Temperature Rise In Tissue Research Articles

STUDY OF THERMAL INTERACTION OF CELL-PHONE RADIATIONS WITHIN HUMAN HEAD TISSUES

In the present investigation, a theoretical model based on Maxwell equations, microscopic form of ohm’s law and Joules law of heating effect is proposed for the study of penetration depth, attenuation coefficient and specific absorption rate (SAR) with varying distance between the source of radiation and exposed human head tissues (skin, fat, brain and bone). In addition, corresponding temperature increase inside these various human head tissues is also calculated. Results of present study indicate that the temperature rise in human tissue depends upon specific absorption rate and the duration for which human body is actually exposed to GSM radiations. By assuming the distance of 1cm and exposure time of 5 minutes, the highest SAR was estimated to be 1681.7 W/Kg for the brain tissue at 900 MHz and 4038.5 W/Kg for 1800 MHz. Maximum skin depth and attenuation coefficient was found to be in the case of fat and brain tissue, respectively amongst rest head tissues. The corresponding highest temperature rise for the brain tissue was calculated to be 2.31K at 900 MHz and 5.54K at 1800 MHz frequencies.

Numerical calculation of temperature increase during MRI due to the presence of total hip replacement implants

Introduction Patients carrying active or passive implants are often excluded from MRI scanning, because of the potential tissue heating, due to the RF radiation emitted by volume or surface coils. Several studies have tried to quantify the resulting temperature rise and, consequently, assess implant compatibility. Purpose The purpose of the current study is to demonstrate the feasibility of evaluating with numerical modeling the worst-case temperature rise in tissues undergoing MRI scanning, due to total hip replacement implants. Materials and methods The simulated setup includes two different CAD models of a total hip replacement implant embedded in the ASTM F2182 phantom filled with tissue mimicking gel. The phantom is placed inside a birdcage RF coil resonant at 64 MHz (1.5T). The SEMCAD-X package is used to solve numerically with the FDTD technique the coupled electromagnetic and heat-transfer problems, in order to calculate the temperature rise in the gel. The results are obtained for a continuous exposure of 20 min to 2 W/kg whole-body SAR, which is the limit for normal operating mode. Results The results show that the maximum energy deposition appears at the tip of the implant stem. The temperature rise in the gel at this point can reach 12 °C, depending on the materials of the implant. There is also a local maximum in the temperature rise next to the implant head, but its value is half or less than that at the tip. Conclusion It is possible to successfully apply modern computational techniques in the timely assessment of medical implants compatibility, thus shortening their development process and increasing patient safety. Disclosure Authors declare that they have no competing interests.

Toward a Wirelessly Powered On-Lens Intraocular Pressure Monitoring System.

This paper presents a wireless on-lens intraocular pressure monitoring system, comprising a capacitance-to-digital converter and a wirelessly powered radio-frequency identification (RFID)-compatible communication system, for sensor control and data communication. The capacitive sensor was embedded on a soft contact lens of 200 μm thickness using commercially available biocompatible lens material, to improve compliance and reduce user discomfort. The sensor chip was shown to achieve effective number of bits greater than 10 over a capacitance range up to 50 pF while consuming only 64-μW power. The on-lens capacitive sensor could detect dielectric variation caused by changes in water content from a distance of 2 cm by using incident power from an RFID reader at 20 dBm. The maximum detectable distance was 11 cm with 30-dBm incident RF power. The rise in eye tissue temperature under 30-dBm RF exposure over an interval of 1s was simulated and found to be less than 0.01°C.

A compact TRM antenna with high impedance surface for SAR reduction at 1800 MHz

In this paper, a compact tapered ring monopole (TRM) antenna with high impedance surface (HIS) is reported. This antenna is characterized by improved gain and reduced back lobe radiation. This provides specific absorption rate (SAR) reduction on human tissues, when used in a mobile phone. The reflection phase property of the HIS is used to increase the radiated field towards the antenna, thus providing a good return loss with 21% impedance bandwidth, 7.4dBi gain and front to back ratio of 21dB. In contrast to the already reported HIS ground planes, the proposed structure has a simple design methodology with compact form factor of 0.52λ×0.52λ×0.026λ at 1.8GHz. The antenna prototype was fabricated and measurements were carried out. Further, numerical simulations were performed for SAR and thermal analysis. It is observed that SAR and consequent temperature rise in human tissues are greatly reduced, when HIS is added to the TRMA.

