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Tanrıverdi V, Gençer NG. Induced Current Electro-Thermal Imaging for Breast Tumor Detection: A Numerical and Experimental Study. Ann Biomed Eng 2024; 52:1078-1090. [PMID: 38319506 DOI: 10.1007/s10439-024-03445-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2023] [Accepted: 01/04/2024] [Indexed: 02/07/2024]
Abstract
This study proposes using magnetically induced currents in medical infrared imaging to increase the temperature contrast due to the electrical conductivity differences between tumors and healthy tissues. There are two objectives: (1) to investigate the feasibility of this active method for surface and deep tumors using numerical simulations, and (2) to demonstrate the use of this method through different experiments conducted with phantoms that mimic breast tissues. Tumorous breasts were numerically modeled and simulated in active and passive modes. At 750 kHz, the applied current was limited for breast tissue-tumor conductivities (0.3 S/m and 0.75 S/m) according to the local specific absorption rate limit of 10 W/kg. Gelatin-based and mashed potato phantoms were produced to mimic tumorous breast tissues. In the simulation studies, the induced current changed the temperature contrast on the imaging surface, and the tumor detection sensitivity increased by 4 mm. An 11-turn 70-mm-long solenoid coil was constructed, 20 A current was applied for deep tumors, and a difference of up to 0.4 ∘ C was observed in the tumor location compared with the temperature in the absence of the tumor. Similarly, a 23-turn multi-layer coil was constructed, and a temperature difference of 0.4 ∘ C was observed. The temperature contrast on the body surface changed, and the tumor detection depth increased with the induced currents in breast IR imaging. The proposed active thermal imaging method was validated using numerical simulations and in vitro experiments.
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Affiliation(s)
- Volkan Tanrıverdi
- Electrical and Electronics Engineering Department, Middle East Technical University, 06800, Ankara, Turkey.
| | - Nevzat G Gençer
- Electrical and Electronics Engineering Department, Middle East Technical University, 06800, Ankara, Turkey
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Kolomeyets NL, Ivonin AG, Peshkin EA, Roshchevskaya IM. Bioelectrical Impedance of the Left Ventricular Myocardium, Lung in Rats after Forced Swimming Training and Subsequent Detraining. J EVOL BIOCHEM PHYS+ 2023. [DOI: 10.1134/s0022093023010064] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/16/2023]
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Kolomeyets NL, Syslonova OV, Smirnova SL, Peshkin EA, Roshchevskaya IM. Bioelectrical Impedance of the Rat Myocardium and Liver under Chronic Exposure to Doxorubicin. J EVOL BIOCHEM PHYS+ 2021. [DOI: 10.1134/s0022093021060144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Vatsyayan R, Cleary D, Martin JR, Halgren E, Dayeh SA. Electrochemical safety limits for clinical stimulation investigated using depth and strip electrodes in the pig brain. J Neural Eng 2021; 18. [PMID: 34015769 DOI: 10.1088/1741-2552/ac038b] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Accepted: 05/20/2021] [Indexed: 11/12/2022]
Abstract
Objective. Diagnostic and therapeutic electrical stimulation are increasingly utilized with the rise of neuromodulation devices. However, systematic investigations that depict the practical clinical stimulation paradigms (bipolar, two-electrode configuration) to determine the safety limits are currently lacking. Further, safe charge densities that were classically determined from conical sharp electrodes are generalized for cylindrical (depth) and flat (surface grid) electrodes completely ignoring geometric factors that govern current spreading and trajectories in tissue.Approach. This work reports the first investigations comparing stimulation limits for clinically used electrodes in two mediums: in benchtop experiments in saline andin vivoin a single acute experiment in the pig brain. We experimentally determine the geometric factors, the water electrolysis windows, and the current safety limits from voltage transients, for the sEEG, depth and surface strip electrodes in both mediums. Using four-electrode and three-electrode configuration measurements and comprehensive circuit models that accurately depict our measurements, we delineate the various elements of the stimulation medium, including the tissue-electrode interface impedance spectra, the medium impedance and the bias-dependent change in the interface impedance as a function of stimulation parameters.Main results. The results of our systematics studies suggest that safe currents in clinical bipolar stimulation determinedin vivocan be as much as 24 times smaller than those determined from benchtop experiments (for depth electrodes at a 1 ms pulse duration). Our detailed circuit modeling attributes this drastic difference in safe limits to the greatly dissimilar electrode/tissue and electrode/saline impedances.Significance. We established the electrochemical safety limits for commonly used clinical electrodesin vivoand revealed by detailied electrochemical modeling how they differ from benchtop evaluation. We argue that electrochemical limits and currents are unique for each electrode, should be measuredin vivoaccording to the protocols established in this work, and should be accounted for while setting the stimulation parameters for clinical applications including for chronic applications.
