摘要:

This review is concerned with (1) certain physiological and structural changes produced in tissues of the central nervous system caused by high level ultrasound and (2) investigations into the physical mechanisms underlying these changes.The cell bodies of neurons in the central nervous system are particularly susceptible to change by ultrasound. The effect of irradiation is immediately evident as a loss of function which may be reversible or irreversible depending on the dosage. Irreversible changes in function are accompanied by changes in the structure of the cell. The susceptibility of neurons studied so far is graded according to size, the larger neurons exhibiting a greater susceptibility. The dose of ultrasound can be adjusted to cause irreversible changes in neurons without causing any observable damage to the vascular and supporting components of the tissue. This selective and specific effect of ultrasound is being used as a tool in neuroanatomical studies now in progress and has considerable potential value in neurosurgery. The ultrasound alters the state of the nerve cells and, therefore, affords a basis for studying intracellular structure and function.The physical basis for the ultrasonically produced biological effects has been investigated part. The following aspects of temperature have been analyzed and rejected: (1) High average (space) level, (2) interface heating, (3) rapid time rate of change, (4) temperature changes resulting from cavitation, (5) heating at gas nuclei. The phenomenon of cavitation is also shown to play no essential direct role in producing the effects.

ISSN:0001-4966    

DOI:10.1121/1.1907002

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

This paper is concerned with the technique of temperature measurement in living tissue during irradiation by high intensity ultrasound. The interpretation of data obtained by the use of thermocouples is presented. The specific biological object used in this study is the spinal cord of rat exposed by laminectomy. This particular preparation serves to illustrate the relative importance of the heat conduction process in contributing to the temperature change as a function of the proximity of the imbedded thermocouple to bone and the time elapsed after initiation of the exposure.The ultrasonic frequency used in these studies was 980 kc. The sound intensities incident on the cord were between 60 and 80 watts/cm2.The experimental results presented in the paper are used to obtain values for the acoustic absorption coefficient of the tissue of the spinal cord. The range of values obtained for the intensity absorption coefficient per centimeter from measurements made on six adult rats at various positions in the spinal cord is 0.19 to 0.23 if the heat capacity of the tissue at constant pressure is 1.00 calorie/cm3.

ISSN:0001-4966    

DOI:10.1121/1.1907011

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

Experiments have been carried out to investigate ultrasound as a possible therapeutic agent. These show that selective heating occurs in nerves and bones treatedin situ. Effects of direct heat on nerves are strikingly similar to the effects of ultrasound. Blocking of nerves by sound or heat with present techniques seems impractical because the margin of safety is too narrow.

ISSN:0001-4966    

DOI:10.1121/1.1906986

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

A review is presented of numerous biophysical studies concerning the action of ultrasound on living matter, with particular reference to therapeutic applications. On the basis of the experiments described. involving various physical, physiochemical, and chemical effects, it is concluded that selective heating caused by the radiation plays the major role quantitatively under therapeutic conditions. However, ultrasound also produces a mechanical effect. The diffusion layer at an interface is decreased by stirring, and thus exchange of metabolites is augmented.

ISSN:0001-4966    

DOI:10.1121/1.1907000

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The results of an experimental investigation of both the linear and nonlinear acoustic impedance of circular orifices with water and 10‐centistoke Dow Corning silicone fluid are presented. Experimental determinations of the end corrections for acoustic resistance and acoustic inductance are in good agreement with the classical end correction as given by Rayleigh for acoustic inductance. A series of determinations of the criteria for the onset of nonlinearity acoustic resistance and acoustic inductance together with photographs of the fluid flow patterns developed are presented. A characteristic of one of the fluid flow patterns is correlated with the onset of nonlinearity.

ISSN:0001-4966    

DOI:10.1121/1.1907003

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

Relations expressing the acoustic inertance and resistance of short open tubes in terms ofkvaare reviewed. The tube radius isa;kvis the complex wave number for viscosity waves. Analogous relations giving the acoustical impedance of a cylindrical cavity in terms ofkTa, wherekTis the thermal wave number, are considered. Viscous and thermal losses have sometimes been incorrectly separated in the literature. Past measurements, showing disagreement between theory and experiment for smallkva, are cited. New measurements of inertance and associated resistance, in the range of|kva|from 1 to 77, are reported. The method of standing wave analysis used. In some instances the inertance tube is incorporated in an adjustable‐cavity resonator. Inertance values after end corrections agree with theory within 2.5 percent. Corrected resistance values generally agree with theory within 3 percent for|kva|<10.Greater discrepancies for larger values ofkvaare attributed to excessive losses in very short cavities. Consideration of present results together with published data for larger values ofkvaindicates close agreement of theory and experiment for a range ofkvaextending at least from unity to several hundred.

