Multifrequency electrical impedance imaging: preliminary in vivo experience in breast

Breast Cancer Detection Using Low-Frequency Bioimpedance Device

Introduction

Early detection of breast cancer saves lives. Existing detecting techniques are invasive. Electrical bioimpedance is a noninvasive technique and has a high diagnostic potential.

Methods

An impedance value different from the normal can predict a physiological abnormality. The idea is to use a designed bioimpedance device to early detect breast cancer. A low-frequency current (1 kHz, 0.9 mA) is injected to each breast to measure the extracellular resistances. The resistances of the two breasts are then measured, and if there is a significant difference, warning is displayed. The performance was tested on a set of reference resistors, and the validation was done in vitro on (Na+Cl-) solutions and in vivo on a group of forty volunteer women.

Results

The results confirm that the electrical conductivity of an ionic solution is proportional to its concentration. The concentration and the resistance are strongly correlated (correlation coefficient of 0.97). The accuracy and the repeatability of the measures were satisfactory. Early detection means that we can detect small extracellular concentration variations into the breast (from 0.6 g/l). In vivo measurements made it possible to set the threshold at 50 ohm. If the difference between the two measured breast resistances is greater than this threshold, we advise the patient to consult a doctor promptly.

Conclusion

The difference between measured resistances of the right and left breast is a pertinent parameter to early detect the presence of a cancer. The lowest resistance value (RR or RL) can provide information on the breast affected by the cancer (right or left). Various improvements in the system are possible but already the results are encouraging. In the future, this system could be integrated into a bra.

Electrical Impedance Spectroscopy for Monitoring Chemoresistance of Cancer Cells

Electrical impedance spectroscopy (EIS) is an electrokinetic method that allows for the characterization of intrinsic dielectric properties of cells. EIS has emerged in the last decade as a promising method for the characterization of cancerous cells, providing information on inductance, capacitance, and impedance of cells. The individual cell behavior can be quantified using its characteristic phase angle, amplitude, and frequency measurements obtained by fitting the input frequency-dependent cellular response to a resistor-capacitor circuit model. These electrical properties will provide important information about unique biomarkers related to the behavior of these cancerous cells, especially monitoring their chemoresistivity and sensitivity to chemotherapeutics. There are currently few methods to assess drug resistant cancer cells, and therefore it is difficult to identify and eliminate drug-resistant cancer cells found in static and metastatic tumors. Establishing techniques for the real-time monitoring of changes in cancer cell phenotypes is, therefore, important for understanding cancer cell dynamics and their plastic properties. EIS can be used to monitor these changes. In this review, we will cover the theory behind EIS, other impedance techniques, and how EIS can be used to monitor cell behavior and phenotype changes within cancerous cells.

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

BACKGROUND

Electrical impedance technology has been well established for the last 20 years. Recently research has begun to emerge into its potential uses in the detection and diagnosis of pre-malignant and malignant conditions. The aim of this study was to systematically review the clinical application of electrical impedance technology in the detection of malignant neoplasms.

METHODS

A search of Embase Classic, Embase and Medline databases was conducted from 1980 to 22/02/2018 to identify studies reporting on the use of bioimpedance technology in the detection of pre-malignant and malignant conditions. The ability to distinguish between tissue types was defined as the primary endpoint, and other points of interest were also reported.

RESULTS

731 articles were identified, of which 51 reported sufficient data for analysis. These studies covered 16 different cancer subtypes in a total of 7035 patients. As the studies took various formats, a qualitative analysis of each cancer subtype's data was undertaken. All the studies were able to show differences in electrical impedance and/or related metrics between malignant and normal tissue.

CONCLUSIONS

Electrical impedance technology provides a novel method for the detection of malignant tissue, with large studies of cervical, prostate, skin and breast cancers showing encouraging results. Whilst these studies provide promising insights into the potential of this technology as an adjunct in screening, diagnosis and intra-operative margin assessment, customised development as well as multi-centre clinical trials need to be conducted before it can be reliably employed in the clinical detection of malignant tissue.