Numerical assessment of a criterion for the optimal choice of the operative conditions in magnetic nanoparticle hyperthermia on a realistic model of the human head

Purpose: This paper presents a numerical study aiming at assessing the effectiveness of a recently proposed optimisation criterion for determining the optimal operative conditions in magnetic nanoparticle hyperthermia applied to the clinically relevant case of brain tumours.Materials and methods: The study is carried out using the Zubal numerical phantom, and performing electromagnetic–thermal co-simulations. The Pennes model is used for thermal balance; the dissipation models for the magnetic nanoparticles are those available in the literature. The results concerning the optimal therapeutic concentration of nanoparticles, obtained through the analysis, are validated using experimental data on the specific absorption rate of iron oxide nanoparticles, available in the literature.Results: The numerical estimates obtained by applying the criterion to the treatment of brain tumours shows that the acceptable values for the product between the magnetic field amplitude and frequency may be two to four times larger than the safety threshold of 4.85 × 108A/m/s usually considered. This would allow the reduction of the dosage of nanoparticles required for an effective treatment. In particular, depending on the tumour depth, concentrations of nanoparticles smaller than 10 mg/mL of tumour may be sufficient for heating tumours smaller than 10 mm above 42 °C. Moreover, the study of the clinical scalability shows that, whatever the tumour position, lesions larger than 15 mm may be successfully treated with concentrations lower than 10 mg/mL. The criterion also allows the prediction of the temperature rise in healthy tissue, thus assuring safe treatment.Conclusions: The criterion can represent a helpful tool for planning and optimising an effective hyperthermia treatment.

Determining iron oxide nanoparticle heating efficiency and elucidating local nanoparticle temperature for application in agarose gel-based tumor model

Magnetic iron oxide nanoparticles (MNPs) have been developed for magnetic fluid hyperthermia (MFH) cancer therapy, where cancer cells are treated through the heat generated by application of a high frequency magnetic field. This heat has also been proposed as a mechanism to trigger release of chemotherapy agents. In each of these cases, MNPs with optimal heating performance can be used to maximize therapeutic effect while minimizing the required dosage of MNPs. In this study, the heating efficiencies (or specific absorption rate, SAR) of two types of MNPs were evaluated experimentally and then predicted from their magnetic properties. MNPs were also incorporated in the core of poly(ethylene glycol-b-caprolactone) micelles, co-localized with rhodamine B fluorescent dye attached to polycaprolactone to monitor local, nanoscale temperatures during magnetic heating. Despite a relatively high SAR produced by these MNPs, no significant temperature rise beyond that observed in the bulk solution was measured by fluorescence in the core of the magnetic micelles. MNPs were also incorporated into a macro-scale agarose gel system that mimicked a tumor targeted by MNPs and surrounded by healthy tissues. The agarose-based tumor models showed that targeted MNPs can reach hyperthermia temperatures inside a tumor with a sufficient MNP concentration, while causing minimal temperature rise in the healthy tissue surrounding the tumor.

Study of the temperature rise induced by a focusing transducer with a wide aperture angle on biological tissue containing ribs**Project supported by the National Basic Research Program of China (Grant Nos. 2012CB921504 and 2011CB707902), the National Natural Science Foundation of China (Grant No. 11274166), the Fundamental Research Funds for the Central Universities, China (Grant No. 020414380001), the Fund from State

We used the spheroidal beam equation to calculate the sound field created by focusing a transducer with a wide aperture angle to obtain the heat deposition, and then we used the Pennes bioheat equation to calculate the temperature field in biological tissue with ribs and to ascertain the effects of rib parameters on the temperature field. The results show that the location and the gap width between the ribs have a great influence on the axial and radial temperature rise of multilayer biological tissue. With a decreasing gap width, the location of the maximum temperature rise moves forward; as the ribs are closer to the transducer surface, the sound energy that passes through the gap between the ribs at the focus decreases, the maximum temperature rise decreases, and the location of the maximum temperature rise moves forward with the ribs.

Photothermal ablation of liver tissue with 1940-nm thulium fiber laser: anex vivostudy on lamb liver

The purpose of this study was to investigate the ablation efficiency of 1940-nm thulium fiber laser on liver tissue, while utilizing a real-time measurement system to monitor the temperature rise in adjacent tissues. Thulium fiber laser was delivered to lamb liver tissue samples via 400-μm bare tip fiber in contact mode. Eight different laser parameter combinations [power, continuous-wave (cw)/pulsed-modulated (pm) mode, and exposure time] were used. Exposure times were chosen to give the same total applied energy of 4 J for comparative purposes. Following laser irradiations, tissues were processed and stained with hematoxylin and eosin for macroscopic evaluation of ablation areas and total altered areas, and ablation efficiencies were calculated. Temperature of the nearby tissue at a distance of 1 mm from the fiber was measured, and rate of temperature change was calculated. A strong correlation between the rate of temperature change and ablation area was noted. Thermal effects increased with increasing power for both modes. The continuous-wave mode yielded higher ablation efficiencies than the pulse-modulated mode. Histological evaluation revealed a narrow vacuolization zone and negligible carbonization for higher-power values.

