This PDF file contains the front matter associated with SPIE Proceedings Volume 7968, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Breast ultrasound tomography is a rapidly developing imaging modality that has the potential to impact breast cancer screening and diagnosis. Double difference (DD) tomography utilizes more accurate differential time-of-flight (ToF) data to reconstruct the sound speed structure of the breast. It can produce more precise and better resolution sound speed images than standard tomography that uses absolute ToF data. We apply DD tomography to phantom data and excised mouse mammary glands data. DD tomograms demonstrate sharper sound speed contrast than the standard tomograms.

At Karlsruhe Institute of Technology a 3D Ultrasound Computer Tomography (USCT) system is under development for early breast cancer detection. With 3.5 million of acquired raw data and up to one billion voxels for one image, the reconstruction of breast volumes may last for weeks in highest possible resolution. The currently applied backprojection algorithm, based on the synthetic aperture focusing technique (SAFT), offers only limited potential for further decrease of the reconstruction time. An alternative reconstruction method could apply signal detected data and rasterizes the backprojected ellipsoids directly. A well-known rasterization algorithm is the Bresenham algorithm, which was originally designed to rasterize lines. In this work an existing Bresenham concept to rasterize circles is extended to comply with the requirements of image reconstruction in USCT: the circle rasterization was adapted to rasterize spheres and extended to floating point parameterization. The evaluation of the algorithm showed that the quality of the rasterization is comparable to the original algorithm. The achieved performance of the circle and sphere rasterization algorithm was 12MVoxel/s and 3.5MVoxel/s. When taking the performance increase due to the reduced A-Scan data into account, an acceleration of factor 28 in comparison to the currently applied algorithm could be reached. For future work the presented rasterization algorithm offers additional potential for further speed up.

Conventional ultrasound techniques use beam-formed, constant sound speed ray models for fast image reconstruction. However, these techniques are inadequate for the emerging new field of ultrasound tomography (UST). We present a new technique for the reconstruction of reflection images from UST data. We have extended the planar Kirchhoff migration method used in geophysics, and combined it with sound speed and attenuation data obtained from the transmission signals to create reflection ultrasound images that are corrected for refractive and attenuative effects. The resulting technique was applied to in-vivo breast data obtained with an experimental prototype. The results indicate that sound speed and attenuation corrections lead to considerable improvements in image quality, particularly in dense tissues where the refractive and scattering effects are the greatest.

A promising candidate for improved imaging of breast cancer is ultrasound computer tomography (USCT). Current experimental USCT systems are still focused in elevation dimension resulting in a large slice thickness, limited depth of field, loss of out-of-plane reflections, and a large number of movement steps to acquire a stack of images. 3DUSCT emitting and receiving spherical wave fronts overcomes these limitations. We built an optimized 3DUSCT with nearly isotropic 3D point spread function, realizing for the first time the full benefits of a 3D system. The 3DUSCT II is based on a semi-ellipsoidal transducer holder cut from polyoxymethylene. The aperture is implemented together with water supply, disinfection unit, temperature control, and movement mechanics in a patient bed. 2041 transducers are mounted in the aperture holder grouped into transducer array systems with embedded amplifiers and emitter electronics. The data acquisition is carried out with 480 parallel channels at 20MHz and with 12 bit resolution. 3.5 million A-Scans with 20 GByte of raw data are acquired for one breast volume. With data acquisition time of less than two minutes for one breast volume, the new system enables the next step of our research: a first clinical study.

Accurate calibration is a requirement of many array signal processing techniques. We investigate the calibration of a transducer array using time delays. We derive a strategy based on the mean square error criterion and discuss how time delays that are not available can be interpolated from existing ones. The proposed method is made robust to noise and model mismatch by means of a novel iterative technique for distance matrix denoising. The convergence of the method is proved. Finally, the accuracy of the proposed calibration algorithm is assessed both in simulated scenarios and using experimental data obtained from an ultrasound scanner designed for breast cancer detection.

The progression of atherosclerotic disease, caused by the formation of plaques within arteries, is a complex process believed to be a function of the localized mechanical properties and hemodynamic loading associated with the arterial wall. It is hypothesized that measurements of vascular stiffness and wall-shear rate (WSR) may provide important information regarding vascular remodeling, endothelial function, and the growth of soft-lipid filled plaques that could help a clinician better diagnose a patient's risk of clinical events such as stroke. To that end, the approach taken in this work was to combine conventional B-mode, Acoustic Radiation Force Impulse (ARFI), Shear Wave Elasticity Imaging (SWEI), and spectral Doppler techniques into a single imaging system capable of simultaneously measuring the tissue displacements and WSR throughout the cardiac cycle and over several heartbeats. Implemented on a conventional scanner, the carotid arteries of human subjects were scanned to demonstrate the initial in vivo feasibility of the method. Two non-invasive ultrasound based imaging methods, SAD-SWEI and SAD-Gated Imaging, were developed that measure ARF-induced on-axis tissue displacements, off-axis transverse wave velocities, and WSR throughout the cardiac cycle. Human carotid artery scans were performed in vivo on 5 healthy subjects. Statistical differences were observed in both on-axis proximal wall displacements and transverse wave velocities during diastole compared to systole.

Second harmonic imaging is currently adopted as standard in commercial echographic systems. A new imaging technique, coined as superharmonic imaging (SHI), combines the 3rd till the 5th harmonics, arising during nonlinear sound propagation. It could further enhance resolution and quality of echographic images. To meet the bandwidth requirement for SHI a dedicated phased array has been developed: a low frequency subarray, intended for transmission, interleaved with a high frequency subarray, used in reception. As the bandwidth of the elements is limited, the spectral gaps in between the harmonics cause multiple reflection artifacts. Recently, we introduce a dual-pulse frequency compounding (DPFC) method to suppress those artifacts at price of a reduced frame rate. In this study we investigate the feasibility of performing the frequency compounding protocol within a single transmission. The traditional DPFC method constructs each trace in a post-processing stage by summing echoes from two emitted pulses, the second slightly frequency-shifted compared to the first. In the newly proposed method, the transmit aperture is divided into two parts: the first half is used to send a pulse at the lower center frequency, while the other half simultaneously transmits at the higher center frequency. The suitability of the protocol for medical imaging applications in terms of the steering capabilities was performed in a simulation study using the FIELD II toolkit. Moreover, an experimental study was performed to deduce the optimal parametric set for implementation of the clinical imaging protocol. The latter was subsequently used to obtain the images of a tissue mimicking phantom containing strongly reflecting wires. For in-vitro acquisitions the SHI probe with interleaved phased array (44 odd elements at 1MHz and 44 even elements at 3.7MHz elements, optimized for echocardiography) was connected to a fully programmable ultrasound system. The results of the Field II simulations demonstrated that the angle between the main and grating lobe amounted to 90°. The difference in the fundamental pressure level between those lobes was equal to -26.8 dB. Those results suggest that the superharmonic content in the grating lobe was acceptably low. A considerable improvement in the axial resolution of the SHI component (0.73 mm) at -6 dB in comparison with the 3rd harmonic (2.23 mm) was observed. A similar comparison in terms of the lateral resolution slightly favored the superharmonic component by 0.2 mm. Additionally, the images of the tissue mimicking phantom exhibited an absence of the multiple reflection artifacts in the focal and post-focal regions. The new method is equally effective in eliminating the ripple artifacts associated with SHI as the dual pulse technique, while the full frame rate is maintained.