Review of methods for intraoperative margin detection for breast conserving surgery

Breast conserving surgery (BCS) is an effective treatment for early-stage cancers as long as the margins of the resected tissue are free of disease according to consensus guidelines for patient management. However, 15% to 35% of patients undergo a second surgery since malignant cells are found close to or at the margins of the original resection specimen. This review highlights imaging approaches being investigated to reduce the rate of positive margins, and they are reviewed with the assumption that a new system would need high sensitivity near 95% and specificity near 85%. The problem appears to be twofold. The first is for complete, fast surface scanning for cellular, structural, and/or molecular features of cancer, in a lumpectomy volume, which is variable in size, but can be large, irregular, and amorphous. A second is for full, volumetric imaging of the specimen at high spatial resolution, to better guide internal radiologic decision-making about the spiculations and duct tracks, which may inform that surfaces are involved. These two demands are not easily solved by a single tool. Optical methods that scan large surfaces quickly are needed with cellular/molecular sensitivity to solve the first problem, but volumetric imaging with high spatial resolution for soft tissues is largely outside of the optical realm and requires x-ray, micro-CT, or magnetic resonance imaging if they can be achieved efficiently. In summary, it appears that a combination of systems into hybrid platforms may be the optimal solution for these two very different problems. This concept must be cost-effective, image specimens within minutes and be coupled to decision-making tools that help a surgeon without adding to the procedure. The potential for optical systems to be involved in this problem is emerging and clinical trials are underway in several of these technologies to see if they could reduce positive margin rates in BCS.

Real-time electrical impedance variations in women with and without breast cancer

The chaotic vascular network surrounding malignant tumors leads to pulsatile blood flow patterns that differ from those in benign regions of the breast. This study aimed to determine if high-speed electrical impedance tomography (EIT) is able to detect conductivity changes associated with cyclic blood-volume changes and to gauge the potential of using these signatures to differentiate malignant from benign regions within the breast. EIT imaging of pulsating latex membranes submerged in saline baths provided initial validation of its use for tracking temporally varying conductivities. Nineteen women (10 with cancer, nine without) were imaged with EIT over the course of several heartbeats in synchrony with pulse-oximetry acquisition. Eight parameters ( rs, ϕ(rt,max), rt,max, Plow:full, Phigh:full, Plow:high) relating the conductivity images and pulse-oximeter signatures were extracted and used as a means of comparing malignant and benign regions of the breast. Significant differences between malignant and benign regions of interest were noted in seven of the eight parameters. The maximum correlation between conductivity and pulse-oximeter signals, rt,max , was observed to be the optimal discriminating parameter with a receiver operating characteristic area under the curve of 0.8 and a specificity of 81% at a sensitivity of 77%. Assessing the dynamic conductivity of breast may provide additional clinical utility to that of standard imaging modalities, but further investigation is necessary to better understand the biophysical mechanisms leading to the observed conductivity changes.

An image reconstruction algorithm for 3-D electrical impedance mammography

The Sussex MK4 electrical impedance mammography system is especially designed for 3-D breast screening. It aims to diagnose breast cancer at an early stage when it is most treatable. Planar electrodes are employed in this system. The challenge with planar electrodes is the inaccuracy and poor sensitivity in the vertical direction for 3-D imaging. An enhanced image reconstruction algorithm using a duo-mesh method is proposed to improve the vertical accuracy and sensitivity. The novel part of the enhanced image reconstruction algorithm is the correction term. To evaluate the new algorithm, an image processing based error analysis method is presented, which not only can precisely assess the error of the reconstructed image but also locate the center and outline the center and outline the shape of the objects of interest. Although the enhanced image reconstruction algorithm and the image processing based error analysis method are designed for the Sussex MK4 system, they are applicable to all electrical impedance tomography systems, regardless of the hardware design. To validate the enhanced algorithm, performance results from simulations, phantoms and patients are presented.

