Electrical Impedance Tomography of Cell Viability in Tissue With Application to Cryosurgery

Proposal and performance evaluation of a new parallel plate continuous cell separation device using dielectrophoresis

Along with the rapid development of cellular biological research in recent years, there has been an urgent need for a high-speed, high-precision method of separating target cells from a highly heterogeneous cell population. Among the various cell separation technologies proposed so far, dielectrophoresis (DEP)-based approaches have shown particular promise because they are noninvasive to cells. We have developed a new DEP-based device to separate large numbers of live and dead cells of the human mammary cell line MCF10A. In this study, we validated the separation performance of this device. The results showed the successful separation of a higher percentage of cells than in previous studies, with a separation efficiency higher than 90%. In the past, there have been no confirmed cases in which a separation rate of over 90% and high-speed processing of a large number of cells were simultaneously achieved. It was shown that the proposed device can process large numbers of cells at high speed and with high accuracy.

Rapid Differentiation of Unfrozen and Frozen-Thawed Tuna with Non-Destructive Methods and Classification Models: Bioelectrical Impedance Analysis (BIA), Near-Infrared Spectroscopy (NIR) and Time Domain Reflectometry (TDR)

The performances of three non-destructive sensors, based on different principles, bioelectrical impedance analysis (BIA), near-infrared spectroscopy (NIR) and time domain reflectometry (TDR), were studied to discriminate between unfrozen and frozen-thawed fish. Bigeye tuna (Thunnus obesus) was selected as a model to evaluate these technologies. The addition of water and additives is usual in the fish industry, thus, in order to have a wide range of possible commercial conditions, some samples were injected with different water solutions (based on different concentrations of salt, polyphosphates and a protein hydrolysate solution). Three different models, based on partial least squares discriminant analysis (PLS-DA), were developed for each technology. This is a linear classification method that combines the properties of partial least squares (PLS) regression with the classification power of a discriminant technique. The results obtained in the evaluation of the test set were satisfactory for all the sensors, giving NIR the best performance (accuracy = 0.91, error rate = 0.10). Nevertheless, the classification accomplished with BIA and TDR data resulted also satisfactory and almost equally as good, with accuracies of 0.88 and 0.86 and error rates of 0.14 and 0.15, respectively. This work opens new possibilities to discriminate between unfrozen and frozen-thawed fish samples with different non-destructive alternatives, regardless of whether or not they have added water.

Retrieval of the conductivity spectrum of tissuesin vitrowith novel multimodal tomography

OBJECTIVE

Imaging of tissue engineered three-dimensional (3D) specimens is challenging due to their thickness. We propose a novel multimodal imaging technique to obtain multi-physical 3D images and the electrical conductivity spectrum of tissue engineered specimensin vitro.

APPROACH

We combine simultaneous recording of rotational multifrequency electrical impedance tomography (R-mfEIT) with optical projection tomography (OPT). Structural details of the specimen provided by OPT are used here as geometrical priors for R-mfEIT.

MAIN RESULTS

This data fusion enables accurate retrieval of the conductivity spectrum of the specimen. We demonstrate experimentally the feasibility of the proposed technique using a potato phantom, adipose and liver tissues, and stem cells in biomaterial spheroids. The results indicate that the proposed technique can distinguish between viable and dead tissues and detect the presence of stem cells.

SIGNIFICANCE

This technique is expected to become a valuable tool for monitoring tissue engineered specimens' growth and viabilityin vitro.

A New Label-Free and Contactless Bio-Tomographic Imaging with Miniaturized Capacitively-Coupled Spectroscopy Measurements

A new bio-imaging method has been developed by introducing an experimental verification of capacitively coupled resistivity imaging in a small scale. This paper focuses on the 2D circular array imaging sensor as well as a 3D planar array imaging sensor with spectroscopic measurements in a wide range from low frequency to radiofrequency. Both these two setups are well suited for standard containers used in cell and culture biological studies, allowing for fully non-invasive testing. This is true as the capacitive based imaging sensor can extract dielectric spectroscopic images from the sample without direct contact with the medium. The paper shows the concept by deriving a wide range of spectroscopic information from biological test samples. We drive both spectra of electrical conductivity and the change rate of electrical conductivity with frequency as a piece of fundamentally important information. The high-frequency excitation allows the interrogation of critical properties that arise from the cell nucleus.

