Ultrasound Heating Research Articles

Magnetic resonance temperature imaging-based quantification of blood flow-related energy losses.

This study presents a new approach for evaluating bioheat transfer equation (BHTE) models used in treatment planning, control and evaluation of all thermal therapies. First, 3D magnetic resonance temperature imaging (MRTI) data are used to quantify blood flow-related energy losses, including the effects of perfusion and convection. Second, this information is used to calculate parameters of a BHTE model: in this paper the widely used Pennes BHTE. As a self-consistency check, the BHTE parameters are utilized to predict the temperatures from which they were initially derived. The approach is evaluated with finite-difference simulations and implemented experimentally with focused ultrasound heating of an ex vivo porcine kidney perfused at 0, 20 and 40 ml/min (n = 4 each). The simulation results demonstrate accurate quantification of blood flow-related energy losses, except in regions of sharp blood flow discontinuities, where the transitions are spatially smoothed. The smoothed transitions propagate into estimates of the Pennes perfusion parameter but have limited effect on the accuracy of temperature predictions using these estimates. Longer acquisition time periods mitigate the effects of MRTI noise, but worsen the effect of flow discontinuities. For the no-flow kidney experiments the estimates of a uniform, constant Pennes perfusion parameter are approximately zero, and at 20 and 40 ml/min the average estimates increase with flow rate to 3.0 and 4.2 kg/m(3) /s, respectively. When Pennes perfusion parameter values are allowed to vary spatially, but remain temporally constant, BHTE temperature predictions are more accurate than when using spatially uniform, constant Pennes perfusion values, with reductions in RMSE values of up to 79%. Locations with large estimated perfusion values correspond to high flow regions of the kidney observed in T1 -weighted MR images. This novel, MRTI-based technique holds promise for improving understanding of thermal therapy biophysics and for evaluating biothermal models.

20704 FDTD法による簡易モデルを用いた集束超音波加温システムの基礎検討

In the clinic, High Intensity Focused Ultrasound (HIFU) is used to non-invasive treatments for cancers. However, it is not easy to rapidly monitor temperature elevations which reach higher than 60℃ and may cause undesirable thermal injuries. On the other hand, hyperthermia treatment is based on the clinical fact that cancer cells are more weaker than healthy cells hi the temperature range of 42-43℃. In this study, we propose a new type of transducer for hyperthermia treatments with focused ultrasound heating energy to expand the heating area. First, we presented a new type of transducer model for computer simulations. Next, we calculated pressure distributions using a Finite-Difference Time-Domain (FDTD) method with the proposed transducer model. From these results, it was found that the proposed transducer was useful for hyperthermia treatments.

Development of robust/predictive control strategies for image-guided ablative treatments using a minimally invasive ultrasound applicator

Purpose: One important challenge in image-guided ablative therapies is the effect of heat diffusion which can cause damage to surrounding organs and limit the ability to achieve a conformal pattern of thermal damage. Furthermore, tissue properties such as perfusion and energy absorption can be dynamic and difficult to measure. This paper attempts to address these problems by proposing new control methods. Materials and methods: A novel predictive approach was developed to compensate for the effect of heat diffusion using a minimally invasive rotating ultrasound heating applicator for ablative therapy. This method can be merged into any closed-loop control strategy. A binary controller, a previously developed adaptive proportional-integral controller, and a model reference adaptive controller were employed and compared, all with the predictive element incorporated. The reason for choosing these controllers was that none of them needed a model of the tissue or exact values of their parameters. Results: The effectiveness of these controllers was demonstrated through both simulation and experimental studies. The results were consistent and demonstrated equivalent performance between controllers. Conclusions: The dominant influence on radial targeting accuracy was the prediction element described in this paper. A binary controller with a predictive element may provide the best balance of performance and simplicity for this application.

Rapid dynamic R1/R2*/temperature assessment: a method with potential for monitoring drug delivery

