Medical imaging examinations form the basis for physicians diagnosing diseases, as evidenced by the increasing use of digital medical images for picture archiving and communications systems (PACS). However, with enlarged medical image databases and rapid growth of patients' case reports, PACS requires image compression to accelerate the image transmission rate and conserve disk space for diminishing implementation costs. For this purpose, JPEG and JPEG2000 have been accepted as legal formats for the digital imaging and communications in medicine (DICOM). The high compression ratio is felt to be useful for medical imagery. Therefore, this study evaluates the compression ratios of JPEG and JPEG2000 standards for computer-aided diagnosis (CAD) of breast tumors in 3-D medical ultrasound (US) images. The 3-D US data sets with various compression ratios are compressed using the two efficacious image compression standards. The reconstructed data sets are then diagnosed by a previous proposed CAD system. The diagnostic accuracy is measured based on receiver operating characteristic (ROC) analysis. Namely, the ROC curves are used to compare the diagnostic performance of two or more reconstructed images. Analysis results ensure a comparison of the compression ratios by using JPEG and JPEG2000 for 3-D US images. Results of this study provide the possible bit rates using JPEG and JPEG2000 for 3-D breast US images.

Volume rendering in 3D ultrasound is a challenging task due to the large amount of computation required for real-time rendering. The shear-warp algorithm has been traditionally used for 3D ultrasound rendering for its effectiveness in lowering computing cost. However, this lowered computing cost does come at the price of reduced image quality due to (a) the presence of final warp interpolation, which smoothes out fine details and (b) sampling only at discrete slice locations, which introduces aliasing, e.g., staircase artifacts. For 3D ultrasound, we have merged pre-integration with the shear-image-order algorithm to overcome both limitations of shear-warp while still enjoying the computational savings. Pre-integration overcomes the aliasing artifacts while shear-image-order preserves details. We have also developed a technique to integrate shading coefficient into pre-integrated rendering. This pre-integrated shear-image-order algorithm, with slightly higher computation than what is required to support the shear-warp algorithm, improves the quality of the rendered image significantly. In this paper, we discuss the pre-integrated shear-image-order algorithm and present the results of subjective quality evaluation on several data sets. We have also analyzed how this algorithm can be implemented on an advanced digital signal processor (DSP) to achieve real-time performance.

In previous work, we investigated 3-D synthetic aperture imaging with 2-D array designs for real-time rectilinear volumetric imaging of targets near the transducer such as the breast and carotid artery. Here we present results for cylindrical 3-D imaging for 3-D transrectal ultrasound (TRUS). The major benefit of this design is the interconnect where an expensive multilayer flex circuit is no longer required. The interconnect uses a row-column addressing scheme to enable different groups of elements. Over 256 transmissions, this design is capable of synthesizing a 256 x 256 = 65,536 element fully sampled 2-D cylindrical array if desired. In receive, the echoes from individual elements along a row are recorded by the system receive channels. For faster volume acquisition time, we present a design where all elements of the 2-D array transmit simultaneously, and signals are recorded one row at a time. For a depth of 6 cm, a volume rate of 50 volumes/s can be achieved. We have performed computer simulations of a 10 MHz 256 x 256 synthetic cylindrical 2-D array with a radius of curvature of 10 mm to determine the radiation pattern. For an 128 x 128 subaperture, the on-axis case (x,y,z) = (0,0,20) mm showed a narrow beam down to -40 dB. In the transversal direction, on-axis lateral beamwidths at -6, -20, and -40 dB were 0.47 mm, 0.81 mm, and 2.54 mm, respectively. As for the longitudinal direction, the beamwidths are slightly narrower than in transversal direction, giving 0.39 mm, 0.72 mm, and 1.51 mm for the same corresponding dB levels.

This work reports on the application of ultrasound elastography to prostate cancer detection using a high resolution three-dimensional (3D) ultrasound imaging system. The imaging was performed at a relatively high frequency (14 MHz), yielding very fine resolution that is optimal for prostate ultrasound imaging. The fine resolution achieved aids in locating smaller lesions than are normally detectable. Elasticity was measured with a quantitative and automatically controlled "Synthetic Digital Rectal Examination (SDRE)" wherein a smoothly increasing force was applied by injecting water, controlled by an electronic syringe pump, into a latex cover over the transrectal transducer. The lesion identified as stiffened tissue was visually enhanced by colorizing and superimposing it over the conventional B-mode image. Experimental results using a tissue-mimicking phantom demonstrated that the reconstruction accuracy of the I-Beam transducer resulted in less than 15% volumetric error. Thus, this high resolution 3D prostate elastography is possible and may provide reliable and accurate determination of the size and the location of cancers, which may result in improved specificity and sensitivity of cancer detection.