In the last 20 years, the number of suboptimal and inadequate ultrasound exams has increased. This trend has been linked to the increasing population of overweight and obese individuals. The primary causes of image degradation in these individuals are often attributed to phase aberration and clutter. Phase aberration degrades image quality by distorting the transmitted and received pressure waves, while clutter degrades image quality by introducing incoherent acoustical interference into the received pressure wavefront. Although significant research efforts have pursued the correction of image degradation due to phase aberration, few efforts have characterized or corrected image degradation due to clutter. We have developed a novel imaging technique that is capable of differentiating ultrasonic signals corrupted by acoustical interference. The technique, named short-lag spatial coherence (SLSC) imaging, is based on the spatial coherence of the received ultrasonic wavefront at small spatial distances across the transducer aperture. We demonstrate comparative B-mode and SLSC images using full-wave simulations that include the effects of clutter and show that SLSC imaging generates contrast-to-noise ratios (CNR) and signal-to-noise ratios (SNR) that are significantly better than B-mode imaging under noise-free conditions. In the presence of noise, SLSC imaging significantly outperforms conventional B-mode imaging in all image quality metrics. We demonstrate the use of SLSC imaging in vivo and compare B-mode and SLSC images of human thyroid and liver.

Photoacoustic imaging will become an important supplement to conventional ultrasound imaging. However, the equipment needed is still too delicate to bring this technique into the daily clinical work. The pulsed light source is the area of interest in the present report. Usually, large and costly laser systems are used to provide high-energy light pulses with a chosen wavelength. Pulsed semiconductor lasers have been demonstrated as a possible alternative light source for the photoacoustic imaging purpose. As an alternative to laser sources, the preliminary result of using a pulsed high-power light emitting diode, LED, for photoacoustic imaging is presented here. The pulsed light source is created from a Luxeon LXHL_PD09 red LED (250mW optical output power at 1 Amp current). The LED is supplied with current pulses 60ns wide and 40A peak. The LED delivers 60ns light pulses with approximately 6W peak power. The phantom used consists of a thin stripe (3mm high x 5mm wide) of green colored gelatin overlaid by a 3cm layer of un-colored gelatin. The light pulses from the LED are collected by a lens system and focused on the green gelatin from beneath the sample. The acoustic response from the green gelatin is detected with a single focused transducer on the upper surface of the 3cm thick colorless gelatin layer. The response is clearly observed when the measurement is taken as an average of 50,000 pulses. Is it concluded that despite the relatively low pulse power, for some purposes, a combination of of LED's could be a candidate for an inexpensive light source.

Photoacoustic tomography is an emerging technology combining the advantages of optical imaging (high contrast) and ultrasonic imaging (high spatial resolution). Applications for photoacoustic tomography are mainly in imaging soft tissue. For photoacoustic imaging the sample is illuminated by a short pulse of electromagnetic energy. Depending on the specific absorption rate (SAR) the electromagnetic radiation is absorbed and the subsequent thermoelastic expansion launches broadband ultrasonic waves. Usually point like piezo-electric detectors are used. Our group introduced integrating detectors a few years ago. This type of detector integrates the pressure at least along one dimension. Integrating line detectors, which integrate the pressure along one dimension, can be realized by using either free-beam or fiber-based interferometers. The latter approach also allows other detector shapes than a line. In this paper we use a fiber-based annular detector for tomography. Thereby the sample is rotated inside the annular detector on a position different from the symmetry axis of the annular detector. Hence the sample is enclosed by the detector and all data from one plane are collected at once. By moving the detector parallel to the symmetrie axis of the ring one can acquire data for a 3D image reconstruction. Therfore, tomography can be performed with only one rotation axis and one translation axis. For image reconstruction a novel algorithm is necessary which was tested on simulated data. Here we present an imaging setup using such a fiber-based annular detector. First measurements of simple structures and subsequent image reconstruction from these real data are shown in this paper.

Prostate cancer is the second leading cause of death in American men after lung cancer. The current screening procedures include Digital Rectal Exam (DRE) and Prostate Specific Antigen (PSA) test, along with Transrectal Ultrasound (TRUS). All suffer from low sensitivity and specificity in detecting prostate cancer in early stages. There is a desperate need for a new imaging modality. We are developing a prototype transrectal photoacoustic imaging probe to detect prostate malignancies in vivo that promises high sensitivity and specificity. To generate photoacoustic (PA) signals, the probe utilizes a high energy 1064 nm laser that delivers light pulses onto the prostate at 10Hz with 10ns duration through a fiber optic cable. The designed system will generate focused C-scan planar images using acoustic lens technology. A 5 MHz custom fabricated ultrasound sensor array located in the image plane acquires the focused PA signals, eliminating the need for any synthetic aperture focusing. The lens and sensor array design was optimized towards this objective. For fast acquisition times, a custom built 16 channel simultaneous backend electronics PCB has been developed. It consists of a low-noise variable gain amplifier and a 16 channel ADC. Due to the unavailability of 2d ultrasound arrays, in the current implementation several B-scan (depth-resolved) data is first acquired by scanning a 1d array, which is then processed to reconstruct either 3d volumetric images or several C-scan planar images. Experimental results on excised tissue using a in-vitro prototype of this technology are presented to demonstrate the system capability in terms of resolution and sensitivity.

Electronic fetal monitoring may be required during the whole pregnancy to closely monitor specific fetal and maternal disorders. Currently used methods suffer from many limitations and are not sufficient to evaluate fetal asphyxia. Fetal activity parameters such as movements, heart rate and associated parameters are essential indicators of the fetus well being, and no current device gives a simultaneous and sufficient estimation of all these parameters to evaluate the fetus well-being. We built for this purpose, a multi-transducer-multi-gate Doppler system and developed dedicated signal processing techniques for fetal activity parameter extraction in order to investigate fetus's asphyxia or well-being through fetal activity parameters. To reach this goal, this paper shows preliminary feasibility of separating normal and compromised fetuses using our system. To do so, data set consisting of two groups of fetal signals (normal and compromised) has been established and provided by physicians. From estimated parameters an instantaneous Manning-like score, referred to as ultrasonic score was introduced and was used together with movements, heart rate and associated parameters in a classification process using Support Vector Machines (SVM) method. The influence of the fetal activity parameters and the performance of the SVM were evaluated using the computation of sensibility, specificity, percentage of support vectors and total classification accuracy. We showed our ability to separate the data into two sets : normal fetuses and compromised fetuses and obtained an excellent matching with the clinical classification performed by physician.