Non-invasive measurement of the temperature rise in tissue surrounding a kidney stone subjected to ultrasonic propulsion.

Transcutaneous focused ultrasound (US) is used to propel kidney stones using acoustic radiation force. It is important to estimate the level of heating generated at the stone/tissue interface for safety assessment. An in-vitro experiment is conducted to measure the temperature rise in a tissue-mimicking phantom with an embedded artificial stone and subjected to a focused beam from an imaging US array. A novel optical-imaging-based thermometry method is described using an optically clear tissue phantom. Measurements are compared to the output from a fine wire thermocouple placed on the stone surface. The optical method has good sensitivity, and it does not suffer from artificial viscous heating typically observed with invasive probes and thermocouples.

Analysis of cooling effect by blood vessel on temperature rise due to ultrasound radiation in tissue phantom

Ultrasound diagnostic equipment using ultrasound pulse–echo techniques is considered minimally invasive and highly versatile. However, one of the causes of damage due to ultrasound radiation is temperature rise caused by the absorption of sound energy. Therefore, it is very important to estimate the temperature rise caused by the radiation of ultrasound. Sound intensity in a medium is analyzed by the finite-difference time-domain (FDTD) method, and the temperature distribution caused by sound is estimated by the heat conduction equation (HCE) method in this study. Because blood vessels keep the temperature constant in tissues, the cooling effect of blood flow has to be taken into account for the precise estimation of temperature rise in human tissues. In general, it is well known that capillary vessels are mainly responsible for the cooling effect in tissues and their effect can be estimated as a function of bloodstream ratio. In this paper, a preliminary study on the cooling effect by a large vessel is described for the precise estimation of temperature rise. Blood flow in blood vessels is analyzed using the Navier–Stokes equation. To confirm the precision of the numerical analysis, the results of the numerical analysis are compared with the experimental results using a soft tissue phantom.

Imaging and sensing based on dual-pulse nonlinear photoacoustic contrast: a preliminary study on fatty liver.

The feasibility of diagnostic imaging and tissue characterization based on a new contrast realized by dual-pulse photoacoustic measurement was studied. Unlike current photoacoustic methods which are mostly focused on the measurement of tissue optical absorption, this contrast revealed by a dual-pulse laser excitation process takes advantage of the temperature dependence of the Grüneisen parameter of tissue. The first laser pulse heats the sample and causes a temperature rise in the target tissue, which leads to a change of the Grüneisen parameter and the amplitude of the photoacoustic signal from the second laser pulse. This new contrast is then quantified by percentile change in the second pulse signal as a result of the first laser pulse. Since the temperature-dependent Grüneisen parameter is tissue specific and closely relevant to chemical and molecular properties of the sample, the dual-pulse photoacoustic measurement can differentiate various tissue types and conditions. The preliminary study on phantoms and a mouse model has suggested the capability of the proposed contrast in the characterization of fatty livers and the potential for future clinical diagnosis of liver conditions.

Development of an endoluminal high-intensity ultrasound applicator for image-guided thermal therapy of pancreatic tumors.

An ultrasound applicator for endoluminal thermal therapy of pancreatic tumors has been introduced and evaluated through acoustic/biothermal simulations and ex vivo experimental investigations. Endoluminal therapeutic ultrasound constitutes a minimally invinvasive conformal therapy and is compatible with ultrasound or MR-based image guidance. The applicator would be placed in the stomach or duodenal lumen, and sonication would be performed through the luminal wall into the tumor, with concurrent water cooling of the wall tissue to prevent its thermal injury. A finite-element (FEM) 3D acoustic and biothermal model was implemented for theoretical analysis of the approach. Parametric studies over transducer geometries and frequencies revealed that operating frequencies within 1-3 MHz maximize penetration depth and lesion volume while sparing damage to the luminal wall. Patient-specific FEM models of pancreatic head tumors were generated and used to assess the feasibility of performing endoluminal ultrasound thermal ablation and hyperthermia of pancreatic tumors. Results indicated over 80% of the volume of small tumors (~2 cm diameter) within 35 mm of the duodenum could be safely ablated in under 30 minutes or elevated to hyperthermic temperatures at steady-state. Approximately 60% of a large tumor (~5 cm diameter) model could be safely ablated by considering multiple positions of the applicator along the length of the duodenum to increase coverage. Prototype applicators containing two 3.2 MHz planar transducers were fabricated and evaluated in ex vivo porcine carcass heating experiments under MR temperature imaging (MRTI) guidance. The applicator was positioned in the stomach adjacent to the pancreas, and sonications were performed for 10 min at 5 W/cm2 applied intensity. MRTI indicated over 40°C temperature rise in pancreatic tissue with heating penetration extending 3 cm from the luminal wall.

