Classification of breast tissue by electrical impedance spectroscopy

Impedance spectroscopy--an outstanding method for label-free and real-time discrimination between brain and tumor tissue in vivo

Until today, brain tumors especially glioblastoma are difficult to treat and therefore, results in a poor survival rate of 0-14% over five years. To overcome this problem, the development of novel therapeutics as well as optimization of neurosurgical procedures to remove the tumor tissue are subject of intensive research. The main problem of the tumor excision, as the primary clinical intervention is the diffuse infiltration of the tumor cells in unaltered brain tissue that complicates the complete removal of residual tumor cells. In this context, we are developing novel approaches for the label-free discrimination between tumor tissue and unaltered brain tissue in real-time during the surgical process. Using our impedance spectroscopy-based measurement system in combination with flexible microelectrode arrays we could successfully demonstrate the discrimination between a C6-glioma and unaltered brain tissue in an in vivo rat model. The analysis of the impedance spectra revealed specific impedance spectrum shape characteristics of physiologic neuronal tissue in the frequency range of 10-500 kHz that were significantly different from the tumor tissue. Moreover, we used an adapted equivalent circuit model to get a deeper understanding for the nature of the observed effects. The impedimetric label-free and real-time discrimination of tumor from unaltered brain tissue offers the possibility for the implementation in surgical instruments to support surgeons to decide, which tissue areas should be removed and which should be remained.

Potential of MREIT conductivity imaging to detect breast cancer: experimental and numerical simulation studies

The conductivity values of cancerous tissues in the breast are significantly higher than those of surrounding normal tissues. Breast imaging using MREIT (Magnetic Resonance Electrical Impedance Tomography) may provide a new noninvasive way of detecting breast cancer in its early stage. In breast MREIT, the conductivity image quality highly depends on the amount of injected currents assuming a certain signal-to-noise ratio (SNR) of an MRI scanner. The injected current should not produce any significant adverse effect especially on the nerve conduction system of the heart and still distinguish a small cancerous anomaly inside the breast. In this paper, we present results of experimental and numerical simulation studies of breast MREIT. From breast phantom experiments, we evaluated practical amounts of noise in measured magnetic flux density data. We built a realistic three-dimensional model of the human breast connected to a simplified model of the chest including the heart. We performed numerical simulations of various scenarios in breast MREIT including different amplitudes of injected currents and predicted SNRs of MR images related with imaging parameters. Simulation results are promising to show that we may detect a cancerous anomaly in the breast while restricting the maximal current density inside the heart below a level of nerve excitation.

Three-dimensional noninvasive ultrasound Joule heat tomography based on the acousto-electric effect using unipolar pulses: a simulation study

Electrical properties of biological tissues are highly sensitive to their physiological and pathological status. Thus it is of importance to image electrical properties of biological tissues. However, spatial resolution of conventional electrical impedance tomography (EIT) is generally poor. Recently, hybrid imaging modalities combining electric conductivity contrast and ultrasonic resolution based on the acousto-electric effect has attracted considerable attention. In this study, we propose a novel three-dimensional (3D) noninvasive ultrasound Joule heat tomography (UJHT) approach based on the acousto-electric effect using unipolar ultrasound pulses. As the Joule heat density distribution is highly dependent on the conductivity distribution, an accurate and high-resolution mapping of the Joule heat density distribution is expected to give important information that is closely related to the conductivity contrast. The advantages of the proposed ultrasound Joule heat tomography using unipolar pulses include its simple inverse solution, better performance than UJHT using common bipolar pulses and its independence of a priori knowledge of the conductivity distribution of the imaging object. Computer simulation results show that using the proposed method, it is feasible to perform a high spatial resolution Joule heat imaging in an inhomogeneous conductive media. Application of this technique on tumor scanning is also investigated by a series of computer simulations.

High density trans-admittance mammography development and preliminary phantom tests

Background

Malignant breast tumor tissue has a significantly different electrical impedance spectrum than surrounding normal tissues. This has led to the development of impedance imaging as a supplementary or alternative method to X-ray mammography for screening and assessment of breast cancers. However low spatial resolution and poor signal to noise ratio has limited the clinical application.

