mode operation of EIT and X-ray mammography in the X-ray mammography geometry. More patient studies with improved hardware, software and algorithms are expected to validate the ability to differentiate benign and malignant lesions, and establish the clinical significance of impedance imaging in the diagnosis of breast cancer
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