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Affiliation(s)
- Ritwik Vatsyayan
- Integrated Electronics and Biointerfaces Laboratory, Department of Electrical and Computer Engineering, University of California, San Diego, CA 92093, United States of America
| | - Daniel Cleary
- Integrated Electronics and Biointerfaces Laboratory, Department of Electrical and Computer Engineering, University of California, San Diego, CA 92093, United States of America.,Department of Neurological Surgery, University of California, San Diego, CA 92097, United States of America
| | - Joel R Martin
- Integrated Electronics and Biointerfaces Laboratory, Department of Electrical and Computer Engineering, University of California, San Diego, CA 92093, United States of America.,Department of Neurological Surgery, University of California, San Diego, CA 92097, United States of America
| | - Eric Halgren
- Department of Radiology, University of California, San Diego, CA 92097, United States of America
| | - Shadi A Dayeh
- Integrated Electronics and Biointerfaces Laboratory, Department of Electrical and Computer Engineering, University of California, San Diego, CA 92093, United States of America
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Kwon H, Malik WQ, Rutkove SB, Sanchez B. Separation of Subcutaneous Fat From Muscle in Surface Electrical Impedance Myography Measurements Using Model Component Analysis. IEEE Trans Biomed Eng 2018; 66:354-364. [PMID: 29993468 DOI: 10.1109/tbme.2018.2839977] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
OBJECTIVE Electrical impedance myography (EIM) is a relatively new technique to assess neuromuscular disorders (NMD). Although the application of EIM using surface electrodes (sEIM) has been adopted by the neurology community in recent years to evaluate NMD status, sEIM's sensitivity as a biomarker of skeletal muscle condition is impacted by subcutaneous fat (SF) tissue. Here, we develop a method that is able to remove the contribution of SF from sEIM data. METHODS We evaluate independent component analysis (ICA) and principal component analysis (PCA) for this purpose. Then, we introduce the so-called model component analysis (MCA). All methods are validated with numerical simulations using impedivity data from SF and muscle tissues. The methods are then tested with measurements performed in diseased individuals ( n=3). RESULTS Simulations demonstrate that MCA is the most accurate method at separating the impedivity of SF and muscle tissues with the accuracy being 99.2%, followed by ICA with 51.4%, and finally PCA with 38.5%. Experimental results from sEIM data measured on the triceps brachii of patients are consistent with muscle grayscale level values obtained using ultrasound imaging. CONCLUSION MCA can be used to separate the impedivity of SF and muscle tissues from sEIM data, thus increasing the sensitivity to detect changes in the muscle. SIGNIFICANCE MCA can make the sEIM technique a better diagnostic tool and biomarker of disease progression and response to therapy by removing the confounding effect of SF tissue in NMD patients with excess subcutaneous fat tissue for any reason.
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Kwon H, Nagy JA, Taylor R, Rutkove SB, Sanchez B. New electrical impedance methods for the in situ measurement of the complex permittivity of anisotropic biological tissues. ACTA ACUST UNITED AC 2017; 62:8616-8633. [DOI: 10.1088/1361-6560/aa8c95] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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Present Uses, Future Applications, and Technical Underpinnings of Electrical Impedance Myography. Curr Neurol Neurosci Rep 2017; 17:86. [DOI: 10.1007/s11910-017-0793-3] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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Meglan DA, Lv W, Cohen RJ, Riviere CN. Techniques for epicardial mapping and ablation with a miniature robotic walker. ROBOTIC SURGERY : RESEARCH AND REVIEWS 2017; 4:25-31. [PMID: 28966928 PMCID: PMC5619864 DOI: 10.2147/rsrr.s127047] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Background Present treatments for ventricular tachycardia have significant drawbacks. To ameliorate these drawbacks, it may be advantageous to employ an epicardial robotic walker that performs mapping and ablation with precise control of needle insertion depth. This paper examines the feasibility of such a system. Methods This paper describes the techniques for epicardial mapping and depth-controlled ablation with the robotic walker. The mapping technique developed for the current form of the system uses a single equivalent moving dipole (SEMD) model combined with the navigation capability of the walker. The intervention technique provides saline-enhanced radio frequency ablation, with sensing of needle penetration depth. The mapping technique was demonstrated in an artificial heart model with a simulated arrhythmia focus, followed by preliminary testing in the porcine model in vivo. The ablation technique was demonstrated in an artificial tissue model and then in chicken breast tissue ex vivo. Results The walker located targets to within 2 mm by using the SEMD mapping technique. No epicardial damage was found subsequent to the porcine trial in vivo. Needle insertion for ablation was controlled to within 2 mm of the target depth. Lesion size was repeatable, with diameter varying consistently in proportion to the volume of saline injected. Conclusion The experiments demonstrated the general feasibility of the techniques for mapping and depth-controlled ablation with the robotic walker.
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Affiliation(s)
| | - Wener Lv
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - Richard J Cohen
- Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - Cameron N Riviere
- The Robotics Institute, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA
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Zurbuchen U, Poch F, Gemeinhardt O, Kreis ME, Niehues SM, Vahldieck JL, Lehmann KS. Determination of the electrical conductivity of human liver metastases: impact on therapy planning in the radiofrequency ablation of liver tumors. Acta Radiol 2017; 58:164-169. [PMID: 27055920 DOI: 10.1177/0284185116639765] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Background Radiofrequency ablation is used to induce thermal necrosis in the treatment of liver metastases. The specific electrical conductivity of a liver metastasis has a distinct influence on the heat formation and resulting tumor ablation within the tissue. Purpose To examine the electrical conductivity σ of human colorectal liver metastases and of tumor-free liver tissue in surgical specimens. Material and Methods Surgical specimens from patients with resectable colorectal liver metastases were used for measurements (size of metastases <30 mm). A four-needle measuring probe was used to determine the electrical conductivity σ of human colorectal liver metastasis (n = 8) and tumor-free liver tissue (n = 5) in a total of five patients. All measurements were performed at 470 kHz, which is the relevant frequency for radiofrequency ablation. The tissue temperature was also measured. Hepatic resections were performed in accordance with common surgical standards. Measurements were performed in the operating theater immediately after resection. Results The median electrical conductivity σ was 0.57 S/m in human colorectal liver metastases at a median temperature of 35.1℃ and 0.35 S/m in tumor-free liver tissue at a median temperature of 34.9℃. The electrical conductivity was significantly higher in tumor tissue than in tumor-free liver tissue ( P = 0.005). There were no differences in tissue temperature between the two groups ( P = 0.883). Conclusion The electrical conductivity is significantly higher in human colorectal liver metastases than in tumor-free liver tissue at a frequency of 470 kHz.