Angiogenesis is the process that correlates to tumor growth, invasion, and metastasis. Breast cancer angiogenesis has been the most extensively studied and now serves as a paradigm for understanding the biology of angiogenesis and its effects on tumor outcome and patient prognosis. Most studies on characterization of angiogenesis focus on pixel/voxel counts more than morphological analysis. Nevertheless, in cancer, the blood flow is greatly affected by the morphological changes, such as the number of vessels, branching pattern, length, and diameter. This paper presents a computer-aided diagnostic (CAD) system that can quantify vascular morphology using 3-D power Doppler ultrasound (US) on breast tumors. We propose a scheme to extract the morphological information from angiography and to relate them to tumor diagnosis outcome. At first, a 3-D thinning algorithm helps narrow down the vessels into their skeletons. The measurements of vascular morphology significantly rely on the traversing of the vascular trees produced from skeletons. Our study of 3-D assessment of vascular morphological features regards vessel count, length, bifurcation, and diameter of vessels. Investigations into 221 solid breast tumors including 110 benign and 111 malignant cases, the p values using the Student's t-test for all features are less than 0.05 indicating that the proposed features are deemed statistically significant. Our scheme focuses on the vascular architecture without involving the technique of tumor segmentation. The results show that the proposed method is feasible, and have a good agreement with the diagnosis of the pathologists.

In this paper, we describe a new freehand ultrasound imaging system for reconstructing the left ventricle from 2D echocardiography slices. An important contribution of the proposed system is its ability to reconstruct from multiple standard views. The multi-view reconstruction procedure results in significant reduction in reconstruction error over single view reconstructions. The system uses object-based 3D volumetric registration, allowing for arbitrary rigid object movements in inter-view acquisition. Furthermore, a new segmentation procedure that combines level set methods with gradient vector flow(GVF) is used for automatically segmenting the 2D ultrasound images, in which low level of contrast, high level of speckle noise, and weak boundaries are common. The new segmentation approach is shown to be robust to these artifacts and is found to converge to the boundary from a wider range of initial conditions than competitive methods. The proposed system has been validated on a physical, 3D ultrasound calibration phantom and evaluated on one actual cardiac echocardiography data set. In the phantom experiment, two calibrated volumetric egg-shape objects were scanned from the top and side windows and reconstructed using the new method. The volume error was measured to be less than 4%. In a real heart data set experiment, qualitative results of 3D surface reconstruction from parasternal and apical views appear significantly improved over single view reconstructions. The estimated volumes from the 3D reconstructions were also found to be in agreement with the manual clinical measurements from 2D slices. Further extension of this work is to compare the quantitative results with more accuracy MRI data.

Ultrasound imaging is a noninvasive technique well-suited for detecting abnormalities like cysts, lesions and blood clots. In order to use 3D ultrasound to visualize the size and shape of such abnormalities, effective boundary detection methods are needed. A robust boundary detection technique using a nearest neighbor map (NNM) and applicable to multi-object cases has been developed. The algorithm contains three modules: pre-processor, main processor and boundary constructor. The pre-processor detects the object(s) and obtains geometrical as well as statistical information for each object, whereas the main processor uses that information to perform the final processing of the image. These first two modules perform image normalization, thresholding, filtering using median, wavelet, Wiener and morphological operation, estimation and boundary detection of object(s) using NNM, and calculation of object size and their location. The boundary constructor module implements an active contour model that uses information from previous modules to obtain seed-point(s). The algorithm has been found to offer high boundary detection accuracy of 96.4% for single scan plane (SSP) and 97.9 % for multiple scan plane (MSP) images. The algorithm was compared with Stick's algorithm and Gibbs Joint Probability Function based algorithm and was found to offer shorter execution time with higher accuracy than either of them. SSP numerically modeled ultrasound images, SSP real ultrasound images, MSP phantom images and MSP numerically modeled ultrasound images were processed.

For efficient and accurate diagnosis of ultrasound images, the appropriate time gain compensation (TGC) and dynamic range (DR) control of ultrasound echo signals are important. TGC is used for compensating the attenuation of ultrasound echo signals along the depth, and DR is for controlling the image contrast. In recent ultrasound systems, those two factors are automatically set by a system and/or manually adjusted by an operator to obtain the desired image quality on the screen. In this paper, we propose an algorithm to find the optimized parameter values for TGC and DR automatically. In TGC optimization, we determine the degree of attenuation compensation along the depth by reliably estimating the attenuation characteristic of ultrasound signals. For DR optimization, we define a novel cost function by properly using the characteristics of ultrasound images. Experimental results are obtained by applying the proposed algorithm to a real ultrasound (US) imaging system. The results prove that the proposed algorithm automatically sets values of TGC and DR in real-time so that the subjective quality of the enhanced ultrasound images may become good enough for efficient and accurate diagnosis.

The quality of medical ultrasound images is limited by inherent poor resolution due to the finite temporal bandwidth of the acoustic pulse and the non-negligible width of the system point-spread function. One of the major difficulties in designing a practical and effective restoration algorithm is to develop a model for the tissue reflectivity that can adequately capture significant image features without being computationally prohibitive. The reflectivities of biological tissues do not exhibit the piecewise smooth characteristics of natural images considered in the standard image processing literature; while the macroscopic variations in echogenicity are indeed piecewise smooth, the presence of sub-wavelength scatterers adds a pseudo-random component at the microscopic level. This observation leads us to propose modelling the tissue reflectivity as the product of a piecewise smooth echogenicity map and a unit-variance random field. The chief advantage of such an explicit representation is that it allows us to exploit representations for piecewise smooth functions (such as wavelet bases) in modelling variations in echogenicity without neglecting the microscopic pseudo-random detail. As an example of how this multiplicative model may be exploited, we propose an expectation-maximisation (EM) restoration algorithm that alternates between inverse filtering (to estimate the tissue reflectivity) and logarithmic wavelet denoising (to estimate the echogenicity map). We provide simulation and in vitro results to demonstrate that our proposed algorithm yields solutions that enjoy higher resolution, better contrast and greater fidelity to the tissue reflectivity compared with the current state-of-the-art in ultrasound image restoration.

