Dielectric properties of human glioma and surrounding tissue

Abstract

Dielectric properties of human glioma and surrounding tissue from five patients were measured. Experiments were performed at frequencies of 5-500 MHz at 24 +/- 0.5 degrees C using a Network Analyser and a coaxial line capacitive sensor. The permittivity and conductivity of tumours were 30% higher than that of the surrounding tissues due to their higher water content. The characteristic of less differentiation in tumours clearly was reflected in the dielectric properties, namely a smaller parameter for the relaxation time distribution of the tumour's dielectric relaxation. With the dielectric data, the power absorption ratios of tumour to surrounding tissue were calculated for four representative electromagnetic (EM) irradiation cases. The calculation shows that power absorption ratios are strongly dependent on the incident direction of the EM wave and optimum frequency. To improve therapeutic efficiency, it is appropriate to have the electric field vector (E) parallel to the interface of tumour/surrounding tissue at optimum frequencies around 100 MHz, and the case of E perpendicular to the interface must be avoided in applications of EM hyperthermia for brain tumours.

Hepatic radiofrequency ablation at low frequencies preferentially heats tumour tissue

“…Several studies that measured dielectric tissue properties at radiofrequencies found significantly higher electrical conductivity of cancerous compared to normal liver tissue [6][7][8][9]13]. This difference becomes more pronounced at lower frequencies, especially below 100 kHz (see Figure 2).…”

“…Smith et al [7] measured liver carcinoma ex vivo between 1 kHz and 13 MHz from a rabbit model and found 6-7.5 times higher electrical conductivity at low frequencies, but 2-5 times lower permittivity compared to normal liver tissue. Lu et al [8] measured human glioma and surrounding tissue ex vivo between 5-500 MHz and found 30% higher permittivity and conductivity in tumours compared to surrounding tissue. They also calculated power absorption between tumour and normal tissue and found that-depending on the direction of the electromagnetic wave-power was absorbed preferentially by either tumour or normal tissue.…”

Recent Progress and Future Challenges in MR Electric Properties Tomography

“…Initial, single cases of brain tumors have been reported for 1.5 T [53] and 7 T [54]. All cases show a tumor conductivity increased roughly by a factor of two compared with the surrounding white matter, as expected from [55]. In [54], the hypothesis is raised that the tumor conductivity correlates with its sodium content.…”

The electric field distribution in the brain during TTFields therapy and its dependence on tissue dielectric properties and anatomy: a computational study

“…Conductivity and permittivity values at 200 kHz were obtained through an extensive literature search for all the tissues represented in the model: scalp (Gabriel et al 1996, Hemingway and McClendon 1932, Yamamoto and Yamamoto 1976, Burger and van Milaan 1943), skull (De Mercato and Garcia Sanchez 1992, Kosterich et al 1983, Reddy and Saha 1984, Law 1993), CSF (Gabriel et al 1996, Baumann et al 1997, Crile et al 1922), GM and WM (Logothetis et al 2007, Ranck 1963, Gabriel et al 2009, Stoy et al 1982, Surowiec et al 1986, Van Harreveld et al 1963, Freygang and Landau 1955, Latikka et al 2001), and tumour (Peloso et al 1984, Surowiec et al 1988, Lu et al 1992, Latikka et al 2001). The ventricles were assumed to be filled with CSF.…”