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Affiliation(s)
| | - Franz Poch
- Charité–Universitätsmedizin Berlin, Berlin, Germany
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Dodde RE, Kruger GH, Shih AJ. Design of Bioimpedance Spectroscopy Instrument With Compensation Techniques for Soft Tissue Characterization. J Med Device 2015; 9:0210011-210018. [PMID: 26029317 PMCID: PMC4410770 DOI: 10.1115/1.4029706] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2014] [Revised: 01/22/2015] [Indexed: 11/08/2022] Open
Abstract
Bioimpedance spectroscopy (BIS) has shown significant potential in many areas of medicine to provide new physiologic markers. Several acute and chronic diseases are accompanied by changes in intra- and extracellular fluid within various areas of the human body. The estimation of fluid in various body compartments is therefore a simple and convenient method to monitor certain disease states. In this work, the design and evaluation of a BIS instrument are presented and three key areas of the development process investigated facilitating the BIS measurement of tissue hydration state. First, the benefit of incorporating DC-stabilizing circuitry to the standard modified Howland current pump (MHCP) is investigated to minimize the effect of DC offsets limiting the dynamic range of the system. Second, the influence of the distance between the bioimpedance probe and a high impedance material is investigated using finite element analysis (FEA). Third, an analytic compensation technique is presented to minimize the influence of parasitic capacitance. Finally, the overall experimental setup is evaluated through ex vivo BIS measurements of porcine spleen tissue and compared to published results. The DC-stabilizing circuit demonstrated its ability to maintain DC offsets at less than 650 μV through 100 kHz while maintaining an output impedance of 1 MΩ from 100 Hz to 100 kHz. The proximity of a bioimpedance probe to a high impedance material such as acrylic was shown to increase measured impedance readings by a factor of 4x as the ratio of the distance between the sensing electrodes to the distance between the bioimpedance probe and acrylic reached 1:3. The average parasitic capacitance for the circuit presented was found to be 712 ± 128 pF, and the analytic compensation method was shown to be able to minimize this effect on the BIS measurements. Measurements of porcine spleen tissue showed close correlation with experimental results reported in published articles. This research presents the successful design and evaluation of a BIS instrument. Specifically, robust measurements were obtained by implementing a DC-stabilized current source, investigating probe-material proximity issues and compensating for parasitic capacitance. These strategies were shown to provide tissue measurements comparable with published literature.
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Affiliation(s)
- Robert E Dodde
- Stryker Corporation , 4100 E. Milham Avenue, Kalamazoo, MI 49001 e-mail:
| | - Grant H Kruger
- Mechanical Engineering, University of Michigan , 1031 H.H. Dow Building, 2350 Hayward Street, Ann Arbor, MI 48109 e-mail:
| | - Albert J Shih
- Mechanical Engineering, University of Michigan , 3001E EECS, 1301 Beal, Ann Arbor, MI 48109 e-mail:
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Prakash S, Karnes MP, Sequin EK, West JD, Hitchcock CL, Nichols SD, Bloomston M, Abdel-Misih SR, Schmidt CR, Martin EW, Povoski SP, Subramaniam VV. Ex vivo electrical impedance measurements on excised hepatic tissue from human patients with metastatic colorectal cancer. Physiol Meas 2015; 36:315-28. [PMID: 25597963 DOI: 10.1088/0967-3334/36/2/315] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Point-wise ex vivo electrical impedance spectroscopy measurements were conducted on excised hepatic tissue from human patients with metastatic colorectal cancer using a linear four-electrode impedance probe. This study of 132 measurements from 10 colorectal cancer patients, the largest to date, reports that the equivalent electrical conductivity for tumor tissue is significantly higher than normal tissue (p < 0.01), ranging from 2-5 times greater over the measured frequency range of 100 Hz-1 MHz. Difference in tissue electrical permittivity is also found to be statistically significant across most frequencies. Furthermore, the complex impedance is also reported for both normal and tumor tissue. Consistent with trends for tissue electrical conductivity, normal tissue has a significantly higher impedance than tumor tissue (p < 0.01), as well as a higher net capacitive phase shift (33° for normal liver tissue in contrast to 10° for tumor tissue).
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Affiliation(s)
- S Prakash
- Department of Mechanical and Aerospace Engineering, The Ohio State University, 201 W. 19th Avenue, Columbus, OH 43210, USA
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Do changes in electrical skin resistance of acupuncture points reflect menstrual pain? A comparative study in healthy volunteers and primary dysmenorrhea patients. EVIDENCE-BASED COMPLEMENTARY AND ALTERNATIVE MEDICINE 2014; 2014:836026. [PMID: 24876879 PMCID: PMC4020393 DOI: 10.1155/2014/836026] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/09/2014] [Revised: 03/20/2014] [Accepted: 03/31/2014] [Indexed: 11/29/2022]
Abstract
Electrical skin resistance (ESR) measurements were performed with a four-electrode impedance detector at 10 points bilaterally on the first day of and the third day after menstruation in 48 healthy volunteers and 46 primary dysmenorrhea (PD) patients, to assess whether ESR changes of acupuncture points can reflect menstrual pain or not. The results showed statistical reductions in ESR imbalance ratio between left and right side that were detected at SP8 (Diji) and GB39 (Xuanzhong) (P < 0.05), and a statistical increase was detected at SP6 (Sanyinjiao) (P = 0.05) on the first day of menstruation compared with those values on the third day after menstruation in dysmenorrhea group. No significant differences were detected at other points within and between two groups (P > 0.05). This study showed that the imbalance of ESR at uterine-relevant points in PD patients is not significantly different from those of healthy women on both the 1st day of and the 3rd day after menstruation. The ESR imbalance ratio of certain points can either be lower or higher during menstruation in PD patients. The ESR property of acupuncture points needs to be investigated in further clinical trials with appropriate points, diseases, larger sample sizes, and optimal device.