Ultrasonic tissue characterization has been gaining increasing attention. This procedure is generally based on the analysis of the echo signal. As the ultrasound echo is degraded by the system Point Spread Function, deconvolution could be employed to provide a tissue response estimate, exploitable for a better characterization. In this context, we present a deconvolution framework expressively designed to improve tissue characterization. Thanks to a new model for tissue reflectivity the proposed framework overcomes limitations associated with standard ones. The performance was evaluated from several tissue-mimicking phantoms. Obtained results show relevant improvements in classification accuracy. From a comparison with standard schemes the superiority of the proposed algorithm was attested.

Time series analysis of ultrasound radio-frequency (RF) signals has been shown to be an effective tissue classification method. Previous studies of this method for tissue differentiation at high and clinical-frequencies have been reported. In this paper, analysis of RF time series is extended to improve tissue classification at the clinical frequencies by including novel features extracted from the time series spectrum. The primary feature examined is the Mean Central Frequency (MCF) computed for regions of interest (ROIs) in the tissue extending along the axial axis of the transducer. In addition, the intercept and slope of a line fitted to the MCF-values of the RF time series as a function of depth have been included. To evaluate the accuracy of the new features, an in vitro animal study is performed using three tissue types: bovine muscle, bovine liver, and chicken breast, where perfect two-way classification is achieved. The results show statistically significant improvements over the classification accuracies with previously reported features.

Ultrasound radio-frequency (RF) time series analysis provides an effective tissue characterization method to differentiate between healthy and cancerous prostate tissues. In this paper, an analytical model is presented that partially describes the variations in tissue acoustic properties that accompany ultrasound RF time series acquisition procedures. These ultrasound-induced effects, which depend on tissue mechanical and thermophysical properties, are hypothesized to be among the major contributors to the tissue typing capabilities of the RF time series analysis. The model is used to derive two tissue characterization features. The two features are used with a support vector machine classifier to characterize three animal tissue types: chicken breast, bovine liver, and bovine steak. Accuracy values as high as 90% are achieved when the proposed features are employed to differentiate these tissue types. The proposed model may provide a framework to optimize the ultrasound RF time series analysis for future clinical procedures.

Substantial progress has been made towards using high-frequency (20-60 MHz) ultrasound to track tumor growth in preclinical cancer models; however, correlation of high-frequency backscattering to tissue microanatomy is an incompletely understood problem. In this paper, a histology-based simulation framework is presented to relate high-frequency backscattering to tissue microanatomy. The software employs a three-dimensional (3-D) microanatomical model that treats tissue as a population of nuclei embedded in a homogeneous cytoplasm to create simulated healthy tissue and simulated tumor that match the nuclei number density, sizes of nuclei, and spatial arrangement of nuclei of a healthy mouse liver and an experimental liver metastasis. A parallel first-order k-space method is used to synthesize B-mode images by computing linear 3-D propagation of focused 40-MHz pulses in the simulated tissues. Gray-level histograms with 13 bins evenly spaced over 256 gray levels are constructed for the simulated images and compared with histograms of corresponding experimental images. The histogram of the simulated healthy tissue matches the histogram of the healthy liver within one standard deviation in all 13 bins when the sound speed and mass density of the nuclei are set to 1503 m/s and 1430 kg/m³. Simulated and experimental speckle distributions for the liver metastasis match in 11 of 13 bins when the sound speed and density of the nuclei are set to 1527 m/s and 1140.5 kg/m³. The simulations suggest that variations in first-order speckle statistics between healthy and cancerous murine liver tissues reflect changes in both tissue acoustic and structural properties.

Fetal bi-parietal diameter (BPD) is known to provide a reliable estimate of gestational age (GA) of a fetus in the first half of pregnancy. In this paper, we present an automated method to identify and measure BPD from B-mode ultrasound images of fetal head. The method (a) automatically detects and places a region-of-interest on the head based on a prior work in our group (b) utilizes the concept of phase congruency for edge detection and (c) employs a cost function to identify the third ventricle inside the head (d) measures the BPD along the perpendicular bisector of occipital frontal diameter (OFD) from the outer rim of the cranium closer to the transducer to the inner rim of the cranium away from the transducer. The cost function is premised on the distribution of anatomical shape, size and presentation of the third ventricle in images that adhere to clinical guidelines describing the scan plane for BPD measurement. The OFD is assumed to lie along the third ventricle. The algorithm has been tested on 137 images acquired from four different scanners. Based on GA estimates and their bounds specified in Standard Obstetric Tables, the GA predictions from automated measurements are found to be within ±2SD of GA estimates from manual measurements by the operator and a second expert radiologist in 98% of the cases. The method described in this paper can also be adapted to assess the accuracy of the scan plane based on the presence/absence of the third ventricle.

We previously developed a 2D locally regularized strain estimation technique that was already validated with ex vivo tissues. In this study, our technique is assessed with in vivo data, by examining breast abnormalities in clinical conditions. Method reliability is analyzed as well as tissue strain fields according to the benign or malignant character of the lesion. Ultrasound RF data were acquired in two centers on ten lesions, five being classified as fibroadenomas, the other five being classified as malignant tumors, mainly ductal carcinomas from grades I to III. The estimation procedure we developed involves maximizing a similarity criterion (the normalized correlation coefficient or NCC) between pre- and post-compression images, the deformation effects being considered. The probability of correct strain estimation is higher if this coefficient is closer to 1. Results demonstrated the ability of our technique to provide good-quality strain images with clinical data. For all lesions, movies of tissue strain during compression were obtained, with strains that can reach 15%. The NCC averaged over each movie was computed, leading for the ten cases to a mean value of 0.93, a minimum value of 0.87 and a maximum value of 0.98. These high NCC values confirm the reliability of the strain estimation. Moreover, lesions were clearly identified for the ten cases investigated. Finally, we have observed with malignant lesions that compared to ultrasound data, strain images can put in relief a more important lesion size, and can help in evaluating the lesion invasive character.

Spectral velocity estimation is considered the gold standard in medical ultrasound. Peak systole (PS), end diastole (ED), and resistive index (RI) are used clinically. Angle correction is performed using a flow angle set manually. With Transverse Oscillation (TO) velocity estimates the flow angle, peak systole (PS_TO), end diastole (ED_TO), and resistive index (RI_TO) are estimated. This study investigates if these clinical parameters are estimated equally good using spectral and TO data. The right common carotid arteries of three healthy volunteers were scanned longitudinally. Average TO flow angles and std were calculated { 52±18 ; 55±23 ; 60±16 }°. Spectral angles { 52 ; 56 ; 52 }° were obtained from the B-mode images. Obtained values are: PS_TO { 76±15 ; 89±28 ; 77±7 } cm/s, spectral PS { 77 ; 110 ; 76 } cm/s, ED_TO { 10±3 ; 14±8 ; 15±3 } cm/s, spectral ED { 18 ; 13 ; 20 } cm/s, RITO { 0.87±0.05 ; 0.79±0.21 ; 0.79±0.06 }, and spectral RI { 0.77 ; 0.88 ; 0.73 }. Vector angles are within ±two std of the spectral angle. TO velocity estimates are within ±three std of the spectral estimates. RI_TO are within ±two std of the spectral estimates. Preliminary data indicates that the TO and spectral velocity estimates are equally good. With TO there is no manual angle setting and no flow angle limitation. TO velocity estimation can also automatically handle situations where the angle varies over the cardiac cycle. More detailed temporal and spatial vector estimates with diagnostic potential are available with the TO velocity estimation.

