Experimental Determination of Thermal Conductivity of Water−Agar Gel at Different Concentrations and Temperatures

Zhang, Min; Che, Zhenhua; Chen, Jianhua; Zhao, Huizhong; Yang, Lei; Zhong, Zhiyong; Lu, Jiahua

doi:10.1021/je100570h

Cited by 88 publications

(65 citation statements)

References 27 publications

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“…The assembly was placed in a 1 L glass beaker filled with ultrasound gel and equilibrated to 37 C in an Isotemp water bath (Fisher Scientific, Essex, UK). Care was taken in pouring the ultrasound gel to avoid formation of any large air bubbles and any small air bubbles that were entrained diffused to negligible sizes during warming.…”

Section: Methods Of Approachmentioning

confidence: 99%

“…In the unfrozen state, measurements were made with the constant power method [36], where the thermal decay was monitored as a constant power was applied to the thermistor for several seconds. This method requires comparator reference standards, for which glycerol and 1% agarose gel were used [34,37]. Measurements were repeated for n ¼ 3 at À2 C, 18 C, and 38 C, equilibrating in a heated/cooled, Neslab RTE 740 ethanol recirculating bath (Thermo Scientific Corp., Essex, UK).…”

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confidence: 99%

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Methods for Characterizing Convective Cryoprobe Heat Transfer in Ultrasound Gel Phantoms

Etheridge

Choi

Ramadhyani³

et al. 2013

Journal of Biomechanical Engineering

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While cryosurgery has proven capable in treating of a variety of conditions, it has met with some resistance among physicians, in part due to shortcomings in the ability to predict treatment outcomes. Here we attempt to address several key issues related to predictive modeling by demonstrating methods for accurately characterizing heat transfer from cryoprobes, report temperature dependent thermal properties for ultrasound gel (a convenient tissue phantom) down to cryogenic temperatures, and demonstrate the ability of convective exchange heat transfer boundary conditions to accurately describe freezing in the case of single and multiple interacting cryoprobe(s). Temperature dependent changes in the specific heat and thermal conductivity for ultrasound gel are reported down to À150 C for the first time here and these data were used to accurately describe freezing in ultrasound gel in subsequent modeling. Freezing around a single and two interacting cryoprobe(s) was characterized in the ultrasound gel phantom by mapping the temperature in and around the "iceball" with carefully placed thermocouple arrays. These experimental data were fit with finite-element modeling in COMSOL Multiphysics, which was used to investigate the sensitivity and effectiveness of convective boundary conditions in describing heat transfer from the cryoprobes. Heat transfer at the probe tip was described in terms of a convective coefficient and the cryogen temperature. While model accuracy depended strongly on spatial (i.e., along the exchange surface) variation in the convective coefficient, it was much less sensitive to spatial and transient variations in the cryogen temperature parameter. The optimized fit, convective exchange conditions for the single-probe case also provided close agreement with the experimental data for the case of two interacting cryoprobes, suggesting that this basic characterization and modeling approach can be extended to accurately describe more complicated, multiprobe freezing geometries. Accurately characterizing cryoprobe behavior in phantoms requires detailed knowledge of the freezing medium's properties throughout the range of expected temperatures and an appropriate description of the heat transfer across the probe's exchange surfaces. Here we demonstrate that convective exchange boundary conditions provide an accurate and versatile description of heat transfer from cryoprobes, offering potential advantages over the traditional constant surface heat flux and constant surface temperature descriptions. In addition, although this study was conducted on Joule-Thomson type cryoprobes, the general methodologies should extend to any probe that is based on convective exchange with a cryogenic fluid. [DOI: 10.1115/1.4023237] Keywords: cryosurgery, cryotherapy, cryoablation, thermal properties, heat transfer modeling, clinical modeling IntroductionCryosurgery is a minimally invasive technique in which freezing temperatures are used to destroy tissue in the body to treat various conditions, including cancer (prosta...