Methods

In order to improve spatial resolution we developed a trans-admittance mammography (TAM) system including an array of 60×60 current sensing electrodes. We adopted a similar setup to X-ray mammography where the breast is situated between two holding plates. The top plate is a large solid metal electrode for applying a sinusoidal voltage over a range of frequencies from 50 Hz to 500 kHz. The bottom plate has 3600 current sensing electrodes that are kept at the ground potential. Currents are generated from the top voltage-applying electrode and spread throughout the breast, entering the TAM system through the array of current sensing electrodes on the bottom plate. The TAM system measures the exit currents through 6 switching modules connected to 600 electrodes each. Each switching module is connected to 12 ammeter channels which are switched sequentially to 50 of the 600 electrodes each measurement time. Each ammeter channel is comprised of a current-to-voltage converter, a gain amplifier, filters, an analog to digital converter, and a digital phase sensitive demodulator.

Results

We found an average noise level of 38 nA, amplitude stability of less than 0.2%, crosstalk of better than -60 dB and 70 dB signal to noise ratio over all channels and operating frequencies. Images were obtained in time difference and frequency difference modes in a saline phantom.

Conclusion

We describe the design, construction, and calibration of a high density TAM system in detail. Successful high resolution time and frequency difference images showed regions of interest with the expected admittivity changes in the frequency spectrum.

Breast EIT using a new projected image reconstruction method with multi-frequency measurements

We propose a new method to produce admittivity images of the breast for the diagnosis of breast cancer using electrical impedance tomography(EIT). Considering the anatomical structure of the breast, we designed an electrode configuration where current-injection and voltage-sensing electrodes are separated in such a way that internal current pathways are approximately along the tangential direction of an array of voltage-sensing electrodes. Unlike conventional EIT imaging methods where the number of injected currents is maximized to increase the total amount of measured data, current is injected only twice between two pairs of current-injection electrodes attached along the circumferential side of the breast. For each current injection, the induced voltages are measured from the front surface of the breast using as many voltage-sensing electrodes as possible. Although this electrode configurational lows us to measure induced voltages only on the front surface of the breast,they are more sensitive to an anomaly inside the breast since such an injected current tends to produce a more uniform internal current density distribution. Furthermore, the sensitivity of a measured boundary voltage between two equipotential lines on the front surface of the breast is improved since those equipotential lines are perpendicular to the primary direction of internal current streamlines. One should note that this novel data collection method is different from those of other frontal plane techniques such as the x-ray projection and T-scan imaging methods because we do not get any data on the plane that is perpendicular to the current flow. To reconstruct admittivity images using two measured voltage data sets, a new projected image reconstruction algorithm is developed. Numerical simulations demonstrate the frequency-difference EIT imaging of the breast. The results show that the new method is promising to accurately detect and localize small anomalies inside the breast.

Detection of prostate cancer by radio-frequency near-field spectroscopy in radical prostatectomy ex vivo specimens

BACKGROUND

The aim of radical prostatectomy (RP) is the complete removal of the prostate gland with negative surgical margins. The presence of cancer at the surgical margin is associated with higher probability of disease progression. Current methods of intraoperative margin assessment are inaccurate or time-consuming.The study goal was to evaluate the ability of a novel device (Dune Medical Devices) to differentiate between cancer and BPH.

METHODS

A total of 49 patients undergoing RP in four medical centers between November 2007 and May 2008 were enrolled in this study.The device was applied to numerous intra- and extra-capsular sites of freshly excised RP specimens. Measurement sites were accurately marked and analyzed histologically. The ability of the device to differentiate between malignant and nonmalignant sites was assessed.

RESULTS

A total of 15,156 measurements from 45 patients were analyzed. Differentiation of the intra-capsular malignant sites from extra-capsular nonmalignant sites (bladder neck and apex regions) depends on the cancer feature size. Differentiation was achieved with sensitivity and specificity of 93.6 (95% confidence interval (CI): 88-98) and 94.1 (95% CI: 93-95), respectively, at feature sizes at or >0.8 mm in diameter. The device was able to discriminate between all intra-capsular malignant (with feature sizes down to a few cells) and nonmalignant measurement sites, with sensitivity and specificity of 80.8 (95% CI: 73-87) and 68.4 (95% CI: 67-69), respectively.

CONCLUSIONS

First results from a radio-frequency near-field spectroscopy sensor look promising for differentiation between cancer and benign prostate tissue. The sensor's dimensions (radius of ~ 1 mm) and design enable use in open, laparoscopic and robotic RP to evaluate the surgical margins intraoperatively.