Breast cancer is the most common cancer among women. The established screening method to detect breast cancer is X-ray mammography. However, X-ray frequently provides poor contrast of tumors located within glandular tissue. In this case, additional modalities like MRI are used for diagnosis in clinical routine. A new imaging approach is Ultrasound Computer Tomography, generating three-dimensional speed of sound images. High speed of sound values are expected to be an indicator of cancerous structures. Therefore, the combination of speed of sound images and X-ray mammograms may benefit early breast cancer diagnosis. In previous work, we proposed a method based on Finite Elements to automatically register speed of sound images with the according mammograms. The FEM simulation overcomes the challenge that X-ray mammograms show two-dimensional projections of a deformed breast whereas speed of sound images render a three-dimensional undeformed breast in prone position. In this work, 15 datasets from a clinical study were used for further evaluation of the registration quality. The quality of the registration was measured by the displacement of the center of a lesion marked in both modalities. We found a mean displacement of 7.1 mm. For visualization, an overlay technique was developed, which displays speed of sound information directly on the mammogram. Hence, the methodology provides a good basis for multimodal diagnosis using mammograms and speed of sound images. It proposes a guidance tool for radiologists who may benefit from the combined information.

The objective of this study is to present imaging parameters and display thresholds of an ultrasound tomography (UST) prototype in order to demonstrate analogous visualization of overall breast anatomy and lesions relative to magnetic resonance (MR). Thirty-six women were imaged with MR and our UST prototype. The UST scan generated sound speed, attenuation, and reflection images and were subjected to variable thresholds then fused together into a single UST image. Qualitative and quantitative comparisons of MR and UST images were utilized to identify anatomical similarities and mass characteristics. Overall, UST demonstrated the ability to visualize and characterize breast tissues in a manner comparable to MR without the use of IV contrast. For optimal visualization, fused images utilized thresholds of 1.46±0.1 km/s for sound speed to represent architectural features of the breast including parenchyma. An arithmetic combination of images using the logical .AND. and .OR. operators, along with thresholds of 1.52±0.03 km/s for sound speed and 0.16±0.04 dB/cm for attenuation, allowed for mass detection and characterization similar to MR.

Despite some shortcomings, mammography is currently the standard of care for breast cancer screening and diagnosis. However, breast ultrasound tomography is a rapidly developing imaging modality that has the potential to overcome the drawbacks of mammography. It is known that women with high breast densities have a greater risk of developing breast cancer. Measuring breast density is accomplished through the use of mammographic percent density, defined as the ratio of fibroglandular to total breast area. Using an ultrasound tomography (UST) prototype, we created sound speed images of the patient's breast, motivated by the fact that sound speed in a tissue is proportional to the density of the tissue. The purpose of this work is to compare the acoustic performance of the UST system with the measurement of mammographic percent density. A cohort of 251 patients was studied using both imaging modalities and the results suggest that the volume averaged breast sound speed is significantly related to mammographic percent density. The Spearman correlation coefficient was found to be 0.73 for the 175 film mammograms and 0.69 for the 76 digital mammograms obtained. Since sound speed measurements do not require ionizing radiation or physical compression, they have the potential to form the basis of a safe, more accurate surrogate marker of breast density.

Breast cancer is the most common type of cancer for women in Europe and North America. The established standard screening method to detect tumors is X-ray mammography. However, X-ray mammography often has low contrast for tumors located within glandular tissue. A new approach is 3D Ultrasound Computer Tomography (USCT), which is expected to detect small tumors at an early stage. This paper describes the development and the results of Finite Element Method (FEM) simulations of the Transducer Array System (TAS) used in our 3D USCT system. Not all required material parameters were available,so the main challenge of this work was to determine these values. After detailed analysis, a set of material parameters was identified which fits the measured data best. The quality of the simulation was evaluated by comparing the simulated impedance characteristics with measured data of the real TAS. The simulation model provides a powerful tool to analyze the 3D USCT TAS. Furthermore, it is now possible to design and optimize future transducers based on simulation.

In this paper results from a non-linear AS (angular spectrum) based ultrasound simulation program are compared to water-tank measurements. A circular concave transducer with a diameter of 1 inch (25.4 mm) is used as the emitting source. The measured pulses are first compared with the linear simulation program Field II, which will be used to generate the source for the AS simulation. The generated non-linear ultrasound field is measured by a hydrophone in the focal plane. The second harmonic component from the measurement is compared with the AS simulation, which is used to calculate both fundamental and second harmonic fields. The focused piston transducer with a center frequency of 5 MHz is excited by a waveform generator emitting a 6-cycle sine wave. The hydrophone is mounted in the focal plane 118 mm from the transducer. The point spread functions at the focal depth from Field II and measurements are illustrated. The FWHM (full width at half maximum) values are 1.96 mm for the measurement and 1.84 mm for the Field II simulation. The fundamental and second harmonic components of the experimental results are plotted compared with the AS simulations. The RMS (root mean square) errors of the AS simulations are 7.19% and 10.3% compared with the fundamental and second harmonic components of the measurements.

At the Karlsruhe Institute of Technology (KIT) a three-dimensional ultrasound computer tomography (3D USCT) system for early breast cancer diagnosis is being developed. This method promises reproducible volume images of the female breast in 3D. Initial measurements and a simulation based optimization method, which took several physical properties into account, led to a new aperture setup. Yet this simulation is computational too demanding to systematically evaluate the different 'virtual' apertures which can be achieved by rotation and lifting of the system. In optics a Fourier based approach is available to simulate imaging systems as linear systems. For the two apertures used in our project and one hypothetical linear array aperture this concept was evaluated and compared to a reference simulation. An acceptable conformity between the new approach and the reference simulation could be shown. With this approach a fast evaluation of optimal 'virtual' apertures for specific measurement objects and imaging constraints can be carried out within an acceptable time constraint.

To date, clinical implementation of high-frequency ultrasound has been limited due to the difficulties in fabricating sufficiently small micro-array transducers. Specifically, if an array is desired with the ability to beam-steer to large angles, an inter-element pitch of approximately .5λ is required to avoid grating lobe artifacts. At high-frequencies (30-70MHz), this introduces major fabrication challenges since the required element pitch is between 10 and 25 microns. A new technique called Phase Coherence Imaging has been introduced in the literature for suppressing grating lobes in large-pitch arrays by calculating a weighting factor proportional to the instantaneous phase coherence of the received element echoes. If the reflected echoes in the grating lobe region are relatively broadband, only some of the echoes will overlap and the resulting weighting factor will be less. Unfortunately, most beamforming techniques result in relatively narrowband echoes in the grating lobe region, making this technique less effective. We have developed a technique that splits the N-element transmit aperture into N/K transmit elements and N receive elements in order to better suppress grating lobes by increasing the bandwidth of the grating lobe echoes. We have also developed a technique that uses a probing pulse from a virtual point source behind the array in order to pre-calculate weighting factors from broadband echoes before conventional transmit beamforming is used. Radiation patterns have been simulated and the amount of grating lobe suppression has been quantified using the proposed techniques. It has been shown that these techniques are very effective in suppressing grating lobes in large-pitch phased-arrays, potentially simplifying high-frequency array fabrication.