ISSN:0001-4966    

DOI:10.1121/1.1907004

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The sound field generated by a vibrating cylinder of infinite length, whose dynamic configuration is periodic in φ andz, is expressed in terms of acoustic impedance ratios. It is noted that symmetrical modes of vibration are suppressed at certain frequencies because the corresponding reactive impedance is infinite, and that allzdependent modes become nonradiating below certain “cut‐off” frequencies, the corresponding impedance being purely reactive. Graphs are presented for the impedance ratios corresponding to certain modes.For modes independent ofz, the sound field is in the form of concentric cylindrical waves. Forzdependent modes, as the plane wave wavelength increases from zero to a certain critical cut‐off value, the sound field changes from a set of concentric cylindrical waves to two sets of conical waves of decreasing vertex angle; at and beyond the cut‐off point, the conical waves have degenerated into a set of plane standing waves normal to thezaxis. Simultaneously, the sound field has ceased being periodic in the radial direction, and the phase velocity in that direction has become infinite.Practical applications of these phenomena are suggested.

ISSN:0001-4966    

DOI:10.1121/1.1907005

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The problem of the spherical acoustic resonator containing a slightly viscous medium is considered. Derivation of the equations of sound waves in a viscous medium is carried out, and it is shown that separation of the particle velocity into a divergenceless vector and a curl‐less vector gives rise to both a vector Helmholtz equation and a scalar Helmholtz equation. By using known solutions to these equations in spherical coordinates and imposing suitable boundary conditions, the frequencies of the free vibrations are calculated as well as the attenuation constants associated with each frequency. The effect of viscosity is, thus, seen to decrease slightly the natural frequencies and to cause a time rate of decay of the free vibrations. The attenuation constant for the purely radial modes of vibration is much smaller than that for modes having tangential velocity components.

ISSN:0001-4966    

DOI:10.1121/1.1907006

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The first part of this investigation deals with the case of a simple‐harmonic wave which becomes eventually distorted into a relatively stable shape resembling the shape of a saw‐tooth wave with rounded‐off corners. A simplified‐picture theory is developed in which the wave is idealized as consisting of a non‐dissipative linear portion of length λ1and a dissipative simple‐harmonic portion of length λ2. The amplitudeAof the distorted wave and its rate of absorption αAare computed (1) from the dissipative wavelength 2λ2and (2) from the “build‐up distance”L = Nλ at which stability of shape is achieved, both λ2andNbeing regarded as experimental data. Tests of the theory are made by using shadowgrams of waves generated in air by a piezoelectric quartz at the frequency of 0.405 megacycle (see reference 2). The second part of the paper presents an approximation treatment of the classical wave equation in which either of two different transformations of variables lead to a quasi‐linear differential equation of the type∂2z/∂y2 = ∂z/∂x+∂(z2)/∂y. In the first transformation, more suitable for periodic waves,xis used for the distance from the source andyfor the time, while the reverse is done in the second transformation, more suitable for shock waves. An exact solution is given for the case of the simple‐harmonic source already discussed in the first part.

ISSN:0001-4966    

DOI:10.1121/1.1907007

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The present paper starts with a brief discussion of the two components of acoustical radiation pressure in contrast with the single component obtained for electromagnetic radiation in vacuum. The two components of acoustical radiation pressure are correlated in a simple manner with the two distinct interaction possibilities of the obstacle and the medium, i.e., interaction with the wave motion only or interaction with the wave motion as well as with the medium itself. This picture appears to be consistent with the earlier conclusions of Brillouin and Richter.Afterwards the result is generalized for dispersive media. It is shown that the component which is usually stated to be independent of the equation of state in the existing nondispersive theories should contain the time parameters of the equation of state in the form of a multiplying factor group, velocity over phase velocity.The present paper stresses the basic concepts rather than mathematical detail and concludes with an extensive bibliography and commentary.

ISSN:0001-4966    

DOI:10.1121/1.1907008

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP