We present the first clinical results of a novel fully automated 3D breast ultrasound system. This system was designed to match a Philips diffuse optical mammography system to enable straightforward coregistration of optical and ultrasound images. During a measurement, three 3D transducers scan the breast at 4 different views. The resulting 12 datasets are registered together into a single volume using spatial compounding. In a pilot study, benign and malignant masses could be identified in the 3D images, however lesion visibility is less compared to conventional breast ultrasound. Clear breast shape visualization suggests that ultrasound could support the reconstruction and interpretation of diffuse optical tomography images.

Three-dimensional (3D) ultrasound data are acquired mostly using a dedicated mechanical probe that houses a 1D array transducer. This 1D transducer swivels back and forth continuously in the elevation direction (continuous scanning) for fast acquisition. When 3D ultrasound data are acquired via continuous scanning but the continuous motion of a transducer is not taken into account during reconstruction, the reconstructed volume contains error. In this study, we systematically analyzed this error, which is a complex function of many parameters. The error increases when the transducer angular speed (ω) increases. Also, it varies depending on the voxel location inside an acquired volume. The mean error is calculated by averaging the errors at all acquired voxel locations. With a 60-degree volume angle, a 60-degree sector angle, 12-cm scan depth and 48 transmit beams per slice, the mean error is 5.3 mm when ω is 0.6 degrees/ms. When ω is reduced to 0.1 degrees/ms, the mean error decreases to 0.81 mm. We also assessed the impact of this error on the reconstructed images of a 3D phantom using simulation. At high angular speeds, the error in reconstructed images becomes noticeable and results in missing parts, geometric distortion and lowered image quality.

The quantitative assessment of regional myocardial function remains an important goal in clinical cardiology. As such, tissue Doppler imaging and speckle tracking based methods have been introduced to estimate local myocardial strain. Recently, volumetric ultrasound has become more readily available, allowing therefore the 3D estimation of motion and myocardial deformation. Our lab has previously presented a method based on spatio-temporal elastic registration of ultrasound volumes to estimate myocardial motion and deformation in 3D, overcoming the spatial limitations of the existing methods. This method was optimized on simulated data sets in previous work and is currently tested in a clinical setting. In this manuscript, 10 healthy volunteers, 10 patient with myocardial infarction and 10 patients with arterial hypertension were included. The cardiac strain values extracted with the proposed method were compared with the ones estimated with 1D tissue Doppler imaging and 2D speckle tracking in all patient groups. Although the absolute values of the 3D strain components assessed by this new methodology were not identical to the reference methods, the relationship between the different patient groups was similar.

Breast cancer is the most common type of cancer among women in Europe and North America. The established screening method to detect breast cancer is X-ray mammography, although X-ray frequently provides poor contrast for tumors located within glandular tissue. A new imaging approach is Ultrasound Tomography generating three-dimensional speed of sound images. This paper describes a method to evaluate the clinical applicability of three-dimensional speed of sound images by automatically registering the images with the corresponding X-ray mammograms. The challenge is 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. This conflict requires estimating the relation between deformed and undeformed breast and applying the deformation to the three-dimensional speed of sound image. The deformation is simulated based on a biomechanical model using the finite element method. After simulation of the compression, the contours of the X-ray mammogram and the projected speed of sound image overlap congruently. The quality of the matching process was evaluated by measuring the overlap of a lesion marked in both modalities. Using four test datasets, the evaluation of the registration resulted in an average tumor overlap of 97%. The developed registration provides a basis for systematic evaluation of the new modality of three-dimensional speed of sound images, e.g. allows a greater understanding of tumor depiction in these new images.

The purpose of this study was to investigate the performance of an ultrasound tomography (UST) prototype relative to magnetic resonance (MR) for imaging overall breast anatomy and accentuating tumors relative to background tissue. The study was HIPAA compliant, approved by the Institutional Review Board, and performed after obtaining the requisite informed consent. Twenty-three patients were imaged with MR and the UST prototype. T₁ weighted images with fat saturation, with and without gadolinium enhancement, were used to examine anatomical structures and tumors, while T₂ weighted images were used to identify cysts. The UST scans generated sound speed, attenuation, and reflection images. A qualitative visual comparison of the MRI and UST images was then used to identify anatomical similarities. A more focused approach that involved a comparison of reported masses, lesion volumes, and breast density was used to quantify the findings from the visual assessment. Our acoustic tomography prototype imaged distributions of fibrous stroma, parenchyma, fatty tissues, and lesions in patterns similar to those seen in the MR images. The range of thresholds required to establish tumor volume equivalency between MRI and UST suggested that a universal threshold for isolating masses relative to background tissue is feasible with UST. UST has demonstrated the ability to visualize and characterize breast tissues in a manner comparable to MRI. Thresholding techniques accentuate masses relative to background anatomy, which may prove clinically useful for early cancer detection.

