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Stroke and myocardial infarction are initiated by rupturing vulnerable atherosclerotic plaques. With noninvasive ultrasound elastography, these plaques might be detected in carotid arteries. However, since the ultrasound beam is generally not aligned with the radial direction in which the artery pulsates, radial and circumferential strains need to be derived from axial and lateral data. Conventional techniques to perform this conversion have the disadvantage that lateral strain is required. Since the lateral strain has relatively poor accuracy, the quality of the radial and circumferential strains is reduced. In this study, the radial and circumferential strain estimates are improved by combining axial strain data acquired at multiple insonification angles. Adaptive techniques to correct for grating lobe interference and other artifacts that occur when performing beam steering at large angles are introduced. Acquisitions at multiple angles are performed with a beam steered linear array. For each beam steered angle, there are two spatially restricted regions of the circular vessel cross section where the axial strain is closely aligned with the radial strain and two spatially restricted regions (different from the radial strain regions) where the axial strain is closely aligned with the circumferential strain. These segments with high quality strain estimates are compounded to form radial or circumferential strain images. Compound radial and circumferential strain images were constructed for a homogeneous vessel phantom with a concentric lumen subjected to different intraluminal pressures. Comparison of the elastographic signal-to-noise ratio ([SNR.sub.e]) and contrast-to-noise ratio ([CNR.sub.e]) revealed that compounding increases the image quality considerably compared to images from 0[degrees] information only. [SNR.sub.e] and [CNR.sub.e] increase up to 2.7 and 6.6 dB, respectively. The highest image quality was achieved by projecting axial data, completed with a small segment determined by either principal component analysis or by application of a rotation matrix. Index Terms--Angular compounding, beam steering, grating lobes, noninvasive ultrasound strain imaging, vulnerable plaque.

In the present paper, we describe a method for constructing a remote ultrasound diagnostic system. Remote diagnosis can be realized using a communication network. We have developed a master--slave type remote medical system to diagnose shoulder diseases, such as dialysis-related amyloid arthropathy (DRAA), by ultrasonographic images. Proper positioning, orientation, and contact force between the ultrasound probe and the affected area of the patient are required in order to acquire proper diagnostic images. Safety and manipulability are also required when operating the remote medical system through a communication network. Therefore, the system has impedance control capability for positioning of the master and slave manipulators in order to convey the contact force and enhance manipulability. In addition, the system has continuous-path control capability for the orientation of the slave manipulator in order to realize smooth and accurate motion of the ultrasound probe, even if the sampling rate of the transmission of the orientation data of the master manipulator is not sufficient. The results of remote diagnostic experiments demonstrated that a healthcare professional could diagnose real patients through a communication network using the constructed system. Index Terms--Continuous-path control, impedance control, master--slave manipulation, remote medical system, remote ultrasound diagnostic system.

Carotid atherosclerosis is the main cause of brain stroke, which is the most common life-threatening neurological disease. Nearly all methods aiming at assessing the risk of plaque rupture are based on its characterization from 2-D ultrasound images, which depends on plaque geometry, degree of stenosis, and echo morphology (intensity and texture). The computation of these indicators is, however, usually affected by inaccuracy and subjectivity associated with data acquisition and operator-dependent image selection. To circumvent these limitations, a novel and simple method based on 3-D freehand ultrasound is proposed that does not require any expensive equipment except the common scanner. This method comprises the 3-D reconstruction of carotids and plaques to provide clinically meaningful parameters not available in 2-D ultrasound imaging, namely diagnostic views not usually accessible via conventional techniques and local 3-D characterization of plaque echo morphology. The labeling procedure, based on graph cuts, allows us to identify, locate, and quantify potentially vulnerable foci within the plaque. Validation of the characterization method was made with synthetic data. Results of plaque characterization with real data are encouraging and consistent with the results from conventional methods and after inspection of surgically removed plaques. Index Terms--Carotid atherosclerosis, labeling with graph cuts, plaque echo morphology, reconstruction, three-dimensional ultrasound.