Review of electromagnetic techniques for breast cancer detection

Breast cancer is anticipated to be responsible for almost 40,000 deaths in the USA in 2011. The current clinical detection techniques suffer from limitations which motivated researchers to investigate alternative modalities for the early detection of breast cancer. This paper focuses on reviewing the main electromagnetic techniques for breast cancer detection. More specifically, this work reviews the cutting edge research in microwave imaging, electrical impedance tomography, diffuse optical tomography, microwave radiometry, biomagnetic detection, biopotential detection, and magnetic resonance imaging (MRI). The goal of this paper is to provide biomedical researchers with an in-depth review that includes all main electromagnetic techniques in the literature and the latest progress in each of these techniques.

Breast tissue image classification based on Semi-supervised Locality Discriminant Projection with Kernels

Breast tissue classification is an important and effective way for computer aided diagnosis of breast cancer. We present Semi-supervised Locality Discriminant Projections with Kernels for breast cancer classification. The contributions of this work lie in: 1) Semi-supervised learning is used into Locality Preserving Projections (LPP) to enhance its performance using side-information together with the unlabelled training samples, while current algorithms only consider the side-information but ignoring the unlabeled training samples. 2) Kernel trick is applied into Semi-supervised LPP to improve its ability in the nonlinear classification. 3) The framework of breast cancer classification with Semi-supervised LPP with kernels is presented. Many experiments are implemented on four breast tissue databases to testify and evaluate the feasibility and affectivity of the proposed scheme.

A software framework for building biomedical machine learning classifiers through grid computing resources

This paper describes the BiomedTK software framework, created to perform massive explorations of machine learning classifiers configurations for biomedical data analysis over distributed Grid computing resources. BiomedTK integrates ROC analysis throughout the complete classifier construction process and enables explorations of large parameter sweeps for training third party classifiers such as artificial neural networks and support vector machines, offering the capability to harness the vast amount of computing power serviced by Grid infrastructures. In addition, it includes classifiers modified by the authors for ROC optimization and functionality to build ensemble classifiers and manipulate datasets (import/export, extract and transform data, etc.). BiomedTK was experimentally validated by training thousands of classifier configurations for representative biomedical UCI datasets reaching in little time classification levels comparable to those reported in existing literature. The comprehensive method herewith presented represents an improvement to biomedical data analysis in both methodology and potential reach of machine learning based experimentation.

MREIT with SENSE acceleration using a dedicated RF coil design

We have adapted a SENSE-accelerated imaging technique to magnetic resonance electrical impedance tomography (MREIT) in order to acquire data faster or improve spatial resolution without increasing the data acquisition time. We also designed and optimized an eight-channel, dedicated phased array coil for this application. The RF coil was designed as two planar arrays so that the open sides could accommodate the MREIT electrodes. A quasi-intrinsic decoupling scheme was used to minimize couplings between coil elements, and a restricted geometry optimization was applied to achieve high and uniform SNR within a given coil geometry and animal size. The impact of variability in the size of animals was also investigated in the optimization. This coil geometry provided approximately three times higher SNR at the center of a phantom when compared to a transmit/receive birdcage coil designed for MREIT of small animals. Therefore, the SNR was superior to the data acquired with volume coils even with three times SENSE acceleration. Both magnitude images and MREIT data were acquired from phantoms with and without SENSE acceleration, and the results were compared. The phantom studies demonstrated that conductivity maps can be reconstructed from MREIT data acquired with three times SENSE acceleration and that no discernible artifacts were observed when accelerated data acquisition was compared to non-accelerated data.

The correlation of in vivo and ex vivo tissue dielectric properties to validate electromagnetic breast imaging: initial clinical experience

Electromagnetic (EM) breast imaging provides low-cost, safe and potentially a more specific modality for cancer detection than conventional imaging systems. A primary difficulty in validating these EM imaging modalities is that the true dielectric property values of the particular breast being imaged are not readily available on an individual subject basis. Here, we describe our initial experience in seeking to correlate tomographic EM imaging studies with discrete point spectroscopy measurements of the dielectric properties of breast tissue. The protocol we have developed involves measurement of in vivo tissue properties during partial and full mastectomy procedures in the operating room (OR) followed by ex vivo tissue property recordings in the same locations in the excised tissue specimens in the pathology laboratory immediately after resection. We have successfully applied all of the elements of this validation protocol in a series of six women with cancer diagnoses. Conductivity and permittivity gauged from ex vivo samples over the frequency range 100 Hz-8.5 GHz are found to be similar to those reported in the literature. A decrease in both conductivity and permittivity is observed when these properties are gauged from ex vivo samples instead of in vivo. We present these results in addition to a case study demonstrating how discrete point spectroscopy measurements of the tissue can be correlated and used to validate EM imaging studies.