Ultrasound images appearance is characterized by speckle, shadows, signal dropout and low contrast which make them really difficult to process and leads to a very poor signal to noise ratio. Therefore, for main imaging applications, a denoising step is necessary to apply successfully medical imaging algorithms on such images. However, due to speckle statistics, denoising and enhancing edges on these images without inducing additional blurring is a real challenging problem on which usual filters often fail. To deal with such problems, a large number of papers are working on B-mode images considering that the noise is purely multiplicative. Making such an assertion could be misleading, because of internal pre-processing such as log compression which are done in the ultrasound device. To address those questions, we designed a novel filtering method based on 1D Radiofrequency signal. Indeed, since B-mode images are initially composed of 1D signals and since the log compression made by ultrasound devices modifies noise statistics, we decided to filter directly the 1D Radiofrequency signal envelope before log compression and image reconstitution, in order to conserve as much information as possible. A bi-orthogonal wavelet transform is applied to the log transform of each signal and an adaptive 1D split and merge like algorithm is used to denoise wavelet coefficients. Experiments were carried out on synthetic data sets simulated with Field II simulator and results show that our filter outperforms classical speckle filtering methods like Lee, non-linear means or SRAD filters.

This paper presents a comparison of different implementations of 3D anisotropic diffusion speckle noise reduction technique on ultrasound images. In this project we are developing a novel volumetric calcification assessment metric for the placenta, and providing a software tool for this purpose. The tool can also automatically segment and visualize (in 3D) ultrasound data. One of the first steps when developing such a tool is to find a fast and efficient way to eliminate speckle noise. Previous works on this topic by Duan, Q. [1] and Sun, Q. [2] have proven that the 3D noise reducing anisotropic diffusion (3D SRAD) method shows exceptional performance in enhancing ultrasound images for object segmentation. Therefore we have implemented this method in our software application and performed a comparative study on the different variants in terms of performance and computation time. To increase processing speed it was necessary to utilize the full potential of current state of the art Graphics Processing Units (GPUs). Our 3D datasets are represented in a spherical volume format. With the aim of 2D slice visualization and segmentation, a "scan conversion" or "slice-reconstruction" step is needed, which includes coordinate transformation from spherical to Cartesian, re-sampling of the volume and interpolation. Combining the noise filtering and slice reconstruction in one process on the GPU, we can achieve close to real-time operation on high quality data sets without the need for down-sampling or reducing image quality. For the GPU programming OpenCL language was used. Therefore the presented solution is fully portable.

Femur bone length is used in the assessment of fetal development and in the prediction of gestational age (GA). In this paper, we present a completely automated two-step method for identifying fetal femur and measuring its length from 2D ultrasound images. The detection algorithm uses a normalized score premised on the distribution of anatomical shape, size and presentation of the femur bone in clinically acceptable scans. The measurement process utilizes a polynomial curve fitting technique to determine the end-points of the bone from a 1D profile that is most distal from the transducer surface. The method has been tested with manual measurements made on 90 third trimester femur images by two radiologists. The measurements made by the experts are strongly correlated (Pearson's coefficient = 0.95). Likewise, the algorithm estimate is strongly correlated with expert measurements (Pearson's coefficient = 0.92 and 0.94). 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 both manual measurements in 89/90 cases and within ±3SD in all 90 cases. The method presented in this paper can be adapted to perform automatic measurement of other fetal limbs.

Tissue deformation in ultrasound imaging poses a challenge to the development of many image registration techniques, including multimodal image fusion, multi-angle compound image and freehand three-dimensional ultrasound. Although deformation correction methods are desired to provide images of uncompressed tissue structure, they have not been well-studied. A novel trajectory-based method to correct a wide range of tissue deformation in ultrasound imaging was developed. In order to characterize tissue deformation under different contact forces, a force sensor provides contact force measurement. Template based image-flow techniques were applied to RF A-lines under different contact forces. A two-dimensional displacement trajectory field was constructed, where pixel coordinates in each scan were plotted against the corresponding contact force. Nonlinear extrapolation algorithms are applied to each trajectory to relocate the corresponding pixel to where it would have been had there been no contact, thereby correcting tissue deformation in the images. This method was validated by using a combination of FEM deformation and ultrasound simulation. It was shown that deformation of the simulated pathological tissue could be corrected. Furthermore, nonlinear polynomial regression was found to give better estimates, than linear regression, when large deformation was present. Estimation accuracy was not improved significantly for a polynomial regression larger than second order.