Noninvasive Imaging of Thermal Fields Induced in Soft Tissues In Vitro by Pulsed Focused Ultrasound Using Analysis of Echoes Displacement

Abstract Therapeutic and surgical applications of focused ultrasound require monitoring of local temperature rises induced inside tissues. From an economic and practical point of view ultrasonic imaging techniques seem to be the most suitable for the temperature control. This paper presents an implementation of the ultrasonic echoes displacement estimation technique for monitoring of local temperature rise in tissue during its heating by focused ultrasound The results of the estimation were compared to the temperature measured with thermocouple. The obtained results enable to evaluate the temperature fields induced in tissues by pulsed focused ultrasonic beams using non-invasive imaging ultrasound technique

Three-dimensional analysis of temperature rise in soft tissue with bone near the focal area caused by focused ultrasonic radiation

Three-dimensional analysis of temperature rise in soft tissue with bone near the focal area caused by focused ultrasonic radiation

Experimental system for in-situ measurement of temperature rise in animal tissue under exposure to acoustic radiation force impulse.

Acoustic radiation force impulse (ARFI) has recently been used for tissue elasticity measurement and imaging. On the other hand, it is predicted that a rise in temperature occurs. In-situ measurement of temperature rise in animal experiments is important, yet measurement using thermocouples has some problems such as position mismatch of the temperature measuring junction of the thermocouple and the focal point of ultrasound. Therefore, an in-situ measurement system for solving the above problems was developed in this study. The developed system is composed mainly of an ultrasound irradiation unit including a custom-made focused transducer with a through hole for inserting a thin-wire thermocouple, and a temperature measurement unit including the thermocouple. The feasibility of the developed system was evaluated by means of experiments using a tissue-mimicking material (TMM), a TMM containing a bone model or a chicken bone, and an extracted porcine liver. The similarity between the experimental results and the results of simulation using a finite element method (FEM) implied the reasonableness of in-situ temperature rise measured by the developed system. The developed system will become a useful tool for measuring in-situ temperature rise in animal experiments and obtaining findings with respect to the relationship between ultrasound irradiation conditions and in-situ temperature rise.

In Vivo Monitoring of HIFU Induced Temperature Rise in Porcine Liver Using Magnetic Resonance Thermometry1

High intensity focused ultrasound (HIFU) is a noninvasive medical procedure during which a large amount of energy is deposited in a short duration, which causes sudden localized rise in tissue temperature, and ultimately, cell necrosis. In the preclinical characterization of thermal fields generated by HIFU systems, the temperature rise in an ex vivo or an in vivo tissue must be accurately measured. The temperature rise can be measured using thin wire thermocouples or magnetic resonance (MR) thermometry. Among the two methods, thermocouples can be embedded invasively in the animal tissue, and HIFU induced temperature rise can be measured by focusing the beam on the thermocouple junction for the desired sonication time. However, the temperature rise measured using thermocouples is subject to several significant sources of error. One source of error associated with direct HIFU sonication of thermocouples is viscous-heating artifact [1]. Positioning errors represent another challenge in measuring temperature by locating beam atop a thermocouple [2]. Consequently, it has been difficult to accept that the temperature recorded by the thermocouple is the actual temperature at the focus of the HIFU beam. Therefore, there is a need for a method that can address these limitations. Unlike the measurement of temperature using thermocouples, the MR thermometry is a noninvasive method that does not suffer from the problems of positioning error and thermal artifacts. The magnetic resonance imaging (MRI) scanner is capable of assessing the transient temperature rise across the treatment volume, as well as measuring the volume of the thermal lesion [3]. Although the MR temperature monitoring was used to evaluate the feasibility of MR-guided HIFU ablation in the liver and kidney [4], the effect of higher acoustic powers on initiation of cavitation and possible maximum temperature rise in these organs were not assessed using MR thermometry. In this study, MR thermometry was used to monitor HIFU ablations performed on in vivo porcine livers, at elevated acoustic powers of 10 W, 30 W, and 40 W to assess the temperature field where initiation of cavitation is known to occur. Temperature rise during the heating phase as well as the temperature decay during the cooling phase was acquired. The transient temperature profiles measured during the heating and cooling phases for the three powers were compared, in order to check the HIFU induced maximum temperature rise.

