Yunjie Yang

A Miniature Electrical Impedance Tomography Sensor and 3-D Image Reconstruction for Cell Imaging

Real-time quantitative imaging is becoming highly desirable to study nondestructively the biological behavior of 3-D cell culture systems. In this paper, we investigate the feasibility of quantitative imaging/monitoring of 3-D cell culture processes via electrical impedance tomography (EIT), which is capable of generating conductivity images in a non-destructive manner with high temporal resolution. To this end, a planar miniature EIT sensor amenable to standard cell culture format is designed, and a 3-D forward model for the sensor is developed for 3-D imaging. Furthermore, a novel 3-D-Laplacian and sparsity joint regularization algorithm is proposed for enhanced 3-D image reconstruction. Simulation phantoms with spheres at various vertical and horizontal positions were imaged for 3-D performance evaluation. In addition, experiments on human breast cancer cell spheroid and a triangular breast cancer cell pellet were carried out for experimental verification. The results have shown that the stable measurement on high conductive cell culture medium and the significant improvement of image quality based on the proposed regularization method are achieved. It demonstrates the feasibility of using the miniature EIT sensor and 3-D image reconstruction algorithm to visualize 3-D cell cultures, such as spheroids or artificial tissues and organs. The established work would expedite real-time quantitative imaging of 3-D cell culture for assessment of cellular dynamics.

Image Reconstruction for Electrical Impedance Tomography Using Enhanced Adaptive Group Sparsity With Total Variation

A novel image reconstruction algorithm for electrical impedance tomography using enhanced adaptive group sparsity with total variation constraint is proposed in this paper. The new algorithm simultaneously utilizes the prior knowledge of regional structure feature and global characteristic of the conductivity distribution. The regional structure feature is encoded by using an enhanced adaptive group sparsity constraint. Meanwhile, the global characteristic of inclusion boundary is considered by imposing total variation constraint on the whole image. An enhanced adaptive pixel grouping algorithm is proposed based on Otsu’s thresholding method, which demonstrates good noise immunity. An accelerated alternating direction method of multipliers is utilized to solve the proposed problem for a faster convergence rate. The performance of the proposed algorithm is thoroughly evaluated by numerical simulation and experiments. Comparing with the state-of-the-art algorithms, such as the L1 regularization, total variation regularization, and our former work on adaptive group sparsity, the proposed method has demonstrated superior spatial resolution and better noise reduction performance. Combined with the total variation constraint, distinct boundary of inclusions has also been obtained.

Correlation of Volume Ratio and Normalized Permittivity in Particle Mixture

The volume ratio in the total solid particle mixture is an important parameter indicating the characteristics of particulate mixtures. Therefore, a simple measurement method is desirable. In this paper, the normalized permittivities of two groups of particle mixtures are tested using electrical capacitance tomography (ECT) with the series and parallel models. The experimental results show that normalized permittivity changes obtained from the series ECT model have a very strong linear relationship with the volume ratio of higher permittivity materials in the mixture. The Maxwell Garnett formula can predict the normalized permittivity only after the permittivity of each type of particle is known. The comparison between two methods suggests that ECT with the series model is a better way to monitor the volume ratio in mixtures comprising two different types of solid particle.

Design and fabrication of microelectrodes for electrical impedance tomography of cell spheroids

Three-dimensional (3D) tumour spheroids exhibit great potential as an in vitro for pharmaceutical drug testing. Spheroids represent more physiologically relevant systems compared to 2D cell culture models. In this work, MCF7 spheroids are cultured in Corning® spheroid microplates to investigate cell morphology and proliferation. Platinum microelectrodes designed to enable electrical impedance tomography (EIT) imaging were fabricated on glass substrates. EIT measurements were performed on 250 μm radius circular electrode tips for 0.71 mm MCF7 spheroid at 20 kHz using time difference imaging method. Initial results indicate the capability of EIT to image cell spheroids.

Exploring the Potential of Electrical Impedance Tomography for Tissue Engineering Applications

In tissue engineering, cells are generally cultured in biomaterials to generate three-dimensional artificial tissues to repair or replace damaged parts and re-establish normal functions of the body. Characterizing cell growth and viability in these bioscaffolds is challenging, and is currently achieved by destructive end-point biological assays. In this study, we explore the potential to use electrical impedance tomography (EIT) as a label-free and non-destructive technology to assess cell growth and viability. The key challenge in the tissue engineering application is to detect the small change of conductivity associated with sparse cell distributions in regards to the size of the hosting scaffold, i.e., low volume fraction, until they assemble into a larger tissue-like structure. We show proof-of-principle data, measure cells within both a hydrogel and a microporous scaffold with an ad-hoc EIT equipment, and introduce the frequency difference technique to improve the reconstruction.

Correlation analysis of solid particles' permittivity and composition using electrical capacitance tomography and Maxwell Garnett formula

The solid volume fraction and volume composition ratio of different solid particles in a silo are important parameters indicating the character of granular mixtures. In this paper, measurement of the two parameters is studied by utilizing Electrical Capacitance Tomography (ECT). This preliminary work focuses on comparing normalized permittivity changes from ECT with those predicted by the Maxwell Garnett formula (MGF) relating to solid volume fraction and volume composition ratio. Experimental results show that normalized permittivity changes from the two methods have a strong linear correlation in gas-solid two- and three-phase systems. This work demonstrates that ECT is a promising technique for monitoring solid volume fraction of single solid particles and the volume composition ratio of mixtures of two different solid particles in a silo.