We are working on integrating front-end electronics with the ultrasound transducer array for real-time 3D ultrasound imaging systems. We achieve this integration by flip-chip bonding a two-dimensional transducer array to an integrated circuit (IC) that comprises the front-end electronics. The front-end IC includes preamplifiers, multiplexers, and pulsers. We recently demonstrated a catheter-based real-time ultrasound imaging system based on a 16x16-element capacitive micromachined ultrasonic transducer (CMUT) array. The CMUT array is flip-chip bonded to a front-end IC that includes a pulser and preamplifier for each element of the array. To simplify the back-end processing and signal routing on the IC for this initial implementation, only a single array element is active at a time (classic synthetic aperture (CSA) imaging). Compared with classic phased array imaging (CPA), where multiple elements are used on transmit and receive, CSA imaging has reduced signal-to-noise ratio and prominent grating lobes. In this work, we evaluate three array designs for the next generation front-end IC. The designs assume there are 16 receive channels and that numerous transmit pulsers are provided by the IC. The designs presented are: plus-transmit x-receive, boundary-transmit x-receive with no common elements, and full-transmit x-receive with no common elements. Each design is compared with CSA and CPA imaging. We choose to implement an IC for the full-transmit x-receive with no common elements (FT-XR-NC) design for our next-generation catheter-based imaging system.

Medical Ultrasound Imaging is widely used clinically because of its relatively low cost, portability, lack of ionizing radiation, and real-time nature. However, even with these advantages ultrasound has failed to permeate the broad array of clinical applications where its use could be of value. A prime example of this untapped potential is the routine use of ultrasound to guide intravenous access. In this particular application existing systems lack the required portability, low cost, and ease-of-use required for widespread acceptance. Our team has been working for a number of years to develop an extremely low-cost, pocket-sized, and intuitive ultrasound imaging system that we refer to as the "Sonic Window." We have previously described the first generation Sonic Window prototype that was a bench-top device using a 1024 element, fully populated array operating at a center frequency of 3.3 MHz. Through a high degree of custom front-end integration combined with multiplexing down to a 2 channel PC based digitizer this system acquired a full set of RF data over a course of 512 transmit events. While initial results were encouraging, this system exhibited limitations resulting from low SNR, relatively coarse array sampling, and relatively slow data acquisition. We have recently begun assembling a second-generation Sonic Window system. This system uses a 3600 element fully sampled array operating at 5.0 MHz with a 300 micron element pitch. This system extends the integration of the first generation system to include front-end protection, pre-amplification, a programmable bandpass filter, four sample and holds, and four A/D converters for all 3600 channels in a set of custom integrated circuits with a combined area smaller than the 1.8 x 1.8 cm footprint of the transducer array. We present initial results from this front-end and present benchmark results from a software beamformer implemented on the Analog Devices BF-561 DSP. We discuss our immediate plans for further integration and testing. This second prototype represents a major reduction in size and forms the foundation of a fully functional, fully integrated, pocket sized prototype.

We propose an efficient array beamformer using spatial matched filtering. In the proposed method, ultrasound waves are transmitted from an array subaperture with fixed transmit focus as in conventional array imaging. At receive, radio frequency (RF) echo signals from each receive channel are passed through a spatial matched filter that is constructed based on the system transmit-receive spatial impulse response. The filtered echo signals are then summed. The filter remaps and spatially registers the acoustic energy from each element so that the pulse-echo impulse response of the summed output is focused with acceptably low side lobes. Analytical beam pattern analysis and simulation results using a linear array show that the proposed spatial filtering method can provide more improved spatial resolution and contrast-to-noise ratio (CNR) compared with conventional dynamic receive focusing (DRF) method by implementing two-way dynamically focused beam pattern throughout the field. We tested the predictions experimentally using an f/1.5, 8-ring annular array with 10 MHz center frequency focused geometrically at 45 mm. The -6 dB beam width measured with spatial filtering and DRF were measured to be 0.13 mm and 16.64 mm, respectively, at a depth of 25 mm. Spatial filtering was applied to the design of high frequency arrays for small animal imaging where delay and sum beamforming is problematic. Predictions of beam properties at 70 MHz will be presented.

