Changes in dielectric properties of ex vivo bovine liver at 915 MHz during heating

We have developed a coaxial measurement system for determining the time and temperature dependence of the dielectric properties of bovine liver at 915 MHz during heating. Our data suggest that changes in dielectric properties due to heating are dominated by the relaxation response of two tissue components: tissue water and proteins. At temperatures above 60 degrees C, the effects of these two components contribute to increases of up to 100% and 5% in the values of conductivity and permittivity respectively. Changes due to tissue water content were found to be reversible with temperature, while changes due to protein denaturation were found to be permanent. The temperature coefficients for reversible changes were found to be 1.82 +/- 0.28% degrees C(-1) and -0.130 +/- (5.9 x 10(-2))% degrees C(-1) for conductivity and permittivity respectively. The critical temperatures and activation energies leading to irreversible changes in conductivity and permittivity were determined using Arrhenius analysis. Frequency factors of (1.14 +/- 0.27) x 10(43) s(-1) and (1.95 +/- 0.49) x 10(36) s(-1) were determined for permittivity and conductivity respectively. The activation energies were calculated to be 70.7 +/- 15.8 kcal mol(-1) for permittivity and 60.1 +/- 14.0 kcal mol(-1) for conductivity.     

Age dependence of dielectric properties of bovine brain and ocular tissues in the frequency range of 400 MHz to 18 GHz

In order to identify possible age-dependent dielectric properties of brain and eye tissues in the frequency range of 400 MHz to 18 GHz, measurements on bovine grey and white matter as well as on cornea, lens (cortical) and the vitreous body were performed using a commercially available open-ended coaxial probe and a computer-controlled vector network analyser. Freshly excised tissues of 52 animals of two age groups (42 adult animals, i.e. 16-24 month old and 10 young animals, i.e. 4-6 month old calves) were examined within 8 min (brain tissue) and 15 min (eye tissue), respectively, of the animals' death. Tissue temperatures for the measurements were 32+/-1 degrees C and 25+/-1 degrees C for brain and eye tissues, respectively. Statistical analysis of the measured data revealed significant differences in the dielectric properties of white matter and cortical lens tissue between the adult and the young group. In the case of white matter the mean values of conductivity and permittivity of young tissue were 15%-22% and 12%-15%, respectively, higher compared to the adult tissue in the considered frequency range. Similarly, young cortical lens tissue was 25%-76% higher in conductivity and 27%-39% higher in permittivity than adult cortical lens tissue.     

An agar phantom for hyperthermia

An agar phantom with wide application in rf heating was developed. The phantom consists of 4 wt./wt. % agar powder, 0.1 wt./wt. % NaN3, 0-0.6 wt./wt. % NaCl, and 95.9-95.3 wt./wt. % water. The conductivity sigma (S/m) of the phantom was independent of frequency at 1-40 MHz, being sigma = 1.74 chi + 0.207 at 23.5 +/- 1 degrees C, where chi is the concentration of NaCl (wt./wt.%). The permittivity was nearly equal to 81 in the range of 5-40 MHz and 0-0.6 wt./wt.% of NaCl. The density and the heat capacity of the phantom were 1.02 X 10(3) kg/m3 and 1.00 kcal/kg degree C, respectively. The phantom had sufficient mechanical strength to permit construction of a torso 60 cm high. With the addition of a preservative, the phantom could be used for experiments on heating, without degeneration, for over one year.     

Taenia crassiceps metacestodes have cytochrome oxidase aa3 but not cytochrome o functioning as terminal oxidase

In mitochondria obtained from Taenia crassiceps metacestodes, carbon monoxide difference spectra reveal signals characteristic of the classical mitochondrial oxidase, cytochrome aa3, as well as signals suggesting the presence of 'cytochrome o'. In the present work, using photodissociation spectrophotometry and analysis of the haem groups, we conclude that there is no haem O in these larvae, and that the only cytochrome that functions as terminal oxidase is cytochrome c oxidase, aa3. At temperatures between -70 and -100 degrees C, the energy of activation for CO reassociation with cytochrome a3 was 10.5 kcal x mol(-1), and for oxygen binding 7.8 kcal x mol(-1).     

