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The structural characteristics of a health3 tendon are related to the anisotropic speckle patterns observed in ultrasonic images. This speckle orientation is disrupted upon damage to the tendon structure as observed in patients with tendinopathy. Quantification of the structural appearance of tendon shows promise in creating a tool for diagnosing, prognosing, or measuring changes in tendon organization over time. The current work describes a first step taken towards this goal--classification of Achilles tendon images into tendinopathy anti control categories. Eight spatial frequency parameters were extracted from regions of interest on tendon images, filtered and classified using linear discriminant analysis. Resulting algorithms had better than 80% accuracy in categorizing tendon image kernels as tendinopathy or control. Tendon images categorized wrongly provided for an interesting clinical association between incorrect classification of tendinopathy kernels as control and the symptom and clinical time history based inclusion criteria. To assess intersession reliability of image acquisition, the first 10 subjects were imaged twice during separate sessions. Test-retest of repeated measures was excellent (r = 0.996, ICC (2,1) : 0.73 with one outlier) indicating a general consistency in imaging techniques. Index Terms--Classifier, image analysis, tendinopathy, tendon, ultrasound.

The article describes the application of minimum variance beamformer to medical ultrasound imaging which show a significant performance improvement in comparison to delay-and-sum (DAS).

The speckle reducing anisotropic diffusion filter can easily adapt the anisotropic diffusion filter to the various characteristics of the speckle noise present in the ultrasound images and also facilitate automatic processing of images. The properties of the numerical scheme associated with this filter are analyzed using a semi-explicit scheme.

The different methods of parallel beamforming are investigated that aims at eliminating the flaw and restoring the shift invariance property. The results have shown that straightforward parallel beamforming reduces the spatial shift invariance property of an ultrasound imaging system and the proposed method of using synthetic transmit beams have enabled higher acquisition rates without loss of image quality.

A research interface for an ultrasound system, which provides several basic capabilities normally unavailable on a clinical screener, is developed under a contract with the National Cancer Institute. The uses of the ultrasound research interface (URI) are illustrated on elastography, computed tomography and spatial compounding.

The impact of contrast agent infusion rates (IR) on thresholds for tissue injury is examined to ascertain the possible influence of IR for microbubble-enhanced ultrasound treatment. Results reveal that introduction of microbubble at IR up to a fixed level might prove successful in helping ultrasound therapy.

A multiparameter approach involving classification of breast masses in ultrasonic B-scan images is described and discussed.

Force-free images can provide diagnostic information unavailable in other image types.

Performance of an ultrasono-therapy transducer with contact detection is examined and reported.

Performance effects of a preclassification stage that subdivides tissue regions of interest (ROI) and classifies subregions based on scatterer structure types are examined and reported.

A procedure is proposed for imaging the relative tissue stiffness in medical ultrasound diagnostic equipment. The procedure makes use of tissue characteristics that respond differently to external vibration.

Centroid shift from signals backscattered from trabecular bone samples in vitro are measured and discussed.

An architecture of a hardware and software platform for ultrasonic diagnosis is described and discussed.

Cell membrane damage induced by diagnostic ultrasound exposure with a contrast agent is described and discussed. Its relation to the display of stimulated acoustical emissions in Doppler images is examined.

An extrapolation technique for strengthening the lateral resolution of pulse-echo imaging systems is described and discussed.

Research describing the attenuation properties of human calcaneus at high frequencies is presented. The results of the study indicate that ultrasonic attenuation exhibits a linear dependence on frequency.

Single-photon emission computed tomography (SPECT) and ultrasonic diffraction tomography (UDT) are tomographic imaging modalities that are based upon entirely different physical processes. In SPECT, from the measured intensity of the electromagnetic wave (i.e., the gamma-ray), one seeks to determine the distribution of the gamma-ray emitter within an object. In UDT, from the measured scattered fields (i.e., the scattered ultrasonic wave), one determines the refractive index distribution. However, in this work, we demonstrate that the mathematics describing image reconstruction and the statistical analysis of image-noise properties are virtually identical for SPECT and UDT. We also conducted computer-simulation studies, which quantitatively corroborated our theoretical analysis.