Sandblasting improves the performance of electrodes of miniature electrical impedance tomography via double layer capacitance

Effect of sandblasting of the copper electrode structures before deposition of gold thin film for micro electrical impedance tomography (EIT) system has been studied experimentally. The comparison has been performed on the unmodified copper electrodes and the sandblasted electrodes before deposition of gold layer, using structural analysis while their performance in EIT system has been measured and analyzed. The results of scanning electron microscopy and atomic force microscopy show that the sandblasting of the electrodes results in the deposition of gold film with smaller grain size and uniformly, comparing to the unmodified structure. The measurement of impedance shows that the sandblasting will increase the double layer capacitance of electrode structure which improves the impedance measurement accordingly.

Spatially resolved electrical impedance methods for cell and particle characterization

Electrical impedance is an established technique used for cell and particle characterization. The temporal and spectral resolution of electrical impedance have been used to resolve basic cell characteristics like size and type, as well as to determine cell viability and activity. Such electrical impedance measurements are typically performed across the entire sample volume and can only provide an overall indication concerning the properties and state of that sample. For the study of heterogeneous structures such as cell layers, biological tissue, or polydisperse particle mixtures, an overall measured impedance value can only provide limited information and can lead to data misinterpretation. For the investigation of localized sample properties in complex heterogeneous structures/mixtures, the addition of spatial resolution to impedance measurements is necessary. Several spatially resolved impedance measurement techniques have been developed and applied to cell and particle research, including electrical impedance tomography, scanning electrochemical microscopy, and microelectrode arrays. This review provides an overview of spatially resolved impedance measurement methods and assesses their applicability for cell and particle characterization.

Issues Critical to the Successful Application of Cryosurgical Ablation of the Prostate

The techniques of present-day cryosurgery performed with multiprobe freezing apparatus and advanced imaging techniques yield predictable and encouraging results in the treatment of prostatic and renal cancers. Nevertheless, and not unique to cryosurgical treatment, the rates of persistent disease demonstrate the need for improvement in technique and emphasize the need for proper management of the therapeutic margin. The causes of persistent disease often relate to a range of factors including selection of patients, understanding of the extent of the tumor, limitations of the imaging techniques, and failure to freeze the tumor periphery in an efficacious manner. Of these diverse factors, the one most readily managed, but subject to therapeutic error, is the technique of freezing the tumor and appropriate margin to a lethal temperature [Baust, J. G., Gage, A. A. The Molecular Basis of Cryosurgery. BJU Int 95, 1187–1191 (2005)]. This article describes the recent experiments that examine the molecular basis of cryosurgery, clarifies the actions of the components of the freeze-thaw cycle, and defines the resultant effect on the cryogenic lesion from a clinical perspective. Further, this review addresses the important issue of management of the margin of the tumor through adjunctive therapy. Accordingly, a goal of this review is to identify the technical and future adjunctive therapeutic practices that should improve the efficacy of cryoablative techniques for the treatment of malignant lesions.

Electrical impedance tomography of electrolysis

The primary goal of this study is to explore the hypothesis that changes in pH during electrolysis can be detected with Electrical Impedance Tomography (EIT). The study has relevance to real time control of minimally invasive surgery with electrolytic ablation. To investigate the hypothesis, we compare EIT reconstructed images to optical images acquired using pH-sensitive dyes embedded in a physiological saline agar gel phantom treated with electrolysis. We further demonstrate the biological relevance of our work using a bacterial E.Coli model, grown on the phantom. The results demonstrate the ability of EIT to image pH changes in a physiological saline phantom and show that these changes correlate with cell death in the E.coli model. The results are promising, and invite further experimental explorations.

A MATLAB-Based Boundary Data Simulator for Studying the Resistivity Reconstruction Using Neighbouring Current Pattern

Phantoms are essentially required to generate boundary data for studying the inverse solver performance in electrical impedance tomography (EIT). A MATLAB-based boundary data simulator (BDS) is developed to generate accurate boundary data using neighbouring current pattern for assessing the EIT inverse solvers. Domain diameter, inhomogeneity number, inhomogeneity geometry (shape, size, and position), background conductivity, and inhomogeneity conductivity are all set as BDS input variables. Different sets of boundary data are generated by changing the input variables of the BDS, and resistivity images are reconstructed using electrical impedance tomography and diffuse optical tomography reconstruction software (EIDORS). Results show that the BDS generates accurate boundary data for different types of single or multiple objects which are efficient enough to reconstruct the resistivity images for assessing the inverse solver. It is noticed that for the BDS with 2048 elements, the boundary data for all inhomogeneities with a diameter larger than 13.3% of that of the phantom are accurate enough to reconstruct the resistivity images in EIDORS-2D. By comparing the reconstructed image with an original geometry made in BDS, it would be easier to study the inverse solver performance and the origin of the boundary data error can be identified.

