The clinical application of electrical impedance technology in the detection of malignant neoplasms: a systematic review

Surgical identification of brain tumour margins through impedance monitoring and electrocorticography and the potential for their combined use: A systematic review

CONTEXT

Primary central nervous system tumours have poor survival outcomes. Surgery, the first-line treatment, presents technical limitations, such as visualising the whole tumour border. Intracranial impedance monitoring and electrocorticography techniques provide insights into the local field potential characteristics, resistance and capacitance properties of brain tissue. We hypothesised that measurements obtained by either modality can distinguish between tumour and healthy brain tissue intraoperatively.

METHODS

A "Preferred Reporting Items for Systematic Reviews and Meta-Analyses" (PRISMA)-compliant systematic review was conducted, searching PubMed, Ovid, Scopus, Cochrane and Web of Science. Studies on electrocorticography and impedance monitoring in patients with brain tumours were included. Data on patient demographics, technical details, obtained results and safety were extracted and analysed in Excel.

RESULTS

Eighteen studies involving 286 patients in total were identified. Ten impedance studies showed that brain tumour tissue has significantly different values than healthy tissue, while its resistivity varies, being either higher or lower. Eight electrocorticography studies indicated increased high gamma power and altered connectivity in tumour tissue. No studies integrated impedance monitoring and electrocorticography in one device.

CONCLUSION

Impedance and electrocorticography measurements have the potential of differentiating between tumour and unaffected issues intra-operatively. Larger studies with standardised protocols are needed to validate these findings. Additionally, the combination of these two modalities has the potential for improved specificity with a single device. Future research should explore the role of these modalities in enhancing tumour margin identification across different tumour subtypes and in improving survival outcomes.

A Clinically Feasible Electrode Array for 3D Intraoperative Electrical Impedance Tomography-Based Surgical Margin Assessment in Robot-Assisted Radical Prostatectomy

OBJECTIVE

A novel small form factor circular electrode array was designed specifically for electrical impedance tomography (EIT) based assessment of surgical margins during robot assisted radical prostatectomy (RARP).

METHODS

The electrode array consists of 33 gold-plated electrodes arranged within a 9.5 mm diameter circular footprint on the end of a surgical probe that can be introduced through a standard 12 mm laparoscopic port used during RARP. The electrode array contains 8 larger, low-contact impedance outer electrodes dedicated for current drive and an internal grid of 25 smaller electrodes for simultaneous voltage measurement. Separating electrode geometry by function is designed to improve current delivery, speed, and resolution while reducing hardware requirements.

RESULTS

Simulations demonstrated that 1 mm diameter hemispherical prostate cancer inclusions could be localized within regions of adipose and benign prostate tissue; 1.5 mm diameter inclusions were required for localization within muscle tissue. A 2.38 mm diameter aluminum rod in 0.2 S/m saline could be localized throughout the imaging domain with a position error of less than 2.5 mm for depths from the electrode array surface of up to 1.7 mm. Ex vivo tissue experiments with a bovine model demonstrate visual congruence of muscle and adipose tissue locations between the sample and reconstructed images.

CONCLUSION

Simulation and experimental results indicate good detection and location of inclusions.

SIGNIFICANCE

These results suggest the proposed electrode array design can provide sufficient accuracy in the detection and localization of prostate cancer against clinically relevant background tissues for use during RARP.

Electrical Tumor Detection Probe Calibrated to Diagnose Gastrointestinal Cancer Mass in Real-Time

Background: The primary objective of this research is to propose an intra-operative tumor detection probe calibrated on human models of gastrointestinal (G.I.) cancers, enabling real-time scanning of dissected masses. Methods: Electrical Gastrointestinal Cancer Detection (EGCD) measures impedimetric characteristics of G.I. masses using a handpiece probe and a needle-based head probe. Impedance Phase Slope (IPS) and impedance magnitude (Z1kHz) are extracted as the classification parameters. EGCD was tested on palpable G.I. masses and compared to histopathology results. Results: Calibration was carried out on 120 GI mass samples. Considering pathological results as the gold standard, most cancer masses showed Z1kHz between 100 Ω and 2500 Ω while their IPS was between -15 and -1. The EGCD total sensitivity and specificity of this categorization in G.I. cancer patients with palpable tumors were 86.4% and 74.4%, respectively (p-value < 0.01). Conclusion: EGCD scoring can be used for 3D scanning of palpable tumors in G.I. tumors during surgery, which can help clarify the tumors' pathological response to neoadjuvant chemotherapy or the nature of intra-operative newly found G.I. tumors for the surgeon to manage their surgical procedure better.