Regional admittivity spectra with tomosynthesis images for breast cancer detection: preliminary patient study

It has been known for some time that many tumors have a significantly different conductivity and permittivity from surrounding normal tissue. This high "contrast" in tissue electrical properties, occurring between a few kilohertz and several megahertz, may permit differentiating malignant from benign tissues. Here we show the ability of electrical impedance spectroscopy (EIS) to roughly localize and clearly distinguish cancers from normal tissues and benign lesions. Localization of these lesions is confirmed by simultaneous, in register digital breast tomosynthesis (DBT) mammography or 3-D mammograms.

Noninvasive imaging of bioimpedance distribution by means of current reconstruction magnetic resonance electrical impedance tomography

We have developed a novel magnetic resonance electrical impedance tomography (MREIT) algorithm-current reconstruction MREIT algorithm-for noninvasive imaging of electrical impedance distribution of a biological system using only one component of magnetic flux density. The newly proposed algorithm uses the inverse of Biot-Savart Law to reconstruct the current density distribution, and then, uses a modified J-substitution algorithm to reconstruct the conductivity image. A series of computer simulations has been conducted to evaluate the performance of the proposed current reconstruction MREIT algorithm with simulation settings for breast cancer imaging applications, with consideration of measurement noise, current injection strength, size of simulated tumors, spatial resolution, and position dependency. The present simulation results are highly promising, demonstrating the high spatial resolution, high accuracy in conductivity reconstruction, and robustness against noise of the proposed algorithm for imaging electrical impedance of a biological system. The present MREIT method may have potential applications to breast cancer imaging and imaging of other organs.

A broadband high-frequency electrical impedance tomography system for breast imaging

Bio-electric impedance signatures arise primarily from differences in cellular morphologies within an organ and can be used to differentiate benign and malignant pathologies, specifically in the breast. Electrical impedance tomography (EIT) is an imaging modality that determines the impedance distribution within tissue and has been used in prior work to map the electrical properties of breast at signal frequencies ranging from a few kHz to 1 MHz. It has been suggested that by extending the frequency range, additional information of clinical significance may be obtained. We have, therefore, developed a new EIT system for breast imaging which covers the frequency range from 10 kHz to 10 MHz. The instrument developed here is a distributed processor tomograph with 64 channels, capable of generating and measuring voltages and currents. Electrical benchmarking has shown the system to have a SNR greater than 94 dB up to 2 MHz, 90 dB up to 7 MHz, and 65 dB at 10 MHz. In addition, the system measures impedances to an accuracy of 99.7 % and has channel-to-channel variations of less than 0.05 %. Phantom imaging has demonstrated the ability to image across the entire frequency range in both single- and multiplane configurations. Further, 96 women have participated safely in breast exams with the system and the associated conductivity spectra obtained from 3-D image reconstructions range from 0.0237 S/m at 10 kHz to 0.2174 S/m at 10 MHz. These findings are consistent with impedance values reported in the literature.

Electrical impedance spectroscopy of benign and malignant prostatic tissues

PURPOSE

The specificity of current screening methods for prostate cancer is limited and it results in approximately 75% to 80% of patients who undergo biopsy having findings negative for cancer. We used electrical impedance spectroscopy to evaluate how significantly the electrical properties of benign and malignant prostatic tissues differ with the goal of providing clinicians with a new biomarker to aid in diagnosis.

MATERIALS AND METHODS

We collected freshly excised prostates from 14 men immediately following radical prostatectomy. The prostates were sectioned into 3 mm slices. Electrical property measurements of conductivity and relative permittivity were recorded from each slice using a coaxially configured probe over the frequency range of 1 kHz to 1 MHz. The area probed was marked so that following tissue fixation and slide preparation histological assessment could be correlated directly with the recorded electrical impedance spectroscopy spectra.