Dielectric properties of brain tissue between 0.01 and 10 GHz

Dielectric permittivity and conductivity are reported for grey and white matter from dog brain tissue between 0.01 and 10 GHz. Between 0.01 and approximately 1 GHz, the permittivity decreases and conductivity increases as a power law of frequency. Above 1 GHz, the conductivity increases quadratically with frequency due to dipolar reorientation of free water molecules in tissue; the apparent rotational relaxation frequency at 37 degrees C is 21--25 GHz, slightly below the 25 GHz characteristic frequency of pure water at that temperature. The microwave data are analysed using the Maxwell mixture theory applicable for a suspension of nonconducting, low permittivity spheres in bulk water. From the increase in conductivity above 1 GHz, and the tissue permittivity at 2--4 GHz, the apparent volume fraction of water is approximately 0.70 and 0.55 for grey and white matter, respectively, about 10--15% lower than respective values from the literature. This discrepancy is apparently due to a small fraction of water which does not contribute to the tissue permittivity above 1 GHz. Empirical equations are given to summarise the dielectric properties of 'average' brain tissue at 37 degrees C for future theoretical studies of microwave absorption in the head.     

Dielectric properties of ocular tissues in the supercooled and frozen states

Values of the relative permittivity and conductivity of the rabbit retina and lens have been measured between 10 MHz and 10 GHz over the temperature range 20 to -20 degrees C. As the temperature was lowered from 20 degrees C the dielectric parameters changed smoothly until -9 degrees C where freezing occurred. At this temperature a sharp transition was observed in both conductivity and relative permittivity, the latter falling to a value of below 10 over most of the frequency range. Analysis shows that this is due to the unfreezable water, from which a value of lens hydration is calculated. This value agrees with that obtained previously at 37 degrees C using conventional dielectric mixture theory, but the associated margin of error is much smaller.     

Dielectric properties of mammalian breast milk at radiofrequencies

The relative permittivity and AC conductivity of breast milk have been investigated in four different mammalian species, human, cow, goat and sheep, in the frequency range 0.1-100 MHz and at a room temperature of 26.5 +/- 0.5 degrees C. The results showed that the sheep milk exhibited the largest dielectric dispersion, followed in decreasing order by milks from the goat, cow and human. The dielectric data were fitted to the Debye and Cole-Cole structural equations and the fitted parameters have been presented for the different species. The curve-fitting analysis has shown that for all the milk samples the Cole-Cole model gave a better fit to the dielectric data than the Debye model, thus suggesting heterogeneity of structure in milk. On the basis of the Cole-Cole model, the relaxation times in the mammalian milks were found to be distributed about the mean values of 162 +/- 10, 171 +/- 9, 177 +/- 14 and 192 +/- 12 ns for human, cow, goat and sheep milks, respectively.     

Influence of the radiopacifier in an acrylic bone cement on its mechanical, thermal, and physical properties: barium sulfate-containing cement versus iodine-containing cement

In all acrylic bone cement formulations in clinical use today, radiopacity is provided by micron-sized particles (typical mean diameter of between about 1 and 2 microm) of either BaSO(4) or ZrO(2). However, a number of research reports have highlighted the fact that these particles have deleterious effects on various properties of the cured cement. Thus, there is interest in alternative radiopacifiers. The present study focuses on one such alternative. Specifically, a cement that contains covalently bound iodine in the powder (herein designated the I-cement) was compared with a commercially available cement of comparable composition (C-ment3), in which radiopacity is provided by BaSO(4) particles (this cement is herein designated the B-cement), on the basis of the strength (sigma(b)), modulus (E(b)), and work-to-fracture (U(b)), under four-point bending, plane-strain fracture toughness (K(IC)), Weibull mean fatigue life, N(WM) (fatigue conditions: +/-15 MPa; 2 Hz), activation energy (Q), and frequency factor (ln Z) for the cement polymerization process (both determined by using differential scanning calorimetry at heating rates of 5, 10, 15, and 20 K min(-1)), and the diffusion coefficient for the absorption of phosphate-buffered saline at 37 degrees C (D). For the B-cement, the values of sigma(b), E(b), U(b), K(IC), N(WM), Q, ln Z, and D were 53 +/- 3 MPa, 3000 +/- 120 MPa, 108 +/- 15 kJ m(-3), 1.67 +/- 0.02 MPa check mark m, 7197 cycles, 243 +/- 17 kJ mol(-1), 87 +/- 6, and (3.15 +/- 0.94) x 10(-12) m(2) s(-1), respectively. For the I-cement, the corresponding values were 58 +/- 5 MPa, 2790 +/- 140 MPa, 118 +/- 45 kJ m(-3), 1.73 +/- 0.11 MPa check mark m, 5520 cycles, 267 +/- 19 kJ mol(-1), 95 +/- 9, and (3.83 +/- 0.25) x 10(-12) m(2) s(-1). For each of the properties of the fully cured cement, except for the rate constant of the polymerization reaction, at 37 degrees C (k'), as estimated from the Q and ln Z results, there is no statistically significant difference between the two cements. k' for the I-cement was about a third that for the B-cement, suggesting that the former cement has a higher thermal stability. The influence of various characteristics of the starting powder (mean particle size, particle size distribution, and morphology) on the properties of the cured cements appears to be complex. When all the present results are considered, there is a clear indication that the I-cement is a viable candidate cement for use in cemented arthroplasties in place of the B-cement.     