Detection of invasive ductal carcinoma by electrical impedance spectroscopy implementing gaussian relaxation-time distribution (EIS-GRTD)

Breast cancer detection and differentiation of breast tissues are critical for accurate diagnosis and treatment planning. This study addresses the challenge of distinguishing between invasive ductal carcinoma (IDC), normal glandular breast tissues (nGBT), and adipose tissue using electrical impedance spectroscopy combined with Gaussian relaxation-time distribution (EIS-GRTD). The primary objective is to investigate the relaxation-time characteristics of these tissues and their potential to differentiate between normal and abnormal breast tissues. We applied a single-point EIS-GRTD measurement to ten mastectomy specimens across a frequency rangef= 4 Hz to 5 MHz. The method calculates the differential ratio of the relaxation-time distribution functionΔγbetween IDC and nGBT, which is denoted byΔγIDC-nGBT,andΔγbetween IDC and adipose tissues, which is denoted byΔγIDC-adipose.As a result, the differential ratio ofΔγbetween IDC and nGBTΔγIDC-nGBTis 0.36, and between IDC and adiposeΔγIDC-adiposeis 0.27, which included in theα-dispersion atτpeak1=0.033±0.001s.In all specimens, the relaxation-time distribution functionγof IDCγIDCis higher, and there is no intersection withγof nGBTγnGBTand adiposeγadipose.The difference inγsuggests potential variations in relaxation properties at the molecular or structural level within each breast tissue that contribute to the overall relaxation response. The average mean percentage errorδfor IDC, nGBT, and adipose tissues are 5.90%, 6.33%, and 8.07%, respectively, demonstrating the model's accuracy and reliability. This study provides novel insights into the use of relaxation-time characteristic for differentiating breast tissue types, offering potential advancements in diagnosis methods. Future research will focus on correlating EIS-GRTD finding with pathological results from the same test sites to further validate the method's efficacy.

Dielectrophoretic and electrochemical impedance mapping of metastatic potential in MDA-MB-231 breast cancer cells using inkjet-printed castellated microarray

The spread of metastatic cancer cells poses a significant challenge in cancer treatment, making innovative approaches for early detection and diagnosis essential. Dielectrophoretic impedance spectroscopy (DEPIS), a powerful tool for cell analysis, combines dielectrophoresis (DEP) and impedance spectroscopy (IS) to separate, sort, cells and analyze their dielectric properties. In this study, we developed and built out-of-plane inkjet-printed castellated arrays to map the dielectric properties of MDA-MB-231 breast cancer cell subtypes across their metastatic potential. This was realized via modulating the expression of connexin 43 (Cx43), a marker associated with poor breast cancer prognosis and increased metastasis. We employed DEP-based trapping, followed by EIS measurements on bulk cell population, for rapid capture and differentiation of the cancer cells according to their metastatic state. Our results revealed a significant correlation between the various MDA-MB-231 metastatic subtypes and their respective dielectrophoretic and dielectric properties. Notably, cells with the highest metastatic potential exhibited the highest membrane capacitance 16.88 ± 3.24 mF m-2, followed by the less metastatic cell subtypes with membrane capacitances below 14.3 ± 2.54 mF m-2. In addition, highly metastatic cells exhibited lower crossover frequency (25 ± 1 kHz) compared to the less metastatic subtypes (≥27 ± 1 kHz), an important characteristic for cell sorting. Finally, EIS measurements showed distinct double layer capacitance (CDL) values at 1 kHz between the metastatic subgroups, confirming unique dielectric and dielectrophoretic properties correlated with the metastatic state of the cell. Our findings underscore the potential of DEPIS as a non-invasive and rapid analytical tool, offering insights into cancer biology and facilitating the development of personalized therapeutic interventions tailored to distinct metastatic stages.