Ultrasound imaging is used within numerous medical disciplines. Extensive and repeated training is needed for efficient use of the technology. Simulator training has been proposed as a complement to other training methods. Advantages of simulator training include access to a large number of normal and rare cases without the need for suitable volunteers and available ultrasound equipment. The imaging of soft tissue can be simulated by considering the interaction between the tissue and the ultrasound field. The objective of this study is to include these effects in real-time simulators. One previous approach has been to simulate a three-dimensional (3D) ultrasound volume off line, and then cross-section the volume in real time. This approach, however, does not take into account the anisotropic resolution of ultrasound imaging. If we assume that the average acoustical properties of tissues are slowly varying and that the speckle pattern is independent of the tissue, we show that ultrasound images can be simulated by multiplying a pre-simulated speckle image by an any-plane cross section of a 3D representation of an anatomy. Thus anisotropic resolution can be simulated in real time. The simulated images were compared to true ultrasound images of soft tissue. Since the speckle was simulated independently of the tissue, the most realistic results were obtained for still images, but the method was also satisfactory for moving images when speckle tracking between views was not important. The method is well applicable to ultrasound training simulators on low cost platforms.

Improvement of ultrasound images should be guided by their diagnostic value. Evaluation of clinical image quality is generally performed subjectively, because objective criteria have not yet been fully developed and accepted for the evaluation of clinical image quality. Based on recommendation 500 from the International Telecommunication Union - Radiocommunication (ITU-R) for such subjective quality assessment, this work presents equipment and a methodology for clinical image quality evaluation for guiding the development of new and improved imaging. The system is based on a BK-Medical 2202 ProFocus scanner equipped with a UA2227 research interface, connected to a PC through X64-CL Express camera link. Data acquisition features subject data recording, loading/saving of exact scanner settings (for later experiment reproducibility), free access to all system parameters for beamformation and is applicable for clinical use. The free access to all system parameters enables the ability to capture standardized images as found in the clinic and experimental data from new processing or beamformation methods. The length of the data sequences is only restricted by the memory of the external PC. Data may be captured interleaved, switching between multiple setups, to maintain identical transducer, scanner, region of interest and recording time on both the experimental- and standardized images. Data storage is approximately 15.1 seconds pr. 3 sec sequence including complete scanner settings and patient information, which is fast enough to get sufficient number of scans under realistic operating conditions, so that statistical evaluation is valid and reliable.

This paper presents a method setup for high-frequency ultrasound ranging based on stepped frequency-modulated continuous waves (FMCW), potentially capable of producing a higher signal-to-noise ratio (SNR) compared to traditional pulse-echo signaling. In current ultrasound systems, the use of higher frequencies (10-20 MHz) to enhance resolution lowers signal quality due to frequency-dependent attenuation. The proposed ultrasound signaling format, step-FMCW, is well-known in the radar community, and features lower peak power, wider dynamic range, lower noise figure and simpler electronics in comparison to pulse-echo systems. In pulse-echo ultrasound ranging, distances are calculated using the transmit times between a pulse and its subsequent echoes. In step-FMCW ultrasonic ranging, the phase and magnitude differences at stepped frequencies are used to sample the frequency domain. Thus, by taking the inverse Fourier transform, a comprehensive range profile is recovered that has increased immunity to noise over conventional ranging methods. Step-FMCW and pulse-echo waveforms were created using custom-built hardware consisting of an arbitrary waveform generator and dual-channel super heterodyne receiver, providing high SNR and in turn, accuracy in detection.

One of the leading causes of medical malpractice claims in emergency medicine is the misdiagnosis of the presence of foreign bodies. Radiolucent foreign bodies are especially difficult to differentiate from surrounding soft tissue, gas, and bone. Current imaging modalities employed for the detection of foreign bodies include: X-ray computed tomography, magnetic resonance, and ultrasound; however, there is no consensus as to which modality is optimal for diagnosis. Because many radiolucent foreign bodies have sufficient contrast for imaging in the optical domain, we are exploring the use of laser-induced optoacoustic imaging for the detection of foreign bodies, especially in craniofacial injuries, in which the foreign bodies are likely to lie within the penetration depth of visible and near infrared wavelengths. Tissue-simulating phantoms containing various common foreign bodies have been constructed. Images of these phantoms have been successfully generated using two laser-based optoacoustic imaging methods with different detection modalities. In order to enhance the image contrast, common foreign bodies are being scanned over a wide range of wavelengths to obtain the spectroscopic properties of the materials commonly associated with these foreign bodies. This spectroscopic characterization will help select specific wavelengths to be used for imaging specific objects and provide useful diagnostic data about the material properties of the object.