This paper presents a recursive approach for parametric delay calculations for a beamformer. The suggested calculation procedure is capable of calculating the delays for any image line defined by an origin and arbitrary direction. It involves only add and shift operations making it suitable for hardware implementation. One delaycalculation unit (DCU) needs 4 parameters, and all operations can be implemented using fixed-point arithmetics. An N-channel system needs N+ 1 DCUs per line - one for the distance from the transmit origin to the image point and N for the distances from the image point to each of the receivers. Each DCU recursively calculates the square of the distance between a transducer element and a point on the beamformed line. Then it finds the approximate square root. The distance to point i is used as an initial guess for point i + 1. Using fixed-point calculations with 36-bit precision gives an error in the delay calculations on the order of 1/64 samples, at a sampling frequency of f_s = 40 MHz. The circuit has been synthesized for a Virtex II Pro device speed grade 6 in two versions - a pipelined and a non-pipelined producing 150 and 30 million delays per second, respectively. The non-pipelined circuit occupies about 0.5 % of the FPGA resources and the pipelined one about 1 %. When the square root is found with a pipelined CORDIC processor, 2 % of the FPGA slices are used to deliver 150 million delays per second.

For more than a century the possibility of imaging the structure of a medium with diffracting wavefields has been limited by the tradeoff between resolution and imaging depth. While long wavelengths can penetrate deep into a medium, the resolution limit precludes the possibility of observing subwavelength structures. Recent progress in microscopy has shown that by exploiting the super-oscillatory properties of evanescent fields, resolution several orders of magnitude smaller than the wavelength can be achieved so leading to Near-field Scanning Optical Microscopy. Based on a similar argument, this paper investigates the possibility of obtaining super resolution in the far-field (here far-field refers to a distance greater than λ, which would enable high resolution imaging at relatively large depth. The theoretical principles which result in the resolution limit are reviewed and a new strategy to overcome it is proposed. An advanced imaging algorithm for linear and two-dimensional array probing systems is presented and its capability of resolving targets as close as λ/3 is demonstrated experimentally, the targets being at several wavelength distance from the array. The results show that the method is superior to conventional techniques such as Synthetic Aperture Focusing, Synthetic Phased Arrays and Time Reversal.

Telematic ultrasonic diagnostics is a relatively new tool in providing health care to patients in remote, islolated communities. Our project facility, "The Virtual Polyclinic - A Specialists' Consulting Network for the Islands", is located on the island of Cres in the Adriatic Sea in Croatia and has been extending telemedical services to the archipelago population since 2000. Telemedicine applications include consulting services by specialists at the University Clinical Hospital Center Rebro in Zagreb and at "Magdalena", a leading cardiology clinic in Croatia. After several years of experience with static high resolution ultrasonic digital immages for referral consulting diagnostics purposes, we now also use dynamic ultrasonic sequences in a project with the Department of Emmergency Gastroenterology at Rebro in Zagreb. The aim of the ongoing project is to compare the advantages and shortcomings in transmitting static ultrasonic digital immages and live sequences of ultrasonic examination in telematic diagnostics. Ultrasonic examination is a dynamic process in which the diagnostic accuracy is highly dependent on the dynamic moment of an ultrasound probe and signal. Our first results indicate that in diffuse parenchymal organ pathology the progression and the follow up of a disease is better presented to a remote consulting specialist by dynamic ultrasound sequences. However, the changes that involve only one part of a parenchymal organ can be suitably presented by static ultrasonic digital images alone. Furthermore, we need less time for digital imaging and such tele-consultations overall are more economical. Our previous telemedicine research and practice proved that we can greatly improve the level of medical care in remote healthcare facilities and cut healthcare costs considerably. The experience in the ongoing project points to a conclusion that we can further optimize remote diagnostics benefits by a right choice of telematic application thus reaching a correct diagnosis and starting an applicable therapy even faster. Nevertheless, a successful implementation of such diagnostics methods may require further improvements in telemedical systems.

The feasibility of echographic imaging of the tissues in healthy lip and in reconstructed cleft lip and estimating the dimensions and the normalized echo level of these tissues is investigated. Echographic images of the upper lip were made with commercial medical ultrasound equipment, using a linear array transducer (7-11 MHz bandwidth) and a non-contact gel coupling. Tissue dimensions were measured by means of software calipers. Echo levels were calibrated and corrected for beam characteristics, gel path and tissue attenuation by using a tissue-mimicking phantom. At central position of philtrum, mean thickness (and standard deviation) of lip loose connective tissue layer, orbicularis oris muscle and dense connective layer was 4.0 (sd 0.1) mm, 2.3 (sd 0.7) mm, 2.2 (sd 0.7) mm, respectively, in healthy lip at rest. Mean (sd) echo level of muscle and dense connective tissue layer with respect to echo level of lip loose connective tissue layer was in relaxed condition: - 19.3 (sd 0.6) dB and - 10.7 (sd 4.0) dB, respectively. Echo level of loose connective tissue layer was +25.6 (sd 4.2) dB relative to phantom echo level obtained in the focus of the transducer. Color mode echo images were calculated, after adaptive filtering of the images, which show the tissues in separate colors and highlight the details of healthy lip and reconstructed cleft lip. Quantitative assessment of thickness and echo level of various lip tissues is feasible after proper calibration of the echographic equipment. Diagnostic potentials of the developed quantitative echographic techniques for non-invasive evaluation of the outcome of cleft lip reconstruction are promising.