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Huo X, Shi X, You F, Fu F, Liu R, Tang C, Lu Q, Dong X. Reliability ofin vivomeasurements of the dielectric properties of anisotropic tissue: a simulative study. Phys Med Biol 2013; 58:3163-76. [DOI: 10.1088/0031-9155/58/10/3163] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Oh TI, Kim YT, Minhas A, Seo JK, Kwon OI, Woo EJ. Ion mobility imaging and contrast mechanism of apparent conductivity in MREIT. Phys Med Biol 2011; 56:2265-77. [PMID: 21411866 DOI: 10.1088/0031-9155/56/7/022] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Magnetic resonance electrical impedance tomography (MREIT) aims to produce high-resolution cross-sectional images of conductivity distribution inside the human body. Injected current into an imaging object induces a distribution of internal magnetic flux density, which is measured by using an MRI scanner. We can reconstruct a conductivity image based on its relation with the measured magnetic flux density. In this paper, we explain the contrast mechanism in MREIT by performing and analyzing a series of numerical simulations and imaging experiments. We built a stable conductivity phantom including a hollow insulating cylinder with holes. Filling both inside and outside the hollow cylinder with the same saline, we controlled ion mobilities to create a conductivity contrast without being affected by the ion diffusion process. From numerical simulations and imaging experiments, we found that slopes of induced magnetic flux densities change with hole diameters and therefore conductivity contrasts. Associating the hole diameter with apparent conductivity of the region inside the hollow cylinder with holes, we could experimentally validate the contrast mechanism in MREIT. Interpreting reconstructed apparent conductivity images of the phantom as ion mobility images, we discuss the meaning of the apparent conductivity seen by a certain probing method. In designing MREIT imaging experiments, the ion mobility imaging method using the proposed stable conductivity phantom will enable us to estimate a distinguishable conductivity contrast for a given set of imaging parameters.
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Affiliation(s)
- Tong In Oh
- Impedance Imaging Research Center and Department of Biomedical Engineering, Kyung Hee University, Korea
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Haemmerich D, Schutt DJ. RF ablation at low frequencies for targeted tumor heating: in vitro and computational modeling results. IEEE Trans Biomed Eng 2010; 58:404-10. [PMID: 20934940 DOI: 10.1109/tbme.2010.2085081] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
RF ablation uses RF current to heat and kill cancer applied via an electrode inserted under image guidance. Tumor has about half the electrical resistivity of normal tissue below 20 kHz, but similar resistivity above 500 kHz. We placed normal porcine liver tissue in contact with agar gel having similar resistivity as tumor within 20-450 kHz. A needle electrode was placed with half of the electrically active tip in each layer. We performed ablation with electric current applied for 12 min at 30 W, either at 20 or 450 kHz (n = 7 each), while measuring temperature via thermocouples 4 and 8 mm from the electrode. Mathematical heat-transfer models were created of an equivalent configuration and temperature profile determined at both frequencies. At 8-mm distance, at 450 kHz, tumor gel phantom and normal tissue obtained similar temperatures (57.5 ± 1.4 versus 58.7 ± 2.5 (°)C); at 20 kHz, tumor phantom obtained significantly higher temperatures than normal tissue (65.6 ± 2.0 versus 57.2 ± 5.6 (°)C, p < 0.01). Computer models confirm these results, and show the ablation zone diameter to be larger within the tumor phantom at 20 kHz compared to 450 kHz. Heating at low RFs may thus allow targeted heating of tumor tissue and reduced heating of normal tissue.
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Affiliation(s)
- Dieter Haemmerich
- Division of Pediatric Cardiology, Medical Universityof South Carolina, Charleston, SC 29403, USA.
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Basati SS, Harris TJ, Linninger AA. Dynamic brain phantom for intracranial volume measurements. IEEE Trans Biomed Eng 2010; 58:1450-5. [PMID: 20501343 DOI: 10.1109/tbme.2010.2050065] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Knowledge of intracranial ventricular volume is important for the treatment of hydrocephalus, a disease in which cerebrospinal fluid (CSF) accumulates in the brain. Current monitoring options involve MRI or pressure monitors (InSite, Medtronic). However, there are no existing methods for continuous cerebral ventricle volume measurements. In order to test a novel impedance sensor for direct ventricular volume measurements, we present a model that emulates the expansion of the lateral ventricles seen in hydrocephalus. To quantify the ventricular volume, sensor prototypes were fabricated and tested with this experimental model. Fluid was injected and withdrawn cyclically in a controlled manner and volume measurements were tracked over 8 h. Pressure measurements were also comparable to conditions seen clinically. The results from the bench-top model served to calibrate the sensor for preliminary animal experiments. A hydrocephalic rat model was used to validate a scaled-down, microfabricated prototype sensor. CSF was removed from the enlarged ventricles and a dynamic volume decrease was properly recorded. This method of testing new designs on brain phantoms prior to animal experimentation accelerates medical device design by determining sensor specifications and optimization in a rational process.
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Affiliation(s)
- Sukhraaj S Basati
- Laboratory for Product and Process Design, Department of Bioengineering, University of Illinois at Chicago, Chicago, IL 60607, USA
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Zurbuchen U, Holmer C, Lehmann KS, Stein T, Roggan A, Seifarth C, Buhr HJ, Ritz JP. Determination of the temperature-dependent electric conductivity of liver tissue ex vivo and in vivo: Importance for therapy planning for the radiofrequency ablation of liver tumours. Int J Hyperthermia 2010; 26:26-33. [DOI: 10.3109/02656730903436442] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
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Gabriel C, Peyman A, Grant EH. Electrical conductivity of tissue at frequencies below 1 MHz. Phys Med Biol 2009; 54:4863-78. [PMID: 19636081 DOI: 10.1088/0031-9155/54/16/002] [Citation(s) in RCA: 377] [Impact Index Per Article: 25.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Schutt DJ, Haemmerich D. Tumor ablation at low frequencies for preferential tumor heating: initial ex-vivo tissue studies. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2009; 2008:238-41. [PMID: 19162637 DOI: 10.1109/iembs.2008.4649134] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
PURPOSE Radiofrequency (RF) ablation is a common treatment modality for inoperable liver cancer. Several studies have demonstrated that significant differences exist between the electrical properties of tumor and normal tissue, especially at lower frequencies. In this study, we investigated in an ex vivo setting whether the use of lower frequencies during ablation results in preferential heating of tumor tissue. MATERIALS AND METHODS We created a setup consisting of adjacent layers (3 cm thick each) of tumor phantom (agar gel) and freshly excised normal porcine liver tissue in a saline bath. A standard RF needle electrode was placed such that half of the active electrode was in each layer. We applied 25 W of power at a frequency of either 20 or 325 kHz to the electrode for 12 minutes. Temperatures were recorded 6 and 10 mm from the electrode in both the phantom and normal tissue layers. RESULTS The ratio of the temperature rise in the tumor phantom to the temperature rise in the normal tissue was significantly higher in the 20 kHz trials after 12 minutes at both 6 mm (1.50+/-0.27 vs. 1.02+/-0.16) and 10 mm (1.34+/-0.28 vs. 0.90+/-0.11) from the electrode (p<0.01). CONCLUSION Tumor ablation at frequencies lower than currently used may preferentially heat tumor tissue, preserving normal tissue at the treatment site.