Virtually every area of ultrasonic imaging research requires accurate estimation of the spatiotemporal impulse response of the instrument, and yet accurate measurements are difficult to achieve. The impulse response can also be difficult to predict numerically for a specific device because small unknown perturbations in array properties can generate significant changes in predicted pulse-echo field patterns. A typical measurement for a 1-D array transducer employs a line scatterer oriented perpendicular to the scan plane. Echoes from line scatterers located throughout the field of view constitute estimates of shift-varying line response functions. We propose an inverse-problem approach to the reconstruction of point-spread functions from line-spread functions. A collection of echoes recorded for a range of line-scatterer rotation angles are treated as projections of sound pressure onto the transducer array surface. Although the reconstruction is mathematically equivalent to filtered backprojection, it provides significant advantages with respect to interpolation that confound straightforward implementations. Field II predictions used to model measurements made on commercial systems suggest the reconstruction accuracy is with 0.32% for noiseless echo data. Application of the method to data acquired from a commercial system are evaluated from the perspective of deconvolution.

Tissue velocity and attenuation inhomogeneities reduce ultrasound image quality in many patients. Over the years a number of methods have been developed to estimate the corrective delays necessary for phase aberration correction. Past methods were based on assumptions of the target or required a separate transducer acting as a transponder point source. A method is proposed which creates a known acoustical source in the tissue suitable for wavefront correction without a priori assumptions of the target or requiring a point source transponder. This method was tested with multiple electronically produced aberrations with RMS focusing errors of 0.25π radians, 0.44π radians, and 0.87π radians at 4.17 MHz. These aberrators were corrected using excised pork kidneys and on the left kidney of human volunteers as targets. Waveform correction on pork kidney led to an improvement in imaging beam amplitude and side-lobe level. Waveform correction on human subjects for a 0.87π radians RMS error aberrator led to a 15.4 dB improvement in imaging beam amplitude and an 11.8 dB improvement in side-lobe level. This method shows promise of overcoming the limitations of previous phase correction methods.

Accurate three dimensional (3D) mapping of bioelectric sources in the body with high spatial resolution is important for the diagnosis and treatment of a variety of cardiac and neurological disorders. Ultrasound current source density imaging (UCSDI) is a new technique that maps electrical current flow in tissue. UCSDI is based on the acousto-electric (AE) effect, an interaction between electrical current and acoustic pressure waves propagating through a conducting material and has distinct advantages over conventional electrophysiology (i.e., without ultrasound). In this study, UCSDI was used to simultaneously image current flow induced in two tissue phantoms positioned at different depths. Software to simulate AE signal was developed in Matlab™ to complement the experimental model and further characterize the relationship between the ultrasound beam and electrical properties of the tissue. Both experimental and simulated images depended on the magnitude and direction of the current, as well as the geometry (shape and thickness) and location of the current sources in the ultrasound field (2.25MHz transducer). The AE signal was proportional to pressure and current with detection levels on the order of 1 mA/cm² at 258kPa. We have imaged simultaneously two separate current sources in tissue slabs using UCSDI and two bridge circuits to accurately monitor current flow through each source. These results are consistent with UCSDI simulations of multiple current sources. Real-time 3D UCSD images of current flow automatically co-registered with pulse echo ultrasound potentially facilitates corrective procedures for cardiac and neural abnormalities.

We present a bent ray reconstruction algorithm for an ultrasound tomography (UT) scanner designed for breast screening. The scanner consists of a circular array of transmitters and receivers which encloses the object to be imaged. By solving a nonlinear system of equations, the reconstruction algorithm estimates the sound speed of the object using the set of travel-time measurements. The main difficulty in this inverse problem is to ensure the convergence and robustness to noise. In this paper, we propose a gradient method to find a solution for which the corresponding travel-times are closest to the measured travel-times in the least squares sense. To this end, first the gradient of the cost function is derived using Fermat's Principle. Then, the iterative nonlinear conjugate gradient algorithm solves the minimization problem. This is combined with the backtracking line search method to efficiently find the step size in each iteration. This approach is guaranteed to converge to a local minimum of the cost function where the convergence point depends on the initial guess. Moreover, the method has the potential to easily incorporate regularity constraints such as sparsity as a priori information on the model. The method is tested both numerically and using in vivo data obtained from a UT scanner. The results confirm the stability and robustness of our approach for breast screening applications.

We present preliminary results obtained using a time domain wave-based reconstruction algorithm for an ultrasound transmission tomography scanner with a circular geometry. While a comprehensive description of this type of algorithm has already been given elsewhere, the focus of this work is on some practical issues arising with this approach. In fact, wave-based reconstruction methods suffer from two major drawbacks which limit their application in a practical setting: convergence is difficult to obtain and the computational cost is prohibitive. We address the first problem by appropriate initialization using a ray-based reconstruction. Then, the complexity of the method is reduced by means of an efficient parallel implementation on graphical processing units (GPU). We provide a mathematical derivation of the wave-based method under consideration, describe some details of our implementation and present simulation results obtained with a numerical phantom designed for a breast cancer detection application. The source code of our GPU implementation is freely available on the web at www.usense.org.

