Bioacoustics Research Lab
University of Illinois at Urbana-Champaign | Department of Electrical and Computer Engineering | Department of Bioengineering
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William D. O'Brien, Jr. publications:

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Title Temperature distributions in tissues during local hyperthermia by stationary or steered beams of unfocused or focused ultrasound.
Author Lele PP, Parker KJ.
Journal Br J Cancer Suppl
Volume
Year 1982
Abstract Temperature distributions resulting from insonation with stationary or steered beams of unfocused or focused ultrasound were measured in tissue-equivalent phantom, beef muscle in vitro, dog muscle mass, and transplanted murine tumours in vivo. Arrays of 4 to 6 thermocouples stepped through the volume of interest under computer control were used to measure the steady-state temperatures at 600 to 800 locations in both in vitro and in vivo experiments. The results were confirmed in spontaneous tumours in dog patients using fewer multi-thermocouple probes. Plane wave ultrasound was found to result in spatially non-uniform hyperthermia even in superficial tumours. The region of maximum temperature rise was small in.extent and was situated at a depth which varied in the different models from 0.5 to 1.0 cm. Neither its location nor its extent could be varied by spatial manipulations of the transducer or by changing the insonation parameters except the ultrasonic frequency. A second region of hyperthermia was produced at depth by reflective heating if an ultrasonically reflective target, such as bone or air-containing tissue, was located below the target tissue. On the other hand, using available steered, focused ultrasound techniques, tumours (whether situated superficially.or at depth) could be heated to a uniform, controllable temperature without undesirable temperature elevation in surrounding normal tissues. The use of steered, focused ultrasound permits deposition of energy to be tailored to the specific needs of each individual tumour. The small size of the focal region enables heating of tumours even when located near ultrasound reflecting targets.


Title Temperature distributions obtainable in tissue as a result of ultrasonic irradiation.
Author ter Haar G.
Journal Proc First Meet Eur Group Hyperthermia Radiat Oncol
Volume
Year 1979
Abstract If the heating properties of ultrasonic beams are to be used for the hyperthermic treatment of tumours, it is important that the interaction of ultrasound with tissue is understood, and that the influence of the various ultrasound and tissue parameters on the resulting temperature distribution is known. This paper shows the way in which ultrasonic intensity, ultrasonic frequency, attenuation coefficient and water bath temperatures affect the shape of these temperature distributions. An example of the interaction of a focussed field with tissue is also shown.


Title Temperature elevation generated by a focused Gaussian beam of ultrasound.
Author Wu JR, Du GH.
Journal Ultrasound Med Biol
Volume
Year 1990
Abstract The steady state temperature elevation generated by a focused Gaussian beam, including the effect of perfusion, has been calculated along the beam axis. The medium is assumed to be a.homogeneous absorbing one. The results indicate: (1) The temperature rise is an increasing function of the intensity gain of the focusing transducer, but never seems to exceed twice that at the interface of the transducer and the medium generated by its unfocused counterpart; and (2) The temperature rise at the interface of the transducer and the medium is not affected significantly by focusing.


Title Temperature elevation in a beam of ultrasound.
Author Nyborg WL, Steele RB.
Journal Ultrasound Med Biol
Volume
Year 1983
Abstract Computations are made of the temperature elevation expected at points along the axis of an unfocussed beam of ultrasound in a homogeneous absorbing medium. A simplified model is used in which the intensity is assumed uniform over a cross section. Heat conduction is taken into account, but not convection or perfusion. Results are presented for frequencies from 1 to 10 MHz and beam diameters from 0.2 to 2.4 cm. The results include limiting temperatures, reached at infinite time, as well as temperature vs time characteristics. As an example for certain conditions (transducer diameter 1.2 cm, frequency 4 MHz, intensity at the transducer 0.1 W/cm2, tissue acoustically similar to liver, transducer thermal conductivity similar to that of tissue) the temperature elevation produced at a distance 2 cm from the transducer is calculated to be 0.61 ?C after 253s; it then increases more and more slowly, approaching, but never exceeding 1.46C.