A simple mathematical model was developed to characterize diagnostic ultrasound behavior at two-body interfaces of known geometry. The model was based on a 2-D curved-on-flat geometry comprising an infinitely long circular cylinder indenting a flat infinite half-space creating a known contact width [W.sub.0]. The effects of indenter radius [R.sub.F] ultrasound resonance wavelength [lambda]/2, and ultrasound beam thickness BT on the size of the predicted interfacial contact width [W.sub.1] were investigated. Since the model was purely geometric in nature, material properties of the mating bodies were not considered. A theoretical sensitivity analysis was performed on the model using geometries representative of commercially available orthopedic total knee replacements (TKRs) and typical diagnostic ultrasound resolutions. This investigation was part of an ongoing project to develop an engineering design tool for measuring surface contact areas at the tibio-femoral interfaces of clinically employed TKR prostheses. Index Terms--Contact area, diagnostic ultrasound, mathematical model, total knee replacement (TKR).

Contrast enhanced ultrasound imaging provides a real-time tool for evaluating vasculature in the liver. Primary liver cancer is known to be perfused exclusively by blood from the hepatic artery, whereas normal liver is also supplied by the portal vein. Visual separation of two different phases of enhancement from the independent feeding vessels is important for diagnosis but remains a challenge. This paper presents a method of using factor analysis for extracting distinct time-intensity curves. A key component to this extraction is the clustering of measured bolus curves and their projection onto a positivity domain to obtain nonnegative curves. This technique provides complementary images representing spatial loadings on each curve. As little as 1% of the data is required to contain unmixed signals to extract time-intensity curves that correlate well with true curves. A method of combining this information to display a regional hepatic perfusion image is proposed, and results are tested on a set of 10 patients. Region of interest analysis suggests it is possible to detect changes in the hepatic perfusion index of liver lesions relative to normal liver parenchyma using contrast ultrasound. Index Terms--Factor analysis, hepatic perfusion index, microbubbles, ultrasound.

Atherosclerosis at the carotid bifurcation resulting in cerebral emboli is a major cause of ischemic stroke. Most strokes associated with carotid atherosclerosis can be prevented by lifestyle/dietary changes and pharmacological treatments if identified early by monitoring carotid plaque changes. Registration of 3-D ultrasound (US) images of carotid plaque obtained at different time points is essential for sensitive monitoring of plaque changes in volume and surface morphology. This registration technique should be nonrigid, since different head positions during image acquisition sessions cause relative bending and torsion in the neck, producing nonlinear deformations between the images. We modeled the movement of the neck using a 'twisting and bending' model with only six parameters for nonrigid registration. We evaluated the algorithm using 3-D US carotid images acquired at two different head positions to simulate images acquired at different times. We calculated the mean registration error (MRE) between the segmented vessel surfaces in the target image and the registered image using a distance-based error metric after applying our 'twisting and bending' model-based nonrigid registration algorithm. We achieved an average registration error of 0.80 [+ or -] 0.26 mm using our nonrigid registration technique, which was a significant improvement in registration accuracy over rigid registration, even with reduced degrees-of-freedom compared to the other nonrigid registration algorithms. Index Terms--Carotid artery plaque, image registration, ultrasound imaging.

This paper introduces a 2-D strain imaging technique based on minimizing a cost function using dynamic programming (DP). The cost function incorporates similarity of echo amplitudes and displacement continuity. Since tissue deformations are smooth, the incorporation of the smoothness into the cost function results in reduced decorrelation noise. As a result, the method generates high-quality strain images of freehand palpation elastography with up to 10% compression, showing that the method is more robust to signal decorrelation (caused by scatterer motion in high axial compression and nonaxial motions of the probe) in comparison to the standard correlation techniques. The method operates in less than 1 s and is thus also potentially suitable for real time elastography. Index Terms--Dynamic programming, freehand ultrasound (US), real time strain imaging, regularization, ultrasound elastography.

Much of the current knowledge of human cardiovascular pathologies and treatment strategies has been gained from understanding the cardiac physioiogies and functions in small animal models, such as mice, rats, and zebrafish. In this paper, we present the development of a high-frame-rate duplex ultrasound biomicroscopy (UBM) capable of B-mode imaging and pulsed-wave (PW) Doppler measurement for in vivo cardiovascular investigation in small animals. A frame rate of 200 frames per second (fps) was accomplished at a view of 5 mm x 8 mm, using a novel high-speed sector probe and specially designed lightweight transducers. In a reduced lateral view of 1.2 mm, a frame rate of 400 fps was achieved to examine more detailed cardiac motion. The UBM utilized transducers with different center frequencies (40-75 MHz) and geometries, which made it useful for various applications in small animal cardiac imaging. The highest spatial resolution the UBM achieved was 25 [micro]m x 56 [micro]m. In addition, the image-guided PW Doppler implemented in the UBM demonstrated the detection of the velocity of a moving wire as low as 0.1 mm/s, and flow in a polyimide tube as small as 200 [micro]m in diameter. Furthermore, the UBM achieved a 15-[micro]V minimal detectable signal and a 60-dB dynamic range using a low-cost PCB-based design. Finally, sample in vivo cardiac images of mouse and zebrafish hearts were given. These results showed that the UBM integrated with B-mode and PW Doppler is useful to investigate the pathophysiological mechanism in the cardiovascular studies.

