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: 2.92). 09/2007; 52(15):4707-19. DOI: 10.1088/0031-9155/52/15/022
Source: PubMed

ABSTRACT 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.

Download full-text


Available from: John G Webster, Jul 07, 2015
1 Follower
  • Source
    [Show abstract] [Hide abstract]
    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 · 2.92 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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 · 2.23 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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.
    Physiological Measurement 05/2009; 30(5):459-66. DOI:10.1088/0967-3334/30/5/003 · 1.62 Impact Factor