Electrical characterization of hydroxyapatite-based bioceramics

This paper studies the AC conductivity and permittivity of hydroxyapatite (HA)-based ceramics from 0.1 Hz-1 MHz at temperatures from room temperature to 1000 degrees C. HA-based ceramics were prepared either as dense ceramics or in porous form with interconnected porosity and were sintered in either air or water vapour. Samples were thermally cycled to examine the influence of water desorption on AC conductivity and permittivity. Surface-bound water was thought to contribute to conductivity for both dense and porous materials at temperatures below 200 degrees C. At temperatures below 700 degrees C the permittivity and AC conductivity of HA was also influenced by the degree of dehydration and thermal history. At higher temperatures (700-1000 degrees C), bulk ionic conduction was dominant and activation energies were of the order of approximately 2 eV, indicating that hydroxyl ions are responsible for conductivity.     

30例健康人血液射频介电常数和电导率的测量

在10kHz～110MHz频率范围,利用4294A阻抗分析仪测量了30例正常健康人血液样本的介电常数和电导率,通过介电常数和电导率频谱、复数平面图、介电损耗频谱、电导率虚部频谱和损耗角正切频谱的数据分析,旨在建立正常人血液的电生理特征参数,为进一步的临床研究提供基础数据和研究方法。结果表明,正常健康人全血介电常数和电导率具有频率依从性,其介电行为具有两个特征频率：第一特征频率f1=0.59MHz;第二特征频率f2=2.12MHz。     

Effects of temperature and shear force on infectivity of the baculovirus Autographa californica M nucleopolyhedrovirus

Virus stability and infectivity during stressful conditions was assessed to establish guidelines for future virus filtration experiments and to contribute to the body of knowledge on a widely used virus. A recombinant baculovirus of Autographa californica M nucleopolyhedrovirus (AcMNPV), vHSGFP, was incubated at 15-65 degrees C. A 2-log decrease in virus infectivity occurred after virus incubation above 45 degrees C. The activation energy of virus deactivation was circa 108 kJ/mol. Dynamic light scattering revealed an increase in apparent virus particle size from 150+/-19 to 249+/-13 nm at 55 degrees C. Protein and DNA concentrations in solution correlated well with virus aggregation as temperature was increased. Infectivity of vHSGFP stored for 5 months at 4 degrees C or exposed to shear stress from stirring (100 rpm, 1.02x10(-5) psi) and pumping (50-250 ml/min, 1.45x10(-5) to 7.25x10(-5) psi) did not change with time. Unlike temperature variations, cold storage and shear stress appeared to have little impact on infectivity.     

Changes in the dielectric properties of ex vivo bovine liver during microwave thermal ablation at 2.45 GHz

In microwave thermal ablation (MTA) therapy, the dielectric properties of the target tissue play an important role in determining the radiation properties of the microwave ablation antenna. In this work, the ex vivo dielectric properties of bovine liver were experimentally characterized as a function of the temperature during MTA at the frequency of 2.45 GHz. The obtained data were compared with measurements performed at the end of the MTA treatment, and considering the heating achieved with a temperature-controlled water bath. Finally, measured data were used to perform a numerical study evaluating the effects of changes in tissue's dielectric properties during the MTA treatment on the radiation properties of a microwave interstitial ablation antenna, as well as on the obtained thermal lesion. Results evidenced a significant decrease of both relative permittivity (about 38%) and electric conductivity (about 33%) in the tissue during treatment as the temperature increased to over 60 °C, with a dramatic drop when the temperature approached 100 °C. Moreover, the numerical study evidenced that changes in tissue's dielectric properties during the MTA treatment affect the distribution of the power absorbed by the tissue (specific absorption rate-SAR, W kg(-1)) surrounding the microwave interstitial ablation antenna, leading to a peak SAR up to 20% lower, as well as to a thermal lesion up to 8% longer. This work may represent a preliminary step towards the future development of a procedure for MTA treatment planning.     