On average, in aging males, the prostate enlarges (benign prostatic enlargement or BPE) and may cause bladder outlet obstruction (BOO). The internationally standardized method for diagnosing BOO is based on measurements of urinary flow rate and bladder pressure, using a catheter inserted into the bladder via the urethra. This method is invasive, time-consuming, and uncomfortable for the patient. We are developing a novel diagnostic method based on perineal recording of sound during urinary flow. Although it is known that (some aspects of) the recorded sound are (among others) related to the degree of obstruction, an exact and unique relation allowing derivation of the degree of obstruction from the sound recording is not known. In a biophysical model of the urethra, we found that the weighted average frequency, the standard deviation, and the skewness of the power spectrum are monotonically related to the degree of obstruction. The standard deviation was the most significant predictor of BOO (89% correct). Based on this model study, we are confident that a simple noninvasive acoustic method for diagnosing BOO caused by BPE can be developed. This would lower the threshold for urodynamic testing of patients with lower urinary tract symptoms resulting in higher therapeutic efficacy. Index Terms--Bladder outlet obstruction (BOO), noninvasive, perineal sound recording.

A new model is developed for tissue reflectivity and showed how it can be used in an expectation-maximum (EM) algorithm to yield a computationally efficient iterative restoration method based on Wiener filtering and wavelet denoising. The results have shown that the EM algorithm is capable of producing restored images having better quality and greater fidelity to the true tissue reflectivity than other restoration methods based on simpler regularizing constraints.

A method is described for performing an ultrasonic study of a single ultrasound contrast agents (UCA) bubble immersed in a tank filled with a liquid by using ultrasonic equipment able to insonify and acquire radio frequency (RF) echo signals coming from an isolated bubble with a high frame rate. The inhibition of subharmonic generation, specific bubble behaviors concerning the stable subharmonic emission and the transient subharmonic emission are detected.

Two chirped excitation methods are proposed and investigated for imaging contrast agents, with mechanical index (MI) ranging from 0.05 to 0.34. The results have shown that chirped excitation contrast imaging is a safe method with comparative resolution, which might improve the detection of flow in smaller and deeper vessels throughout the body.

A novel estimation method is described by using spectral cross-correlation between consecutive power spectra obtained from the backscattered radio frequency (RF) signals at different depths in order to estimate the local attenuation coefficient. The simulation results have shown that the local attenuation coefficient estimates obtained from spectral cross-correlation are within 2.3% of the actual value with small estimation variances.

The low-power ultrasound (US) exposure is possible through a ventral surface of the mouse head, where a simple modular design has allowed the sonication through the ventral aspect of a mouse during optical imaging. The ventral approach can be used for elucidating temporal and spatial details of low-power US treatments, but it is not appropriate when precise targeting or power amplitudes are required, due to beam attenuation, reflection and steering.

The statistics of the radio frequency (RF) signal in the case of partially developed speckle is studied. The probability density function of the associated distribution, the corresponding moments, and estimators for the parameters of the distribution is presented using the K distribution framework.

A high-frequency, cardiac-imaging system for small animals is built with a spatial resolution of approximately 120-mum, and two scanning methods are developed to minimize the motion artifacts, and their performance is verified. The block scanning mode is able to reconstruct cardiac images in the smallest number of hearbeats, but it is suitable only for obtaining images at the isovolumic contraction and the isovolumic relaxation cardiac phases.

A new partial discharge (PD) location method based on UHF and ultrasonic-phased arrays receiving theory is presented, which has a possibility to locate multiple PDs. The laboratory experimental tests on the plane sensor element indicates that it has a good performance within the frequency band of the main ultrasonic energy produced by PD in transformer oil.

A study is designed to predict theoretically and measure experimentally the dissipation and heating effects of encapsulated ultrasound contract agent (UCA) in a well-controlled and calibrated environment. The ultrasonic effects of the microbbuble concentration, transmitted intensity, and frequency on power dissipation and stability of the UCA is studied, suggesting that higher frequencies are more efficiently absorbed by commonly used UCA.