RESULTS

Prostatic adenocarcinoma, benign prostatic hyperplasia, nonhyperplastic glandular tissue and stroma were the primary tissue types probed with electrical impedance spectroscopy. Conductivity ranged from 0.093 S/m at 1 kHz to 0.277 S/m at 1 MHz. Relative permittivity ranged from 8.5 x 10(5) at 1 kHz down to 1.3 x 10(3) at 1 MHz. There were significant conductivity differences between cancer and stroma at all frequencies (p <0.01). There were significant permittivity differences between cancer and benign prostatic hyperplasia at frequencies greater that 92 kHz (p <0.01). Significant correlations were observed between electrical properties, and the concentration of stromal and glandular tissues present in the tissue area histologically assessed.

CONCLUSIONS

The electrical properties of benign and malignant prostate tissues differ significantly. This should be considered for use as a diagnostic tool. The differences observed between cancer and benign prostatic hyperplasia are especially important since current screening methods do not reliably differentiate between the 2 conditions.

Electrical Impedance Spectroscopy of the Human Prostate

Tissue electrical impedance is a function of its architecture and has been used to differentiate normal and cancer tissues in a variety of organs including breast, cervix, skin, and bladder. This paper investigates the possibility of differentiating normal and malignant prostate tissue using bioimpedance spectra. A probe was designed to measure impedance spectra over the range of 10 kHz to 1 MHz. The probe was fully characterized using discrete loads and saline solutions of different concentrations. Impedance spectra of five ex vivo prostates were measured in the operating room immediately following radical prostatectomy. Wilcoxon signed-rank tests were used to compare the normal and malignant findings. The impedance probe had a signal-to-noise ratio (SNR) > 84 dB across the entire spectrum and measured a tissue volume of approximately 46 mm(3). At 10 kHz, prostate conductivity (or) ranged from 0.232 S/m to 0.310 S/m for tumor and from 0.238 S/m to 0.901 S/m for normal tissue. At 1 MHz the ranges were 0.301 S/m to 0.488 S/m for tumor and 0.337 S/m to 1.149 S/m for normal. Prostate permittivity (epsilonr) ranged from 6.64 x10(4) to 1.25 x 10(5) for tumor and from 9.08 x 10(4) to 4.49 x 10(5) for normal tissues at 10 kHz. And, at 1 MHz the er ranges were 9.23 x 10(2) to 1.88 x 10(3) for tumor and 1.16 x 10(3) to 2.18 x 10(3) for normal tissue. Both sigma and epsilonr of tumor tissue were found to be significantly lower than that of normal tissue (P < 0.0001). Conductivity and permittivity are both higher in normal prostate tissues than they are in malignant tissue making them suitable parameters for tissue differentiation. This is in agreement with trends observed in other tissues reported in much of the literature. Expanded studies are needed to further validate this finding and to explore the biological mechanism responsible for generating the results.

Feasibility of breast cancer lesion detection using a multi-frequency trans-admittance scanner (TAS) with 10 Hz to 500 kHz bandwidth

We describe a new multi-frequency technique for breast cancer detection. Applying a constant voltage with multiple sinusoidal frequencies between a reference electrode on a distal part of a patient and a scan probe placed on the breast, we measure exit currents from an array of electrodes inside the probe that are kept at the ground potential. The distribution of measured exit currents is called the trans-admittance map and the instrument is called the trans-admittance scanner (TAS). We assume a three-dimensional homogeneous domain including an internal lesion with a complex conductivity different from that of the background. Mathematically analyzing the multi-frequency trans-admittance map obtained on the surface of the domain, we found that both conductivity and permittivity ratios between the background and the lesion are crucial in extracting any useful information about the lesion from the map. Choosing two frequencies in the range of 10 Hz to 500 kHz with one significantly lower than the other and assuming that conductivity values of the background and the lesion do not change much from the low to high frequency, the lesion underneath the probe can be detected only when the conductivity ratio between the background and the lesion is different from the permittivity ratio between the background and the lesion at the chosen high frequency. Results of numerical simulations and saline phantom experiments using a developed TAS system are well matched with the mathematical analysis. The biggest advantage of this multi-frequency technique is that we do not need separately measured reference data in the absence of any lesion. We suggest future studies of a more sophisticated lesion detection algorithm based on the analysis and findings described in this paper.