Reflection ultrasound (US) has been utilized as an adjunct imaging modality for over 30 years. TechniScan, Inc. has developed unique, transmission and concomitant reflection algorithms which are used to reconstruct images from data gathered during a tomographic breast scanning process called Warm Bath Ultrasound (WBU™). The transmission algorithm yields high resolution, 3D, attenuation and speed of sound (SOS) images. The reflection algorithm is based on canonical ray tracing utilizing refraction correction via the SOS and attenuation reconstructions. The refraction correction reflection algorithm allows 360 degree compounding resulting in the reflection image. The requisite data are collected when scanning the entire breast in a 33° C water bath, on average in 8 minutes. This presentation explains how the data are collected and processed by the 3D transmission and reflection imaging mode algorithms. The processing is carried out using two NVIDIA® Tesla™ GPU processors, accessing data on a 4-TeraByte RAID. The WBU™ images are displayed in a DICOM viewer that allows registration of all three modalities. Several representative cases are presented to demonstrate potential diagnostic capability including: a cyst, fibroadenoma, and a carcinoma. WBU™ images (SOS, attenuation, and reflection modalities) are shown along with their respective mammograms and standard ultrasound images. In addition, anatomical studies are shown comparing WBU™ images and MRI images of a cadaver breast. This innovative technology is designed to provide additional tools in the armamentarium for diagnosis of breast disease.

Ultrasound tomography is an attractive imaging method for the detection of breast cancer. The complex anatomy of the breast with its different spatial scales and material property contrasts make accurate reconstructions very challenging. This paper proposes a hybrid approach whereby Travel-of-Flight and Diffraction Tomography are combined together to achieve high-resolution and high-accuracy sound-speed reconstructions. The method is validated with several numerical phantoms.

Our laboratory has focused on the development of ultrasound tomography (UST) for breast imaging. To that end we have been developing and testing a clinical prototype in the Karmanos Cancer Institute's (KCI) breast center. The development of our prototype has been guided by clinical feedback from data accumulated from over 300 patients recruited over the last 4 years. Our techniques generate whole breast reflection images as well as images of the acoustic parameters of sound speed and attenuation. The combination of these images reveals major breast anatomy, including fat, parenchyma, fibrous stroma and masses. Fusion imaging, utilizing thresholding, is shown to visualize mass characterization and facilitates separation of cancer from benign masses. These results indicate that operator-independent whole-breast imaging and the detection and characterization of cancerous breast masses are feasible using acoustic tomography techniques. Analyses of the prototype images suggests that we can detect the variety of mass attributes noted by current ultrasound-BIRADS criteria, such as mass shape, acoustic mass properties and architecture of the tumor environment. These attributes help quantify current BIRADS criteria (e.g. "shadowing" or high attenuation) and provide greater possibilities for defining a unique signature of cancer. The potential for UST to detect and characterize breast masses was quantified using UST measurements of 86 masses from the most recent cohort of patients imaged with the latest version of our prototype. Our preliminary results suggest that the development of a formal predictive model, in support of larger future trials, is warranted.

Since a 1976 study by Wolfe, high breast density has gained recognition as a factor strongly correlating with an increased incidence of breast cancer. These observations have led to mammographic density being designated a "risk factor" for breast cancer. Clinically, the exclusive reliance on mammography for breast density measurement has forestalled the inclusion of breast density into statistical risk models. This exclusion has in large part been due to the ionizing radiation associated with the method. Additionally, the use of mammography as valid tool for measuring a three dimensional characteristic (breast density) has been criticized for its prima facie incongruity. These shortfalls have prompted MRI studies of breast density as an alternative three-dimensional method of assessing breast density. Although, MRI is safe and can be used to measure volumetric density, its cost has prohibited its use in screening. Here, we report that sound speed measurements using a prototype ultrasound tomography device have potential for use as surrogates for breast density measurement. Accordingly, we report a strong positive linear correlation between volume-averaged sound speed of the breast and percent glandular tissue volume as assessed by MR.