High precision Multifrequency Electrical Impedance Tomography System and Preliminary imaging results on saline tank

To establish a high precision data acquisition system for multi-frequency electrical impedance tomography (EIT), a series of methods were introduced. Those methods include building a driving signal with up to four frequency components to diminish the effect of the dynamic change of tissues resistivity, extracting the impedance information by a digital demodulator that can improve the SNR by 8 times. The system that established can work at a wide range from 1.6kHz to 380kHz. Its CMRR is 74dB at 100kHz. The output impedance of current source is 2MΩ at that frequency. And measurement precision on a 100ohm resistor is better than -80dB in full bandwidth. Both the quasi-static and the dynamic imaging results based on a saline tank can reflect the resistivity changes inside the phantom clearly. Therefore, the system was competent in multifrequency EIT research work.

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.

Feasibility of 7 Tesla breast magnetic resonance imaging determination of intrinsic sensitivity and high-resolution magnetic resonance imaging, diffusion-weighted imaging, and (1)H-magnetic resonance spectroscopy of breast cancer patients receiving neoadjuvant therapy

OBJECTIVES

To evaluate the feasibility of 7T breast magnetic resonance imaging (MRI) by determining the intrinsic sensitivity gain compared with 3T in healthy volunteers and to explore clinical application of 7T MRI in breast cancer patients receiving neoadjuvant chemotherapy (NAC).

MATERIALS AND METHODS

In 5 volunteers, the signal-to-noise ratio (SNR) was determined on proton density MRI at 3T using a conventional 4-channel bilateral breast coil and at 7T using a dedicated 2-channel unilateral breast coil, both obtained at identical scan parameters. Subsequently, consecutive breast cancer patients on NAC were included. The 7T breast MRI protocol consisted of diffusion-weighted imaging, 3D high-resolution (450 μm isotropic) T1-weighted fat-suppressed gradient-echo sequences and quantified single voxel (1)H-magnetic resonance spectroscopy. Morphology was scored according to the MRI Breast Imaging-Reporting and Data System (BI-RADS)-lexicon, and the images were compared with 3T and histopathologic findings. Image quality was evaluated using a 5-point scale.

RESULTS

A 5.7-fold higher SNR was measured at 7T than at 3T, which reflects the advantages of a higher field strength and the use of optimized radiofrequency coils. Three breast cancer patients were included and received a total of 13 7T MRI examinations. The image quality of the high-resolution examinations was at least satisfactory, and good to excellent in 9 of the 13 examinations performed. More anatomic detail was depicted at 7T than at 3T. In 1 case, a fat plane between the muscle and tumor was visible at 7T, but not at the clinically performed 3T examination, suggesting that there was no muscle invasion, which was confirmed by pathology. Changes in tumor apparent diffusion coefficient values could be monitored in 2 patients and were found to increase during NAC, consistent with published results from studies at lower field strengths. Apparent diffusion coefficient values increased respectively from 0.33 × 10(-3) mm(2)/s to 1.78 × 10(-3) mm(2)/s after NAC and from 1.20 × 10(-3) mm(2)/s to 1.44 × 10(-3) mm(2)/s during NAC. Choline concentrations as low as 0.77 mMol/kg(water) could be detected. In 1 patient, choline levels showed an overall decrease from 4.2 mMol/kw(water) to 2.6 mMol/kg(water) after NAC and the tumor size decreased correspondingly from 3.9 × 4.1 × 5.6 cm(3) to 2.0 × 2.7 × 2.4 cm(3). All 7T MRI findings were consistent with pathology analysis.

CONCLUSION

Dedicated 7T breast MRI is technically feasible, can provide more SNR than at 3T, and has diagnostic potential.

A fisher information matrix interpretation of the NOSER algorithm in electrical impedance tomography

In this paper, we employ the concept of the Fisher information matrix (FIM) to reformulate and improve on the "Newton's One-Step Error Reconstructor" (NOSER) algorithm. FIM is a systematic approach for incorporating statistical properties of noise, modeling errors and multi-frequency data. The method is discussed in a maximum likelihood estimator (MLE) setting. The ill-posedness of the inverse problem is mitigated by means of a nonlinear regularization strategy. It is shown that the overall approach reduces to the maximum a posteriori estimator (MAP) with the prior (conductivity vector) described by a multivariate normal distribution. The covariance matrix of the prior is a diagonal matrix and is computed directly from the Fisher information matrix. An eigenvalue analysis is presented, revealing the advantages of using this prior to a Gaussian smoothness prior (Laplace). Reconstructions are shown using measured data obtained from a shallow breathing of an adult human subject. The reconstructions show that the FIM approach clearly improves on the original NOSER algorithm.