Breast ultrasound tomography has the potential to improve the cost, safety and reliability of breast cancer screening and diagnosis over the gold-standard of mammography. Vital to achieving this potential is the development of imaging algorithms to unravel the complex anatomy of the breast and its mechanical properties. The solution most commonly relied upon is Time-of-Flight Tomography but this exhibits low resolution due to the presence of diffraction effects. Iterative full-wave inversion methods present one solution to achieve higher resolution, but these are slow and are not guaranteed to converge to the correct solution. Presented here is HARBUT, the Hybrid Algorithm for Robust Breast Ultrasound Tomography, which utilises the complementary strengths of Time-of-Flight and Diffraction Tomography resulting in a direct, fast, robust and accurate high resolution method of reconstructing the sound-speed through the breast. The new algorithm is shown to produce accurate reconstructions with realistic data from a complex 3D simulation, with masses as small as 4mm being clearly visible.

Surgical procedures often have the unfortunate side-effect of causing the patient significant trauma while accessing the target site. Indeed, in some cases the trauma inflicted on the patient during access to the target greatly exceeds that caused by performing the therapy. Heart disease has traditionally been treated surgically using open chest techniques with the patient being placed "on pump" - i.e. their circulation being maintained by a cardio-pulmonary bypass or "heart-lung" machine. Recently, techniques have been developed for performing minimally invasive interventions on the heart, obviating the formerly invasive procedures. These new approaches rely on pre-operative images, combined with real-time images acquired during the procedure. Our approach is to register intra-operative images to the patient, and use a navigation system that combines intra-operative ultrasound with virtual models of instrumentation that has been introduced into the chamber through the heart wall. This paper illustrates the problems associated with traditional ultrasound guidance, and reviews the state of the art in real-time 3D cardiac ultrasound technology. In addition, it discusses the implementation of an image-guided intervention platform that integrates real-time ultrasound with a virtual reality environment, bringing together the pre-operative anatomy derived from MRI or CT, representations of tracked instrumentation inside the heart chamber, and the intra-operatively acquired ultrasound images.

Prostate biopsy is the clinical standard for the definitive diagnosis of prostate cancer. To overcome the limitations of 2D TRUS-guided biopsy systems when targeting pre-planned locations, systems have been developed with 3D guidance to improve the accuracy of cancer detection. Prostate deformation due to needle insertion and biopsy gun firing is a potential source of error that can cause target misalignments during biopsies. We use non-rigid registration of 2D TRUS images to quantify the deformation during the needle insertion and the biopsy gun firing procedure, and compare this effect in biopsies performed using a handheld TRUS probe with those performed using a mechanically assisted 3D TRUS guided biopsy system. Although the mechanically assisted biopsy system had a mean deformation approximately 0.2 mm greater than that of the handheld approach, it yielded a lower relative increase of deformation near the needle axis during the needle insertion stage and greater deformational stability of the prostate during the biopsy gun firing stage. We also analyzed the axial and lateral components of the tissue motion; our results indicated that the motion is weakly biased in the direction orthogonal to the needle, which is less than ideal from a targeting standpoint given the long, narrow cylindrical shape of the biopsy core.

Registration of intra-operative ultrasound with preoperative CT is highly desirable as a navigational aid for surgeons and interventional radiologists. Image-based solutions generally achieve poor results due to substantially different image appearance of ultrasound and CT. A method is presented that uses surface information and tracked ultrasound to improve registration results. Tracked ultrasound is combined with surface and image-based registration techniques to register ultrasound to CT. Surface data is acquired using an optically tracked range sensor, for example time-of-flight camera. Range data is registered to CT using robust point-set registration; this registration provides an approximate transformation from tracker to CT coordinates. The ultrasound probe is also optically tracked. The probe position and surface-based registration provide a first estimate for the position of the ultrasound image in CT coordinates. This estimate is subsequently refined by a final image-based registration stage. Initial tests using Coherent Point Drift algorithm for registering surface data to CT show favorable results. Tests using both simulated and real time-of-flight range data have good convergence over a wide initial translation and rotation misalignment domain. Preliminary testing using time-of-flight surface data suggests that surface to CT registration may be useful as an initial guess enabling later more precise (but less robust) image based methods for registering ultrasound images to CT. We believe this method will enable image-based algorithms to robustly converge to an optimal registration solution.

The use of electromagnetic (EM) tracking is an important guidance tool that can be used to aid procedures requiring accurate localization such as needle injections or catheter guidance. Using EM tracking, the information from different modalities can be easily combined using pre-procedural calibration information. These calibrations are performed individually, per modality, allowing different imaging systems to be mixed and matched according to the procedure at hand. In this work, a framework for the calibration of a 3D transesophageal echocardiography probe to EM tracking is developed. The complete calibration framework includes three required steps: data acquisition, needle segmentation, and calibration. Ultrasound (US) images of an EM tracked needle must be acquired with the position of the needles in each volume subsequently extracted by segmentation. The calibration transformation is determined through a registration between the segmented points and the recorded EM needle positions. Additionally, the speed of sound is compensated for since calibration is performed in water that has a different speed then is assumed by the US machine. A statistical validation framework has also been developed to provide further information related to the accuracy and consistency of the calibration. Further validation of the calibration showed an accuracy of 1.39 mm.

Routine applications of ultrasound imaging in medical diagnostics combine array technology and bemaforming (BF) algorithms for image formation. Although BF is very robust, it discards a signicant proportion of the information encoded in ultrasonic signals. Therefore, BF can reconstruct some of the geometrical features of an object but with resolution limited by the transmitted wavelength according to the Rayleigh criterion. Recent studies have shown that imaging formation techniques based on inverse scattering rather than standard BF can overcome the Rayleigh limit to achieve subwavelength resolution. This allows for high resolution images to be obtained at relatively large wavelengths that can penetrate deep into highly attenuative media such as human tissue. In this paper we present the rst experimental demonstration of subwavelength resolution in glycerol whose ultrasonic attenuation is in the order of 1 dB/cm/MHz and which is comparable to the attenuation observed in tissue. Using a commercial clinical scanner and strands of human hairs we show that the inverse scattering approach outperforms current sonography revealing features that are undetected by sonography.