A hybrid imaging system is proposed for cancer detection, diagnosis and therapy monitoring by integrating three complementary imaging techniques - ultrasound, photoacoustic and elasticity imaging. Indeed, simultaneous imaging of the anatomy (ultrasound imaging), cancer-induced angiogenesis (photoacoustic imaging) and changes in biomechanical properties (elasticity imaging) of tissue is based on many synergistic features of these modalities and may result in a unique and important imaging tool. To facilitate the design and development of a real-time imaging system for clinical applications, we have investigated the core components of the imaging system using numerical simulations. Differences and similarities between each imaging technique were considered and contrasted. The results of our study suggest that the integration of ultrasound, photoacoustic and elasticity imaging is possible using a custom designed imaging system.

Ultrasonic imaging has the potential to enhance our capability to detect and diagnose breast cancers, but its imaging quality and resolution need to be significantly improved. We make use of the principle of the time-reversal mirror to develop an image-reconstruction method for ultrasonic breast imaging. It reconstructs images of scatterers (e.g., tumors) that generate/scatter ultrasonic waves by backpropagating measured ultrasonic signals into a heterogeneous breast model on computers using the principle of time-reversal mirror. We use solutions of the (two-way) full wave equation and one-way wave equation in heterogeneous media for backpropagation. We found that the one-way wave-equation-based imaging method can produce higher-resolution images than the two-way propagation-based imaging method when the data acquisition aperture is limited (for a linear transducer array). With a full aperture, our imaging results demonstrate that imaging with time-reversed ultrasound can produce high-quality images of the breast.

This paper proposed a novel ultrasonic imaging approach for detecting brachytherapy seeds. Accurate and fast seed localization plays a key role in computing dosimetry for prostate brachytherapy. However, currently used B-mode transrectal ultrasound (TRUS) does not adequately visualize implanted seeds, because the diameter of the seed is quite small and visualization is hampered by speckle noise and angulation of the specular reflection of the seeds. Based on the fact that much more ultrasound wave energy is reflected from metal seeds than from other scatterers in tissue, we developed a new seed detection method directly using ultrasound radio frequency (RF) signals (the raw high frequency echoes before the formation of B-mode TRUS images). It monitors the average power (a version of 2-norm) of the RF signals to measure the reflected wave energy. Each RF scan line is subdivided into a sequence of short segments with the same length and spacing. The average power of each segment is computed by the Fourier based spectra or parametric spectral analysis approaches. In the new method, the logarithmic compression is not applied to the raw RF data, and the average power is proportional to the sum of the square of the signal amplitude. Therefore, it produces significantly higher contrast than conventional B-mode TRUS. Furthermore, the average power algorithm can be implemented very efficiently since no numerical optimization is required. Phantom and ex-vivo experiments show that the average power technique successfully detects implanted brachytherapy seeds, and produces superior results compared with B-mode TRUS imaging.

In this study, we have tested the ability of four imaging modalities to investigate foreign objects in soft tissue. We inserted wood, plastic, glass, and aluminum objects into a pork sample to simulate traumatized soft tissue. Each object was inserted into the skin, then passed through the fat tissue layer and penetrated into the muscle layer. We then took images of the pork sample using four different modalities: (1) a C-Scan imaging prototype which consists of an unfocused transducer, a compound acoustic lens, and a 2D ultrasound sensor array based on the piezoelectric sensing complementary metal-oxide semiconductor (PE-CMOS) technology; (2) a portable B-Scan ultrasound system; (3) a conventional X-ray system; (4) and a computed radiography (CR) X-ray system. We found that the aluminum and glass objects were clearly visible in both conventional X-ray and CR X-ray images with good contrast-to-noise ratio (CNR); however, the wood and plastic objects could not be clearly seen using these modalities. However, we found that the wood, plastic, and glass objects, as well as the thicker aluminum object, were clearly visible in the C-Scan ultrasound images. Furthermore, the fold fibro structures of the fat and muscle tissues in the pork were observable using this modality. The C-Scan prototype images produce neither speckle nor geometry distortion. Both of these issues are commonly seen in B-Scan ultrasound. The results of this study also indicate that the C-Scan images have better CNRs for most foreign objects when compared to other imaging modalities.

Early detection through screening is the best defense against morbidity and mortality from breast cancers. Mammography is the most used screening tool for detecting early breast cancer because it can easily obtain the view of whole breast. However, because the ultrasound images are cross-sectional images, not projection images like mammography, and the ultrasound probe does not fully cover the breast width, it is not a convenient screening tool when adjunct with screening mammography. The physician needs a lot of examination time to perform the breast screening. Recently, some whole breast ultrasound scanning machines are developed. The examination could be performed by an experienced technician. Because the probe width still does not fully cover the breast width, several scanning passes are required to obtain the whole breast image. The physician still cannot have a full view of breast. In this paper, an image stitching technique is proposed to stitch multi-pass images into a full-view image. The produced full-view image can reveal the breast anatomy and assists physicians to reduce extra manual adjustment.