A compensated radiolucent electrode array for combined EIT and mammography

Electrical impedance tomography (EIT), a non-invasive technique used to image the electrical conductivity and permittivity within a body from measurements taken on the body's surface, could be used as an indicator for breast cancer. Because of the low spatial resolution of EIT, combining it with other modalities may enhance its utility. X-ray mammography, the standard screening technique for breast cancer, is the first choice for that other modality. Here, we describe a radiolucent electrode array that can be attached to the compression plates of a mammography unit enabling EIT and mammography data to be taken simultaneously and in register. The radiolucent electrode array is made by depositing thin layers of metal on a plastic substrate. The structure of the array is presented along with data showing its x-ray absorbance and electrical properties. The data show that the electrode array has satisfactory radiolucency and sufficiently low resistance.

A reconstruction algorithm for breast cancer imaging with electrical impedance tomography in mammography geometry

The conductivity and permittivity of breast tumors are known to differ significantly from those of normal breast tissues, and electrical impedance tomography (EIT) is being studied as a modality for breast cancer imaging to exploit these differences. At present, X-ray mammography is the primary standard imaging modality used for breast cancer screening in clinical practice, so it is desirable to study EIT in the geometry of mammography. This paper presents a forward model of a simplified mammography geometry and a reconstruction algorithm for breast tumor imaging using EIT techniques. The mammography geometry is modeled as a rectangular box with electrode arrays on the top and bottom planes. A forward model for the electrical impedance imaging problem is derived for a homogeneous conductivity distribution and is validated by experiment using a phantom tank. A reconstruction algorithm for breast tumor imaging based on a linearization approach and the proposed forward model is presented. It is found that the proposed reconstruction algorithm performs well in the phantom experiment, and that the locations of a 5-mm-cube metal target and a 6-mm-cube agar target could be recovered at a target depth of 15 mm using a 32 electrode system.

Magnetic resonance electrical impedance tomography of the breast: a simulation study on basic imaging setup

Magnetic resonance electrical impedance tomography (MREIT) has been developed as a new medical imaging modality providing high-resolution conductivity and current density images. This paper is about MREIT of the breast. To show the feasibility of breast MREIT, we carried numerical simulations and breast phantom experiments. We found that an anomaly with 4 mm diameter can be visualized in a reconstructed conductivity image using 5 mA injection current if the SNR of the corresponding MR magnitude image is at least 150. We propose a desirable electrode configuration and show our first experimental results of the breast MREIT. Developing an RF coil for the breast MREIT, we plan to conduct various experimental studies including tissue phantoms.

In vivo EIS characterization of tumour tissue properties is dominated by excess extracellular fluid

Electrical impedance spectroscopy (EIS) is a non-ionizing, non-invasive technique which can be used to detect the presence of malignant tumours based on their electrical properties. Although it has been suggested that the edema which accompanies tumours strongly influences EIS tumour characterization, such information has not, until now, been documented in the literature. Growing intramuscular rodent tumours were imaged using magnetic resonance imaging (MRI) and EIS at several time points post-tumour implantation. The amount of edema associated with the tumours was calculated from the MRI images. Electrical parameters (resistivity, permittivity, fluid index ratio and peak frequency) were extracted from the EIS spectra. Taken together, the resulting electrical parameters strongly indicate that edema is the dominating pathological feature in EIS characterization and can at times conceal the presence of the tumour. Receiver operating characteristic analysis supports these findings.

Basic setup for breast conductivity imaging using magnetic resonance electrical impedance tomography

We present a new medical imaging technique for breast imaging, breast MREIT, in which magnetic resonance electrical impedance tomography (MREIT) is utilized to get high-resolution conductivity and current density images of the breast. In this work, we introduce the basic imaging setup of the breast MREIT technique with an investigation of four different imaging configurations of current-injection electrode positions and pathways through computer simulation studies. Utilizing the preliminary findings of a best breast MREIT configuration, additional numerical simulation studies have been carried out to validate breast MREIT at different levels of SNR. Finally, we have performed an experimental validation with a breast phantom on a 3.0 T MREIT system. The presented results strongly suggest that breast MREIT with careful imaging setups could be a potential imaging technique for human breast which may lead to early detection of breast cancer via improved differentiation of cancerous tissues in high-resolution conductivity images.