Clinical ultrasound (US) imaging and therapy require a precise knowledge of the intensity distribution of the acoustic field. Although piezoelectric hydrophones are most common, these devices are limited in terms of, for example, type of materials, cost, and performance at high frequency and pressure. As an alternative to conventional acoustic detectors, we describe acoustoelectric hydrophones, developed using photolithographic fabrication techniques, where the induced voltage (phase and amplitude) is proportional to both the US pressure and bias current injected through the device. In this study a number of different hydrophone designs were created using indium tin oxide (ITO). A constriction of the current path within the hydrophone created a localized "sensitivity zone" of high current density. The width of this zone ranged from 30 to 1000 μm, with a thickness of 100 nm. A raster scan of the US transducer produced a map of the acoustic field. Hydrophones were evaluated by mapping the pressure field of a 2.25 MHz single element transducer, and their performance was compared to a commercial capsule hydrophone. Focal spot sizes at -6 dB were as low as 1.75 mm, comparing well with the commercial hydrophone measurement of 1.80 mm. Maximum sensitivity was 2 nV/Pa and up to the 2nd harmonic was detected. We expect improved performance with future devices as we optimize the design. Acoustoelectric hydrophones are potentially cheaper and more robust than the piezoelectric models currently in clinical use, potentially providing more choice of materials and designs for monitoring therapy or producing arrays for imaging.

A 9-element annular array is presented that employs a newly-proposed interconnection scheme that simplifies the fabrication process. The fabricated array is a hybrid transducer structure incorporating both a piezoelectric layer and a silicon substrate in the same device. The interconnection scheme consists of a set of 9 equal area Cr/Au electrodes with a 2 mm aperture and 17 μm kerfs patterned on the surface of the silicon substrate using photolithography. A grid of Cr/Au electrodes was patterned on the surface of the piezoelectric layer, and the two layers were connected using an anisotropic conductive adhesive. To avoid the severe alignment restrictions that would result if the two electrode patterns were identical, a grid-pattern of square electrodes was substituted on the piezoelectric layer with a smaller diagonal dimension than the spaces between the silicon electrodes. A Tungsten-loaded epoxy backing layer was added to the acoustic stack and an impedance plot was measured for a single array element. Both 22 MHz and 40 MHz arrays were manufactured and the impedance plots show good correspondence with KLM modeling. A pulse-echo response was generated for the 22 MHz array, showing no degradation due to the silicon layer.

Most single element hydrophones depend on a piezoelectric material that converts pressure changes to electricity. These devices, however, can be expensive, susceptible to damage at high pressure, and/or have limited bandwidth and sensitivity. The acousto-electric (AE) hydrophone is based on the AE effect, an interaction between electrical current and acoustic pressure generated when acoustic waves travel through a conducting material. As we have demonstrated previously, an AE hydrophone requires only a conductive material and can be constructed out of common laboratory supplies to generate images of an ultrasound beam pattern consistent with more expensive hydrophones. The sensitivity is controlled by the injected bias current, hydrophone shape, thickness and width. In this report we describe simulations aimed at optimizing the design of the AE hydrophone with experimental validation using new devices composed of a resistive element of indium tin oxide (ITO). Several shapes (e.g., bowtie and dumbbell) and resistivities were considered. The AE hydrophone with a dumbbell configuration achieved the best beam pattern of a 2.25MHz ultrasound transducer with lateral and axial resolutions consistent with images generated from a commercial hydrophone (Onda Inc.). The sensitivity of this device was ~2 nV/Pa. Our simulations and experimental results both indicate that designs using a combination of ITO and gold (ratio of resistivities = ~18) produce the best results. We hope that design optimization will lead to new devices for monitoring ultrasonic fields for biomedical imaging and therapy, including lithotripsy and focused ultrasound surgery.

This paper presents the fabrication of a conformal, ring-annular ultrasound imaging array. Two-dimensional (2D) ultrasound scanning is possible with ring-annular array transducers in which a number of piezoelectric elements are arranged in a circle. The 2D scanning technique can be realized through time delays, potentially allowing for 3D imaging. Ring-annular array transducers have previously been shown to have increased bandwidth, better signal-to-noise, and uniform scanning in space in contrast to 2D matrix arrays of an equal number elements and aperture size. Conformal, ring-annular transducers have the ability to match the curvature of body surfaces, and have the additional advantage that the flexible array elements can be mechanically focused to provide enhanced focusing capabilities relative to rigid ring-annular arrays. The process developed for the fabrication of conformal, ring-annular ultrasound array is presented. A microfabrication approach is used to produce ring-annular arrays featuring flexible joints with high durability, and capable of scaling in size and element architectures. The fabrication process yields a ring of piezoelectric transducer elements held together with polyimide, which is the basis of the flexible joints that enable conformal ultrasonography. The described fabrication process is used to produce a ring-annular array with a single ring containing piezoelectric elements, but the process can be extended to form arrays with multiple annular-rings of varying sizes. The transducer had a fundamental thickness-mode resonant frequency of 12 MHz, a 6 dB bandwidth of 23%, and an acoustic pulse width of 1.8 μs in water.