A Narrative Review on the Clinical Utility of Electrical Impedance Spectroscopy for Diagnosing High-Grade Cervical Intraepithelial Neoplasia

Colposcopy constitutes a pivotal step in the diagnosis and management of cervical intraepithelial neoplasia; nevertheless, the method has several inherent and external limitations. Electrical impedance spectroscopic (EIS) has been among the adjuncts that have been developed to increase the diagnostic accuracy of colposcopy. EIS is based on the principle that the trajectory of electrical current alters depending on the consistency of the tissues. In the present study, we investigate the diagnostic accuracy and clinical utility of EIS by means of searching the available evidence. Our search yielded 17 articles during the period 2005-2023. Subsequently, we focused on the performance metrics of the included studies. The general concept is that EIS, in combination with colposcopy, is a method with increased sensitivity and specificity in detecting high-grade cervical intraepithelial neoplasia as compared to colposcopy alone. However, we documented a heterogeneous distribution of these and other metrics, including the positive predictive value, the negative predictive value, and the area under the receiver operating characteristic curve (AUC). Additionally, we located potential confounders that might hamper the measurements of EIS and, as such, warrant further investigation in future research. We conclude that future studies should be directed towards randomized multicentric trials, whereas the advent of artificial intelligence might improve the diagnostic accuracy of the method by helping incorporate a large amount of data.

Improved Configurations for 3D Acoustoelectric Tomography With a Minimal Number of Electrodes

OBJECTIVE

Acoustoelectric tomography (AET) is a hybrid imaging technique combining ultrasound and electrical impedance tomography (EIT). It exploits the acoustoelectric effect (AAE): an US wave propagating through the medium induces a local change in conductivity, depending on the acoustoelectric properties of the medium. Typically, AET image reconstruction is limited to 2D and most cases employ a large number of surface electrodes.

METHODS

This article investigates the detectability of contrasts in AET. We characterize the AEE signal as a function of the medium conductivity and electrode placement, using a novel 3D analytical model of the AET forward problem. The proposed model is compared to a finite element method simulation.

RESULTS

In a cylindrical geometry with an inclusion contrast of 5 times the background and two pairs of electrodes, the maximum, minimum, and mean suppression of the AEE signal are 68.5%, 3.12%, and 49.0%, respectively, over a random scan of electrode positions. The proposed model is compared to a finite element method simulation and the minimum mesh sizes required successfully model the signal is estimated.

CONCLUSION

We show that the coupling of AAE and EIT leads to a suppressed signal and the magnitude of the reduction is a function of geometry of the medium, contrast and electrode locations.

SIGNIFICANCE

This model can aid in the reconstruction of AET images involving a minimum number of electrodes to determine the optimal electrode placement.

Detection of High-Grade Cervical Intraepithelial Neoplasia by Electrical Impedance Spectroscopy in Women Diagnosed with Low-Grade Cervical Intraepithelial Neoplasia in Cytology

The authors attempt to address the importance of timely detection and management of cervical intraepithelial neoplasia (CIN) to prevent cervical cancer. The study focused on the potential of electrical impedance spectroscopy (EIS) as an adjunct to colposcopy, aiming to enhance the accuracy of identifying high-grade cervical lesions. Colposcopy, a widely used technique, exhibited variable sensitivity in detecting high-grade lesions, which relies on the expertise of the operator. The study's primary objective is to evaluate the effectiveness of combining colposcopy with EIS in detecting high-grade cervical lesions among patients initially diagnosed with low-grade CIN based on cytology. We employed a cross-sectional observational design, recruiting 101 women with abnormal cervical cytology results. The participants underwent colposcopy with acetic acid and subsequent EIS using the ZedScan device. The ZedScan results are categorized into color-coded probability levels, with red indicating the highest likelihood of high-grade squamous intraepithelial lesions (HSIL) occurrence. Results revealed that ZedScan exhibits a sensitivity rate of 89.5% and a specificity rate of 84% for detecting high-grade lesions. Colposcopy, on the other hand, recorded a sensitivity rate of 85.5% and a specificity rate of 92%. The agreement rate between ZedScan and biopsy is 79.2%, as indicated by a kappa coefficient of 0.71, while the agreement rate between colposcopy and biopsy is 74.3%, with a kappa coefficient of 0.71.

