Approved for public release; distribution is unlimited / The computerized measurement of thermoacoustically generated temperature gradients in short, thin plates is reported. The computerized data acquisition system is delineated. The temperature difference developed across a stack of short plates was measured as a function of the longitudinal position of the plates in a resonant tube for acoustic pressure amplitudes of 0.5 to 6.6 kPa, and static (or mean) pressures from 100 to 440 kPa, in argon and helium for the first through the third harmonic frequencies of the tube. Measured data were compared with predictions based on work done by Wheat ley and others [J. Wheatley, et al., Journal of the Acoustical Society of America, v. 74, pp. 153-170, 1983] and results reported by Muzzerall (Master's Thesis in Engineering Acoustics, Naval Postgraduate School, Monterey, CA, September 1987). For low acoustic and static pressures, there is good agreement between measured data and theory. As the acoustic pressure amplitudes increase there is a general degradation of agreement up to the point at which it appears saturation of the thermoacoustic effect occurs. / http://archive.org/details/computerizedmeas00kite / Lieutenant Commander, United States Navy

<p>QC 20170517</p>

No description available.

A system comprising of a personal microcomputer and a Digital Signal Processor board has been assembled and programmed for real-time spectral analysis of Doppler ultrasound signals. Three spectrum analysis techniques were implemented to run in real-time on the system: The fast Fourier transform (FFT), the autoregressive (AR) model, and the moving average (MA) model. The FFT and the AR techniques were investigated in some depth. The advantages of using such a system are that it is entirely programmable, cheap, reliable, and that the processed information can be stored on diskettes. The inputs to the system are the forward and reverse components of the Doppler ultrasonic signal, and the outputs are the sonogram, the frequency envelope, and the intensity weighted mean frequency curve, which are presented on the screen and can be saved to diskette. Five frequency ranges can be selected by the operator, from 1.28 kHz to 20.48 kHz, corresponding to sampling frequencies from 2.56 kHz to 40.96 kHz. Most commercial systems for real-time spectral analysis of Doppler ultrasonic signals implement the modified FFT-periodogram technique for power spectral density estimation (PSDE), which is computationally very efficient but has some shortcomings, especially for the analysis of relatively short records. With the AR model approach the spectra can be estimated from short segments, no antileakage window is necessary and the spectral resolution is better than for the FFT. A study of some methods for order selection used with the autoregressive model for the spectrum analysis of Doppler signals is reported and the use of a fixed order of around 12 is suggested for the AR model. The implementation of the AR PSDE approach in real-time, in a reasonably priced system, is a step towards the practical use of the so called 'modern techniques' for spectral analysis of Doppler ultrasonic signals, but further work has to be done on the validation of the technique in clinical usage.

The cardiovascular system is an important part of the human body since it transports both energy and oxygen to all cells throughout the body. Diseases in this system are often dangerous and cardiovascular diseases are the number one killer in the western world. Common cardiovascular diseases are heart attack and stroke, which origins from obstructed blood flow. It is generally important to understand the causes for these cardiovascular diseases. The main causes for these diseases are atherosclerosis development in the arteries (hardening and abnormal growth). This transform of the arterial wall is believed to be influenced by the mechanical load from the flowing blood on the artery and especially the tangential force the wall shear stress. To retrieve wall shear stress information in arteries invivo is highly interesting due to the coupling to atherosclerosis and indeed a challenge. The goal of this thesis is to develop, describe and evaluate an in-vivo method for subject specific wall shear stress estimations in the human aorta, the largest artery in the human body. The method uses an image based computational fluid dynamics approach in order to estimate the wall shear stress. To retrieve in-vivo geometrical descriptions of the aorta magnetic resonance imaging capabilities is used which creates image material describing the subject specific geometry of the aorta. Magnetic resonance imaging is also used to retrieve subject specific blood velocity information in the aorta. Both aortic geometry and velocity is gained at the same time. Thereafter the image material is interpreted using level-set segmentation in order to get a three-dimensional description of the aorta. Computational fluid dynamics simulations is applied on the subject specific aorta in order to calculate time resolved wall shear stress distribution at the entire aortic wall included in the actual model. This work shows that it is possible to estimate subject specific wall shear stress in the human aorta. The results from a group of healthy volunteers revealed that the arterial geometry is very subject specific and the different wall shear stress distributions have general similarities but the level and local distribution are clearly different. Sensitivity (on wall shear stress) to image modality, the different segmentation methods and different inlet velocity profiles have been tested, which resulted in these general conclusions: The aortic diameter from magnetic resonance imaging became similar to the reference diameter measurement method. The fast semi-automatic level-set segmentation method gave similar geometry and wall shear stress results when compared to a reference segmentation method. Wall shear stress distribution became different when comparing a simplified uniform velocity profile inlet boundary condition with a measured velocity profile. The method proposed in this thesis has the possibility to produce subject specific wall shear stress distribution in the human aorta. The method can be used for further medical research regarding atherosclerosis development and has the possibility for usage in clinical work.