Focusing and apodization are an essential part of signal processing in ultrasound imaging. Although the fundamental principles are simple, the dramatic increase in computational power of CPUs, GPUs, and FPGAs motivates the development of software based beamformers, which further improves image quality (and the accuracy of velocity estimation). For developing new imaging methods, it is important to establish proof-of-concept before using resources on real-time implementations. With this in mind, an effective and versatile Matlab toolbox written in C++ has been developed to assist in developing new beam formation strategies. It is a general 3D implementation capable of handling a multitude of focusing methods, interpolation schemes, and parametric and dynamic apodization. Despite being flexible, it is capable of exploiting parallelization on a single computer, on a cluster, or on both. On a single computer, it mimics the parallization in a scanner containing multiple beam formers. The focusing is determined using the positions of the transducer elements, presence of virtual sources, and the focus points. For interpolation, a number of interpolation schemes can be chosen, e.g. linear, polynomial, or cubic splines. Apodization can be specified by a number of window functions of fixed size applied on the individual elements as a function of distance to a reference point, or it can be dynamic with an expanding or contracting aperture to obtain a constant F-number, or both. On a standard PC with an Intel Quad-Core Xeon E5520 processor running at 2.26 GHz, the toolbox can beamform 300.000 points using 700.000 data samples in 3 seconds using a transducer with 192 elements, dynamic apodization in transmit and receive, and cubic splines for interpolation. This is 19 times faster than our previous toolbox.

Acoustic radiation force impulse (ARFI) imaging has been previously described for the visualization of the cardiovascular system, including assessment of cerebral and lower-limb vascular disease, myocardial function, and cardiac RF ablation monitoring. Given that plaque imposes a 3-dimensional burden on the artery and that accurate visualization of all lesion borders are important for ablation guidance, it would be convenient if an entire plaque or lesion volume could be acquired, either using a 3D system or 2D freehand scanning. Currently, ARFI imaging uses single-frame acquisition, with acquisition times ranging from 100-200ms. Such a system would be cumbersome for real-time, freehand scanning. In this work, we evaluate the feasibility of using ARFI for freehand, real-time scanning of the cardiovascular system. New techniques are presented which acquire B-mode / ARFI/ and Color-flow Doppler (BACD) information in less than 50 ms. Freehand feasibility is evaluated by sweeping the BACD system across lesion phantoms and vascular phantoms modeling a thin-cap fibroatheroma at sweep rates currently utilized in conventional B-mode systems. Stationary in vivo BACD images were then formed from the carotid artery of a canine model, demonstrating the system's potential. The results suggest that little loss in either ARFI or Doppler quality occurs during translational-stage controlled, quasi-freehand sweeps.

An in vitro flow system has been used to assess the flow disturbances downstream of the stenosis in a family of seven carotid bifurcation phantoms modelling varying plaque build-up both axially symmetrically (concentrically) and asymmetrically (eccentrically). Radio frequency data were collected for 10 s at each of over 1000 sites within each model, and a sliding 1024-point FFT is applied to the data to extract the Doppler spectrum every 12 ms. From this, the ensemble average over 10 cardiac cycles of the spectral mean velocity, and the root mean square over these same 10 cardiac cycles - the turbulence intensity (TI), can be obtained as a function of an ensemble averaged cardiac cycle at each spatial point in all phantoms. TI was investigated by looking at the average over a 25 mm² square region of interest in the ICA centered 2 cm distal to the apex of the bifurcation. TI in the region of interest increased with stenosis severity; at 23ms following peak systole, the time point when TI was maximal for the majority of models, this ranged from 2.4±0.1 cm/s in the non-diseased model to 6.6±0.3, 16.0±1.4 and 26.1±1.3 cm/s in the 30, 50 and 70% concentrically stenosed (by NASCET criteria) models, respectively. Similarly, TI was 8.3±0.7, 19.9±1.1, and 26.2±1.2 cm/s in the 30, 50 and 70% eccentrically stenosed models, respectively. Differences in TI between models, both in increasing stenosis severity and between eccentricities, were statistically different except between the 70% concentric and eccentric models.

Ultrasound imaging with low dose contrast injection would be of interest to better characterize the cardiac flow dynamics inside the left ventricle (LV). The aim of this study was to combine speckle tracking (ST) with regularization based on Navier-Stokes (NS) equations in an iterative manner in order to improve the pure ST results when the inflow velocities were high. It was tested in a Computational Fluid Dynamics (CFD) based Ultrasound simulation environment. On two subsequent images in diastasis, block-matching was applied using normalized cross-correlation as a similarity measure and spline-interpolation for subsample motion estimation. During regularization, the difference between the measured and the regularized velocity field was added as an external force to a finite difference implementation of the NS equations. This regularized velocity field was used as prior to the ST procedure between the following pair of images by guiding and reshaping the search region appropriately. This iterative approach was performed in the forward and the backward temporal direction to obtain the flow fields of the whole filling phase. The RMSE of all velocity estimates (amplitude & angle) within each frame was calculated using the CFD velocity vector fields as the ground truth and these findings were contrasted to pure ST. In this study, we could thus show that LV flow tracking by combining ST with NS based regularization in an iterative manner improves the accuracy of the pure ST results even at high inflow velocity.

We report on the use of ultrasound tomography (UST) to characterize breast cancer and study the local and distant tumor environments. We have imaged the tumor and its environment in 3 cases of breast cancer using a UST prototype and its associated image reconstruction algorithms. After generating images of reflection, sound speed and attenuation, the images were fused in combinations that allowed visualization and characterization of the interior of the tumor as well as the tissue immediate to the tumor and beyond. The reflection UST images demonstrated the presence of spiculation, and architectural distortion, indicators of both local tumor invasion and distant involvement with surrounding tissues. Furthermore, the sound speed images showed halos of elevated sound speed surrounding the tumors, indicating a local environment characterized by stiff tissues. The combination of sound speed and attenuation images revealed that the tumor interiors were the stiffest tissues in the region studied. These features and characteristics are commensurate with the known biomechanical properties of cancer and may be manifestations of the desmoplastic process that is associated with tumor invasion. We propose that UST imaging may prove to be a valuable tool for characterizing cancers and studying the tumor invasion process.

High-resolution ultrasonography (HRUS) has potentialities in differential diagnosis between malignant and benign thyroid lesions, but interpretative pitfalls remain and accuracy is still poor. We developed an image processing technique for characterizing the intra-nodular vascularization of thyroid lesions. Twenty nodules (ten malignant) were analyzed by 3-D contrast-enhanced ultrasound imaging. The 3-D volumes were preprocessed and skeletonized. Seven vascular parameters were computed on the skeletons: number of vascular trees (NT); vascular density (VD); number of branching nodes (or branching points) (NB); mean vessel radius (MR); 2-D (DM) and 3-D (SOAM) tortuosity; and inflection count metric (ICM). Results showed that the malignant nodules had higher values of NT (83.1 vs. 18.1), VD (00.4 vs. 0.01), NB (1453 vs. 552), DM (51 vs. 18), ICM (19.9 vs. 8.7), and SOAM (26 vs. 11). Quantification of nodular vascularization based on 3-D contrast-enhanced ultrasound and skeletonization could help differential diagnosis of thyroid lesions.