Ultrasound backscattering is well adapted to study the red blood cell (RBC) aggregation phenomenon and growth of RBC aggregates since the backscattered ultrasonic intensity depends on the sixth power of the mean radius of the scattering centers when considered as spherical. Thus, small variations of aggregate size induce large variations of the backscattered intensity. From measurements of the ultrasonic backscattering coefficient (ultrasonic backscattering cross section per unit volume of suspension), an analytical model describing its variation versus time, for human aggregated red blood cells in sedimentation, is proposed. Results given by the model allow to define three phases in the phenomenon: 1) a starting phase characterized by a duration [t.sub.s]; 2) a stationary final phase beginning at time [t.sub.f]; 3) a growing intermediate phase characterized by its duration [t.sub.f] - [t.sub.s]. The analytical model has been applied to describe RBC aggregation in dextran 70 000 dalton of different concentrations, and at various hematocrits. Knowledge of the durations [t.sub.s], [t.sub.f] and the maximum slope s of the curve during the intermediate phase, determined with the model, allows a means to study RBC aggregate growth. Index Terms - Analytical model, red blood cell aggregation, sedimentation, ultrasound backscattering.

A study was conducted to test a theoretical analysis for interpreting statistical characteristics of spectral parameters used for ultrasonic evaluation in the prostate and liver. Theoretical results are compared with clinical data obtained from abdominal and prostate examinations. These results are congruent with clinical data and are applicable to spectrum analysis examinations of other organs.

A theoretical and numerical study of the acoustic field intensity within a curved flow conduit having 1) diameter similar to the wavelength of the interrogating frequency and 2) speed of sound mismatch with the surrounding medium is presented. The field intensity is shown to vary significantly and in a monotonic fashion across the flow conduit. The resulting insonation of emboli transiting through the Doppler sample volume is explored with a Monte Carlo study of the behavior of the embolus to blood power ratio (EBR). The numerical simulation findings are shown to be in good agreement with previously reported experimental results. A method is explored for estimating embolus diameter when this refraction artifact is present, and shown to yield excellent results when applied to experimental data. Further work toward clinical application of these results is discussed.

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.

An experiment to verify a theory describing ultrasound backscattering from emboli in flowing blood is presented. The theoretical predictions for the backscattered power versus embolus size are based on the measurement of the embolus to blood ratio (EBR) of backscattered acoustic power. This tool is necessary for in vivo clinical application because it removes the need to characterize attenuation and reflection loss in heterogeneous tissue. The experiment presented utilizes a customized ultrasound pulse Doppler that is capable of interrogating a sample volume with two different frequencies concurrently. A flow circuit including a 3.6-mm-diameter conduit in polyacrylamide gel in which emboli are observed with the dual frequency Doppler is described. The flow within the circuit has acoustic backscatter coefficient similar to blood due to a calibrated concentration of 31.1-[Mu] diameter polystyrene microspheres. Polystyrene micro-sphere 'emboli' having nominal diameters of 161 and 239 [Mu] are placed in this flow loop and time series Doppler shift signatures are recorded. These signatures are investigated and a refraction artifact hypothesis is proposed to explain systematic deviation of the signatures away from theoretically expected results. Results show that gross discrimination of embolus size is feasible.

A comparison study is reported on the ultrasonic assessment of human trabecular and bovine trabecular bone samples. Both ultrasonic velocity and ultrasonic attenuation were evaluated through a transmission insertion technique and correlated with bone mineral density as determined with single photon absorptiometry. For a 1-MHz ultrasonic transducer pair and the human cancellous bone samples the correlations were 0.91 and 0.89 between density and velocity and attenuation, respectively. For a 500-kHz ultrasonic transducer pair the correlations were 0.89 and 0.81 between density and velocity and attenuation, respectively. For the bovine bone samples, the correlations were 0.90 and -0.31 for the velocity and attenuation, respectively, for the 1 MHz transducer pair. For the 500-kHz transducers, the correlations were 0.85 and -0.17 for the velocity and attenuation, respectively. By combining both velocity and attenuation in a multivariate regression, an improvement was achieved in the estimation of bone density in the human samples for both the 500-kHz and 1-MHz transducer pairs. No significant improvement was achieved in the multivariate regressions for the bovine bone samples. In conclusion, the results indicate that ultrasonic measurements are in general highly correlated with bone mineral density in trabecular bone samples. This correlation is more consistent and strong in relatively low density human samples compared with the higher density bovine samples.