Effect of thaw temperatures in reducing enzyme activity in human thyroid tissues

An identified impediment to the advancement of science in the field of proteomics is the deterioration of proteins in tissue upon removal of the tissue from its natural state. To reduce this degradation, human tissues are frozen and stored in either liquid nitrogen or -80°C environments. It is believed that frozen tissue in ultralow temperatures preserves proteins against enzyme degradation. Various molecular, biophysical, and biochemical analytical studies require that frozen tissues be thawed before being used for analyses. Depending on downstream analyses, tissues are thawed at different temperatures (37°C, room temperature or 4°C). However, there is very little literature that describes the effects of different thaw temperatures on enzymatic inactivation in tissue lysates. We investigated the effects of preprocessing variable thaw temperature on postprocessed lysates using tyrosine phosphatase and phosphatase and tensin homolog activity assays. In our study we examined the thawing of frozen human thyroid tissues at the traditional temperatures of 4°C (on ice), 37°C (in an oven), and the novel temperature of 95°C (using Stabilizor T1™). The tissue lysates were processed without the addition of enzymatic inhibitors. Our results showed that in benign, malignant, and diseased tissues, high temperature thawing is effective in reducing enzymatic activity. In normal tissue, the reduction is dependent on individual enzymes. This suggests that if tissue lysates are to be obtained from frozen tissues without the addition of inhibitors, high temperature thawing might have marked improvement in downstream non-enzymatic analyses of diseased and neoplastic tissues.

Current status of ablative therapies for renal tumors

The increase in detection of small (≤ 4 cm) renal cortical neoplasms has made nephron-sparing surgery the new standard of care for T1a renal lesions. Advances in minimally invasive surgery have improved the surgical approach to these lesions to include laparoscopic partial nephrectomy and renal ablative therapies. In this review, we discuss the indications, outcomes, and potential complications of the commonly used ablative modalities in urologic practice. We will expand on renal cryoablation and review the mechanism of action, surgical approaches, and evidence based medicine using this modality.

Intracranial nonthermal irreversible electroporation: in vivo analysis

Nonthermal irreversible electroporation (NTIRE) is a new minimally invasive technique to treat cancer. It is unique because of its nonthermal mechanism of tumor ablation. Intracranial NTIRE procedures involve placing electrodes into the targeted area of the brain and delivering a series of short but intense electric pulses. The electric pulses induce irreversible structural changes in cell membranes, leading to cell death. We correlated NTIRE lesion volumes in normal brain tissue with electric field distributions from comprehensive numerical models. The electrical conductivity of brain tissue was extrapolated from the measured in vivo data and the numerical models. Using this, we present results on the electric field threshold necessary to induce NTIRE lesions (495-510 V/cm) in canine brain tissue using 90 50-mus pulses at 4 Hz. Furthermore, this preliminary study provides some of the necessary numerical tools for using NTIRE as a brain cancer treatment. We also computed the electrical conductivity of brain tissue from the in vivo data (0.12-0.30 S/m) and provide guidelines for treatment planning and execution. Knowledge of the dynamic electrical conductivity of the tissue and electric field that correlates to lesion volume is crucial to ensure predictable complete NTIRE treatment while minimizing damage to surrounding healthy tissue.

Selective isolation of live/dead cells using contactless dielectrophoresis (cDEP)

Contactless dielectrophoresis (cDEP) is a recently developed method of cell manipulation in which the electrodes are physically isolated from the sample. Here we present two microfluidic devices capable of selectively isolating live human leukemia cells from dead cells utilizing their electrical signatures. The effect of different voltages and frequencies on the gradient of the electric field and device performance was investigated numerically and validated experimentally. With these prototype devices we were able to achieve greater than 95% removal efficiency at 0.2-0.5 mm s(-1) with 100% selectivity between live and dead cells. In conjunction with enrichment, cDEP could be integrated with other technologies to yield fully automated lab-on-a-chip systems capable of sensing, sorting, and identifying rare cells.

Imaging cryosurgery with EIT: tracking the ice front and post-thaw tissue viability

Cryosurgery employs freezing for targeted destruction of undesirable tissues such as cancer. Ice front imaging has made controlled treatment of deep body tumors possible. One promising method, recently explored for this task, is EIT, which recovers images of electrical impedance from measurements made at boundary electrodes. However, since frozen tissue near the ice front survives, ice front imaging is insufficient. Monitoring treatment effect would enable iterative cryosurgery, where extents of ablation and need for further treatment are assessed upon thawing. Since lipid bilayers are strong barriers to low frequency electrical current and cell destruction implies impaired membranes, EIT should be able to detect the desired effect of cryosurgery: cell death. Previous work has tested EIT for ice front imaging with tank studies while others have simulated EIT in detecting cryoablation, but in vivo tests have not been reported in either case. To address this, we report 3D images of differential conductivity throughout the freeze-thaw cycle in a rat liver model in vivo with histological validation, first testing our system for ice front imaging in a gel and for viability imaging post-thaw in a raw potato slice.