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Affiliation(s)
- David J Schutt
- Medical University of South Carolina, Charleston, SC 29425, USA
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Linninger A, Basati S, Dawe R, Penn R. An impedance sensor to monitor and control cerebral ventricular volume. Med Eng Phys 2009; 31:838-45. [PMID: 19419900 DOI: 10.1016/j.medengphy.2009.03.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2008] [Revised: 01/15/2009] [Accepted: 03/30/2009] [Indexed: 10/20/2022]
Abstract
This paper presents a sensor for monitoring and controlling the volume of the cerebrospinal fluid-filled ventricles of the brain. The measurement principle of the sensor exploits electrical conductivity differences between the cerebrospinal fluid and the brain tissue. The electrical contrast was validated using dog brain tissue. Experiments with prototype sensors accurately measured the volume content of elastically deformable membranes and gel phantoms with conductivity properties made to match human brain. The sensor was incorporated into a fully automatic feedback control system designed to maintain the ventricular volume at normal levels. The experimental conductivity properties were also used to assess the sensor performance in a simulated case of hydrocephalus. The computer analysis predicted voltage drops over the entire range of ventricular size changes with acceptable positional dependence of the sensor electrodes inside the ventricular space. These promising experimental and computational results of the novel impedance sensor with feedback may serve as the foundation for improved therapeutic options for hydrocephalic patients relying on volume sensing, monitoring or active feedback control.
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Affiliation(s)
- Andreas Linninger
- Laboratory for Product and Process Design (LPPD), Department of Bioengineering, University of Illinois at Chicago, Chicago, IL 60607, USA.
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Haemmerich D, Schutt DJ, Wright AW, Webster JG, Mahvi DM. Electrical conductivity measurement of excised human metastatic liver tumours before and after thermal ablation. Physiol Meas 2009; 30:459-66. [PMID: 19349647 DOI: 10.1088/0967-3334/30/5/003] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We measured the ex vivo electrical conductivity of eight human metastatic liver tumours and six normal liver tissue samples from six patients using the four electrode method over the frequency range 10 Hz to 1 MHz. In addition, in a single patient we measured the electrical conductivity before and after the thermal ablation of normal and tumour tissue. The average conductivity of tumour tissue was significantly higher than normal tissue over the entire frequency range (from 4.11 versus 0.75 mS cm(-1) at 10 Hz, to 5.33 versus 2.88 mS cm(-1) at 1 MHz). We found no significant correlation between tumour size and measured electrical conductivity. While before ablation tumour tissue had considerably higher conductivity than normal tissue, the two had similar conductivity throughout the frequency range after ablation. Tumour tissue conductivity changed by +25% and -7% at 10 Hz and 1 MHz after ablation (0.23-0.29 at 10 Hz, and 0.43-0.40 at 1 MHz), while normal tissue conductivity increased by +270% and +10% at 10 Hz and 1 MHz (0.09-0.32 at 10 Hz and 0.37-0.41 at 1 MHz). These data can potentially be used to differentiate tumour from normal tissue diagnostically.
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Affiliation(s)
- Dieter Haemmerich
- Department of Pediatrics, Medical University of South Carolina, Charleston, SC, USA.
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Wtorek J, Bujnowski A, Nowakowski A, Stojek W, Trzeciak B, Rogowski J, Siebert J. Monitoring of myocardium state during off-pump coronary artery by-pass grafting. Physiol Meas 2008; 29:S393-405. [DOI: 10.1088/0967-3334/29/6/s33] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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23
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Chong CE, Tan YL. A new geometric factor for in situ resistivity measurement using four slender cylindrical electrodes. IEEE Trans Biomed Eng 2008; 55:594-602. [PMID: 18269995 DOI: 10.1109/tbme.2007.903704] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The four-electrode method is commonly used for in situ measurement of the electrical resistivity of biological tissues. In this paper, a new geometric factor between the resistivity and measured resistance using the four-electrode interface is derived in the prolate spheroidal coordinates and experimentally validated. Evaluation of the experimental results shows that the resistivities determined using both the derived geometric factor and a commercial conductivity meter are in close agreement even when the length of the immersed electrodes becomes long with respect to the inter-electrode spacing. The evaluation also shows the effect of the relative size of the sample volume when the limitation to semi-infinite volume begins to result in poor accuracy.
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Affiliation(s)
- Chee-Earn Chong
- School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798.
