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The performance of ultrasound imaging through cancellous bone for pedicle screw guidance is discussed. Results suggest the feasibility of ultrasound imaging through cancellous bone at higher frequencies.

The generation of narrowband radiation-force components at harmonic modulation frequencies model obtained by using two finite-amplitude confocal quasi-continuous-wave (CW) ultrasound beams excited at slightly different frequencies is described.

A generalized amplitude modulation signal model was developed to collectively account for the transit time effects of the ultrasound beam geometry and the range gate characteristics. Signal model and simulation results shows generalized insights on the characteristics of transit time broadening such as, for scatters passing through the center of the sample volume, the broadening extent mainly depends on beam-forming characteristics at higher beam-flow angles.

A study was conducted to analyze the statistical performance of a two-dimensional narrowband time-domain root-MUSIC blood velocity estimator using simulated and flow phantom wideband ultrasonic data. The relationship of the method to beam and vessel coordinates was also examined in the study. Results indicated that increases in sensitivity and effective clutter suppression can be determined using the method.

A study was conducted to characterize a time-domain two-dimensional narrowband velocity estimate technique that can be utilized in a color flow mapping device that supports features associated with wideband and narrowband velocity estimators. Results indicated that the method supported the use of the dominant eigenvector of the Doppler correlation matrix to minimize the Cramer-Rao bound of the narrowband velocity.

Researchers have sought to assess the accuracy and computational efficiency of various methods which have been used to measure the field profile from 1-D arrays. Particular attention was given to various estimates used for time and frequency domain solutions. It was found that the trapezoidal far-field approximation method produces accurate results with around the same computational time as the exact method. In the frequency domain, the Fresnel approximation method produces an accurate solution for the unsteered array.

Backscattering of an incident ultrasound beam by blood gives rise to a Doppler spectrum whose characteristics are affected not only by the velocity distribution, but also by certain basic aspects of the RBC's behavior. Starting from fundamental assumptions, an explicit expression is derived for the Doppler spectrum in terms of the variance in the scatterer number density and the backscattering cross section. This shows that the Doppler power at a given frequency is weighted by the backscattering cross section and the manner in which the red blood cells (RBC's) are packed (packing factor). Since spatial variations in the flow field can result in changes in the variance and backscattering cross section, the mean Doppler frequency will not necessarily be proportional to the mean flow through the sample volume. Experimental results for two different flow fields are used to illustrate these effects. The implications of these findings are discussed in relation to volumetric flow estimation and the power mode display used in some color Doppler flow imaging systems.

A new Doppler ultrasound intravascular method is described for the measurement of volumetric flow. Based on the principles described by Hottinger and Meindl, it uses a novel semispherical transducer mounted at the tip of a catheter, which generates sample volumes in the form of a thin semispherical shell. Volumetric flow is calculated by using the average velocity determined from the received Doppler spectrum and the area of intersection of a sample volume that completely intersects flow across the vessel. Although a catheter-size transducer was not developed, a larger version was tested using an in vitro steady flow model. Maximum average flow error was limited to 9% for steady flows of 2 to 7 L/min. This error is believed to be a result of the nonuniform intensity generated by the prototype transducer, as well as slight variations in the received power, rather than any fundamental limitations of the flow measurement method itself. Since this study has verified the design principles and feasibility of this new approach, we believe that more detailed experimental investigations are warranted.

Ultrasound B-mode imaging at 7MHz enables echogenicity and velocity measurements of 28% hematocrit porcine whole blood in a large diameter tube under conditions of steady flow. A digitized image correlation technique permits the calculation of shear rate profiles. The flow shear rate parameters determine optimal block dimension. A combined study of profiles and corresponding shear rate profile provide details of shear rate-dependent aggregation.

Research describing a general solution for the isotropic/homogenous scalar wave equation in cylindrical coordinates is presented. It is shown that by choosing the correct free parameter values, narrow beamwidth and large field depth X-waves are achievable.

Describes the properties of X-waves, a special class of diffractionless beams, propagating in a system with cylindrical symmetry and in a medium with classical viscous losses. Information on X-waves; Discussion on the properties of the waves for both infinite and finite size transducers; Properties for different viscous liquids.

Part I. Presents a study which examined a robust time-domain two-dimensional narrowband velocity estimation method for use in a ultrasound flow imaging. Overview of blood velocity estimation; Theoretical estimator performance; Conclusions.