Assessment of the Viability of Transplant Organs with 3D Electrical Impedance Tomography

Methods that can determine the extent of tissue damage in transplant organs, before the decision to transplant has been made, have the potential to improve the outcome of the procedure by preventing unfit organs from being transplanted into the patient. The raised confidence in the organ state with such a technique would also increase availability. Now restricted due to the fear of introducing a failed organ resulting from the relative lack of viability data during transport, stringent criteria for donation would relax. Electrical impedance tomography is an imaging modality that recovers the spatial variation of the complex impedivity in the body from electrical measurements made on the periphery. In this study, we apply 3D EIT with the complete electrode model to a sample conductivity distribution that might result from an organ that is losing its viability due to prolonged ischemia. The reconstructed images show that EIT has the potential to become an adjuvant method for the field of organ transplantation.

Detecting cryoablation with EIT and the benefit of including ice front imaging data

Imaging has made cryosurgery, the destruction of unwanted tissue through freezing, valuable. Electrical impedance tomography (EIT) has been explored as a method to determine the volume of tissue that is frozen during the procedure. However, studies have shown that tissue near the edge of the frozen zone often survives since in this region it may only be the extra-cellular space that is frozen. This threatens the usefulness of cryosurgery for cancer therapy since inaccurate ablation either allows the cancer to survive or increases the chances of complications. Since low-frequency conductivity of tissue increases due to cell membrane impairment, and ablated tissue implies impaired membranes, EIT has the capability to recover images of tissue viability. Cryosurgery is a technique that can benefit from this: EIT scans before freezing and after thawing can show changes in conductivity and hence viability due to treatment. Assuming unfrozen tissue will survive treatment, we explore the use of differential EIT in combination with intra-operative ice front imaging modes that are currently in clinical practice to recover enhanced-resolution images of cryosurgical treatment efficacy in a set of simulated experiments. We also investigate the sensitivity to violation of this assumption and predict tolerable levels of measurement noise.

Liver Tumor Gross Margin Identification and Ablation Monitoring during Liver Radiofrequency Treatment

PURPOSE

To determine whether tissue visible light spectroscopy (VLS) used during radiofrequency (RF) ablation of liver tumors could aid in detecting when tissue becomes adequately ablated, locate grossly ablated regions long after temperature and hydration measures would no longer be reliable, and differentiate tumor from normal hepatic tissue based on VLS spectral characteristics.

MATERIALS AND METHODS

Studies were performed on human liver in vivo and animal liver ex vivo. In three ex vivo cow livers, RF-induced lesions were created at 80 degrees C. A 28-gauge needle embedded with VLS optical fibers was inserted alongside an RF ablation array, and tissue spectral characteristics were recorded throughout ablation. In one anesthetized sheep in vivo, a VLS needle probe was passed through freshly ablated liver lesions, and ablated region spectral characteristics were recorded during probe transit. In two human subjects, a VLS needle probe was passed through liver tumors in patients undergoing hepatic tumor resection without ablation, and tumor spectral characteristics were recorded during probe transit.

RESULTS

In bovine studies, there was significant change in baseline absorbance (P < .0001) as a result of increased light scattering as liver was ablated. Liver exhibited native differential absorbance peaks at 550 nm that disappeared during ablation, suggesting that optical spectroscopy detects markers of tissue altered during ablation. In sheep, liver gross ablation margins were clearly defined with millimeter resolution during needle transit through the region, suggesting that VLS is sensitive to gross margins of ablation, even after the temperature has normalized. In humans, absorbance decreased as the needle passed from normal tissue into tumor and normalized after emerging from the tumor, suggesting that absence of native liver pigment may serve as a marker for the gross margins and presence of tumors of extrahepatic origin.

CONCLUSIONS

In human subjects, VLS during RF liver tumor ablation depicted gross hepatic tumor margins in real time; in animal subjects, VLS achieved monitoring of when and where RF ablation endpoints were achieved, even long after the tissue cooled. Real-time in vivo monitoring and treatment feedback may be possible with the use of real-time VLS sensors placed along side of, or embedded into, the RF probe, which can then be used as an adjunct to standard imaging during tumor localization and RF ablation treatment.