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.

Comparison of methods for optimal choice of the regularization parameter for linear electrical impedance tomography of brain function

Electrical impedance tomography has the potential to provide a portable non-invasive method for imaging brain function. Clinical data collection has largely been undertaken with time difference data and linear image reconstruction methods. The purpose of this work was to determine the best method for selecting the regularization parameter of the inverse procedure, using the specific application of evoked brain activity in neonatal babies as an exemplar. The solution error norm and image SNR for the L-curve (LC), discrepancy principle (DP), generalized cross validation (GCV) and unbiased predictive risk estimator (UPRE) selection methods were evaluated in simulated data using an anatomically accurate finite element method (FEM) of the neonatal head and impedance changes due to blood flow in the visual cortex recorded in vivo. For simulated data, LC, GCV and UPRE were equally best. In human data in four neonatal infants, no significant differences were found among selection methods. We recommend that GCV or LC be employed for reconstruction of human neonatal images, as UPRE requires an empirical estimate of the noise variance.

Electrical Impedance Scanning for the Early Detection of Breast Cancer in Young Women: Preliminary Results of a Multicenter Prospective Clinical Trial

Purpose

To evaluate the feasibility and patient satisfaction with electrical impedance scanning (EIS) for early detection of breast cancer in young women.

Methods

Women undergoing screening clinical breast examination, imaging, or biopsy were eligible for EIS examination with T-Scan 2000ED (Mirabel Medical Systems, Austin, TX). Multiple logistic regression analysis evaluated the association between clinical variables and EIS performance. Patients completed a screening EIS satisfaction questionnaire (1 = least satisfied to 5 = most satisfied).

Results

Twenty-nine cancers were identified among 1,103 women. Sixty-six percent (19 of 29) of cancers were nonpalpable and 55% (16 of 29) were in women age ≤ 50 years. EIS sensitivity and specificity in women younger than 40 years was 50% and 90%, respectively. Exogenous estrogen use (P < .001) and menopausal status (P = .007) correlated significantly with EIS performance. False-positive rates were increased in postmenopausal women and those taking exogenous hormones. No correlation was evident between EIS performance and family history, prior breast cancer, breast density, or palpability. EIS-positive women younger than age 40 were 4.5 times more likely to have breast carcinoma than were women randomly selected from the general population. Patients were highly satisfied with the comfort, speed, and reporting of EIS screening (mean score, 4.8).

Conclusion

EIS seems promising for early detection of breast cancer, and identification of young women at increased risk for having the disease at time of screening. Positive EIS-associated breast cancer risk compares favorably with relative risks of conditions commonly used to justify early breast cancer screening. Patients are satisfied with a screening paradigm involving breast EIS.

Distributed network imaging and electrical impedance tomography of minimally invasive surgery

Minimally invasive surgery has become highly dependent on imaging. For instance, the effectiveness of cryosurgery in treating cancer is dependent on knowledge of freezing extent, and relies on real-time imaging techniques for monitoring. However, medical imaging is often very expensive and therefore not available to most of the world population. Here we propose the concept of distributed network imaging (DNI) which could make medical imaging and minimally invasive surgery available to all who need these advanced medical modalities. We demonstrate the concept through electrical impedance tomography (EIT) of cryosurgery. The central idea is to develop an inexpensive measurend (data collection hardware) at a remote site and then to connect the measurend apparatus to an advanced image reconstruction server, which can serve a large number of distributed measurends at remote sites, using existing communication conduits (Ethernet, telephone, satellite, etc.). These conduits transfer the raw data from the measurend to the server and the reconstructed image from the server to the measurend. Electrical impedance tomography (EIT) is an imaging modality which utilizes tissue impedance variation to construct an image. The EIT measurend which consists of electrodes, a power supply, and means to measure voltage is inexpensive, and therefore suitable for DNI. EIT is also very well-suited to imaging cryosurgery since frozen tissue impedance is much higher than that of unfrozen tissue. In this study, we first develop numerical models to illustrate the theoretical ability of EIT to image cryosurgery. We begin with a simplified two dimensional model, and then extend the study to the more appropriate three dimensional model. Our simulated finite element phantoms and pixel-based Newton-Raphson reconstruction algorithms were able to produce easily identifiable images of frozen regions within tissue. Then, we demonstrate the feasibility of the DNI concept though a case study using EIT to image an in vitro liver cryosurgery procedure through a modem. We find that the acquired raw data packets are less than 5KB per image and the images, using compression, do not exceed 50KB per image.