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24
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Garay L, Ramos EG, Cardiel E, Muñoz R, Hernández PR. In vivo and in situ measurement of electrical impedance for determination of distention in proximal stomach of rats. Med Eng Phys 2006; 28:648-55. [PMID: 16483828 DOI: 10.1016/j.medengphy.2005.10.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2004] [Revised: 07/06/2005] [Accepted: 10/18/2005] [Indexed: 12/29/2022]
Abstract
We present a non-invasive, in vivo and in situ study of proximal stomach (PS) distention based on electrical impedance measurements that could be used together with distal stomach (DS) motility measurements as a response to different boluses. Stomach motility has been reported in the literature, as a response to different boluses, under in vivo conditions. However, previous studies on stomach motility have been mainly considered clinical parameters of the digestive process. The physiological complexity of the stomach requires the use of biological models when a detailed analysis of stomach function due to bolus ingestion is required. In this work, the determination of the PS distention in rats is presented. It is based on electrical resistive impedance measurements of the external stomach wall, related to different liquid bolus volumes. Trials were performed under in vivo and in situ conditions. A four-point technique with a vacuum-affixed linear electrode array was used for impedance measurements. A pouch was created in the stomach to retain the saline solution bolus in the PS for a longer time. Resulting impedance changes were directly related to the bolus volumes introduced into the PS and dependent on initial conditions and compensation mechanisms of the in vivo system. With the stomach pouch, a direct relationship between resistive impedance and bolus volume was obtained in all measurements. With no stomach pouch, 93% of the cases showed this relationship. Therefore, the obtained relationship will permit new non-invasive studies in the stomach about the effects of different types of bolus on the distention in the PS of rats.
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Affiliation(s)
- L Garay
- Centro de Investigación y de Estudios Avanzados del I.P.N., Av. I.P.N. 2508, C.P. 07360, México D.F., México
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25
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del Rio CL, McConnell PI, Clymer BD, Dzwonczyk R, Michler RE, Billman GE, Howie MB. Early time course of myocardial electrical impedance during acute coronary artery occlusion in pigs, dogs, and humans. J Appl Physiol (1985) 2005; 99:1576-81. [PMID: 15961608 DOI: 10.1152/japplphysiol.00830.2004] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Changes in myocardial electrical impedance (MEI) and physiological end points have been correlated during acute ischemia. However, the importance of MEI's early time course is not clear. This study evaluates such significance, by comparing the temporal behavior of MEI during acute total occlusion of the left anterior descending coronary artery in anesthetized humans, dogs, and pigs. Here, interspecies differences in three MEI parameters (baseline, time to plateau onset, and plateau value normalized by baseline) were evaluated using Kruskal-Wallis ANOVA and post hoc tests ( P < 0.05). Noteworthy differences in the MEI time to plateau onset were observed: In dogs, MEI ischemic plateau was reached after 46.3 min (SD 12.9) min of occlusion, a significantly longer period compared with that of pigs and humans [4.7 (SD 1.2) and 4.1 min (SD 1.9), respectively]. However, no differences could be observed between both animal species regarding the normalized MEI ischemic plateau value (15.3% (SD 4.7) in pigs, vs. 19.6% (SD 2.6) in dogs). For all studied MEI parameters, only swine values resembled those of humans. The severity of myocardial supply ischemia, resulting from coronary artery occlusion, is known to be dependent on collateral flow. Thus, because dogs possess a well-developed collateral system (unlike humans or pigs), they have shown superior resistance to occlusion of a coronary artery. Here, the early MEI time course after left anterior descending coronary artery occlusion, represented by the time required to reach ischemic plateau, was proven to reflect such interspecies differences.
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Affiliation(s)
- Carlos L del Rio
- Department of Anesthesiology, The Ohio State University, Columbus, 43210, USA.
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Ahn AC, Wu J, Badger GJ, Hammerschlag R, Langevin HM. Electrical impedance along connective tissue planes associated with acupuncture meridians. Altern Ther Health Med 2005; 5:10. [PMID: 15882468 PMCID: PMC1142259 DOI: 10.1186/1472-6882-5-10] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2004] [Accepted: 05/09/2005] [Indexed: 12/23/2022]
Abstract
Background Acupuncture points and meridians are commonly believed to possess unique electrical properties. The experimental support for this claim is limited given the technical and methodological shortcomings of prior studies. Recent studies indicate a correspondence between acupuncture meridians and connective tissue planes. We hypothesized that segments of acupuncture meridians that are associated with loose connective tissue planes (between muscles or between muscle and bone) visible by ultrasound have greater electrical conductance (less electrical impedance) than non-meridian, parallel control segments. Methods We used a four-electrode method to measure the electrical impedance along segments of the Pericardium and Spleen meridians and corresponding parallel control segments in 23 human subjects. Meridian segments were determined by palpation and proportional measurements. Connective tissue planes underlying those segments were imaged with an ultrasound scanner. Along each meridian segment, four gold-plated needles were inserted along a straight line and used as electrodes. A parallel series of four control needles were placed 0.8 cm medial to the meridian needles. For each set of four needles, a 3.3 kHz alternating (AC) constant amplitude current was introduced at three different amplitudes (20, 40, and 80 μAmps) to the outer two needles, while the voltage was measured between the inner two needles. Tissue impedance between the two inner needles was calculated based on Ohm's law (ratio of voltage to current intensity). Results At the Pericardium location, mean tissue impedance was significantly lower at meridian segments (70.4 ± 5.7 Ω) compared with control segments (75.0 ± 5.9 Ω) (p = 0.0003). At the Spleen location, mean impedance for meridian (67.8 ± 6.8 Ω) and control segments (68.5 ± 7.5 Ω) were not significantly different (p = 0.70). Conclusion Tissue impedance was on average lower along the Pericardium meridian, but not along the Spleen meridian, compared with their respective controls. Ultrasound imaging of meridian and control segments suggested that contact of the needle with connective tissue may explain the decrease in electrical impedance noted at the Pericardium meridian. Further studies are needed to determine whether tissue impedance is lower in (1) connective tissue in general compared with muscle and (2) meridian-associated vs. non meridian-associated connective tissue.