Local drug delivery by hyperthermia-induced drug release from thermosensitive liposomes (TSLs) may reduce the systemic toxicity of chemotherapy, whilst maintaining or increasing its efficacy. Relaxivity contrast agents can be co-encapsulated with the drug to allow the visualization of the presence of liposomes, by means of R2 *, as well as the co-release of the contrast agent and the drug, by means of R1, on heating. Here, the mathematical method used to extract both R2 * and R1 from a fast dynamic multi-echo spoiled gradient echo (ME-SPGR) is presented and analyzed. Finally, this method is used to monitor such release events. R2 * was obtained from a fit to the ME-SPGR data. Absolute R1 was calculated from the signal magnitude changes corrected for the apparent proton density changes and a baseline Look-Locker R1 map. The method was used to monitor nearly homogeneous water bath heating and local focused ultrasound heating of muscle tissue, and to visualize the release of a gadolinium chelate from TSLs in vitro. R2 *, R1 and temperature maps were measured with a 5-s temporal resolution. Both R2 *and R1 measured were found to change with temperature. The dynamic R1 measurements after heating agreed with the Look-Locker R1 values if changes in equilibrium magnetization with temperature were considered. Release of gadolinium from TSLs was detected by an R1 increase near the phase transition temperature, as well as a shallow R2 * increase. Simultaneous temperature, R2 * and R1 mapping is feasible in real time and has the potential for use in image-guided drug delivery studies.

High intensity ultrasound assisted heating to improve solubility, antioxidant and antibacterial properties of chitosan-fructose Maillard reaction products

This study investigated chitosan-fructose Maillard reaction (MR) induced by high intensity ultrasound-assisted (UA) water-bath heating at 80 °C in a model system consisting of 1% chitosan and 0.5, 1 or 1.5% fructose solution (FS). Based on the yield of Maillard reaction products (MRPs), the optimal UA heating conditions were 7, 5 and 8 h for 0.5, 1 and 1.5% FS, respectively, whereas they were 7, 8, and 7 h for 0.5, 1 and 1.5% FS, respectively for water-bath heating alone. Under the optimal conditions, the solubility of MRPs produced by UA heating reached 8.35–9.65 g/L versus 5.32–7.37 g/L without UA heating. The yield of MRPs from UA heating and water-bath heating alone was 12.45–18.86% and 5.78–10.02%, respectively. Reducing power (0.40–0.65), DPPH free radical scavenging capacity (79.71–98.70%) and ORAC (533.30–1218.62 μmol TE/L) of MR solutions from UA heating were higher than those from water-bath heating alone. MRPs showed higher antibacterial activity against Staphylococcus aureus (MIC of 2500 mg/L) and Escherichia coli (MIC of ∼313–625 mg/L) than that of native chitosan, but no difference was found in MRPs from water-bath heating alone. This study suggested that the high intensity UA water-bath heating could produce water soluble chitosan-fructose MRPs with significantly improved functionality.

The Effect of Prenatal Ultrasound Heating Throughout Gestation on Rabbit Fetal Weight

The aim of this in vivo experimental study is to determine the association between ultrasound exposure time and rabbit fetal weight. A total of 14 pregnant does were exposed to ultrasound heating for 30, 60, and 90 minutes of ultrasound exposure at their middle of each gestational stage, while another 4 pregnant does served as control. Total of 136 fetuses (1st stage, n=34 (25%); 2nd stage, n=28 (20.6%); 3rd stage, n=74 (54.4%)) were analyzed for fetal body weight. There were significant differences in fetal weight at all stages (p<0.05; 95% CI do not cross 0) of all groups at different length of exposure time. There were also negative correlation between groups with different exposure durations and fetal weight in the 1st and the 3rd stage (p<0.05; r = -0.40, p<0.05; r = -0.23 respectively). Exposure time was found poorly associated with fetal weight in the 1st and the 3rd stage (p<0.05; r2 = 0.15 and 0.04 respectively). This study suggests the heating effect of ultrasound exposure might act as a noxious agent that promotes intrauterine growth restriction in developing fetus that might consequently impacts the rabbit fetal weight. Therefore a considerably increase in awareness of negligible effects aroused from prenatal ultrasound exposure was concerned as it was widely applied to pregnant women.

ChemInform Abstract: Synthesis of Highly Basic Hexasubstituted Biguanides by Environmentally Friendly Methods.

AbstractVarious methods such as high speed vibrational milling, high pressure, ultrasound, microwave irradiation, and conventional heating conditions are employed for the reaction of tetramethylguanidine with carbodiimides.

Feasibility of non-invasive temperature estimation by the assessment of the average gray-level content of B-mode images