Title Temperature elevation in focused Gaussian ultrasonic.beams at various insonation times.
Author Filipczynski L, Kujawska T, Wojcik J..Department of Ultrasonics, Polish Academy of Sciences, Warsaw.
Journal Ultrasound Med Biol
Volume
Year 1993
Abstract Transient solution of the thermal conductivity equation for the three-dimensional case of the.Gaussian ultrasonic focused beam was derived and applied for cases relevant to medical.ultrasonography. Quantitative results for the case of a homogeneous medium with constant.values of thermal coefficients and constant absorption as well as for the two-layer tissue model.used in obstetrics were presented for various diagnostic probes used in ultrasonography. The.possible effects of perfusion and nonlinear propagation were neglected. The results obtained are.in agreement with results of other authors when considering the steady-state and the infinitely.short insonation time. The computations show the influence of the insonation time on the.temperature elevation, thus making it possible to introduce its value as a factor in limiting the.possible harmful effects in ultrasonography. This has been shown in diagrams presenting the.temperature distribution along the beam axis of 6 different diagnostic probes for various.insonation times and demonstrating the corresponding temperature decrease when limiting the.insonation time to 5 and 1 min. For instance, the highest temperature elevation (for probe number.1, see Table 1) decreases 2.6 and 5 times with respect to the steady-state temperature when the.insonation time equals 5 and 1 min, respectively.


Title Temperature elevation in the rat fetus due to ultrasound exposure.
Author Abraham V, Ziskin MC, Heyner S.
Journal Ultrasound Med Biol
Volume
Year 1989
Abstract The temperature elevation resulting from sonically generated heat in rat fetuses was measured for various intensity levels. The temperature elevation produced inside the fetus was higher than that on the outside surface. In live fetuses, a portion of the heat generated was carried off by the circulating blood. The temperature elevation curves were used to estimate the absorption coefficient of rat fetuses. Absorption coefficient values range from 0.065 to 0.086 Np/cm at 1 MHz. The present results are consistent with a theoretical model of temperature elevation in a heated sphere.


Title Temperature elevation in tissues generated by finite-amplitude tone bursts of ultrasound.
Author Wu J, Du G.
Journal J Acoust Soc Am
Volume
Year 1990
Abstract The temperature elevation in tissues generated by an ultrasonic beam of plane sawtooth wave tone bursts along its axis is calculated based on a solution of an extended Burgers? equation for a medium with loss due to various relaxation processes. The absorption coefficient of the medium is assumed to be proportional to frequency to the b th power (1*b*1.4). The results show that when the power generated by a transducer is kept constant, an enhancement of temperature rise in the medium due to narrow- and high-amplitude bursts of ultrasound is evident. For example, if spatial-peak temporal-average intensity, I(sub)SPTA = 0.1 W/cm2 = const, the temperature rise generated by sawtooth wave tone bursts with a duty factor of 10(exp)-4 [I(sub) SPPA = 1000 W/cm2 at the low-loss fluid and tissue interface where the sawtooth wave just forms) is about twice that generated by its corresponding linear continuous wave counterpart.