Real-time acquisition of 3D volumes is an emerging trend in medical imaging. True real-time 3D ultrasonic imaging is particularly valuable for echocardiography and trauma imaging as well as an intraoperative imaging technique for surgical navigation. Since the frame rate of ultrasonic imaging is fundamentally limited by the speed of sound, many schemes of forming multiple receive beams with a single transmit event have been proposed. With the advent of parallel receive beamforming, several architectures to form multiple (4-8) scan lines at a time have been suggested. Most of these architectures employ uniform sampling and input memory banks to store the samples acquired from all the channels. Some recent developments like crossed electrode array, coded excitation, and synthetic aperture imaging facilitate forming an entire 2D plane with a single transmit event. These techniques are speeding up frame rate to eventually accomplish true real-time 3D ultrasonic imaging. We present an FPGA-based scalable architecture capable of forming a complete scan plane in the time it usually takes to form a single scan line. Our current implementation supports 32 input channels per FPGA and up to 128 dynamically focused beam outputs. The desired focusing delay resolution is achieved using a hybrid scheme, with a combination of nonuniform sampling of the analog channels and linear interpolation for nonsparse delays within a user-specified minimum sampling interval. Overall, our pipelined architecture is capable of processing the input RF data in an online fashion, thereby reducing the input storage requirements and potentially providing better image quality.

Segmentation of the heart muscle in 3D echocardiographic images provides a tool for visualization of cardiac anatomy and assessment of heart function, and serves as an important pre-processing step for cardiac strain imaging. By incorporating spatial and temporal information of 3D ultrasound image sequences (4D), a fully automated method using image statistics was developed to perform 3D segmentation of the heart muscle. 3D rf-data were acquired with a Philips SONOS 7500 live 3D ultrasound system, and an X4 matrix array transducer (2-4 MHz). Left ventricular images of five healthy children were taken in transthoracial short/long axis view. As a first step, image statistics of blood and heart muscle were investigated. Next, based on these statistics, an adaptive mean squares filter was selected and applied to the images. Window size was related to speckle size (5x2 speckles). The degree of adaptive filtering was automatically steered by the local homogeneity of tissue. As a result, discrimination of heart muscle and blood was optimized, while sharpness of edges was preserved. After this pre-processing stage, homomorphic filtering and automatic thresholding were performed to obtain the inner borders of the heart muscle. Finally, a deformable contour algorithm was used to yield a closed contour of the left ventricular cavity in each elevational plane. Each contour was optimized using contours of the surrounding planes (spatial and temporal) as limiting condition to ensure spatial and temporal continuity. Better segmentation of the ventricle was obtained using 4D information than using information of each plane separately.

Conventional methods for mapping cardiac current fields lack either spatial resolution (e.g. ECG) or are time consuming (e.g., intra-cardiac catheter electrode mapping). We present a method based on the acousto-electric effect (AEE) with potential for rapid mapping of current fields in the heart with high spatial resolution. The AEE is a pressure-induced conductivity modulation, in which focused ultrasound can be used as a spatially localized pressure source. When an ultrasound beam is focused between a pair of recording electrodes in a homogeneous conductive medium, an induced voltage will be produced due to the pressure-modulated conductivity and local current density. The amplitude of the voltage change should be proportional to fluctuations in current density, such as those generated during the cardiac cycle, in the region of focused ultrasound. Preliminary experiments demonstrate the feasibility of this method. A 540 kHz ultrasound transducer is focused between two tin electrodes lying parallel to the beam axis. These electrodes inject current into a 0.9% saline solution. A pair of insulated stainless steel electrodes exposed at the tip is used to record voltage. To simulate a cardiac current, a low frequency current waveform is injected into the sample such that the peak current density (8 mA/cm²) approximates cardiac currents. The transducer is pulsed at different delays after waveform initiation. Delays are chosen such that the low frequency waveform is adequately sampled. Using this approach an emulated ECG waveform has been successfully reconstructed from the ultrasound modulated voltage traces.

In this paper a novel method is proposed for live endocardial boundary identification. The goal is to achieve an optimal solution to the problem of real-time automatic detection and tracking of endocardial border in ultrasonic image sequences acquired through Intracardiac Echocardiography (ICE). Border identification of 2D ultrasonic images, which normally consists of a number of stages namely preprocessing, segmentation, detection and visualization of the border, is a cumbersome task. ICE's potential in guidance of minimally invasive interventions requires online boundary detection of its inherently less speckled images. Numerous studies have addressed this issue in echographic images by proposing various methods applicable at each stage. With this repository of methods available, a comparative study is performed on single-image segmentation approaches. An algorithm based on order-statistics operators is proposed to achieve fast border delineation in a sequence of images. This method can outperform other approaches in terms of time and robustness, and does not require user interaction.

