Dielectric properties of human normal, malignant and cirrhotic liver tissue: In vivo and ex vivo measurements from 0.5 to 20 GHz using a precision open-ended coaxial probe

Department of Surgery, University of Wisconsin–Madison, Madison, Wisconsin, United States
Physics in Medicine and Biology (Impact Factor: 2.76). 09/2007; 52(15):4707-19. DOI: 10.1088/0031-9155/52/15/022
Source: PubMed


Hepatic malignancies have historically been treated with surgical resection. Due to the shortcomings of this technique, there is interest in other, less invasive, treatment modalities, such as microwave hepatic ablation. Crucial to the development of this technique is the accurate knowledge of the dielectric properties of human liver tissue at microwave frequencies. To this end, we characterized the dielectric properties of in vivo and ex vivo normal, malignant and cirrhotic human liver tissues from 0.5 to 20 GHz. Analysis of our data at 915 MHz and 2.45 GHz indicates that the dielectric properties of ex vivo malignant liver tissue are 19 to 30% higher than normal tissue. The differences in the dielectric properties of in vivo malignant and normal liver tissue are not statistically significant (with the exception of effective conductivity at 915 MHz, where malignant tissue properties are 16% higher than normal). Also, the dielectric properties of in vivo normal liver tissue at 915 MHz and 2.45 GHz are 16 to 43% higher than ex vivo. No statistically significant differences were found between the dielectric properties of in vivo and ex vivo malignant tissue (with the exception of effective conductivity at 915 MHz, where malignant tissue properties are 28% higher than normal). We report the one-pole Cole-Cole parameters for ex vivo normal, malignant and cirrhotic liver tissue in this frequency range. We observe that wideband dielectric properties of in vivo liver tissue are different from the wideband dielectric properties of ex vivo liver tissue, and that the in vivo data cannot be represented in terms of a Cole-Cole model. Further work is needed to uncover the mechanisms responsible for the observed wideband trends in the in vivo liver data.