Chapter 1, an introduction to the use of ultrasound in physiotherapy and in hyperthermia is given. Previous studies in ultrasound physiotherapy and hyperthermia are reviewed but the emphasis is given to those which investigated the mechanisms responsible for the beneficial effects of therapeutic ultrasound and for the efficacy of cell killing of ultrasound hyperthermia. A review of the studies of the non-thermal effects of ultrasound is the subject of Chapter 2. Some recent studies carried out in this field in our laboratory are included. Knowledge of acoustical power, spatial peak and spatial average intensities are central to useful studies of bioeffects and to patient safety in the cases of therapy and clinical hyperthermia. Some techniques for measurements of ultrasound dosimetry which have been employed (and studied) are outlined in Chapter 3. At present the total power output from a therapeutic transducer is often derived by measuring the radiation force of the ultrasonic beam exerting on either a total absorber or a total reflector suspended at 45 to vertical. In Chapter 4 and Chapter 5, I discuss some new problems of these techniques and the magnitude of errors which might be caused. Chapter 6 and Chapter 7 present the results of theoretical studies of the field distri-butions from a plane circular piston transducer under both progressive and standing wave conditions. The effect of wave diffraction on the field distribution, bulk streaming and mea-surement of radiation force using a plane reflector is discussed. The ratio of the spatial peak to spatial average intensity for plane circular transducers in a progressive field is theoretic-cally calculated and compared with experimental results. The question of how to define the standing wave ratio is considered by taking into account of the effect of wave diffraction. Chapter 8 and Chapter 9 concern the thermal distributions generated by ultrasound in tissues. An experimental study of the temperature distributions in tissue/bone phantoms induced by therapeutic ultrasound using infra-red technique is described in Chapter 8. In Chapter 9 the thermal patterns generated by a plane circular transducer in a 3-D tissue model were calculated and they were compared with the experimental results described in the previous chapter. The thermal distributions generated by an applicator consisting of five divergent transducers were simulated in the same tissue model. Possible advantages of using such an applicator for ultrasound therapy and for treating large superficial tumours are discussed.

No description available.

Ultrasound (the frequency range above 20 KHz) at intensities of 0-3.0 Wcm-2 is used in physical medicine to treat a variety of conditions (joint contractures, fibrosis and scarring and severe pain due to disorders such as frozen shoulder and capsulitis). It is believed to produce a reduction in pain and swelling and increase movement of joints affected by diseases such as arthritis. It is also used to generate hyperthermia for the treatment of neoplastic tumours. The technique involves irradiating tissues with either continuous or pulsed mode ultrasound, using either the field from a single or multielement transducer. Geometrically similar ultrasound transducers even from the same batch can have significantly different efficiencies and the resulting field distributions can also vary. There are several pieces of information required to characterize an ultrasound source. They are frequency, power output, spatial average and spatial peak intensity and details of ultrasonic field distribution. This application of ultrasound requires an experimental method to define the intensity distribution generated by a transducer or array of transducers. A number of different techniques have been used to record intensity distribution. These include sheets of liquid crystal on an absorbing surface, detection of signals using hydrophone probes, thermocouple probes, thermistor probes and the Schlieren technique. The dye/paper method and Starch iodine plate have been developed for the observation of the ultrasonic fields and evaluation of the source pattern.

A new type of ultrasound power meter is described which is robust, portable, easy to operate and therefore suitable for use in the work place by non-specialist personnel. The device should be of particular value in the field of ultrasonic therapy, where a lack of suitable instrumentation has discouraged performance monitoring of ultrasound machines in the past although numerous surveys have found the calibration of such equipment generally to be poor. The mode of operation is based on absorption of the ultrasound beam within a liquid, which expands as the energy becomes degraded to heat. The rate of this thermal expansion is monitored by means of a capacitative liquid level sensor, the output signal being suitably processsed and passed to a microcomputer for analysis. Correction for interchange of heat with the surroundings is carried out automatically by the micro, by recording the 'background drift' in liquid volume for a few seconds prior to insonation and subtracting this from the expansion rate observed during input of ultrasound. Calibration is achieved by measuring the (corrected) expansion rates brought about by known powers supplied from an electrical heating coil. When using the new power meter for measurements of therapeutic ultrasound the performance compares favourably with that of other techniques: the reproducibility is on the order of 5% above about 0.5W, becoming less good below this (reaching about 20% at the minimum measurable power of 25-50mW). Design modifications which may improve performance at low power levels and possibly allow measurement of dignostic ultrasound are suggested.

In this thesis we consider the problem of the dynamic fluid-structure interaction between a finite elastic structure and the acoustic field in an unbounded fluid-filled exterior domain. We formulate the exterior acoustic problem as an integral equation over the structure surface. However, the classical boundary integral equation formulations of this problem do not have unique solutions at certain characteristic frequencies (which depend on the surface) and it is necessary to employ modified boundary integral equation formulations which are valid for all frequencies. The modified integral equation formulation used here involves certain arbitrary parameters and we shall study the effect of these parameters on the stability and accuracy of the numerical methods used to solve the integral equation. We then couple the boundary element analysis of the exterior acoustic problem with a finite element analysis of the elastic structure to investigate the interaction between the structure and the acoustic field. Recently there has been some controversy over whether or not the coupled problem suffers from the non-uniqueness problems associated with the classical integral equation formulations of the exterior acoustic problem. We resolve this question by demonstrating that the solution to the coupled problem is not unique at the characteristic frequencies and that we need to employ an integral equation formulation valid for all frequencies. We discuss the accuracy of our numerical results for both the acoustic problem and the coupled problem, for a number of axisymmetric and fully three-dimensional problems. Finally, we apply our method to the problem of a piezoelectric sonar transducer transmitting an acoustic signal in water, and observe reasonable agreement between our theoretical predictions and some experimental results.