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.

Abstract-Radio-frequency (RF) hepatic ablation, offers an alternative method for the treatment of hepatic malignancies. We employed finite-element method (FEM) analysis to determine tissue temperature distribution during RF hepatic ablation. We constructed three-dimensional (3-D) thermal-electrical FEM models consisting of a four-tine RF probe, hepatic tissue, and a large blood vessel (10-mm diameter) located at different locations. We simulated our FEM analyses under temperature-controlled (90 C) 8-min ablation. We also present a preliminary result from a simplified two-dimensional (2-D) FEM model that includes a bifurcated blood vessel. Lesion shapes created by the four-tine RF probe were mushroom-like, and were limited by the blood vessel. When the distance of the blood vessel was 5 mm from the nearest distal electrode 1) in the 3-D model, the maximum tissue temperature (hot spot) appeared next to electrods A. The location of the hot spot was adjacent to another electrode 2) on the opposite side when the blood vessel was 1 mm from electrode A. The temperature distribution in the 2-D model was highly nonuniform due to the presence of the bifurcated blood vessel. Underdosed areas might be present next to the blood vessel from which the tumor can regenerate.

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.

Radio-frequency (RF) ablation is an important means of treatment of nonresectable primary and metastatic liver tumors. RF ablation, unlike cryoablation (a method of tumor destruction that utilizes cold rather than heat), must be performed with a single probe placed serially. The ablation of any but the smallest tumor requires the use of multiple overlapping treatment zones. We evaluated the performance of a configuration incorporating two hooked probes (RITA model 30). The probes were lined up along the same axis in parallel 20 mm apart. Three different modes applied voltage to the probes. The first mode applied energy in monopolar mode (current flows from both probes to a dispersive electrode). The second mode applied the energy to the probes in bipolar mode (current flows from one probe to the other). The third method applied the energy sequentially in monopolar mode (in 2-s intervals switched between the probes). We used the finite-element method (FEM) and analyzed the electric potential profile and the temperature distribution at the end of simulation of a 12-min ablation. The alternating monopolar mode allowed precise independent control of the amount of energy deposited at each probe. The bipolar mode created the highest temperature in the area between the probes in the configuration we examined. The monopolar mode showed the worst performance since the two probes in close vicinity create a disadvantageous electric field configuration. We, thus, conclude that alternating monopolar RF ablation is superior to the other two methods.

The principal cause of the clinical failure of bioprosthetic heart valves fabricated from glutaraldehyde-pretreated porcine aortic valves is calcification. Other prostheses composed of tissue-derived and polymeric biomaterials also are complicated by deposition of mineral. We have previously demonstrated that: (a) Failure due to calcification of clinical bioprosthetic valves can be simulated by either a large animal circulatory model or subdermal implants in rodents. (b) Calcification of bioprosthetic tissue has complex host, implant, and mechanical determinants. (c) The initial calcification event in the rat subdermal model is the mineral deposition in devitalized cells intrinsic to the bioprosthetic tissue within 48 to 72 h, followed later by collagen mineralization. (d) Initiation of bioprosthetic tissue mineralization, like that of physiological bone formation, has "matrix vesicles" as early nucleation sites. (e) Alkaline phosphatase (AP), an enzyme also associated with matrix vesicles involved in bone mineral nucleation, is present in both fresh and fixed bioprosthetic tissue at sites of initial mineralization. (f) Certain inhibitors of bioprosthetic tissue calcification (e.g., Al3+, Fe3+) are localized to the sites at which alkaline phosphatase is present. On the basis of these results, we hypothesize that alkaline phosphatase is a key element in the pathogenesis of mineralization of bioprosthetic tissue. In the present studies, we focused on the relationship of AP to early events in calcification, and the inhibition of both calcification and AP activity by FeCl3 and AlCl3 preincubations. Subdermal implants of glutaraldehyde pretreated bovine pericardium (GPBP) were done in 3-week-old rats. AP was characterized by enzymatic hydrolysis of paranitrophenyl phosphate (pnpp), and by histochemical studies. Calcification was evaluated chemically (by atomic adsorption spectroscopy) and morphologically (by light microscopy). The results of these studies are as follows: (a) Extractable AP activity is present in fresh but not glutaraldehyde-pretreated bovine pericardial tissue. However, histochemical studies reveal active AP within the intrinsic devitalized cells of GPBP, despite extended glutaraldehyde incubation. (b) Extrinsic AP is rapidly adsorbed following implantation, with peak activity at 72 h (424 +/- 67.2 nm pnpp/mg protein/min enzyme activity [units]), but markedly lesser amounts at 21 days (96.8 +/- 3.9 units). (c) Simultaneously to the AP activity maximum, bulk calcification is initiated, with GPBP calcium levels rising from 1.2 +/- 0.1 (unimplanted) to 2.4 +/- 0.2 micrograms/mg at 72 h, to 55.6 +/- 3.1 micrograms/mg at 21 days, despite a marked decline in AP activity at this later time.(ABSTRACT TRUNCATED AT 400 WORDS)

As a prerequisite for a human clinical trial using interleukin (IL)-12 gene therapy, the biodistribution and safety of IL-12, administered as an intradermal naked DNA injection, was evaluated in mice. The pNGVL3-mIL12 plasmid used in this study is a nonviral vector designed to induce a high level of IL-12 protein expression during a transient transfection of the host cell. The biodistribution was evaluated by a polymerase chain reaction (PCR) assay that is capable of detecting less than 100 copies of the plasmid in the context of host DNA. Twenty-four hours after three intradermal injections of 0.5 microg or 5 microg of pNGVL3-mIL12 plasmid, the plasmid was detectable in various internal organs, the blood, and the injection site. The plasmid was detectable in the gonads of only one animal at the high-dose treatment 24 hr after the injections. In the majority of the organs the plasmid was undetectable throughout the study. Possible side effects were monitored by histology and clinical chemistry, and the level of IL-12 protein expression was assessed by enzyme-linked immunosorbent assay (ELISA). No treatment-related histologic abnormalities were detected and the blood chemistry parameters showed no toxicity. The IL-12 protein was undetectable at all times at the injection site and interferon (IFN)-gamma levels at the injection site and in the serum were at background levels. The results of this murine safety study indicate that based on the distribution pattern of the plasmid in the body and the undetectable toxicities in the tissues, the use of the pNGVL3-hIL12 plasmid in cancer gene therapy clinical trials can be considered as safe.