This paper describes the method of using the finite-element analysis software, PZFlex, to direct the design of a novel ultrasound imaging system which uses conformal transducer arrays. Current challenges in ultrasound array technology, including 2D array processing, have motivated exploration into new data acquisition and reconstruction techniques. Ultimately, these efforts encourage a broader examination of the processes used to effectively validate new array configurations and image formation procedures. Commercial software available today is capable of efficiently and accurately modeling detailed operational aspects of customized arrays. Combining quality simulated data with prototyped reconstruction techniques presents a valuable tool for testing novel schemes before committing more costly resources. To investigate this practice, we modeled three 1D ultrasound arrays operating multistatically instead of by the conventional phased-array approach. They are: a simple linear array, a half-circle array with 180-degree coverage, and a full circular array for inward imaging. We present the process used to create unique array models in PZFlex, simulate operation and obtain data, and subsequently generate images by inputting data into a reconstruction algorithm in MATLAB. Further discussion describes the tested reconstruction algorithm and includes resulting images.

MRI-guided focused-ultrasound is a non-invasive technique that can enhance the delivery of therapeutic agents. The objective of this work was to develop a focused-ultrasound system for preclinical research in small animals that is capable of sonicating with high spatial precision within a closed-bore MRI. The system features a computer-controlled, non-magnetic, three-axis positioning system that uses piezoelectric actuators and linear optical encoders to position a focused-ultrasound transducer to targeted tissues under MRI guidance. The actuator and encoder signals are transmitted through low-pass-filtered connectors on a grounded RF-penetration panel to prevent artifacts during image acquisition. The transducer is attached to the positioning system by a rigid arm and is submerged within a closed water tank. The arm passes into the tank through flexible bellows to ensure that the system remains sealed. An RF coil acquires high-resolution images in the vicinity of the target tissue. An aperture on the water tank, centered about the RF coil, provides an access point for target sonication. Registration between ultrasound and MRI coordinates involves sonicating a temperature-sensitive phantom and measuring the centroid of the thermal focal zone in 3D with MR thermometry. Linear distances of 5 cm with a positioning resolution of 0.05 mm can be achieved for each axis. The system was operated successfully on MRI scanners from different vendors at both 1.5 and 3.0 T, and simultaneous motion and imaging was possible without any mutual interference or imaging artifacts. This system is used for high-throughput small-animal experiments to study the efficacy of ultrasound-enhanced drug delivery.

Steerability in percutaneous medical devices is highly desirable, enabling a needle or needle-like instrument to avoid sensitive structures (e.g. nerves or blood vessels), access obstructed anatomical targets, and compensate for the inevitable errors induced by registration accuracy thresholds and tissue deformation during insertion. Thus, mechanisms for needle steering have been of great interest in the engineering community in the past few years, and several have been proposed. While many interventional applications have been hypothesized for steerable needles (essentially anything deliverable via a regular needle), none have yet been demonstrated as far as the authors are aware. Instead, prior studies have focused on model validation, control, and accuracy assessment. In this paper, we present the first integrated steerable needle-interventional device. The ACUSITT integrates a multi-tube steerable Active Cannula (AC) with an Ultrasonic Interstitial Thermal Therapy ablator (USITT) to create a steerable percutaneous device that can deliver a spatially and temporally controllable (both mechanically and electronically) thermal dose profile. We present our initial experiments toward applying the ACUSITT to treat large liver tumors through a single entry point. This involves repositioning the ablator tip to several different locations, without withdrawing it from the liver capsule, under 3D Ultrasound image guidance. In our experiments, the ACUSITT was deployed to three positions, each 2cm apart in a conical pattern to demonstrate the feasibility of ablating large liver tumors 7cm in diameter without multiple parenchyma punctures.

The most widely performed test for patients suspected of having carotid atherosclerosis is Doppler ultrasound (DUS). Unfortunately, limitations in sensitivity and specificity prevent DUS from being the sole diagnostic tool. Novel DUS velocity-derived parameters, such as turbulence intensity (TI), may provide enhanced hemodynamic information within the carotid artery, increasing diagnostic accuracy. In this study, we evaluate a new technique for recording, storing and analyzing DUS in a clinical environment, and determine the correlation between TI and conventional DUS measurements. We have recruited 32 patients with a mean age of 69±11 yrs. An MP3 recorder was used to digitally record Doppler audio signals three times at three sites: the common carotid artery, peak stenosis and region of maximum turbulence. A Fourier-based technique was used to calculate TI, facilitating clinical application without additional ECGgating data. TI was calculated as the standard deviation of Fourier-filtered mean velocity data. We found that TI and clinical PSV were linearly dependent (P<0.001) within the region of maximum turbulence and the precision of all TI measurements was found to be 14%. We have demonstrated the ability to record Doppler waveform data during a conventional carotid exam, and apply off-line custom analysis to Doppler velocity data to produce measurements of TI.