A study determines the effects of diminished low frequency response by the single-pole high-pass filtering of simulated lithotrispy and diagnostic pulses for a range of cutoff frequencies. Simulation results for the pulse and filter models show that the hydrophone or the associated low frequency response have pronounced effects on the measured waveform. Guidelines for the low frequency response of hydrophones are discussed.

A mathematical model for ultrasonic backscattering in a transmural cube of normal myocardium based on Born approximation helps characterize the correlation between angle of insonification of lateral and basal views, and backscattering. Basal face insonification results in large transmural changes while the maximum variation between basal and lateral views was 18 dB. The mathematical model confirms the experimental results and also indicates the anisotropic characteristics of the backscattering and the correlation between fiber orientation and backscatter.

Use of a C-scan microscopy system and a 60 MHz PVDF copolymer transducer enables the determination of the ultrasonic properties of ocular tissues of cornea, sclera, iris and ciliary body in the 50 to 100 MHz frequency range at 37 degrees Celsius. The acoustic properties of the four ocular tissues depend on their respective structures, with sclera displaying the maximum attenuation coefficient, velocity and backscatter coefficient than other tissues. Scleral tissue, but not the other three tissues, can easily undergo differentiation.

Output levels and bioeffects indices due to ultrasound exposure, which were obtained from diagnostic ultrasound exposure data, were submitted to the US Food and Drug Administration (FDA). The data provided information regarding the exposure levels of current devices relevant to ultrasound-induced biological effects.

The backscattering coefficient of saline suspensions of porcine red blood cells was measured for hematocrits up to about 90%. It was found that the coefficient peaks at approximately 15%, but then, contrary to what a simple 'gap theory' might suggest, it decays smoothly to zero, without showing another peak at high hematocrits. A one-dimensional (1-D) slab scattering model, in which the number of slabs per unit length represents the hematocrit and whose thickness and acoustical properties are similar to red cells/plasma, was also used to investigate the relation between the backscattered power and hematocrit. Monte-Carlo simulations performed for randomized boundary conditions show a similar relation to that of the 3-D system. The experimental data is compared to the Percus-Yevick theory for the packing of hard spheres, and the simulated data is compared to the Percus-Yevick theory for infinite slabs.

The temperature rise at the interface between skin tissue and a focused diagnostic ultrasound from linear arrays or sector scanners was investigated. The study, which assumed an adiabatic tissue surface for absorption-caused heating, produced an acoustic-thermal model that considers the effects of focusing and attenuation. Its application on 1400 transducers revealed that optimal heating occurs at thetransducer-tissue interface than at the focal region.

In vivo and in vitro ultrasonic experiments to evaluate the autoregressive spectral estimation approach againstthe fast Fourier transform-based periodogram method of approximating mean scatterer spacing are presented. The tissue characterization experiments show the superiority of the autoregressive-moving average technique in providing superresolution, noise suppression, bias reduction and lesser ringing artifacts.

A proposed method in producing diced two-dimensional array materials from lead zirconate titanate-5A and epoxy is presented with measurements of pulse shapes and radiation patterns derived from the arrays' single elements. The conventional diced-array element patterns are simulated using a cross-coupling continuous wave diffraction theory which conforms well with experimental data. However, isolated element single mode vibration characteristics which are coupled electrically and by a single acoustic wave propagating through the array limits the method.

Ultrasonic diagnosis was performed in an in vitro experiment to study the occurence of transient cavitation, the speedy build-up and collapse of a gas-filled cavity. The experiment used a Hewlett-Packard clinical diagnostic scanner to probe water with 30 MegaHertz (MHz) pulses. Observations revealed cavitation in water with polystrene spheres at 2.5 MHz in the M-mode and Doppler mode coinciding with negative acoustic pressure of 1.1 MegaPascals or more.

The development, construction and subsequent testing of a sector-vortex phased-array applicator for ultrasound hyperthermia are discussed. Designed as a 32-element, two-track system for 750 kHz operation, the applicator yielded annular focal fields without any undesired foci. This is obtained by the Mth order Bessel function approximation during driven array phase distributiom. Its focal acoustic power compared to computer simulation forecasts is evaluated.

Research describing ultrasound induced lung hemorrhage in rats and mice as a consequence of safety concerns for diagnostic ultrasound is presented. Two experiments are reported that compare the incidence and size of lesions induced for cross species comparison.

Research is presented describing the development of a distortion detecting device for use with ultrasonic imaging systems.