Diffusion and distribution of dimethyl sulphoxide in the isolated guinea-pig taenia coli

1. The diffusion of the cryoprotective non-electrolyte dimethyl sulphoxide (DMSO) in the isolated guinea-pig taenia coli at 37, 25 and 0 degrees C has been studied using [(35)S]DMSO.2. Within 1 hr after immersion at 37 degrees C in Krebs solution containing 20% (w/v) DMSO and trace amounts of [(35)S]DMSO, the non-electrolyte was distributed uniformly throughout a volume equivalent to the total initial water content of the muscle.3. The kinetics of efflux of [(35)S]DMSO from muscles at constant volume were analysed on the basis of two models: one incorporated radial diffusion in extracellular fluid with simultaneous permeation into the cells, the other involved only radial diffusion in homogeneous cylinders of tissue having no internal barriers to diffusion; the former was found to give a better representation of the efflux kinetics.4. If it was assumed that the rate of diffusion of DMSO in the extracellular space of taenia coli was the same as that in the bathing medium, the values of the extracellular space and the permeability of smooth muscle to DMSO, obtained from the analysis of the efflux kinetics, were 454 +/- 19 ml./kg and 2.36 +/- 0.05 x 10(-6) cm sec(-1) at 37 degrees C.5. The activation energy for the transfer of DMSO across the surface of the cell was estimated to be 6.0 kcal/mole at 37 degrees C, 6.6 kcal/mole at 25 degrees C and 11.6 kcal/mole at 0 degrees C, indicating either that the equivalent pore radius of the cells decreased with temperature or that the cell permeability represented the sum of two fluxes, one through the aqueous pores of the cell and the other through the lipid phase of the cell membrane, each with a different energy of activation.6. A net flux of water across the surface of the cells, superimposed on the efflux of DMSO, markedly affected the rate of diffusion of the non-electrolyte out of the whole tissue; however, it was considered that an analysis of the efflux kinetics was not possible under these conditions.7. These results provide a basis for methods which will be used to investigate the possibility of preserving tissue in unfrozen aqueous media at sub-zero temperatures.     

Permeability characteristics of human oocytes in the presence of the cryoprotectant dimethylsulphoxide.

Equilibration of oocytes with cryoprotectants is a prerequisite of low temperature storage. However, cryoprotectant exposure may induce damage via osmotic stress. Knowledge of cell membrane permeability characteristics and their temperature dependence would facilitate the design of cryopreservation protocols in which osmotic stress is minimized and the incidence of intracellular freezing is reduced. To obtain such data, the volume change of donated human oocytes following exposure to cryoprotectant was measured at a variety of temperatures. After removal of cumulus cells, each oocyte was placed in a 5 microl droplet of phosphate-buffered medium. The oocyte was held in position by suction generated using a fine pipette and perfused with 1 ml 1.5 mol/l dimethylsulphoxide (DMSO) at 30, 24 or 10 degrees C. The volume of the oocyte before, during and after perfusion was recorded by videomicroscopy. Oocyte volume was calculated from radius measurements and the Kedem-Katchalsky (K-K) passive coupled transport coefficients, namely L(p) (hydraulic permeability), P(DMSO) (permeability to DMSO) and sigma (reflection coefficient) were derived. The resulting coefficients were L(p) = 1. 65 +/- 0.15, 0.70 +/- 0.06 and 0.28 +/- 0.04 microm/min.atm; P(DMSO) = 0.79 +/- 0.10, 0.25 +/- 0.04 and 0.06 +/- 0.01 microm/s and sigma = 0.97 +/- 0.01, 0.94 +/- 0.03 and 0.96 +/- 0.01 at 30, 24 and 10 degrees C respectively. The activation energy for L(p) was 14.70 and for P(DMSO) was 20.82 kcal/mol. The permeability parameters of human oocytes are higher than those of murine oocytes, suggesting that they require a shorter period of exposure to DMSO with concomitantly reduced toxic effects.     

