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Design of a microscopic electrical impedance tomography system for 3D continuous non-destructive monitoring of tissue culture.

Lee EJ, Wi H, McEwan AL, Farooq A, Sohal H, Woo EJ, Seo JK, Oh TI - Biomed Eng Online (2014)

Bottom Line: We developed a new micro-EIT system and report on simulation and experimental results of its macroscopic model.From numerical and experimental results, we estimate that at least 20 × 40 electrodes with 120 μm spacing are required to monitor the complex shape of ingrowth neotissue inside a scaffold with 300 μm pore.Future challenges include manufacturing a bioreactor-compatible container with a dense array of electrodes and a larger number of measurement channels that are sensitive to the reduced voltage gradients expected at a smaller scale.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering and Impedance Imaging Research Center, Kyung Hee University, 46-701 Yongin, Korea. tioh@khu.ac.kr.

ABSTRACT

Background: Non-destructive continuous monitoring of regenerative tissue is required throughout the entire period of in vitro tissue culture. Microscopic electrical impedance tomography (micro-EIT) has the potential to monitor the physiological state of tissues by forming three-dimensional images of impedance changes in a non-destructive and label-free manner. We developed a new micro-EIT system and report on simulation and experimental results of its macroscopic model.

Methods: We propose a new micro-EIT system design using a cuboid sample container with separate current-driving and voltage sensing electrodes. The top is open for sample manipulations. We used nine gold-coated solid electrodes on each of two opposing sides of the container to produce multiple linearly independent internal current density distributions. The 360 voltage sensing electrodes were placed on the other sides and base to measure induced voltages. Instead of using an inverse solver with the least squares method, we used a projected image reconstruction algorithm based on a logarithm formulation to produce projected images. We intended to improve the quality and spatial resolution of the images by increasing the number of voltage measurements subject to a few injected current patterns. We evaluated the performance of the micro-EIT system with a macroscopic physical phantom.

Results: The signal-to-noise ratio of the developed micro-EIT system was 66 dB. Crosstalk was in the range of -110.8 to -90.04 dB. Three-dimensional images with consistent quality were reconstructed from physical phantom data over the entire domain. From numerical and experimental results, we estimate that at least 20 × 40 electrodes with 120 μm spacing are required to monitor the complex shape of ingrowth neotissue inside a scaffold with 300 μm pore.

Conclusion: The experimental results showed that the new micro-EIT system with a reduced set of injection current patterns and a large number of voltage sensing electrodes can be potentially used for tissue culture monitoring. Numerical simulations demonstrated that the spatial resolution could be improved to the scale required for tissue culture monitoring. Future challenges include manufacturing a bioreactor-compatible container with a dense array of electrodes and a larger number of measurement channels that are sensitive to the reduced voltage gradients expected at a smaller scale.

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Related in: MedlinePlus

The reconstructed projection images using 800 voltage electrodes on each side, 2400 in total.(a) no noise added, (b) 3% Gaussian random noise added, and (c) 5% Gaussian random noise added to the simulated data.
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Fig9: The reconstructed projection images using 800 voltage electrodes on each side, 2400 in total.(a) no noise added, (b) 3% Gaussian random noise added, and (c) 5% Gaussian random noise added to the simulated data.

Mentions: First, we computed the boundary voltage data using equation 1 and the same setup as the experimental system with 360 sensing electrodes (8×15 or 120 sensing electrodes on each side) from the three different current injections. The spatial resolution of the reconstructed impedance image was not enough to recognize the letters because of the distance between the adjacent electrodes and the size of the testing material. The center-to-center spacing of adjacent electrodes was 254 μm and the line width of the letters was 240 μm. For example there was more voxels crossing the edge of ‘E’-letter than voxels wholly within or outside the ‘E’-letter. Therefore, the measured voltage maps from 360 sensing electrodes produced smeared reconstructed images. When we increased the number of voltage sensing electrodes to 20×40 or 800 on each side (2400 in total), the reconstructed projection images show an improved resolution in Figure 9. In this case, the distance between sensing electrodes was 120 μm so that the edges of the letters were defined more clearly. From this observation one can get better resolution when implementing the large number of voltage sensing electrodes. However, the number of voltage sensing electrodes will be limited by the sensitivity of the voltage measurement system and the amount of noise present as the voltage gradient and hence amplitude of measured voltage reduces as the electrodes distance decreases. Further the impedance of the voltage sensing electrodes will increase as they become smaller, placing more challenging requirements on the instrumentation amplifier input impedance for the voltage measurement system.Figure 9


Design of a microscopic electrical impedance tomography system for 3D continuous non-destructive monitoring of tissue culture.