Tissue-Engineered Cochlear Fibrosis Model Links Complex Impedance to Fibrosis Formation for Cochlear Implant Patients

Cochlear implants are a life-changing technology for those with severe sensorineural hearing loss, partially restoring hearing through direct electrical stimulation of the auditory nerve. However, they are known to elicit an immune response resulting in fibrotic tissue formation in the cochlea that is linked to residual hearing loss and suboptimal outcomes. Intracochlear fibrosis is difficult to track without postmortem histology, and no specific electrical marker for fibrosis exists. In this study, a tissue-engineered model of cochlear fibrosis is developed following implant placement to examine the electrical characteristics associated with fibrotic tissue formation around electrodes. The model is characterized using electrochemical impedance spectroscopy and an increase in the resistance and a decrease in capacitance of the tissue using a representative circuit are found. This result informs a new marker of fibrosis progression over time that is extractable from voltage waveform responses, which can be directly measured in cochlear implant patients. This marker is tested in a small sample size of recently implanted cochlear implant patients, showing a significant increase over two postoperative timepoints. Using this system, complex impedance is demonstrated as a marker of fibrosis progression that is directly measurable from cochlear implants to enable real-time tracking of fibrosis formation in patients, creating opportunities for earlier treatment intervention to improve cochlear implant efficacy.

Bioimpedance: A Tool for Screening Oral Cancer - A Systematic Review

Objective

The successful management of cancer depends on proper screening and treatment methods. Bioimpedance spectroscopy (BIS) is an established technique in detecting breast cancer, cervical cancer, and prostate cancer. This systematic review sought to investigate the current evidence regarding the clinical application of bioimpedance in the detection of oral squamous cell carcinoma and oral potentially malignant disorders.

Study Design

The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed to perform this review. Electronic databases such as PubMed, MEDLINE, Embase, EBSCOhost, and Google Scholar were searched till March 2022. Articles published in the English medical literature on human participants report on the application of BIS in the screening of precancerous and cancerous lesions. The primary endpoint was defined as the ability to differentiate between normal and cancerous tissue.

Results

A total of 6754 articles were identified; of which 481 were eligible for inclusion. Only five articles met the eligibility criteria and were included in the study. Qualitative analysis for each study was done to assess the data provided. All the studies demonstrated a significant divergence in BIS metrics between cancerous and normal tissue at 20 Hz and 50 KHz.

Conclusion

Bioimpedance appears to be a promising novel tool for the detection of various malignancies which can be used in community screening due to its noninvasiveness and portability.

Electrical Impedance Tomography: From the Traditional Design to the Novel Frontier of Wearables

Electrical impedance tomography (EIT) is a medical imaging technique based on the injection of a current or voltage pattern through electrodes on the skin of the patient, and on the reconstruction of the internal conductivity distribution from the voltages collected by the electrodes. Compared to other imaging techniques, EIT shows significant advantages: it does not use ionizing radiation, is non-invasive and is characterized by high temporal resolution. Moreover, its low cost and high portability make it suitable for real-time, bedside monitoring. However, EIT is also characterized by some technical limitations that cause poor spatial resolution. The possibility to design wearable devices based on EIT has recently given a boost to this technology. In this paper we reviewed EIT physical principles, hardware design and major clinical applications, from the classical to a wearable setup. A wireless and wearable EIT system seems a promising frontier of this technology, as it can both facilitate making clinical measurements and open novel scenarios to EIT systems, such as home monitoring.

Electrical Impedance Analysis for Lung Cancer: A Prospective, Multicenter, Blind Validation Study

Hypothesis

Patients with cancer have different impedances or conductances than patients with benign normal tissue; thus, we can apply electrical impedance analysis (EIA) to identify patients with cancer.

Method

To evaluate EIA’s efficacy and safety profile in diagnosing pulmonary lesions, we conducted a prospective, multicenter study among patients with pulmonary lesions recruited from 4 clinical centers (Zhongshan Hospital Ethics Committee, Approval No. 2015-16R and 2017-035(3). They underwent EIA to obtain an Algorithm Composite Score or ‘Prolung Index,’ PI. The classification threshold of 29 was first tested in an analytical validation set of 144 patients and independently validated in a clinical validation set of 418 patients. The subject’s final diagnosis depended on histology and a 2-year follow-up.

