Finite amplitude effects on the thresholds for lesion production in tissues by unfocused ultrasound

Abstract

The phenomenon of thermal lesion production in tissues by unfocused ultrasound has been modeled under the assumptions (1) that damage to the tissues is the result of a chemical rate process and (2) that the time-temperature exposure of the tissue results from a competition between the rate of heat generation by absorption of ultrasonic energy and thermal diffusion. The model was tested by observing thresholds for color change in samples of excised bovine liver at 6 cm from a 2.25-MHz, 1.27-cm-diam piston source and 11.5 cm from a 4.4-MHz, 1.27-cm source. The observations disagreed sharply with predictions of the linear model. However, after recognition of the fact that finite amplitude phenomena modify the effective absorption coefficients of the tissues, the model gives excellent predictions of observed thresholds simply by using intensity dependent values of the absorption coefficients in the numerical calculations. Thermoelectric and radiation force methods were used to demonstrate the noblinear absorption phenomenon in excised liver. In contrast with the case of focused ultrasound, the thresholds for lesion formation by unfocused sources (1) occur at lower intensities, (2) are strongly dependent upon frequency, and (3) because acoustic saturation in the coupling medium imposes lower limits on tissue intensities for unfocused than for focused ultrasound, unfocused lesions are limited to relatively long exposure times.

Quantitative MRI-based temperature mapping based on the proton resonant frequency shift: Review of validation studies

“…It should be noted that the above equation, and the underlying Arrhenius model on which it was based, was developed as a simplification of experimental data. Other models for tissue damage have been proposed as well [33][34][35].…”

Effects of High-Energy Focused Ultrasound on Kidney Tissue in the Rat and the Dog

“…For a given amount of energy, destruction may involve two distinct physical effects depending on acoustic inten sity: a thermal effect, on one hand, which is obtained by using long periods of exposure and low ultrasonic intensi ties, as is the case in certain therapeutic procedures such as treatment of benign prostatic hypertrophy with ultra sound hyperthermia; cavitation, on the other hand, which applications. Various experiments on tissue (cat brain, rabbit kidney, liver and testes) have been carried out in this context by several authors [2][3][4][5][6], They have demon strated that tissue lesions particularly occur at the focus of the ultrasound transducer, caused by focused thermal effect [7] when acoustic energy is delivered with moderate intensity (less than 500 W/cm2) and the time of exposure is greater than 1 s. When acoustic energy is delivered with high-intensity ultrasound (greater than 3,000 W/cm2) and short exposure time, tissue lesions linked to cavitation occur [8]. Recently Vallancien et al [9] and Ter Haar et al [10] obtained lesions of localized tissue necrosis respec tively in cat liver and in pig kidney in vivo, by using highintensity focused ultrasound.…”

Temperature elevation in tissues generated by finite-amplitude tone bursts of ultrasound

“…The enhancement of temperature elevation in tissues due to the presence of harmonics of finite-amplitude ultrasonic beams has been known for some time (Carstensen et al, 1981(Carstensen et al, , 1982(Carstensen et al, , 1990Swindell, 1985). However, as pointed out by Bacon and Carstensen (1990) that in many clinical ultrasound applications, the contribution of the harmonics to tissue heating is not important.…”

“…Ultrasound is one of the most desirable ways of creating local hyperthermia, since it can be focused deep into tissues (Lele, 1979). In ultrasonic hyperthermia applications, more effective transducers and transducer arrays are now being developed to generate a precisely controllable and uniform temperature rise restricted to a preselected volume Lerner et al, 1973;Filipczynski, 1978Filipczynski, , 1986Carstensen et al, 1981;Hynynen et al, 1982) have studied and predicted the temperature rise due to ultrasound for some special situations. Chan et al (1973) were the first to solve a onedimensional bioheat equation numerically including perfusion by using the method of finite differences in a situation of multiple layered tissues (fat, muscle, and bone).…”

“…Ultrasonic examination in obstetrics is one of the examples: A fetus is examined by ultrasound through the full bladder, which is filled with low-absorptive fluid. Existing theoretical treatments of the temperature elevation generated by finite-ampliutde ultrasound, for example, shock waves, to the best of our knowledge, did not take full account of the interaction of the shock waves with the medium through which it propagates, but only included the nonlinear effects by recognizing the fact that the effective absorption coefficients of the medium are functions of intensity of the waves (Carstensen et al, 1981(Carstensen et al, , 1982. In other words, the heat source function, qo was still assumed to be equal to 2aI as is that of a linear single-frequency wave case (see discussion in Sec.…”