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Affiliation(s)
- Andrew C Ahn
- Division for Research and Education in Complementary and Integrative Medical Therapies, Harvard Medical School, Boston, MA, USA
| | - Junru Wu
- Departments of Physics, University of Vermont, Burlington, VT, USA
| | - Gary J Badger
- Department of Medical Biostatistics, University of Vermont, Burlington, VT, USA
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Süselbeck T, Thielecke H, Weinschenk I, Reininger-Mack A, Stieglitz T, Metz J, Borggrefe M, Robitzki A, Haase KK. In vivo intravascular electric impedance spectroscopy using a new catheter with integrated microelectrodes. Basic Res Cardiol 2004; 100:28-34. [PMID: 15614589 DOI: 10.1007/s00395-004-0501-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/06/2004] [Revised: 10/08/2004] [Accepted: 10/25/2004] [Indexed: 10/26/2022]
Abstract
Interventional techniques are necessary, which allow the characterization of intravascular pathological processes. Electric impedance spectroscopy (EIS) can provide cellular information of biological tissue. We tested the feasibility of intravascular EIS by using a new impedance catheter system with integrated microelectrodes in an experimental animal model. Eighteen stents were implanted into the iliac arteries of female New Zealand White rabbits (n = 11) to induce intimal proliferation. After 14, 28 and 56 days the electric impedance was measured inside and outside of the stented arterial segments by using a balloon catheter with four integrated microelectrodes. The impedance was recorded at a frequency ranging from 1 Hz to 1 MHz. After the measurements, the stents were explanted and histomorphometry was performed. The impedance inside and outside the stent was analysed and compared with the histomorphometric data. Fourteen (n = 6), 28 (n = 5) and 56 (n = 6) days after stent implantation the difference of the electrical impedance between the native and the stented iliac artery segment increased from -924 +/- 715 Ohm to 3689 +/- 1385 Ohm (14 days vs. 28 days; p < 0.05) and 8637 +/- 2881 Ohm (14 days vs. 56 days; p < 0.05), respectively. The increase of the electrical impedance corresponded to an increased neointimal proliferation in the stented arterial segment of 3.6% +/-0.7% after 14 days, 8.4% +/- 4.8% after 28 days (14 days vs. 28 days; p < 0.05) and 10.0% +/- 4.1% after 56 days (14 days vs. 56 days; p < 0.01). Intravascular EIS can be performed by a balloon catheter with integrated microelectrodes and allows the detection of neointimal proliferation after stent implantation.
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Affiliation(s)
- Tim Süselbeck
- Department of Medicine, University Hospital of Mannheim, 68167, Mannheim, Germany.
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Ivorra A, Gómez R, Noguera N, Villa R, Sola A, Palacios L, Hotter G, Aguiló J. Minimally invasive silicon probe for electrical impedance measurements in small animals. Biosens Bioelectron 2003; 19:391-9. [PMID: 14615098 DOI: 10.1016/s0956-5663(03)00204-5] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
It is commonly accepted that electrical impedance provides relevant information about the physiological condition of living tissues. Currently, impedance measurements are performed with relatively large electrodes not suitable for studies in small animals due to their poor spatial resolution and to the damage that they cause to the tissue. A minimally invasive needle shaped probe for electrical impedance measurements of living tissues is presented in this paper. This micro-probe consists of four square platinum electrodes (300 microm x 300 microm) on a silicon substrate (9 mm x 0.6 mm x 0.5 mm) and has been fabricated by using standard Si microelectronic techniques. The electrodes are not equally spaced in order to optimise the signal strength and the spatial resolution. Characterisation data obtained indicate that these probes provide high spatial resolution (measurement radius <4 mm) with a useful wide frequency band going from 100 Hz to 100 kHz. A series of in vivo experiments in rat kidneys subjected to ischemia was performed to demonstrate the feasibility of the probes and the measurement system. The impedance modulus and phase were measured at 1 kHz since this frequency is sufficiently low to permit the study of the extracellular medium. The extracellular pH and K+ were also simultaneously measured by using commercial miniaturised Ion Selective Electrodes. The induced ischemia period (45 min) resulted in significant changes of all measured parameters (Delta/Z/ approximately 65%; DeltapH approximately 0.8; DeltaK+ approximately 30 mM).
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Affiliation(s)
- A Ivorra
- Centro Nacional de Microelectónica (IMB-CSIC), Campus UAB, E-08193 Bellaterra, Barcelona, Spain
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Haemmerich D, Staelin ST, Tsai JZ, Tungjitkusolmun S, Mahvi DM, Webster JG. In vivo electrical conductivity of hepatic tumours. Physiol Meas 2003; 24:251-60. [PMID: 12812412 DOI: 10.1088/0967-3334/24/2/302] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Knowledge of electrical tissue conductivity is necessary to determine deposition of electromagnetic energy and can further be used to diagnostically differentiate between normal and neoplastic tissue. We measured 17 rats with a total of 24 tumours of the K12/TRb rat colon cancer cell line. In each animal we measured in vivo hepatic tumour and normal tissue conductivity at seven frequencies from 10 Hz to 1 MHz, at different tumour stages between 6 and 12 weeks after induction. Conductivity of normal liver tissue was 1.26 +/- 0.15 mS cm(-1) at 10 Hz, and 4.61 +/- 0.42 mS cm(-1) at 1 MHz. Conductivity of tumour was 2.69 +/- 0.91 mS cm(-1) at 10 Hz, and 5.23 +/- 0.82 mS cm(-1) at 1 MHz. Conductivity was significantly different between normal and tumour tissue (p < 0.05). We determined the percentage of necrosis and fibrosis at the measurement site. We fitted the conductivity data to the Cole-Cole model. For the tumour data we determined Spearman's correlation coefficients between the Cole-Cole parameters and age, necrosis, fibrosis and tumour volume and found significant correlation between necrosis and the Cole-Cole parameters (p < 0.05). We conclude that necrosis within the tumour and the associated membrane breakdown is likely responsible for the observed change in conductivity.