Title Temperature elevations computed for three-layer and four-layer obstetrical tissue models in nonlinear and linear ultrasonic propagation cases.
Author Wojcik J, Filipczynski L, Kujawska T.
Journal Ultrasound Med Biol
Volume
Year 1999
Abstract The authors computed temperature elevations in a three-layer and a four-layer tissue model, assuming the crucial obstetrical case when the ultrasonic pulse propagating through the abdominal wall and the fluid-filled bladder penetrates into soft fetal tissues. To consider nonlinear propagation, the authors applied a new theory of nonlinear increase of absorption recently developed by the first author. Computations were carried out for pulses with a carrier frequency of 3 MHz, duration time of 1.33 microseconds, and pulse repetition frequency of 3.3 kHz. Similar computations were carried out for a four-layer tissue model corresponding to the third trimester of gestation. The ceramic piezoelectric transducer 2 cm in diameter radiated the ultrasonic beam focused at a distance of 6.5 cm. The intensities at the radiating transducer (at the source) were I(SAPA) = 10 and 5 W/cm2. Temperature elevations and distributions were determined numerically for various values of low-amplitude absorption coefficients assumed to be the same as attenuation coefficients. It was shown in the three-layer tissue model that the maximum temperature elevation can be about 50% higher for nonlinear than for linear propagation.The maximum fetal temperature elevation in this case was 2.36 degrees C for nonlinear and 1.84 degrees C for linear propagation. The temperature elevation in the abdominal wall was lower than those temperatures when the attenuation of the abdominal wall was assumed to be a low value of 0.05 Np/cm.MHz (0.45 dB/cm.MHz). However, when it was increased to 0.16 Np/cm.MHz (1.4 dB/cm.MHz), the temperature elevation of the abdominal wall reached 3.2 degrees C and the maximum fetal elevation was 1.65 degrees C. In such cases, the abdominal wall became the principal source of heat production. In this case, the difference between fetal temperature elevations for nonlinear and linear propagation was only about 10%. The results obtained in the four-layer tissue model, in which the uterus tissue also was represented, show that temperature elevations in this case are about 3.6 times lower than in the three-layer tissue model, with comparable attenuation of the abdominal wall. Differences between nonlinear and linear propagation in the four-layer tissue model are negligible. The temperature elevations obtained were proportional to the pulse repetition frequency, without changing temperature distributions in the ultrasonic beam. In this manner, fetal temperature elevations can be reduced by reducing the repetition frequency.


Title Temperature increase estimates for transabdominal obstetrical exposures.
Author O'Brien WD Jr.
Journal Proc Ultrason Symp IEEE
Volume
Year 1998
Abstract The purpose of the contribution is to estimate the temperature increase for transabdominal obstetrical exposures. The monopole-source solution was used to calculate the 3D complex acoustic pressure field for focused circular apertures from which the 3D temperature distribution was calculated using the bio-heat transfer equation in a layered, perfused media. For the 114 cases, the acoustic field was normalized to the transmit acoustic power required for the derated spatial peak, temporal average intensity ISPTA.3 equal to 720 mW/cm2 for the applicable homogeneous tissue model, the maximum value allowed by the FDA 510(k) diagnostic ultrasound equipment approval process. For the ISPTA.3=720 mW/cm2 condition, the axial temperature increase profiles and maximum temperature increases were determined within the anterior abdominal wall and conceptus. Also, from the normalized acoustic field, the soft-tissue thermal index TIS was determined according to the procedures of the output display standard. The results suggest that the TIS is an adequate indicator for monitoring the myometrium's, and possibly the fetus', maximum temperature increase.


Title Temperature increase in a two-layer obstetric model of tissues in the case of linear and nonlinear propagation of a continuous ultrasonic wave.
Author Filipczynski L, Wojcik J.
Journal Arch Acoust
Volume
Year 1995
Abstract The object of the present study was the analysis of temperature effects which arise in a two-layer tissue model applied in obstetrics, from the point of view of continuous wave radiation of a focussed Gaussian ultrasound beam. In particular, the authors considered nonlinear propagation using the weak shock theory and compared the results of the analysis with those obtained assuming linear propagation. It was demonstrated that for 3 MHz, 10 cm focal length of the beam, the transducer diameter of 1 cm and the intensity of 0.1 W/cm2 the schock parameter does not then exceed 1.66(exp)0 cm. For a radiated intensity equal to 1 W/cm2 the shock coefficient is higher than unity, causing losses related to nonlinear propagation. The temperature distributions were determined along the beam axis using both the weak shock theory and the linear propagation procedure.


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