Non-invasive assessment of radiation injury with electrical impedance spectroscopy

A detailed understanding of non-targeted normal tissue response is necessary for the optimization of radiation treatment plans in cancer therapy. In this study, we evaluate the ability of electrical impedance spectroscopy (EIS) to non-invasively determine and quantify the injury response in soft tissue after high dose rate (HDR) irradiation, which is characterized by large localized dose distributions possessing steep spatial gradients. The HDR after-loading technique was employed to irradiate small volumes of muscle tissue with single doses (26-52 Gy targeted 5 mm away from the source). Impedance measurements were performed on 29 rats at 1, 2 and 3 month post-irradiation, employing 31 frequencies in the 1 kHz to 1 MHz range. Over the first 3 months, conductivity increased by 48% and 26% following target doses of 52 Gy and 26 Gy 5 mm from the HDR source, respectively. Injury, assessed independently through a grid-based scoring method showed a quadratic dependence on distance from source. A significant injury (50% of cells atrophied, necrotic or degenerating) in 1.2% of the volume, accompanied by more diffuse injury (25% of cells atrophied, necrotic or degenerating) in 9% of the tissue produced a conductivity increase of 0.02 S m(-1) (8% over a baseline of 0.24 S m(-1)). This was not statistically significant at p = 0.01. Among treatment groups, injury differences in 22% of the volume led to statistically significant differences in conductivity of 0.07 S m(-1) (23% difference in conductivity). Despite limitations, the success of EIS in detecting responses in a fraction of the tissue probed, during these early post-irradiation time-points, is encouraging. Electrical impedance spectroscopy may provide a useful metric of atrophy and the development of fibrosis secondary to radiation that could be further developed into a low-cost imaging method for radiotherapy monitoring and assessment.

Multi-frequency electrical impedance tomography of the breast: new clinical results

Electrical impedance tomography (EIT) has been used in the recent past for a number of clinical applications. In this work we present recent tomographic and spectroscopic findings for breast imaging from clinical exams completed at Dartmouth. The results presented here are based on 18 normal and 24 abnormal subjects. The participants were classified as normal or abnormal using the American College of Radiology (ACR) indexing system for mammograms. The EIT data were collected for ten discrete frequencies in the range 10 kHz-1 MHz using a single array of 16 electrodes. The finite element method was used to reconstruct the images. The images were examined visually and were compared with mammograms. The results were also analyzed based on zonal averages of property values and breast tissue radiodensities. Statistical analysis showed a significance difference between the mean conductivity and permittivity values of normal and abnormal subjects for various zones defined on the reconstructed images. Tissues with high radiodensity also had increased conductivity and permittivity.

Modality independent elastography (MIE): a new approach to elasticity imaging

The correlation between tissue stiffness and health is an accepted form of organ disease assessment. As a result, there has been a significant amount of interest in developing methods to image elasticity parameters (i.e., elastography). The modality independent elastography (MIE) method combines a nonlinear optimization framework, computer models of soft-tissue deformation, and standard measures of image similarity to reconstruct elastic property distributions within soft tissue. In this paper, simulation results demonstrate successful elasticity image reconstructions in breast cross-sectional images acquired from magnetic resonance (MR) imaging. Results from phantom experiments illustrate its modality independence by reconstructing elasticity images of the same phantom in both MR and computed tomographic imaging units. Additional results regarding the performance of a new multigrid strategy to MIE and the implementation of a parallel architecture are also presented.