In medical ultrasound imaging, scan conversion is used to geometrically transform polar coordinate ultrasound data into Cartesian raster data for display. In scan conversion, Moiré undersampling artifacts can be avoided by using various interpolation techniques such as nearest neighbor and bilinear. However, this interpolation-based scan conversion introduces blurring of fine details in ultrasound images. In this paper, a new beamforming technique, named compounded direct pixel beamforming (CDPB), is proposed to remove blurring artifacts from scan conversion. In CDPB, receive focusing is performed directly on each display pixel in Cartesian coordinates with raw radio-frequency (RF) data from two adjacent transmit firings so that artifacts from scan conversion can be substantially removed. To evaluate the proposed CDPB method, 64-channel pre-beamformed RF data were captured by a commercial ultrasound machine (SA-9900, Medison Corp., Seoul, Korea) from a tissue mimicking phantom (ATS Laboratories, Bridgeport, CT, USA). To quantify the performance of the proposed method, the information entropy contrast (IEC) value was measured. From the experiments, the proposed method provided IEC improvement by 2.8 over the conventional scan conversion method. These results indicate that the proposed new beamforming method could be used for enhancing the image quality in medical ultrasound imaging.

In medical ultrasound imaging, a multi-beamforming (MBF) method is used for supporting high frame rate imaging or functional imaging where multiple scanlines are reconstructed from a single excitation event. For efficient MBF, a time-sharing technique (i.e., MBF-TS) can be applied. However, the MBF-TS could degrade image quality due to the decreased beamforming frequency. In this paper, the multi-access register-based MBF (MBF-MAR) method running on the post-fractional filtering (PFF) architecture is presented. In PFF-MBF-MAR, instead of lowering beamforming frequency, a multi-access register at each channel is utilized for generating multiple scanlines simultaneously. To evaluate the performance of the proposed PFF-MBF-MAR method, the phantom experiment was conducted where 64- channel pre-beamformed radio-frequency (RF) data were captured from a tissue mimicking phantom by using a modified commercial ultrasound system (SONOLINE G40, Siemens Inc., USA) using a 3-MHz phased array probe. From the phantom experiment, the PFF-MBF-MAR method showed 4.7 dB and 0.6 improvements in the signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR), respectively, compared to the PFF-MBF-TS method, while slightly increasing the hardware complexity (<5.2%). The similar results were achieved with the in vivo thyroid data. These results indicate that the proposed PFF-MBF-MAR method can be used for high frame rate imaging or functional imaging without sacrificing image quality while slightly increasing the hardware complexity.

An actuated hand-held impedance-controlled ultrasound probe has been developed. The controller maintains a prescribed contact state (force and velocity) between the probe and a patient's body. The device will enhance the diagnostic capability of free-hand elastography and swept-force compound imaging, and also make it easier for a technician to acquire repeatable (i.e. directly comparable) images over time. The mechanical system consists of an ultrasound probe, ball-screw-driven linear actuator, and a force/torque sensor. The feedback controller commands the motor to rotate the ball-screw to translate the ultrasound probe in order to maintain a desired contact force. It was found that users of the device, with the control system engaged, maintain a constant contact force with 15 times less variation than without the controller engaged. The system was used to determine the elastic properties of soft tissue.

Respiratory motion affects the accurate quantification of the hepatic fusion, which does not benefit the early detection and treatment of hepatic cancers. A new strategy based on template matching is proposed to correct respiratory motion in the free-breathing time-series contrast-enhanced ultrasound (CEUS) images. Ultrasound machines generally have a dual-display feature of contrast and tissue windows under contrast-enhanced mode. The tissue window is used to track the targeted tumor in the contrast window. Therefore, the registration of contrast images is first achieved by the registration of the corresponding tissue images due to the low variation of grey level in the tissue image. Then, a simple double-selection method is proposed to select the similar images from a large number of successive matched images via the global and local threshold setting. Finally, the motion-corrected contrast images can be acquired by using the position mapping. This strategy was tested on 4 free-breathing CEUS image sequences using the sum of absolute differences metric. Results showed that the time-intensity curves could be extracted more accurately with this strategy. Moreover, the quality of curve fitting and the corresponding parametric imaging computed on the motion-corrected sequences was improved significantly. In conclusion, the image-based strategy can quickly correct the respiratory motion in CEUS image sequences, which is potentially suitable for the local quantification of hepatic perfusion studies.

Recent developments of new medical treatment techniques put challenging demands on ultrasound imaging systems in terms of both image quality and raw data size. Traditional sampling methods result in very large amounts of data, thus, increasing demands on processing hardware and limiting the flexibility in the postprocessing stages. In this paper, we apply Compressed Sensing (CS) techniques to analog ultrasound signals, following the recently developed Xampling framework. The result is a system with significantly reduced sampling rates which, in turn, means significantly reduced data size while maintaining the quality of the resulting images.

Analytical expressions for the time-domain Green's function that exactly solve the wave equation for power-law media with an attenuation term that is proportional to frequency to the power were recently derived. These analytical expressions are causal for power-law exponents less than one and noncausal for power-law exponents greater than or equal to one. A causal expression for the lossy impulse response for a circular piston is obtained for power-law exponent when the impulse response of the time-domain Rayleigh-Sommerfeld integral is evaluated by superposing the causal Green's function in space and in time. The lossy impulse response is also computed in the frequency-domain for the same piston. Numerical results are computed in the time and frequency-domains for a circular piston with a radius of 15mm. Problems with aliasing are identified in the frequency-domain impulse response calculation, whereas these problems are avoided in the time-domain calculation.

By real-time visual feedback of 3D scatter diagram of pulsatile tissue-motion, freehand ultrasonic diagnosis of neonatal ischemic diseases has been assisted at the bedside. The 2D ultrasonic movie was taken with a conventional ultrasonic apparatus (ATL HDI5000) and ultrasonic probes of 5-7 MHz with the compact tilt-sensor to measure the probe orientation. The real-time 3D visualization was realized by developing an extended version of the PC-based visualization system. The software was originally developed on the DirectX platform and optimized with the streaming SIMD extensions. The 3D scatter diagram of the latest pulsatile tissues has been continuously generated and visualized as projection image with the ultrasonic movie in the current section more than 15 fps. It revealed the 3D structure of pulsatile tissues such as middle and posterior cerebral arteries, Willis ring and cerebellar arteries, in which pediatricians have great interests in the blood flow because asphyxiated and/or low-birth-weight neonates have a high risk of ischemic diseases such as hypoxic-ischemic encephalopathy and periventricular leukomalacia. Since the pulsatile tissue-motion is due to local blood flow, it can be concluded that the system developed in this work is very useful to assist freehand ultrasonic diagnosis of ischemic diseases in the neonatal cranium.

Speckle noise is a random granular texture produced by mutual interference of a set of scattered wavefronts, so it is inherent to ultrasonic imaging. Depending on the phase of the wavefronts, the interference may be constructive or destructive. In this work, we developed an interference based speckle filter (ISF), whose first step is to attenuate the destructive interference, because it carries little information about the imaged structures. In order to do that, we considered, for each pixel, the maximum between the median and the original value. To eliminate the remaining bright speckles, we applied a median filter. The resulting image had minimized speckle effects. We have created two basic numeric phantoms, a linear array ultrasound and an intravascular ultrasound phantoms, and we have simulated 20 random initializations of speckle noise for each phantom. Then, we filtered the noisy images using several filters: ISF, median, Wiener, anisotropic diffusion and speckle reducing anisotropic diffusion (SRAD). To evaluate and compare their performances, we have calculated mean and standard deviation of a homogeneous region, square root mean error and structural similarity (SSIM) for each one. ISF presented an overall 0.91 rate for SSIM, while SRAD and Wiener filter performed SSIM 0.87 and 0.85 rates, respectively. This filter is easy to implement, because it requires only a sequence of three basic operations (Median, MaxValue and Median) and it is also easy to set the input parameters (the two radii of the median filters). Mostly important, it is able to smooth speckle effects without blurring edges.

