Differential synchronous demodulation for electrical impedance tomography

Koukourlis, C.S.; Kyriakou, George; Sahalos, John N.

doi:10.1088/0143-0815/13/a/006

Cited by 6 publications

(1 citation statement)

References 6 publications

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“…The third measurement channel circuit (figure 1(c)) was built as a frequency converter, the signal being demodulated before amplification (Koukourlis et al 1992a(Koukourlis et al , b, 1993.…”

Section: Methods and Circuit Descriptionmentioning

confidence: 99%

Influence of electrode impedance changes on the common-mode rejection ratio in bioimpedance measurements

Petrova¹

1999

Physiol. Meas.

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Bioelectrical impedance in vivo measurements suffer from many potential sources of error due to the patient-instrument interface. The total common-mode rejection ratio (CMRR(T)) was investigated experimentally for three measurement channel circuit versions, including electrode-skin impedance imbalance. The first version was of the 'classical' type. The second one makes use of a differential filter at the input of the instrumentation amplifier. The third circuit was a frequency-converting structure, where the signal was demodulated before being amplified. The differential demodulator was based on synchronous sampling using floating capacitors. The experiments were accomplished with simulated imbalance of the real and imaginary parts of electrode-skin impedances. To reduce unwanted common-mode voltage, a differential accurately balanced current source was used. Considering an application in impedance cardiography, the experiments were carried out at a single frequency of 40 kHz. The results showed the advantage of the circuits using frequency conversion and differential input filter, rendering at least 15 dB higher CMRR(T). The most significant reduction of CMRR(T) resulted from imbalance of the capacitance component of voltage-sensing electrode impedances. The third circuit showed an unexpected behaviour of CMRR(T) improvement with higher imbalance of the electrode-skin impedance resistance component.

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Section: Methods and Circuit Descriptionmentioning

confidence: 99%

Influence of electrode impedance changes on the common-mode rejection ratio in bioimpedance measurements

Petrova¹

1999

Physiol. Meas.

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Performance of a differential synchronous demodulator for electrical impedance tomography

Koukourlis

Trigonidis

Kyriakou

et al. 1992

Clin. Phys. Physiol. Meas.

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Current approaches to analogue instrumentation design in electrical impedance tomography

Boone

Holder

1996

Physiol. Meas.

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Electrical impedance tomography (EIT) is a novel medical imaging method, which allows reconstructed tomographic images of the internal impedance of a subject to be made with the use of a ring of electrodes. High precision impedance measurements are needed, because the image reconstruction process is ill-conditioned and small errors in measurement can lead to large errors in the final image. In practice, there are formidable instrumentation problems, due to the interaction of finite current drive output impedance, recording amplifier common mode rejection, and unequal skin-electrode impedances. A number of different EIT systems have been constructed or are under development. These employ differing strategies, such as additional electrodes, multiple electrode current injection, or recording at multiple frequencies, to improve image accuracy. This paper reviews the nature of the instrumentation problems and the designs employed by differing groups in attempting to overcome them.

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Differential synchronous demodulation for electrical impedance tomography

Abstract: A differential synchronous demodulator developed for electrical impedance tomography applications is presented. The demodulator proves to have high CMRR due to its architecture.

Cited by 6 publications

References 6 publications

Influence of electrode impedance changes on the common-mode rejection ratio in bioimpedance measurements

Influence of electrode impedance changes on the common-mode rejection ratio in bioimpedance measurements

Performance of a differential synchronous demodulator for electrical impedance tomography

Current approaches to analogue instrumentation design in electrical impedance tomography

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