A simple preprocessessing procedures are introduced which modifies the acquired radio-frequency images, so that the noise in the long-transformation domain becomes very close in its behavior to a white Gaussian Noise. As a result, the preprocessing allows filtering methods based on assuming the noise to be white and Gaussian, to perform in nearly optimal conditions.

The influence of scatter type on two existing attenuation estimation algorithms is analyzed and a novel technique for handling large statistical variations based on combined assumptions of monotonicity and smoothness is presented. Visible differences in attenuation estimates from each technique were revealed, which are supported by the theoretical analysis suggesting that the novel technique for reducing statistical variations is sufficient to allow some degree of correction of shadowing and enhancement.

A finite-element study of acoustic interactions in capacitive microfabricated ultrasonic transducers (CMUTs) and experimental results obtained by laser interferometry measurements is reported. The good agreement found between finite element modeling results and optical displacement measurements demonstrates that acoustic interactions through the liquid represent a major source of cross coupling in CMUTs.

Aberration due to inhomogeneous intervening tissue can be a significant problem in therapeutic ultrasound surgery. Further, modified model with a damping shows the difference frequency sound source, induced by mixing two sound beams in presence of 0.1% Optison, resulting sound source, showing omni-directional characteristic, therefore, can be considered as a pseudo point source.

Microbubble destruction occurred through two modes, acoustic dissolution at 400 and 600 kPa and fragmentation at 800 kPa peak negative pressure and lipid composition significantly impacted the acoustic dissolution rate, fragmentation propensity, and mechanism of excess lipid shedding. Results showed that composition plays a role, increasing shell cohesiveness through choosing longer phospholipid acyl chain lengths decreased the rate of acoustic dissolution and propensity for fragmentation.

A new Doppler US (ultra sound) spectral enhancement method and its implementation are proposed. The experiments on some clinical Doppler US signals from umbilical arteries confirm the superior denoising performance of the new method.

The ultrasonic power absorbed by a microbubble is estimated through numerically solving a version of the Rayleigh-Plesset equation is described. The enhancement in temperature elevation gradually decreased as the microbubble agent was eliminated from the body.

An ultrasonic strain measurement-based 2-D and 3-D shear modulus reconstruction techniques for differential diagnosis of malignancies on human superficial tissues are described. Results of the 3-D reconstruction are found the most accurate for a nearly incompressible medium.

A measure of focusing efficiency was introduced for high-intensity, focused ultrasound (HIFU) and, the measure consisted of the fraction of the total acoustic power emitted that linearly propagated through a circle located at the focus. An annular array with 27 wavelength-wide rings was extended to be the basis of a twin phased-array device for prostate hyperthermia treatment.

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.

The aim of this paper is to demonstrate the feasibility of an approach: dual-frequency subtraction imaging, for suppressing artifacts produced by reverberation of strong echoes among specular reflectors. This method is based upon the principle that specularly reflected echoes from flat boundaries are frequency-independent whereas the diffusely scattered echoes from small scatterers are frequency-dependent. The approach was assessed on phantoms including one consisting of two parallel plastic plates between layers of foam sponges using a prototype experimental system. Preliminary results show that this method is superior to simple thresholding techniques or signal compression and holds great promise for suppressing reverberation artifacts in ultrasonic images.

Recently, there has been great interest in a new class of solutions to the isotropic/homogeneous scalar wave equation which represents localized waves or limited diffraction beams in electromagnetics, optics, and acoustics. Applications of these solutions to ultrasonic medical imaging, tissue characterization, and nondestructive evaluation of materials have also been reported. This paper reports a real-time medical imager which uses limited diffraction Bessel beams, X waves, Axicons, or conventional beams. Results (in vitro and in vivo) show that the images obtained with limited diffraction beams have higher resolution and good contrast over larger depth of field compared to images obtained with conventional focused beams. These results suggest the potential clinical usefulness of limited diffraction beams.

We evaluate a recently proposed approach (1)-(3) to the inverse problem of detection of the presence and estimation of the location of a known object from data collected in a set of diffraction tomographic experiments. We verify on experimental data the validity of the filtered backpropagation algorithms developed in (1)-(3), demonstrate their robustness to modeling errors and to severe limitations in the angular coverage of the tomographic data, and illustrate a potential application in medical imaging of soft tissue.