We developed a novel multi-beat image fusion technique using a special spatiotemporal interpolation for sparse, irregularly sampled data (ISI). It is applied to irregularly distributed 3D cardiac ultrasound data acquired with a fast rotating ultrasound (FRU) transducer. ISI is based on Normalized Convolution with Gaussian kernels tuned to irregular beam data spacing over cardiac phase (τ), and beam rotation (θ) and elevation angles (φ). Methods: images are acquired with the FRU transducer developed in our laboratory, a linear phased array rotating mechanically continuously at very high speed (240-480rpm). High-quality 2D images are acquired at ~100 frames/s over 5-10 seconds. ECG is recorded simultaneously. Images are irregularly distributed over τ and θ, because rotation is not synchronized to heartrate. ISI was compared quantitatively to spatiotemporal nearest neighbor interpolation (STNI) on synthetic (distance function) data of a pulsating ellipsoid for 32 angles (θ) and 37 phases (τ). ISI was also tested qualitatively on 20 in-vivo cardiac image sets and compared to classical temporal binning with trilinear voxel interpolation, at resolutions of 256*256*400 for 16 phases. Results: From the synthetic data simulations, ISI showed absolute distance errors (mean±SD) of 1.23 ± 1.52mm; considerably lower than for STNI (3.45 ± 3.03mm). For in-vivo images, ISI voxel sets showed reduced motion artifacts, suppression of noise and interpolation artifacts and better delineation of endocardium. Conclusions: ISI improves the quality of 3D+T images acquired with a fast rotating transducer in simulated and in-vivo data. It may also be useful for similar spatiotemporal irregularly distributed data, e.g. freehand 3D echocardiography.

Ultrasound imaging is a well established technology for echocardiography on humans. For cardiac imaging in small animals whose hearts beat at a rate higher than 300 beats per minute, the spatial and temporal resolution of current clinical ultrasonic scanners are far from ideal and simply inadequate for such applications. In this research, a real-time high frequency ultrasound imaging system was developed with a frame rate higher than 80 frames per second (fps) for cardiac applications in small animals. The device has a mechanical sector scanner using magnetic drive mechanism to reduce moving parts and ensure longevity. A very lightweight (< 0.28 g) single element transducer was specially designed and constructed for this research to achieve a frame rate of at least 80 fps. The 30-50 MHz transducers swept through an arc at the end of a pendulum for imaging the heart of small animals. The imaging electronics consisted of a low noise pulser/receiver, a high-speed data acquisition board, and digital signal processing algorithms. In vivo results on mouse embryos showed that real time ultrasound imaging at frame rate exceeding 80 fps could demonstrate detailed depiction of cardiac function with a spatial resolution of around 50 microns, which allows researchers to fully examine and monitor small animal cardiac functions.

Preliminary results relating to the design, fabrication, and characterization of a 3600 (60 x 60) element, fully sampled, 5 MHz two dimensional (2D) array are presented. The viable element yield of the new array was estimated at 98.3%. Single-element pulse-echo experiments indicate that the center frequency is 4.7 MHz - 7.8% below the resonant frequency determined by Finite Element Analysis (FEA) simulation. Pulse-echo signal fractional bandwidth was measured to be 60.3% at the -6 dB level. Ringdown was longer than anticipated in experimental pulse echo voltage waveforms, which we attribute in part to a lack of matching layer and a low-loss backing material. Based on plane-wave pulse-echo experiments in a water-tank, single element signal-to-noise ratio (SNR) was calculated to be 6.0 when using a plane-wave transmit (all elements excited). Experimental angular beam patterns were more directional than predicted with the standard soft-baffle equation, but in good agreement with FEA simulations that take account of finite acoustic crosstalk.

Observed medical ultrasound images are degraded representations of true tissue images. The degradation is a combination of blurring due to the finite resolution of the imaging system and the observation noise. This paper presents a new wavelet based deconvolution method for medical ultrasound imaging. We design a new orthogonal wavelet basis known as the symmetrical mirror wavelet basis that can provide more desirable frequency resolution. Our proposed ultrasound image restoration with wavelets consists of an inversion of the observed ultrasound image using the estimated two-dimensional (2-D) point spread function (PSF) followed by denoising in the designed wavelet basis. The tissue image restoration is then accomplished by modelling the tissue structures with the generalized Gaussian density (GGD) function using the Bayesian estimation. Both subjective and objective measures show that the deconvolved images are more appealing in the visualization and resolution gain.

A new Plane wave fast color flow imaging method (PWM) has been investigated, and performance evaluation of the PWM based on experimental measurements has been made. The results show that it is possible to obtain a CFM image using only 8 echo-pulse emissions for beam to flow angles between 45^o. and 75^o. Compared to the conventional ultrasound imaging the frame rate is ~ 30-60 times higher. The bias, B_est of the velocity profile estimate, based on 8 pulse-echo emissions, is between 3.3 % and 6.1 % for beam to flow angles between 45^o. and 75^o, and the standard deviation, σ_est of the velocity profile estimate is around 2 % for beam to flow angles between 45^o. and 75^o. relative to the peak velocity, when the flow angle is known in advance. A study is performed to investigate how different parameters influence the blood velocity estimation. The results confirmed expectations for beam to flow angles between 45^o. and 75^o. The parameter study shows that the PWM using Directional velocity estimation gives the best results using spatial sampling interval ≤λ/10, correlation range ≥10λ, and number of directional signals ≥6. It is hereby shown that, by carefully choosing the set of parameters, PWM is feasible for fast CFM imaging with an acceptable bias and standard deviation.