This paper assesses the potential of the average gray-level (AVGL) from ultrasonographic (B-mode) images to estimate temperature changes in time and space in a non-invasive way.Experiments were conducted involving a homogeneous bovine muscle sample, and temperature variations were induced by an automatic temperature regulated water bath, and by therapeutic ultrasound. B-mode images and temperatures were recorded simultaneously. After data collection, regions of interest (ROIs) were defined, and the average gray-level variation computed. For the selected ROIs, the AVGL–Temperature relation were determined and studied. Based on uniformly distributed image partitions, two-dimensional temperature maps were developed for homogeneous regions. The color-coded temperature estimates were first obtained from an AVGL–Temperature relation extracted from a specific partition (where temperature was independently measured by a thermocouple), and then extended to the other partitions. This procedure aimed to analyze the AVGL sensitivity to changes not only in time but also in space.Linear and quadratic relations were obtained depending on the heating modality. We found that the AVGL–Temperature relation is reproducible over successive heating and cooling cycles. One important result was that the AVGL–Temperature relations extracted from one region might be used to estimate temperature in other regions (errors inferior to 0.5°C) when therapeutic ultrasound was applied as a heating source. Based on this result, two-dimensional temperature maps were developed when the samples were heated in the water bath and also by therapeutic ultrasound. The maps were obtained based on a linear relation for the water bath heating, and based on a quadratic model for the therapeutic ultrasound heating. The maps for the water bath experiment reproduce an acceptable heating/cooling pattern, and for the therapeutic ultrasound heating experiment, the maps seem to reproduce temperature profiles consistent with the pressure field of the transducer, and in agreement with temperature maps developed by COMSOL®MultiPhysics simulations.

Effects of processing parameters on cellular ceramics obtained by paraffin emulsified suspensions

Cellular ceramics were processed by emulsification of alumina suspensions with melted paraffin. Stabilization upon drying was promoted by collagen additions and solidification of the paraffin droplets. Consolidation allows easy elimination of the paraffin droplets on heating at relatively low rate (1–5°Cmin−1), with a plateau at 200°C, and then heating up to the firing temperature (1550°C). A Taguchi plan was used to assess the relative impact of solids loading, paraffin to suspension volume ratio, ultrasound stirring time and heating rate on microstructural features of sintered bodies. Increasing solids loading suppresses the cellular size, with negative impact on total porosity, whereas increasing paraffin:suspension volume ratio contributes to enhance porosity with a slight increase in average cellular size. Ultrasound stirring yields a slight decrease in porosity and also average cellular size. The heating schedule in the early stages of paraffin elimination contributes to changes in cellular size distribution, with important effects on compressive strength.

Influence of low Intensity Ultrasound and Ohmic Heating on Growth and Metabolism of Microorganisms

Influence of low Intensity Ultrasound and Ohmic Heating on Growth and Metabolism of Microorganisms

Local heating of a liquid-like medium by a phase-conjugate ultrasound beam with self-adaptive focusing

Local heating of a liquid-like medium by means of self-adaptive focusing of a high-power phase conjugate ultrasound wave has been experimentally implemented. A sample of organic silicon polymer with a reflecting inhomogeneity was placed in water and exposed to a plane ultrasound beam so as to make the reflected acoustic field partially to enter the phase conjugation device. A parametrically amplified and conjugate wave was self-adaptively focused back to the inhomogeneity. Thermocouple measurements revealed ultrasound heating, which was localized near the inhomogeneity and depended weakly on its position within the aperture of the incident ultrasound beam. Themaximum heating value was about 6.5°C in 120 s with a frequency of ultrasound of 4.75MHz and a mean power of phase conjugate wave of about 0.1W.

Estimating temperature in perfused tissue phantoms subject to ultrasound heating

Thermal therapies using induced ultrasound temperature require more research on spatial-temporal temperature propagation over tissues to allow non-invasive and more efficient treatment. This article presents a comparison between the temperature variations induced by therapeutic ultrasound (TU) on phantoms including or not a blood vessel and reports the usage of a square fitting curve to estimate the temperature based on the temporal echo shifts (TES) computed from the RF-lines signals collected by an imaging ultrasound (IU). Three in-vitro experiments were developed based on a gel phantom: a homogeneous phantom and two perfused phantoms, one mimicking right hepatic artery the other common carotid artery. Phantoms were heated with a TU device emitting continuously and temperature was measured by thermocouples placed 50 mm distant from TU transducer face. Experimental results show that a 3 mm blood vessel could reduce temperature in more than 50 % if placed at the TU's axial line when compared with non-perfused phantom. Despite all the dependencies, results also show that temperature estimation can be accomplished when a second order polynomial is applied through TES results. This study confirms that TES relates nonlinearly with temperature and constitutes a reliable noninvasive method of monitoring temperature in perfused tissues.