High-frequency-ultrasound transducers are widely used but are typically based either on planar piezoceramic sections that are lapped down to smaller thicknesses or on piezopolymers that may be deformed into more complex geometries. Piezoceramics then require dicing to obtain arrays or can be fractured into spherical geometries to achieve focusing. Piezopolymers are not as efficient for very small element sizes and are normally available only in discrete thicknesses. Thick-film (TF) transducers provide a means of overcoming these limits because the piezoelectric film is deposited with the required thickness, size and geometry, thus avoiding any subsequent machining. Thick-film transducers offer the potential of a wide range of geometries such as single-elements and annular or linear arrays. Here, a single-element focused transducer was developed using a piezoceramic composition adapted to high-power operation which is commonly used at standard MHz frequencies. After fabrication, the transducer was characterized. Using specific transmit-receive electronics and a water tank adapted to high-frequency devices, the transducer was excited using a short pulse to evaluate its bandwidth and imaging capabilities. Finally, it was excited by a one-period sine wave using several power levels to evaluate its capacity to produce high-intensity focused ultrasound at frequencies over 20 MHz.

Elastography, computation of elasticity modulus of tissue is one of medical imaging methods with applications such as tumor detection and ablation therapy. Phase-based time delay estimation methods exploit the frequency information of the RF data to obtain strain estimates [1]. Although iterative Phase zero estimation is more computationally efficient in comparison to methods that seek for the absolute maximum cross-correlation between precompression and postcompression echo signals, it is quite sensitive to noise. The reason for this sensitivity is that for this iterative method an initial guess for the time shift is needed for each pixel. To estimate time shifts for the sample k, the time shift resulted from iterative phase zero method applied on sample k-1 is used as an initial value. This makes the method sensitive to noise because the error is propagating sample by sample and if the method gets unstable for any pixel, it will give unstable result for the following pixels in image line. Proposed strategy in this work to overcome this problem is to first estimate the displacement using Dynamic Programming [2] and use the results from DP as an initial guess of displacement for each pixel in iterative Phase zero method. Recently, regularized methods that incorporate the prior of tissue continuity in time delay estimation have been shown to produce low-noise and high contrast strain images [3,5]. In this work, we also incorporate the prior of tissue motion continuity in the phase zero method to make the zero-phase method more robust to signal decorrelation.

The ability of an ultrasound system to differentiate signals in the presence of clutter is of key clinical importance. There are several sources of clutter but assessing their relative importance and developing methods of reducing them remain areas of active research. We have developed a novel method called short-lag-spatial-coherence (SLSC) imaging that allows formation of high quality ultrasound images in the presence of clutter. The method is based on the van-Cittert- Zernike theorem. Specifically, the images are formed by utilizing the spatial coherence of the pressure field at the surface of the transducer. We compare matched SLSC and B-mode images beamformed from simulated data and data acquired on human liver in vivo. SLSC images have higher contrast and CNR then their B-mode counterparts for all acoustic-noise conditions (low, medium, and high noise). Nevertheless, SLSC brings highest improvement of target detectability in the medium noise environment. When the received signal is saturated with noise, both Bmode and SLSC produce low-quality images.

Assessment of Carotid Intima-Media Thickness (CIMT) by B-mode ultrasound is a technically mature and reproducible technology. Given the high morbidity, mortality and the large societal burden associated with CV diseases, as a safe yet inexpensive tool, CIMT is increasingly utilized for cardiovascular (CV) risk stratification. However, CIMT requires a precise measure of the thickness of the intima and media layers of the carotid artery that can be tedious, time consuming, and demand specialized expertise and experience. To this end, we have developed a highly user-friendly system for semiautomatic CIMT image interpretation. Our contribution is the application of active contour models (snake models) with hard constraints, leading to an accurate, adaptive and user-friendly border detection algorithm. A comparison study with the CIMT measurement software in Siemens Syngo® Arterial Health Package shows that our system gives a small bias in mean (0.049 ±0.051mm) and maximum (0.010 ± 0.083 mm) CIMT measures and offers a higher reproducibility (average correlation coefficients were 0.948 and 0.844 in mean and maximum CIMT respectively (P <0.001)). This superior performance is attributed to our novel interface design for hard constraints in the snake models.

Breast ultrasound tomography (BUST) is currently being developed for the early detection of cancer. Images of mechanical properties across the breast are formed using ultrasonic signals transmitted through the breast immersed in water. This is possible because the perturbation to the free propagation of ultrasound induced by the presence of the breast encodes information about the material properties of the breast. To achieve high sensitivity with BUST it is therefore crucial that the perturbation is most sensitive to the internal lesions inside the breast. However, the perturbation is also affected by the shape of the breast which can cause significant and undesired refraction effects. To understand the effect of breast shape on the transmission of ultrasound, this paper investigates transmission through a cone with properties similar to that of breast tissue. We show that it is possible to identify two regimes of transmission depending on the physical properties of the cone and transducers. While the first regime is suitable for BUST measurements, the second regime is highly affected by the breast shape and measurements are not reliable for accurate reconstructions. We provide a physical approximation that describes transmission in the first regime and which will aid the design of future BUST systems.

It is difficult for ultrasound to image small targets such as breast microcalcifications. Synthetic aperture ultrasound imaging has recently developed as a promising tool to improve the capabilities of medical ultrasound. We use two different tissueequivalent phantoms to study the imaging capabilities of a real-time synthetic aperture ultrasound system for imaging small targets. The InnerVision ultrasound system DAS009 is an investigational system for real-time synthetic aperture ultrasound imaging. We use the system to image the two phantoms, and compare the images with those obtained from clinical scanners Acuson Sequoia 512 and Siemens S2000. Our results show that synthetic aperture ultrasound imaging produces images with higher resolution and less image artifacts than Acuson Sequoia 512 and Siemens S2000. In addition, we study the effects of sound speed on synthetic aperture ultrasound imaging and demonstrate that an accurate sound speed is very important for imaging small targets.

Handheld ultrasound is useful for intra-operative imaging, but requires additional tracking hardware to be useful in navigated intervention settings, such as biopsies, ablation therapy, injections etc. Unlike common probe-andneedle tracking approaches involving global or local tracking, we propose to use a bracket with a combination of very low-cost local sensors - cameras with projectors, optical mice and accelerometers - to reconstruct patient surfaces, needle poses, and the probe trajectory with multiple degrees of freedom, but no global tracking overhead. We report our experiences from a rst series of benchtop and in-vivo human volunteer experiments.