Technology review: the use of electrical impedance scanning in the detection of breast cancer

The present paper focuses on electrical impedance scanning. The basic science behind the new modality, measurements of breast tissue impedance in vivo and in vitro, and the studies performed with a newly available commercial machine are discussed. Electrical impedance scanning has been generating interest for several reasons, including comfort to the patient, the relatively low cost, and studies suggest that it may be effective in detecting disease in mammographically dense breasts.

Electrical impedance tomography of human brain function using reconstruction algorithms based on the finite element method

Electrical impedance tomography (EIT) is a recently developed technique which enables the internal conductivity of an object to be imaged using rings of external electrodes. In a recent study, EIT during cortical evoked responses showed encouraging changes in the raw impedance measurements, but reconstructed images were noisy. A simplified reconstruction algorithm was used which modelled the head as a homogeneous sphere. In the current study, the development and validation of an improved reconstruction algorithm are described in which realistic geometry and conductivity distributions have been incorporated using the finite element method. Data from computer simulations and spherical or head-shaped saline-filled tank phantoms, in which the skull was represented by a concentric shell of plaster of Paris or a real human skull, have been reconstructed into images. There were significant improvements in image quality as a result of the incorporation of accurate geometry and extracerebral layers in the reconstruction algorithm. Image quality, assessed by blinded subjective expert observers, also improved significantly when data from the previous evoked response study were reanalysed with the new algorithm. In preliminary images collected during epileptic seizures, the new algorithm generated EIT conductivity changes which were consistent with the electrographic ictal activity. Incorporation of realistic geometry and conductivity into the reconstruction algorithm significantly improves the quality of EIT images and lends encouragement to the belief that EIT may provide a low-cost, portable functional neuroimaging system in the foreseeable future.

A review of electrical impedance techniques for breast cancer detection

Some evidence has been found that malignant breast tumors have lower electrical impedance than surrounding normal tissues. Although the separation of malignant tumors from benign lesions based on impedance measurements needs further investigation, electrical impedance could be used as an indicator for breast cancer detection. In this paper, we provide a systematic technical review of the existing electrical impedance techniques proposed for breast cancer detection, with an emphasis on noninvasive impedance imaging techniques. The electrical impedance of human breast tissue is first introduced, with tabulation of previous in vitro impedance measurement results on cancerous and normal breast tissues, and a brief description on the limited in vivo impedance measurements completed with invasive, or noninvasive, non-imaging techniques. A detailed review on noninvasive impedance imaging techniques for breast cancer detection, such as electrical impedance tomography (EIT) and electrical impedance mapping (EIM), is then presented. We suggest that for better breast cancer detection, an invasive impedance technique may be enhanced by combination with other cancer indicators. 3D EIT should be improved through collective efforts. EIM using a pair of electrode arrays is a viable method with great potential. Magnetic induction tomography and other magnetic induction based impedance imaging for breast cancer detection are promising and merit further exploration as well.

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.

Imaging the breast with EIS: an initial study of exam consistency

Use of electrical impedance spectroscopy (EIS) to image the breasts of women with both normal and abnormal conditions requires the ability to deliver a consistent and repeatable exam. To investigate the degree to which our current imaging system can meet this requirement we conducted an initial study of exam consistency. The trial involved the imaging of 25 breasts stratified into four separate substudies with increasing levels of electrode placement uncertainty. The degree of complexity ranged from single-placement single-session imaging to multiple-placement single-session imaging to multiple-placement multiple-session imaging. Both visual analysis and quantitative comparisons using mean squared difference (MSD) measures between pairs of permittivity and conductivity images were performed. A new breast interface with the improved vertical and radial electrode array positioning capability required to complete this study is described. Not surprisingly, the results show a dominant trend of increased image variability with increased electrode placement uncertainty. Importantly, quantitative levels of image consistency are reported through MSD analysis. On average across all frequencies analysed, MSDs for single placements are well below 1%, near 2-3% for repositioned breasts during the same session and approximately 15% for re-examined breasts in multiple sessions conducted over time. Overall, these results suggest that EIS breast exams are consistent provided the electrode placement is well controlled, typically with better than 1 cm accuracy.