Resolution and contrast in magnetic resonance electrical impedance tomography (MREIT) and its application to cancer imaging

It has been reported that the electrical impedance of malignancies could be 20-40 times lower than healthy tissues and benign formations. Therefore, in vivo impedance imaging of suspicious lesions may prove to be helpful in improving the sensitivity and specificity of detecting malignant tumors. Several systems have been developed to map the conductivity distribution inside a volume of tissue, however they suffer from poor spatial resolution because the measurements are taken only from surface electrodes. MRI based impedance imaging (MREIT) is a novel method, in which weak electrical currents are injected into the tissue and the resulting perturbations in the magnetic field are measured using MRI. This method has been shown to provide better resolution compared to previous techniques of impedance imaging because the measurements are taken from inside the object on a uniform grid. Thus, it has the potential to be a useful modality that may detect malignancies earlier. Several phantom imaging experiments were performed to investigate the spatial resolution and dynamic range of contrast of this technique. The method was also applied to a live rat bearing a R3230 AC tumor. Tumor location was identified by contrast enhanced imaging.

A Mathematical Model for Breast Cancer Lesion Estimation: Electrical Impedance Technique Using TS2000 Commercial System

We present a mathematical model to analyze transadmittance data for the detection of breast cancer using TransScan TS2000 commercial system. The model was constructed based on the assumption that a lesion exists near the surface of a breast region. The breast region that is considered as a background is assumed to be homogeneous at least near the surface where we attach a planar array of electrodes. Based on the model, we developed a lesion estimation algorithm utilizing single- or multifrequency transadmittance data. The approximate ratio of two conductivity values for the lesion and background needs to be known to estimate the size of the lesion even though the location estimate does not require this ratio. From the results of numerical simulations with added noise, we suggest better ways of interpreting TS2000 transadmittance images for the detection of breast cancer with improved accuracy. Since this study provides a rigorous mathematical modeling of TS2000 commercial system, it will be possible to apply the technique to lesion estimation problems based on more realistic models of breast regions in future studies.

Electrical impedance spectroscopy of the breast: clinical imaging results in 26 subjects

Electrical impedance spectroscopy (EIS) is a potential, noninvasive technique to image women for breast cancer. Studies have shown characteristic frequency dispersions in the electrical conductivity and permittivity of malignant versus normal tissue. Using a multifrequency EIS system, we imaged the breasts of 26 women. All patients had mammograms ranked using the American College of Radiology (ACR) BIRADS system. Of the 51 individual breasts imaged, 38 were ACR 1 negative, six had ACR 4-5 suspicious lesions, and seven had ACR 2 benign findings such as fibroadenomas or calcifications. A radially translatable circular array of 16 Ag/AgCl electrodes was placed around the breast while the patient lay prone. We applied trigonometric voltage patterns at ten frequencies between 10 and 950 kHz. Anatomically coronal images were reconstructed from this data using nonlinear partial differential equation methods. Typically, ACR 1-rated breasts were interrogated in a single central plane whereas ACR 2-5-rated breasts were imaged in multiple planes covering the region of suspicion. In general, a characteristic homogeneous image emerged for mammographically normal cases while focal inhomogeneities were observed in images from women with malignancies. Using a specific visual criterion, EIS images identified 83% of the ACR 4-5 lesions while 67% were detected using a numerical criterion. Overall, multifrequency electrical impedance imaging appears promising for detecting breast malignancies, but improvements must be made before the method reaches its full potential.

Scanning electric conductivity gradients with ultrasonically-induced Lorentz force

The ions in a fluid element oscillating under the effect of a sound wave in the presence of a magnetic field are submitted to Lorentz force. This gives rise to a bulk current density proportional to the medium's electric conductivity. In the present study, the integrality of this interaction current was collected using a pair of plane electrodes located on opposite sides of the sample. A focused transducer produced ultrasound bursts of 10 micros duration, 500 kHz frequency and 1.5 MPa peak pressure. The magnetic field was created by a purpose-built 0.35 T permanent magnet. Wiener inverse filtering was used to retrieve the system response from the recorded waveforms. The final signal was shown to be proportional to the gradient of sigma/rho along ultrasound propagation axis. Electric conductivity, sigma, predominantly controls this parameter since mass density, rho, does not vary in great proportions in biological media. Rectangular blocks of Agar gel and a layered bacon sample were used as models of biological media. The signals obtained in gel blocks had a longitudinal spatial resolution better than 1 mm. The successive layers of the bacon sample were clearly resolved. The advantages of this new modality for tissue characterization include the permeability of body tissue to magnetic field and ultrasound, the harmlessness of the applied fields and the improved spatial resolution in the measurement of a tissue's electric conductivity distribution.