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Available from: John G Webster, Oct 05, 2015
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    • "In the frequency range of ∼1 kHz to ∼10 2 MHz, electrical properties have been demonstrated in several studies to be significantly altered as a function of tissue malignancy (Joines 1994, O'Rourke et al 2007, Swarup et al 1991), holding promise for detection and characterization of tumors (Fear et al 2002). Efforts have been made to develop imaging methodologies for noninvasive characterization and imaging of electrical properties, including electrical impedance tomography (EIT) (Paulson et al 1993, Metherall et al 1996), magnetic resonance electrical impedance tomography (MREIT) (Zhang 1992, Kwon et al 2002, Gao et al 2005, Lee et al 2011) and magnetoacoustic tomography with magnetic induction (MAT-MI) (Xu and He 2005, Li et al 2007, Xia et al 2007, 2010, Hu et al 2010, Mariappan et al 2011). More recently, a new technology, named electrical properties tomography (EPT) (Haacke et al 1991, Wen 2003, Katscher et al 2009, Zhang et al 2010), has been introduced to noninvasively image tissue conductivity and permittivity at proton Larmor frequency, based on complex-valued maps of radiofrequency (RF) field (B 1 ) measured in magnetic resonance imaging (MRI) experiments. "
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    ABSTRACT: Electrical properties tomography (EPT) is a recently developed noninvasive technology to image the electrical conductivity and permittivity of biological tissues at Larmor frequency in magnetic resonance scanners. The absolute phase of the complex radio-frequency magnetic field (B1) is necessary for electrical property calculation. However, due to the lack of practical methods to directly measure the absolute B1 phases, current EPT techniques have been achieved with B1 phase estimation based on certain assumptions on object anatomy, coil structure and/or electromagnetic wave behavior associated with the main magnetic field, limiting EPT from a larger variety of applications. In this study, using a multi-channel transmit/receive coil, the framework of a new general approach for EPT has been introduced, which is independent on the assumptions utilized in previous studies. Using a human head model with realistic geometry, a series of computer simulations at 7 T were conducted to evaluate the proposed method under different noise levels. Results showed that the proposed method can be used to reconstruct the conductivity and permittivity images with noticeable accuracy and stability. The feasibility of this approach was further evaluated in a phantom experiment at 7 T.
    Physics in Medicine and Biology 06/2013; 58(13):4395-4408. DOI:10.1088/0031-9155/58/13/4395 · 2.76 Impact Factor
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    • "The focusing performance of the proposed hyperthermia system was tested by assigning different electrical properties to the tumor compared to the surrounding tissue due to uncertainties and the lack of precise values of these properties in the literature. Several studies have shown that malignant tissue has a higher electrical conductivity and permittivity than normal tissue in the breast and the human liver at microwave frequencies [31,44,45]. The difference between healthy tissue and tumor is attributed to the increased water content of the latter, which results in an increased permittivity and an increased conductivity [46]. "
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    ABSTRACT: Hyperthermia is considered one of the new therapeutic modalities for cancer treatment and is based on the difference in thermal sensitivity between healthy tissues and tumors. During hyperthermia treatment, the temperature of the tumor is raised to 40-45°C for a definite period resulting in the destruction of cancer cells. This paper investigates design, modeling and simulation of a new non-invasive hyperthermia applicator system capable of effectively heating deep seated as well as superficial brain tumors using inexpensive, simple, and easy to fabricate components without harming surrounding healthy brain tissues. The proposed hyperthermia applicator system is composed of an air filled partial half ellipsoidal chamber, a patch antenna, and a head model with an embedded tumor at an arbitrary location. The irradiating antenna is placed at one of the foci of the hyperthermia chamber while the center of the brain tumor is placed at the other focus. The finite difference time domain (FDTD) method is used to compute both the SAR patterns and the temperature distribution in three different head models due to two different patch antennas at a frequency of 915 MHz. The obtained results suggest that by using the proposed noninvasive hyperthermia system it is feasible to achieve sufficient and focused energy deposition and temperature rise to therapeutic values in deep seated as well as superficial brain tumors without harming surrounding healthy tissue. The proposed noninvasive hyperthermia system proved suitable for raising the temperature in tumors embedded in the brain to therapeutic values by carefully selecting the systems components. The operator of the system only needs to place the center of the brain tumor at a pre-specified location and excite the antenna at a single frequency of 915 MHz. Our study may provide a basis for a clinical applicator prototype capable of heating brain tumors.
    BioMedical Engineering OnLine 08/2012; 11(1):47. DOI:10.1186/1475-925X-11-47 · 1.43 Impact Factor
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    • "tissue environment is prone to strong interference caused by normal tissue heterogeneities. The first example is the in vivo and ex vivo measurements of dielectric properties of human normal, malignant, and cirrhotic liver tissues using a precision openended coaxial probe from 0.5 to 20 GHz [4]. Based on these findings, the dielectric properties of cancerous liver tissues used in [9] for a feasibility study of liver tumor size estimation are merely 2.5% − 35% higher than normal. "
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    ABSTRACT: We present a new approach to the problem of detecting cancerous tissues at low-to-medium signal-to-noise ratios (SNRs) in an interference-prone biological medium, where the dielectric properties of the surrounding heterogeneous healthy tissues are comparable to those of the tumors. Suppose that microwave contrast agents, such as microbubbles or nanocomposites, are selectively delivered to the cancer site via systemic administration, and the difference between the backscatter responses (differential signal) before and after the administration of contrast medium to the tissue anomalies can be extracted. We can then formulate the problem from the perspective of signal model selection. Subsequently, two information theoretic criteria (ITC), namely the Akaike information criterion (AIC) and the minimum description length (MDL), are applied as a blind method to reliably detect the malignant tumor and estimate its location using ITC-oriented strategies. Finally, numerical examples based on a 2-D canonical biological phantom, which synthesizes an interference-prone microwave imaging scenario, are carried out to evaluate the performance of the proposed ITC-based algorithms. The dielectric properties of the phantom are varied to investigate diagnostics of three types of dysplastic tissues: liver, lung, and breast cancers. We also use a 3-D anatomically realistic breast model as a testbed to verify the effectiveness of the proposed method.
    IEEE transactions on bio-medical engineering 12/2011; 59(3):766-76. DOI:10.1109/TBME.2011.2179035 · 2.35 Impact Factor
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