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Affiliation(s)
- Dieter Haemmerich
- Department of Surgery, University of Wisconsin-Madison, 600 Highland Avenue, WI 53792, USA.
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Cao H, Speidel MA, Tsai JZ, Van Lysel MS, Vorperian VR, Webster JG. FEM analysis of predicting electrode-myocardium contact from RF cardiac catheter ablation system impedance. IEEE Trans Biomed Eng 2002; 49:520-6. [PMID: 12046696 DOI: 10.1109/tbme.2002.1001965] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
We used the finite-element method (FEM) to model and analyze the resistance between the catheter tip electrode and the dispersive electrode during radio-frequency cardiac catheter ablation for the prediction of myocardium-electrode contact. We included deformation of the myocardial surface to achieve accurate modeling. For perpendicular catheter contact, we measured the side view of myocardial deformation using X-ray projection imaging. We averaged the deformation contour from nine samples, and then incorporated the contour information into our FEM model. We measured the resistivity of the bovine myocardium using the four-electrode method, and then calculated the resistance change as the catheter penetrated into the myocardium. The FEM result of resistance versus catheter penetration depth matches well with our experimental data.
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Affiliation(s)
- Hong Cao
- Department of Electrical and Computer Engineering, University of Wisconsin, Madison 53706, USA
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Tsai JZ, Will JA, Hubbard-Van Stelle S, Cao H, Tungjitkusolmun S, Choy YB, Haemmerich D, Vorperian VR, Webster JG. In-vivo measurement of swine myocardial resistivity. IEEE Trans Biomed Eng 2002; 49:472-83. [PMID: 12002179 DOI: 10.1109/10.995686] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
We used a four-terminal plunge probe to measure myocardial resistivity in two directions at three sites from the epicardial surface of eight open-chest pigs in-vivo at eight frequencies ranging from 1 Hz to 1 MHz. We calibrated the plunge probe to minimize the error due to stray capacitance between the measured subject and ground. We calibrated the probe in saline solutions contained in a metal cup situated near the heart that had an electrical connection to the pig's heart. The mean of the measured myocardial resistivity was 319 ohm x cm at 1 Hz down to 166 ohm x cm at 1 MHz. Statistical analysis showed the measured myocardial resistivity of two out of eight pigs was significantly different from that of other pigs. The myocardial resistivity measured with the resistivity probe oriented along and across the epicardial fiber direction was significantly different at only one out of the eight frequencies. There was no significant difference in the myocardial resistivity measured at different sites.
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Affiliation(s)
- Jang-Zern Tsai
- Department of Electrical and Computer Engineering, University of Wisconsin, Madison 53706 USA
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Tsai JZ, Will JA, Hubbard-Van Stelle S, Cao H, Tungjitkusolmun S, Choy YB, Haemmerich D, Vorperian VR, Webster JG. Error analysis of tissue resistivity measurement. IEEE Trans Biomed Eng 2002; 49:484-94. [PMID: 12002180 DOI: 10.1109/10.995687] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
We identified the error sources in a system for measuring tissue resistivity at eight frequencies from 1 Hz to 1 MHz using the four-terminal method. We expressed the measured resistivity with an analytical formula containing all error terms. We conducted practical error measurements with in-vivo and bench-top experiments. We averaged errors at all frequencies for all measurements. The standard deviations of error of the quantization error of the 8-bit digital oscilloscope with voltage averaging, the nonideality of the circuit, the in-vivo motion artifact and electrical interference combined to yield an error of +/- 1.19%. The dimension error in measuring the syringe tube for measuring the reference saline resistivity added +/- 1.32% error. The estimation of the working probe constant by interpolating a set of probe constants measured in reference saline solutions added +/- 0.48% error. The difference in the current magnitudes used during the probe calibration and that during the tissue resistivity measurement caused +/- 0.14% error. Variation of the electrode spacing, alignment, and electrode surface property due to the insertion of electrodes into the tissue caused +/- 0.61% error. We combined the above errors to yield an overall standard deviation error of the measured tissue resistivity of +/- 1.96%.
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Affiliation(s)
- Jang-Zern Tsai
- Department of Electrical and Computer Engineering, University of Wisconsin, MadisonI 53706 USA
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Haemmerich D, Ozkan R, Tungjitkusolmun S, Tsai JZ, Mahvi DM, Staelin ST, Webster JG. Changes in electrical resistivity of swine liver after occlusion and postmortem. Med Biol Eng Comput 2002; 40:29-33. [PMID: 11954705 DOI: 10.1007/bf02347692] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The resistivity of swine liver tissue was measured in vivo, during induced ischaemia and post-mortem, so that associated changes in resistivity could be quantified. Plunge electrodes, the four-terminal method and a computer-automated measurement system were used to acquire resistivities between 10Hz and 1 MHz. Liver resistivity was measured in vivo in three animals at 11 locations. At 10 Hz, resistivity was 758 +/- 170 ohm x cm. At 1 MHz, the resistivity was 250 +/- 40 ohm x cm. The resistivity time course was measured during the first 10 min after the liver blood supply in one animal had been occluded. Resistivity increased steadily during occlusion. The change in resistivity of an excised tissue sample was measured during the first 12h after excision in one animal. Resistivity increased during the first 2h by 53% at 10 Hz and by 32% at 1 MHz. After 2h, resistivity decreased, probably owing to membrane breakdown. The resistivity data were fitted to a Cole-Cole circle, from which extracellular resistance Re, intracellular resistance Ri and cell membrane capacitance Cm were estimated. Re increased during the first 2h by 95% and then decreased, suggesting an increase in extracellular volume. Cm increased during the first 4 h by 40%, possibly owing to closure of membrane channels, and then decreased, suggesting membrane breakdown. Ri stayed constant during the initial 6h and then increased.
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Affiliation(s)
- D Haemmerich
- Department of Biomedical Engineering, University of Wisconsin, Madison, USA
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