Standard spatial compounding, via averaging acquisitions from different angles, has proved to be an efficient technique for speckle pattern reduction in ultrasound B-mode images. However, the resulting images may be blurred due to the averaging of point spread functions and the misalignment of the different views. These blurring artefacts result in a loss of important anatomical features that may be critical for medical diagnosis. In this paper, we evaluate some spatial compounding techniques, focusing on how to combine the different acquisitions. The evaluated methods are: weighed averaging, wavelet coefficient fusion and multiview deconvolution. To some extent, these techniques take into account the limitations of spatial compounding, by proposing alternative fusion methods that can reduce speckle artefacts while preserving standard spatial resolution and anatomical features. We experimented these compounding methods with synthetic images to show that these advanced techniques could outperform traditional averaging. In particular, multiview deconvolution techniques performed best, showing improvement in respect to averaging (6.81 dB) for realistic levels of speckle noise and spatial degradation. Wavelet fusion technique ranked second (2.25 dB), and weighted average third (0.70 dB). On the other hand, weighted averaging was the least time consuming, followed by wavelet fusion (x2) and multiview deconvolution (x5). Wavelet fusion offered an interesting trade-off between performance and computational cost. Experiments on 3D breast ultrasound imaging, showed consistent results with those obtained on synthetic images. Tissue was linearly scanned with a 2D probe in different directions, and volumes were compounded using the aforementioned techniques. This resulted in a high-resolution volume, with better tissue delineation and less speckle patterning.

We have developed a new coded excitation technique where sigma-delta sampling and the corresponding single-bit pre-compression are utilized to reduce hardware complexity while improving signal-to-noise ratio (SNR) and penetration. From phantom studies, we have obtained a 10.03 dB SNR improvement with the proposed sigma-delta sampling-based coded excitation (SDS-CE) system compared to the conventional pulse-echo excitation method at the same voltage level. This improvement allows the necessary voltage level for the SDS-CE to be lowered to one sixth (e.g., ±10 V) of that for the conventional pulse-echo excitation method with the excitation voltage of ±60 V to achieve a comparable SNR and penetration depth. To evaluate the hardware complexity in the proposed method, the number of gates was estimated based on the 0.35-μm CMOS fabrication process. The proposed SDS-CE method can save 55.4%, 79.0% and 56.8% gates needed compared to the conventional pulse-echo method and the coded excitation method based on pre and post-compression, respectively. The proposed SDS-CE could lead to the integration of the transmitter and receiver circuitries into a single chip due to the improved SNR and reduced hardware complexity.

Three-dimensional freehand ultrasound has found several clinical applications, such as image-guided surgery and radiotherapy, since the last decade. A key step of all the freehand ultrasound imaging systems is calibration. Calibration is the procedure to estimate a two to three-dimensional transformation matrix which precisely maps two-dimensional ultrasound images to the physical coordinate. This paper presents a novel freehand ultrasound calibration algorithm which is based on a sequential least squares method, known as the Unscented Kalman Filter (UKF) algorithm. This method has significant advantages over the prior approaches, where the block least squares techniques have been employed to perform the ultrasound probe calibration. One of the advantages is that it computes the calibration parameters as well as their variances sequentially by processing the sample points, collected from ultrasound images of a designed phantom, one by one. Variance evaluation can be used to generate a confidence measure for the estimated calibration matrix. It also enables us to stop the calibration procedure once the desired confidence measure is met or informs us to collect more sample points to improve the calibration accuracy. The proposed calibration method is evaluated by using a custom designed N-wire phantom. The simulation results confirm that the proposed calibration algorithm converges to the same solution as the block least squares algorithms, while having the above mentioned practical advantages.

Tissue engineering is an interdisciplinary field that combines various aspects of engineering and life sciences and aims to develop biological substitutes to restore, repair or maintain tissue function. Currently, the ability to have quantitative functional assays of engineered tissues is limited to existing invasive methods like biopsy. Hence, an imaging tool for non-invasive and simultaneous evaluation of the anatomical and functional properties of the engineered tissue is needed. In this paper we present an advanced in-vivo imaging technology - ultrasound biomicroscopy combined with complementary photoacoustic and elasticity imaging techniques, capable of accurate visualization of both structural and functional changes in engineered tissues, sequential monitoring of tissue adaptation and/or regeneration, and possible assistance of drug delivery and treatment planning. The combined imaging at microscopic resolution was evaluated on tissue mimicking phantoms imaged with 25 MHz single element focused transducer. The results of our study demonstrate that the ultrasonic, photoacoustic and elasticity images synergistically complement each other in detecting features otherwise imperceptible using the individual techniques. Finally, we illustrate the feasibility of the combined ultrasound, photoacoustic and elasticity imaging techniques in accurately assessing the morphological and functional changes occurring in engineered tissue.

The ultrasonic vibraton potential refers to the production of a voltage that varies in time when ultrasound passes through a colloidal or ionic solution. The vibration potential can be used as an imaging method for soft tissue by recording its phase, time of arrival, and magnitude relative to the launching of a burst of ultrasound. A theory of the effect can be found from Maxwell's equations. Experimental results demonstrating the imaging method are shown for bodies with simple geometries.