Results

In total, 418 patients completed the entire protocol for clinical validation, with 186 true positives, 145 true negatives, 52 false positives, and 35 false negatives. The sensitivity, specificity, and diagnostic yield were 84% (95% CI 79.3%-89.0%), 74% (95% CI 67.4%-79.8%), and 79% (95%CI 75.3%-83.1%), respectively, and did not differ according to age, sex, smoking history, body mass index, or lesion types. The sensitivity of small lesions was comparable to that of large lesions (p = 0.13). Four hundred eighty-four patients who underwent the analysis received a safety evaluation. No adverse events were considered to be related to the test.

Conclusion

Electrical impedance analysis is a safe and efficient tool for risk stratification of pulmonary lesions, especially for patients with a suspicious lung lesion.

Tissue Characterization Using an Electrical Bioimpedance Spectroscopy-Based Multi-Electrode Probe to Screen for Cervical Intraepithelial Neoplasia

The successful management of cervical intraepithelial neoplasia (CIN) with proper screening and treatment methods could prevent cervical cancer progression. We propose a bioimpedance spectroscopic measurement device and a multi-electrode probe as an independent screening tool for CIN. To evaluate the performance of this screening method, we enrolled 123 patients, including 69 patients with suspected CIN and 54 control patients without cervical dysplasia who underwent a hysterectomy for benign disease (non-CIN). Following conization, the electrical properties of the excised cervical tissue were characterized using an electrical bioimpedance spectroscopy-based multi-electrode probe. Twenty-eight multifrequency voltages were collected through the two concentric array electrodes via a sensitivity-optimized measurement protocol based on an electrical energy concentration method. The electrical properties of the CIN and non-CIN groups were compared with the results of the pathology reports. Reconstructed resistivity tended to decrease in the CIN and non-CIN groups as frequency increased. Reconstructed resistivity from 625 Hz to 50 kHz differed significantly between the CIN and non-CIN groups (p < 0.001). Using 100 kHz as the reference, the difference between the CIN and non-CIN groups was significant. Based on the difference in reconstructed resistivity between 100 kHz and the other frequencies, this method had a sensitivity of 94.3%, a specificity of 84%, and an accuracy of 90% in CIN screening. The feasibility of noninvasive CIN screening was confirmed through the difference in the frequency spectra evaluated in the excised tissue using the electrical bioimpedance spectroscopy-based multi-electrode screening probe.

[Organoids for the advancement of intraoperative diagnostic procedures]

In the context of cancer surgery, there is always a trade-off between oncological safety and preservation of function. This is especially true in pelvic surgery due to the close relationship to the pelvic floor muscles, blood supply and nerves. Currently, risk models, preoperative imaging, the surgeon's assessment, and the intraoperative frozen section serve as the basis for decision-making. New imaging techniques and standardization in frozen section have significantly improved this in recent years. However, limitations remain due to time delays as well as more difficult correct anatomical assignment in the follow-up. Alternative intraoperative techniques may overcome this limitation in the future. Patient-derived organoids have emerged as an important new research vehicle in recent years. They are based on tumor stem cells that, under special culture conditions, form three-dimensional replicas of the original tissue. This makes them ideally suited for testing individual system therapies but also as a validation technique for new intraoperative diagnostic procedures. The Research Training Group 2543/I, which is funded by the German Research Foundation, is researching the potential of new diagnostic methods in an interdisciplinary team regarding validation in addition to intraoperative frozen sections.

Correlation between electrical characteristics and biomarkers in breast cancer cells

Both electrical properties and biomarkers of biological tissues can be used to distinguish between normal and diseased tissues, and the correlations between them are critical for clinical applications of conductivity (σ) and permittivity (ε); however, these correlations remain unknown. This study aimed to investigate potential correlations between electrical characteristics and biomarkers of breast cancer cells (BCC). Changes in σ and ε of different components in suspensions of normal cells and BCC were analyzed in the range of 200 kHz-5 MHz. Pearson's correlation coefficient heatmap was used to investigate the correlation between σ and ε of the cell suspensions at different stages and biomarkers of cell growth and microenvironment. σ and ε of the cell suspensions closely resembled those of tissues. Further, the correlations between Na⁺/H⁺ exchanger 1 and ε and σ of cell suspensions were extremely significant among all biomarkers (p_ε < 0.001; p_σ < 0.001). There were significant positive correlations between cell proliferation biomarkers and ε and σ of cell suspensions (p_ε/σ < 0.05). The microenvironment may be crucial in the testing of cellular electrical properties. ε and σ are potential parameters to characterize the development of breast cancer.