Synergistic Ablation of Liver Tissue and Liver Cancer Cells with High-Intensity Focused Ultrasound and Ethanol

We investigated the combined effect of ethanol and high-intensity focused ultrasound (HIFU), first, on heating and cavitation bubble activity in tissue-mimicking phantoms and porcine liver tissues and, second, on the viability of HepG2 liver cancer cells. Phantoms or porcine tissues were injected with ethanol and then subjected to HIFU at acoustic power ranging from 1.2 to 20.5 W (HIFU levels 1–7). Cavitation events and the temperature around the focal zone were measured with a passive cavitation detector and embedded type K thermocouples, respectively. HepG2 cells were subjected to 4% ethanol solution in growth medium (v/v) just before the cells were exposed to HIFU at 2.7, 8.7 or 12.0 W for 30 s. Cell viability was measured 2, 24 and 72 h post-treatment. The results indicate that ethanol and HIFU have a synergistic effect on liver cancer ablation as manifested by greater temperature rise and lesion volume in liver tissues and reduced viability of liver cancer cells. This effect is likely caused by reduction of the cavitation threshold in the presence of ethanol and the increased rate of ethanol diffusion through the cell membrane caused by HIFU-induced streaming, sonoporation and heating.

The Effect of the Electrical Stimulation on Temperature Rise in the Retinal Tissue for Visual Prostheses

Visual perception which is one of the most valuable perceptions for human beings may be lost over time because of various diseases such as Age Related Macular Degeneration (AMD) and Retinitis Pigmentosa (RP). These degenerative diseases cause severe damage to the certain parts of visual pathway and irreversible blindness. For the past last decades, with the improvements in the areas such as microelectronics, neuroscience and bioengineering, researches conducting on design and implementation of visual prosthetics become a promising therapeutic approach for the visual restoration. Visual perception, called phosphene, is reported to be obtained in studies which are based on electrical stimulation of the intact parts of the visual pathway. There are major factors that have to be considered in the design stage of a visual prosthesis system. One of them is the temperature change of the targeted retinal tissue and its surrounding due to electrical stimulation. In this study, a model is created to investigate thermal influence of an implant placed internal surface of the retinal tissue and solution is made using finite element analysis. It is shown that the temperature rise has highest value near the stimulation electrode and its surroundings in the case of using the model with thermal insulation. When the heat transfer mechanism is added to the simulation model, it is seen that the temperature rise is less and looks more realistic. With additive effect of heat transfer to the surrounding tissue and distance from stimulation electrode, temperature decreases away from the stimulation electrode.

High intensity focused ultrasound ablation of ethanol-treated liver tissues and cancer cells

We have investigated the combined effect of HIFU and ethanol injection on the temperature rise and cavitation in porcine liver tissues and on the viability and proliferation rate of HepG2 liver cancer cells. Tissues were injected with 95% ethanol before being subjected to the HIFU beam generated by a 1.1 MHz transducer with acoustic power ranged from 1.17 W to 20.52 W. Cavitation events and the temperature in and around the focal zone were measured by a passive cavitation detector and type K thermocouples, respectively. In the cell study, 100 μl of HepG2 cell suspension (2.7 million cells/ml) was placed in a 0.2 ml thin-wall PCR tube. Ethanol 2% or 4% in the cell growth medium was added to the cell suspension, and the cells were then exposed to HIFU for 30 s. The data of these experiments show that the pre-treatment of tissues with ethanol reduces the threshold power for inertial cavitation and increases the temperature rise. Both the viability and proliferation rate were significantly decreased in cells treated with ethanol and HIFU, as compared to individual treatments. The results of our study indicate that ethanol injection and HIFU have a synergistic effect on liver cancer ablation.

Analysis of Temperature Rise Induced by High-Intensity Focused Ultrasound in Tissue-Mimicking Gel Considering Cavitation Bubbles

High-intensity focused ultrasound (HIFU) causes a selective temperature rise in tissue and is used as a noninvasive method for tumor treatment. However, there is a problem in that it typically takes several hours to treat a large tumor. The development of a highly efficient method is required to shorten the treatment time. It is known that cavitation bubbles generated by HIFU enhance HIFU heating. In this study, the enhancement of the heating effect by cavitation was estimated in a numerical simulation solving a bio-heat transfer equation (BHTE) by increasing the absorption coefficients in and out of the volume of cavitation bubbles. The absorption coefficients were obtained by a curve fitting the temperature rise near the focal point between experiment and simulation. The results show that cavitation bubbles caused the increase in ultrasonic absorption not only in but also near the volume of cavitation bubbles.