In vivo evaluation of multi‐echo hybrid PRF/T1 approach for temperature monitoring during breast MR‐guided focused ultrasound surgery treatments

To evaluate the precision of in vivo temperature measurements in adipose and glandular breast tissue using a multi-echo hybrid PRF/T1 pulse sequence. A high-bandwidth, multi-echo hybrid PRF/T1 sequence was developed for monitoring temperature changes simultaneously in fat- and water-based tissues. The multiple echoes were combined with the optimal weightings for magnitude and phase images, allowing for precise measurement of both T1 and the proton resonance frequency (PRF) shift. The sequence was tested during in vivo imaging of 10 healthy volunteers in a breast-specific MR-guided focused ultrasound system and also during focused ultrasound heating of excised breast adipose tissue. The in vivo results indicated that the sequence can measure PRF temperatures with 1.25 × 1.25 × 3.5 mm resolution, 1.9 s temporal resolution, and 1.0°C temperature precision, and can measure T1 values with 3.75 × 3.75 × 3.5 mm resolution, 3.8 s temporal resolution, and 2.5%-4.8% precision. The excised tissue heating experiments demonstrate the sequence's ability to monitor temperature changes simultaneously in water- and fat-based tissues. The addition of a high-bandwidth, multi-echo readout to the hybrid PRF/T1 sequence improves the precision of each measurement, providing a sequence that will be beneficial to several MR-guided thermal therapies.

Prenatal ultrasound heating impacts on fluctuations in haematological analysis of Oryctolagus cuniculus.

Prenatal Ultrasound (US) is commonly used as a routine procedure on pregnant women. It is generally perceived as a safe procedure due to the use of non-ionizing radiation. However, the neurotoxicity of diagnostic prenatal US was detected to have a correlation with high susceptibility to early developing fetus. This research involved in vivo experimental model by using 3(rd) trimester pregnant Oryctolagus cuniculus and exposing them to US exposures for 30, 60, and 90 minutes at their gestational day (GD) 28-29. The output power and intensities, spatial peak temporal average intensity (ISPTA) of US were varied from 0.4 to 0.7 W and 0.13 to 0.19 W/cm(2) respectively were tested initially in free-field, water. Haematological analysis was carried out to detect any changes in blood constituents. Statistically significant differences were detected in red blood cell (RBC) count (P<0.001), haemoglobin (Hb) concentration (P<0.001) and also platelet (PLT) count (P<0.001) in newborn of Oryctolagus cuniculus. These findings indicate the possibility of US heating in causing defects on studied animal.

Dual perfluorocarbon nanodroplets enhance high intensity focused ultrasound heating and extend therapeutic window in vivo

Perfluorocarbon microbubbles are known to enhance high intensity focused ultrasound (HIFU) ablation by cavitation. However, they can result in superficial skin heating, minimizing their clinical translation. Perfluorocarbon nanodroplets activate only at the higher pressures present at the acoustic focus. We hypothesized that a mixed perfluorocarbon nanodroplet formulation would minimize surface heating while still enhancing ablation. Tissue-mimicking phantoms containing microbubbles or nanodroplets were sonicated (1 MHz, 15 W, 60 s) to assess heating and lesion formation in vitro. Microbubbles or nanodroplets were injected into rats (n = 3) and HIFU (1 MHz, 15 W, 15 s) was focused into each liver while under MRI guidance. Temperature throughout the liver was tracked by MR thermometry. In vitro, microbubbles caused excess surface heating during HIFU, whereas nanodroplets did not. In vivo, microbubbles typically circulate for less than 15 min. In comparison, the nanodroplets remained viable in circulation for at least 96 min. HIFU lesions of consistent volume were produced during this time and reached the same maximal temperature rise (Δ550 °C). In the absence of nanodroplets or microbubbles, significantly greater power (25 W) and twice as much time (30 s) was required to generate an ablation lesion in the liver. These results demonstrate the ability of nanodroplets to more safely shorten ablation procedures.

Coupling of drug containing liposomes to microbubbles improves ultrasound triggered drug delivery in mice

Local extravasation and triggered drug delivery by use of ultrasound and microbubbles is a promising strategy to target drugs to their sites of action. In the past we have developed drug loaded microbubbles by coupling drug containing liposomes to the surface of microbubbles. Until now the advantages of this drug loading strategy have only been demonstrated in vitro. Therefore, in this paper, microbubbles with indocyanine green (ICG) containing liposomes at their surface or a mixture of ICG-liposomes and microbubbles was injected intravenously in mice. Immediately after injection the left hind leg was exposed to 1MHz ultrasound and the ICG deposition was monitored 1, 4 and 7days post-treatment by in vivo fluorescence imaging. In mice that received the ICG-liposome loaded microbubbles the local ICG deposition was, at each time point, about 2-fold higher than in mice that received ICG-liposomes mixed with microbubbles. We also showed that the perforations in the blood vessels allow the passage of ICG-liposomes up to 5h after microbubble and ultrasound treatment. An increase in tissue temperature to 41°C was observed in all ultrasound treated mice. However, ultrasound tissue heating was excluded to cause the local ICG deposition. We concluded that coupling of drug containing liposomes to microbubbles may increase ultrasound mediated drug delivery in vivo.

