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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

Projected impedance images on three imaging planes and reconstructed 3D images.(a–c) The two-dimensional projected images of (γt/γ)-1 and (d–f) the three-dimensional reconstructed images using the projected images of (a–c) reconstructed with a back projection algorithm.
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Fig7: Projected impedance images on three imaging planes and reconstructed 3D images.(a–c) The two-dimensional projected images of (γt/γ)-1 and (d–f) the three-dimensional reconstructed images using the projected images of (a–c) reconstructed with a back projection algorithm.

Mentions: Figures 6(a–c) show the measured voltage maps according to the primary, , and two different secondary currents, , , in the homogenous agar container. We could see the current density distribution inside the sample container corresponding to the selection of the current driving electrodes, as expected. Figures 6(d–f) show the voltage difference maps of u-u0 measured by the KHU Mark2 micro-EIT system when applying primary and secondary current in the large-scale container with 3 anomalies. Here, u is the measured voltage in the presence of objects seen in Figure 4 and u0 is the reference voltage without objects. Figures 6, (a) and (d) correspond to the injection current from to , (b) and (e) correspond to the injection current from to , and (c) and (f) correspond to the injection current from to with and without the anomalies, respectively.The two dimensional impedance images for each of the imaging planes were reconstructed using the projected image reconstruction algorithm in Figures 7(a–c). These were combined with the back projection algorithm to reconstruct three dimensional images. Figures 7(d–f) present three dimensional images in various view angles. The shapes of the three different objects were deformed and blurred from the original shapes because of the intrinsic property of the electric current flow. However, the shapes in the bottom image were consistent with actual shape of the objects in Figure 4. The shape deformation along the z-direction was greater since we did not measure data on the top surface. The center of imaging domain had low sensitivity compared to the boundary region.Figure 6


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)

Projected impedance images on three imaging planes and reconstructed 3D images.(a–c) The two-dimensional projected images of (γt/γ)-1 and (d–f) the three-dimensional reconstructed images using the projected images of (a–c) reconstructed with a back projection algorithm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig7: Projected impedance images on three imaging planes and reconstructed 3D images.(a–c) The two-dimensional projected images of (γt/γ)-1 and (d–f) the three-dimensional reconstructed images using the projected images of (a–c) reconstructed with a back projection algorithm.
Mentions: Figures 6(a–c) show the measured voltage maps according to the primary, , and two different secondary currents, , , in the homogenous agar container. We could see the current density distribution inside the sample container corresponding to the selection of the current driving electrodes, as expected. Figures 6(d–f) show the voltage difference maps of u-u0 measured by the KHU Mark2 micro-EIT system when applying primary and secondary current in the large-scale container with 3 anomalies. Here, u is the measured voltage in the presence of objects seen in Figure 4 and u0 is the reference voltage without objects. Figures 6, (a) and (d) correspond to the injection current from to , (b) and (e) correspond to the injection current from to , and (c) and (f) correspond to the injection current from to with and without the anomalies, respectively.The two dimensional impedance images for each of the imaging planes were reconstructed using the projected image reconstruction algorithm in Figures 7(a–c). These were combined with the back projection algorithm to reconstruct three dimensional images. Figures 7(d–f) present three dimensional images in various view angles. The shapes of the three different objects were deformed and blurred from the original shapes because of the intrinsic property of the electric current flow. However, the shapes in the bottom image were consistent with actual shape of the objects in Figure 4. The shape deformation along the z-direction was greater since we did not measure data on the top surface. The center of imaging domain had low sensitivity compared to the boundary region.Figure 6

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