Lee EJ, Wi H, McEwan AL, Farooq A, Sohal H, Woo EJ, Seo JK, Oh TI - Biomed Eng Online (2014)

The reconstructed projection images using 800 voltage electrodes on each side, 2400 in total.(a) no noise added, (b) 3% Gaussian random noise added, and (c) 5% Gaussian random noise added to the simulated data.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4196084&req=5

Fig9: The reconstructed projection images using 800 voltage electrodes on each side, 2400 in total.(a) no noise added, (b) 3% Gaussian random noise added, and (c) 5% Gaussian random noise added to the simulated data.
Mentions: First, we computed the boundary voltage data using equation 1 and the same setup as the experimental system with 360 sensing electrodes (8×15 or 120 sensing electrodes on each side) from the three different current injections. The spatial resolution of the reconstructed impedance image was not enough to recognize the letters because of the distance between the adjacent electrodes and the size of the testing material. The center-to-center spacing of adjacent electrodes was 254 μm and the line width of the letters was 240 μm. For example there was more voxels crossing the edge of ‘E’-letter than voxels wholly within or outside the ‘E’-letter. Therefore, the measured voltage maps from 360 sensing electrodes produced smeared reconstructed images. When we increased the number of voltage sensing electrodes to 20×40 or 800 on each side (2400 in total), the reconstructed projection images show an improved resolution in Figure 9. In this case, the distance between sensing electrodes was 120 μm so that the edges of the letters were defined more clearly. From this observation one can get better resolution when implementing the large number of voltage sensing electrodes. However, the number of voltage sensing electrodes will be limited by the sensitivity of the voltage measurement system and the amount of noise present as the voltage gradient and hence amplitude of measured voltage reduces as the electrodes distance decreases. Further the impedance of the voltage sensing electrodes will increase as they become smaller, placing more challenging requirements on the instrumentation amplifier input impedance for the voltage measurement system.Figure 9

Bottom Line: We developed a new micro-EIT system and report on simulation and experimental results of its macroscopic model.From numerical and experimental results, we estimate that at least 20 × 40 electrodes with 120 μm spacing are required to monitor the complex shape of ingrowth neotissue inside a scaffold with 300 μm pore.Future challenges include manufacturing a bioreactor-compatible container with a dense array of electrodes and a larger number of measurement channels that are sensitive to the reduced voltage gradients expected at a smaller scale.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering and Impedance Imaging Research Center, Kyung Hee University, 46-701 Yongin, Korea. tioh@khu.ac.kr.

ABSTRACT

Background: Non-destructive continuous monitoring of regenerative tissue is required throughout the entire period of in vitro tissue culture. Microscopic electrical impedance tomography (micro-EIT) has the potential to monitor the physiological state of tissues by forming three-dimensional images of impedance changes in a non-destructive and label-free manner. We developed a new micro-EIT system and report on simulation and experimental results of its macroscopic model.

Methods: We propose a new micro-EIT system design using a cuboid sample container with separate current-driving and voltage sensing electrodes. The top is open for sample manipulations. We used nine gold-coated solid electrodes on each of two opposing sides of the container to produce multiple linearly independent internal current density distributions. The 360 voltage sensing electrodes were placed on the other sides and base to measure induced voltages. Instead of using an inverse solver with the least squares method, we used a projected image reconstruction algorithm based on a logarithm formulation to produce projected images. We intended to improve the quality and spatial resolution of the images by increasing the number of voltage measurements subject to a few injected current patterns. We evaluated the performance of the micro-EIT system with a macroscopic physical phantom.

Results: The signal-to-noise ratio of the developed micro-EIT system was 66 dB. Crosstalk was in the range of -110.8 to -90.04 dB. Three-dimensional images with consistent quality were reconstructed from physical phantom data over the entire domain. From numerical and experimental results, we estimate that at least 20 × 40 electrodes with 120 μm spacing are required to monitor the complex shape of ingrowth neotissue inside a scaffold with 300 μm pore.

Conclusion: The experimental results showed that the new micro-EIT system with a reduced set of injection current patterns and a large number of voltage sensing electrodes can be potentially used for tissue culture monitoring. Numerical simulations demonstrated that the spatial resolution could be improved to the scale required for tissue culture monitoring. Future challenges include manufacturing a bioreactor-compatible container with a dense array of electrodes and a larger number of measurement channels that are sensitive to the reduced voltage gradients expected at a smaller scale.

Show MeSH
Related in: MedlinePlus