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Section: Methods Of Approachmentioning

confidence: 99%

mentioning

confidence: 99%

Methods for Characterizing Convective Cryoprobe Heat Transfer in Ultrasound Gel Phantoms

Etheridge

Choi

Ramadhyani³

et al. 2013

Journal of Biomechanical Engineering

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“…We also assumed a change in the thermal conductivity with temperature of +0.003 K −1 [11]. The 0.8% agar gel physical properties were extracted from [14], [12], and [13].…”

Section: B Governing Equations and Tissue Characteristicsmentioning

confidence: 99%

“…where T is the temperature in Kelvin and C is the agar concentration of the gel (0.8%) [14]). Although agar electrical conductivity varies with its concentration [12], it is not clear from [2] whether the gel was made with saline solution or with pure water.…”

Section: B Governing Equations and Tissue Characteristicsmentioning

confidence: 99%

Radiofrequency Ablation of Osteoma Osteoide: A Finite Element Study

et al. 2015

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Abstract-We proposed a finite element model to numerically study radiofrequency ablation of a benign bone tumor called osteoma osteoide. We reproduced the setup of a previous experimental study in order to validate the computer model. The physical parameters of the involved tissues were obtained by fitting the experimental and theoretical temporal evolution of temperatures. As The maximum error of the model is around 6°C (10%), which occurred for only 20 s. For the rest of the time (more than 350 s) the error was between 5 and 8%.

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“…During the experiment, we filled the cavity with deionized water and immersed the ultrasonic probe in the water without direct contact with the agar layer. Because the agar jelly had similar thermal conductivity and heat capacity to that of water [21,22], by simple calculation, it would take more than 10 minutes for the overall sample temperature to rise by 1 degree even if all the laser light energy was absorbed and became heat. Combining our previous experimental result with this calculation, we believe that the base temperature of the sample did not change much when imaging, thereby eliminating the effect from the varied Gruneisen parameter on the 2nd order beating signals.…”

Section: Application-nonlinear Photoacoustic Microscopymentioning

confidence: 99%

Nonlinear photoacoustic microscopy via a loss modulation technique: from detection to imaging

Lai¹,

Lee²,

Chang³

et al. 2014

Opt. Express

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Abstract:In order to achieve high-resolution deep-tissue imaging, multiphoton fluorescence microscopy and photoacoustic tomography had been proposed in the past two decades. However, combining the advantages of these two imaging systems to achieve optical-spatial resolution with an ultrasonic-penetration depth is still a field with challenges. In this paper, we investigate the detection of the two-photon photoacoustic ultrasound, and first demonstrate background-free two-photon photoacoustic imaging in a phantom sample. To generate the background-free two-photon photoacoustic signals, we used a high-repetition rate femtosecond laser to induce narrowband excitation. Combining a loss modulation technique, we successfully created a beating on the light intensity, which not only provides pure sinusoidal modulation, but also ensures the spectrum sensitivity and frequency selectivity. By using the lock-in detection, the power dependency experiment validates our methodology to frequencyselect the source of the nonlinearity. This ensures our capability of measuring the background-free two-photon photoacoustic waves by detecting the 2nd order beating signal directly. Furthermore, by mixing the nanoparticles and fluorescence dyes as contrast agents, the two-photon photoacoustic signal was found to be enhanced and detected. In the end, we demonstrate subsurface two-photon photoacoustic bio-imaging based on the optical scanning mechanism inside phantom samples.

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Experimental Determination of Thermal Conductivity of Water−Agar Gel at Different Concentrations and Temperatures

Cited by 88 publications

References 27 publications

Methods for Characterizing Convective Cryoprobe Heat Transfer in Ultrasound Gel Phantoms

Methods for Characterizing Convective Cryoprobe Heat Transfer in Ultrasound Gel Phantoms

Radiofrequency Ablation of Osteoma Osteoide: A Finite Element Study

Nonlinear photoacoustic microscopy via a loss modulation technique: from detection to imaging

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