Bioimpedance imaging: an overview of potential clinical applications

Bayford, Richard; Tizzard, Andrew

doi:10.1039/c2an35874c

Cited by 67 publications

(55 citation statements)

References 71 publications

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“…Additional testing on in vivo rat liver tissue showed statistical significance between healthy and electroporated tissue, and showed similar trends to bioimpedance data obtained in parallel (Golberg et al, 2011). The apparent simplicity, relative to active frequency based techniques used in measurement of bioimpedance (Martinsen andGrimnes, 2011, Bayford andTizzard, 2012), makes biogalvanic characterisation a promising technique for intra-operative tissue characterisation. However the validity of assumptions made regarding the tissue-electrode interface reactions and mechanical contact conditions require further assessment prior to its application in clinical tissue characterisation.…”

Section: Introductionmentioning

confidence: 72%

Technological assessment of the biogalvanic method for tissue characterization

et al. 2014

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Abstract. Biogalvanic cells have the potential to be used in characterising biological tissue properties and ultimately tissue health. A biogalvanic cell is established by placing two differing metal electrodes across a target tissue allowing an electrical tissue-specific internal resistance to be determined. A novel data analysis method using least-squares fitting has been developed to more effectively determine the parameters of the biogalvanic system model proposed in the literature. The validity of the method has been examined through characterisation of electrical models, ex vivo porcine tissue, and in vivo porcine tissue. Strong agreement between test results and the proposed characterisation model has been shown. However, determined internal resistances are influenced by mechanical strain, current modulation direction and tissue thickness, indicating complexities at the electrode-tissue interface. These complexities undermine some assumptions upon which the biogalvanic model is based. Ultimately this technique could offer potential for use in minimally invasive surgery for discriminating tissue health but requires improved understanding and control of testing conditions.

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Section: Introductionmentioning

confidence: 72%

Technological assessment of the biogalvanic method for tissue characterization

et al. 2014

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“…EIT images represent changes in regional bio impedance. The images are derived from multiple skin electrodes positioned on the thoracic circumference [2]. Small alternating currents are applied to the electrodes and changes in conductivity of the underlying tissue are measured.…”

Section: Introductionmentioning

confidence: 99%

Electrical impedance tomography during major open upper abdominal surgery: a pilot-study

et al. 2014

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BackgroundElectrical impedance tomography (EIT) of the lungs facilitates visualization of ventilation distribution during mechanical ventilation. Its intraoperative use could provide the basis for individual optimization of ventilator settings, especially in patients at risk for ventilation-perfusion mismatch and impaired gas exchange, such as patients undergoing major open upper abdominal surgery. EIT throughout major open upper abdominal surgery could encounter difficulties in belt positioning and signal quality. Thus, we conducted a pilot-study and tested whether EIT is feasible in patients undergoing major open upper abdominal surgery.MethodsFollowing institutional review board’s approval and written informed consent, we included patients scheduled for major open upper abdominal surgery of at least 3 hours duration. EIT measurements were conducted prior to intubation, at the time of skin incision, then hourly during surgery until shortly prior to extubation and after extubation. Number of successful intraoperative EIT measurements and reasons for failures were documented. From the valid measurements, a functional EIT image of changes in tidal impedance was generated for every time point. Regions of interest were defined as horizontal halves of the picture. Monitoring of ventilation distribution was assessed using the center of ventilation index, and also using the total and dorsal ventilated lung area. All parameter values prior to and post intubation as well as extubation were compared. A p < 0.05 was considered statistically significant.ResultsA total of 120 intraoperative EIT measurements during major abdominal surgery lasting 4-13 hours were planned in 14 patients. The electrode belt was attached between the 2nd and 4th intercostal space. Consecutive valid measurements could be acquired in 13 patients (93%). 111 intraoperative measurements could be retrieved as planned (93%). Main obstacle was the contact of skin electrodes. Despite the high belt position, distribution of tidal volume showed a significant shift of ventilation towards ventral lung regions after intubation. This was reversed after weaning from mechanical ventilation.ConclusionsDespite a high belt position, monitoring of ventilation distribution is feasible in patients undergoing major open upper abdominal surgery lasting from 4 to 13 hours. Therefore, further interventional trials in order to optimize ventilatory management should be initiated.

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“…The chip is primarily intended for a parallel current drive EIT system implemented as a wearable device using active electrodes for neonatal lung function monitoring in intensive care units. It is also suitable for other EIT and bioimpedance applications [1] requiring wideband, accurate current drivers.…”

Section: Discussionmentioning

confidence: 99%

“…4 with the feedback loop open. 1 1 The feedback loop was broken and the negative input of the preamplifier was set to a dc level that matches the output dc level of the voltage buffer which was almost 0 V.…”

Section: Frequency Compensationmentioning

confidence: 99%

“…We are working on the development of a parallel current drive EIT system with "active" electrodes, primarily for neonatal lung function imaging [1], [7]. The encapsulation of the current driver (and impedance measurement circuitry) within the electrode shell removes lead capacitance problems and therefore enables fast, accurate impedance measurements at relatively high frequencies [22], [23].…”

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confidence: 99%

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High-Power CMOS Current Driver With Accurate Transconductance for Electrical Impedance Tomography

Constantinou

Triantis

Bayford

et al. 2014

IEEE Trans. Biomed. Circuits Syst.

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Current drivers are fundamental circuits in bioimpedance measurements including electrical impedance tomography (EIT). In the case of EIT, the current driver is required to have a large output impedance to guarantee high current accuracy over a wide range of load impedance values. This paper presents an integrated current driver which meets these requirements and is capable of delivering large sinusoidal currents to the load. The current driver employs a differential architecture and negative feedback, the latter allowing the output current to be accurately set by the ratio of the input voltage to a resistor value. The circuit was fabricated in a 0.6- μm high-voltage CMOS process technology and its core occupies a silicon area of 0.64 mm (2) . It operates from a ± 9 V power supply and can deliver output currents up to 5 mA p-p. The accuracy of the maximum output current is within 0.41% up to 500 kHz, reducing to 0.47% at 1 MHz with a total harmonic distortion of 0.69%. The output impedance is 665 k Ω at 100 kHz and 372 k Ω at 500 kHz.

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Bioimpedance imaging: an overview of potential clinical applications

Cited by 67 publications

References 71 publications

Technological assessment of the biogalvanic method for tissue characterization

Technological assessment of the biogalvanic method for tissue characterization

Electrical impedance tomography during major open upper abdominal surgery: a pilot-study

High-Power CMOS Current Driver With Accurate Transconductance for Electrical Impedance Tomography

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