Ultrasound-assisted Acid red dye removal using leather fibre wastes as matrix: ‘intra wastes interaction’ approach

It is desirable to make effective use of solid wastes, as well as waste liquors, of the dye house generated from leather processing. The present study deals with the adsorption of Acid red 26 (Xylidine ponceau) dye using leather fibre waste (buffing dust) as substrate matrix by the means of ultrasound, magnetic stirring and conventional heating. The research examined the effect of various process parameters: ultrasonic power, concentration of dye, temperature and time. The dye uptake data have been fitted with Freundlich and Langmuir isotherms, indicating a useful dye adsorption process. A mechanism for dye adsorption in leather fibres has also been proposed. This study shows that it is possible to remove dyes from dye house effluent streams using leather waste fibres of buffing dust by means of ultrasound. Two different toxic wastes produced by the same industry can be effectively contained. This ‘Intra wastes interaction’ approach could reduce the burden of discarding wastes of other materials in the leather industry.

Ultrasound thermal mapping based on a hybrid method combining cross-correlation and zero-crossing tracking

A hybrid method for estimating temperature with spatial mapping using diagnostic ultrasound, based on detection of echo shifts from tissue undergoing thermal treatment, is proposed. Cross-correlation and zero-crossing tracking are two conventional algorithms used for detecting echo shifts, but their practical applications are limited. The proposed hybrid method combines the advantages of both algorithms with improved accuracy in temperature estimation. In vitro experiments were performed on porcine muscle for preliminary validation and temperature calibration. In addition, thermal mapping of rabbit thigh muscle in vivo during high-intensity focused ultrasound heating was conducted. Results from the in vitro experiments indicated that the difference between the estimated temperature change by the proposed hybrid method and the actual temperature change measured by the thermocouple was generally less than 1 °C when the increase in temperature due to heating was less than 10 °C. For the in vivo study, the area predicted to experience the highest temperature coincided well with the focal point of the high-intensity focused ultrasound transducer. The computational efficiency of the hybrid algorithm was similar to that of the fast cross-correlation algorithm, but with an improved accuracy. The proposed hybrid method could provide an alternative means for non-invasive monitoring of limited temperature changes during hyperthermia therapy.

Toward real-time temperature monitoring in fat and aqueous tissue during magnetic resonance-guided high-intensity focused ultrasound using a three-dimensional proton resonance frequency T1 method

To present a three-dimensional (3D) segmented echoplanar imaging (EPI) pulse sequence implementation that provides simultaneously the proton resonance frequency shift temperature of aqueous tissue and the longitudinal relaxation time (T1 ) of fat during thermal ablation. The hybrid sequence was implemented by combining a 3D segmented flyback EPI sequence, the extended two-point Dixon fat and water separation, and the double flip angle T1 mapping techniques. High-intensity focused ultrasound (HIFU) heating experiments were performed at three different acoustic powers on excised human breast fat embedded in ex vivo porcine muscle. Furthermore, T1 calibrations with temperature in four different excised breast fat samples were performed, yielding an estimate of the average and variation of dT1 /dT across subjects. The water only images were used to mask the complex original data before computing the proton resonance frequency shift. T1 values were calculated from the fat-only images. The relative temperature coefficients were found in five fat tissue samples from different patients and ranged from 1.2% to 2.6%/°C. The results demonstrate the capability of real-time simultaneous temperature mapping in aqueous tissue and T1 mapping in fat during HIFU ablation, providing a potential tool for treatment monitoring in organs with large fat content, such as the breast.

Grooved conjugation ferrite element for ultrasound heating of a biological tissue phantom

A possibility of using a parametric ultrasound phase conjugation system with a grooved ferrite element for hyperthermal heating of a biological tissue phantom is experimentally investigated. The grooved surface of the ferrite element improves the quality of phase conjugation. With focused conjugate beams, this is supposed to lead to an increase in the ultrasound intensity and accordingly to more effective heating of the medium due to ultrasound absorption. The results of the investigation prove this supposition: ultrasound heating by 8.0°C in about 80 s is obtained for a sample with an inserted thermocouple placed between a focused piezoelectric transducer, which radiated a test wave with a frequency of 5.0MHz, and a system for phase conjugation and amplification of ultrasound.