人血液细胞介电谱的实验研究

在0．01～100MHz范围内，测量人血液细胞的介电谱，确立人血液细胞对交流电场的介电响应的数据特征。利用频域阻抗技术测量了正常人血液细胞交流阻抗，绘制细胞的介电常数和电导率与电场频率的关系曲线。建立了人血液细胞的介电谱和Cole—Cole图，明确了人血细胞的介电频响的数据特征。在射频电场中，人血液细胞的介电常数和电导率具有频率依赖性，表现为具有两个特征频率的介电弛豫：第一介电弛豫发生在fc。为1．42MHz，第二介电弛豫产生在fcz为3．32MHz。     

A heterogeneous human tissue mimicking phantom for RF heating and MRI thermal monitoring verification

This paper describes a heterogeneous phantom that mimics a human thigh with a deep-seated tumor, for the purpose of studying the performance of radiofrequency (RF) heating equipment and non-invasive temperature monitoring with magnetic resonance imaging (MRI). The heterogeneous cylindrical phantom was constructed with an outer fat layer surrounding an inner core of phantom material mimicking muscle, tumor and marrow-filled bone. The component materials were formulated to have dielectric and thermal properties similar to human tissues. The dielectric properties of the tissue mimicking phantom materials were measured with a microwave vector network analyzer and impedance probe over the frequency range of 80-500 MHz and at temperatures of 24, 37 and 45 °C. The specific heat values of the component materials were measured using a differential scanning calorimeter over the temperature range of 15-55 °C. The thermal conductivity value was obtained from fitting the curves obtained from one-dimensional heat transfer measurement. The phantom was used to verify the operation of a cylindrical four-antenna annular phased array extremity applicator (140 MHz) by examining the proton resonance frequency shift (PRFS) thermal imaging patterns for various magnitude/phase settings (including settings to focus heating in tumors). For muscle and tumor materials, MRI was also used to measure T1/T2* values (1.5 T) and to obtain the slope of the PRFS phase change versus temperature change curve. The dielectric and thermal properties of the phantom materials were in close agreement to well-accepted published results for human tissues. The phantom was able to successfully demonstrate satisfactory operation of the tested heating equipment. The MRI-measured thermal distributions matched the expected patterns for various magnitude/phase settings of the applicator, allowing the phantom to be used as a quality assurance tool. Importantly, the material formulations for the various tissue types may be used to construct customized phantoms that are tailored for different anatomical sites.     

101例手术切除的结直肠癌组织介电特性的探讨

探究采用开端同轴线射频技术测量得到的结直肠癌组织和正常结直肠组织的介电特性是否具有显著差异,探讨能否应用该技术判断结直肠癌的病理类型。101例手术切除的新鲜离体结肠／直肠癌标本来自南方医科大学珠江医院手术室,应用开端同轴线仪器在170～500 MHz频率段分别检测癌组织和正常组织的相对介电常数和电导率。粗略选取170．32、212．90、255．48、298．06、383．22、468．38、500．00 MHz几个频率点的介电特性纳入统计分析。术后对标本行病理切片检查。结直肠癌组织的相对介电常数和电导率均比正常结直肠组织高（P＜0．01）,粘液腺癌组织的电导率在170．32、212．90、255．48、298．06、383．22 MHz时比腺癌组织高（P＜0．05）,结直肠癌高、中、低分化三种不同分化程度的介电特性无统计学意义（P＞0．05）。应用开端同轴线仪器可以快速而准确地辨别结直肠癌组织和正常结直肠组织,同时可以判断结直肠癌的病理类型。     

Effect of temperature on the RF dielectric properties of human breast milk

The dielectric dispersion of human breast milk has been investigated by means of a resonance technique over the frequency range 0.1-100 MHz and at six temperatures from 10 to 60 degrees C. A computer analysis of the data was carried out on the basis of the Cole-Cole structural model and the fitted parameters have been presented. The dependence on temperature of both the viscosity of the human milk and its dielectric relaxation has been discussed. The heat of activation delta H of the milk, calculated in accordance with Eyring's theory of rate processes was found to be 19.5 +/- 0.6 kJ mol-1 for the dielectric relaxation process and 20.2 +/- 0.8 kJ mol-1 for viscous flow.     

Effects of temperature on the early stages of rat spinal motoneurone development in vitro

Effects of temperature on rat spinal motoneurone morphogenesis during the early stages of development were investigated in vitro through a statistical morphometric analysis, and examined in the frame of a basic theoretical aggregation growth model. Morphological measurements in the 31.0-39.4 degrees C range revealed that: (1) primary neurite initiation was promoted by increased temperatures; (2) collateral branches formation was particularly enhanced over 37 degrees C; and (3) the elongation properties of all processes were not significantly altered. In parallel, an Arrhenius analysis proved that: (4) an activation energy of about 23 kcal/mol was required for primary neurites to emerge from a soma. These results suggest that the very first molecular events underlying neuritogenesis are rather sensitive to temperature and could imply both the transport and assembly properties of microtubules.