Motion estimation from digital video is an ill-posed problem that requires a regularization approach. Regularization introduces a smoothness constraint that can reduce the resolution of the velocity estimates. The problem is further complicated for ultrasound videos (US), where speckle noise levels can be significant. Motion estimation using optical flow models requires the modification of several parameters to satisfy the optical flow constraint as well as the level of imposed smoothness. Furthermore, except in simulations or mostly unrealistic cases, there is no ground truth to use for validating the velocity estimates. This problem is present in all real video sequences that are used as input to motion estimation algorithms. It is also an open problem in biomedical applications like motion analysis of US of carotid artery (CA) plaques. In this paper, we study the problem of obtaining reliable ultrasound video motion estimates for atherosclerotic plaques for use in clinical diagnosis. A global optimization framework for motion parameter optimization is presented. This framework uses actual carotid artery motions to provide optimal parameter values for a variety of motions and is tested on ten different US videos using two different motion estimation techniques.

Although Virtual Histology (VH) is the in-vivo gold standard for atherosclerosis plaque characterization in IVUS images, it suffers from a poor longitudinal resolution due to ECG-gating. In this paper, we propose an image-based approach to overcome this limitation. Since each tissue have different echogenic characteristics, they show in IVUS images different local frequency components. By using Redundant Wavelet Packet Transform (RWPT), IVUS images are decomposed in multiple sub-band images. To encode the textural statistics of each resulting image, run-length features are extracted from the neighborhood centered on each pixel. To provide the best discrimination power according to these features, relevant sub-bands are selected by using Local Discriminant Bases (LDB) algorithm in combination with Fisher's criterion. A structure of weighted multi-class SVM permits the classification of the extracted feature vectors into three tissue classes, namely fibro-fatty, necrotic core and dense calcified tissues. Results shows the superiority of our approach with an overall accuracy of 72% in comparison to methods based on Local Binary Pattern and Co-occurrence, which respectively give accuracy rates of 70% and 71%.

Thermal ablation has been proved safe and effective as the treatment for liver tumors that are not suitable for resection. Currently, manually performed thermal ablation is greatly dependent on the surgeon's acupuncture manipulation against hand tremor. Besides that, inaccurate or inappropriate placement of the applicator will also directly decrease the final treatment effect. In order to reduce the influence of hand tremor, and provide an accurate and appropriate guidance for a better treatment, we develop an ultrasound-directed robotic system for thermal ablation of liver tumors. In this paper, we will give a brief preliminary report of our system. Especially, three innovative techniques are proposed to solve the critical problems in our system: accurate ultrasound calibration when met with artifacts, realtime reconstruction with visualization using Graphic Processing Unit (GPU) acceleration and 2D-3D ultrasound image registration. To reduce the error of point extraction with artifacts, we propose a novel point extraction method by minimizing an error function which is defined based on the geometric property of our N-fiducial phantom. Then realtime reconstruction with visualization using GPU acceleration is provided for fast 3D ultrasound volume acquisition with dynamic display of reconstruction progress. After that, coarse 2D-3D ultrasound image registration is performed based on landmark points correspondences, followed by accurate 2D-3D ultrasound image registration based on Euclidean distance transform (EDT). The effectiveness of our proposed techniques is demonstrated in phantom experiments.

Despites many limitations, liver biopsy remains the gold standard method for grading and staging liver biopsy. Several modalities have been developed for a non invasive assessment of liver diseases. Real-time elastography may constitute a true alternative to liver biopsy by providing an image of tissular elasticity distribution correlated to the fibrosis grade. In this paper, we investigate a new approach for the assessment of liver fibrosis by the classification of fibrosis morphometry. Multiresolution histogram, based on a combination of intensity and texture features, has been tested as feature space. Thus, the ability of such multiresolution histograms to discriminate fibrosis grade has been proven. The results have been tested on seventeen patients that underwent a real time elastography and FibroScan examination.

Factor analysis is an efficient technique to the analysis of dynamic structures in medical image sequences and recently has been used in contrast-enhanced ultrasound (CEUS) of hepatic perfusion. Time-intensity curves (TICs) extracted by factor analysis can provide much more diagnostic information for radiologists and improve the diagnostic rate of focal liver lesions (FLLs). However, one of the major drawbacks of factor analysis of dynamic structures (FADS) is nonuniqueness of the result when only the non-negativity criterion is used. In this paper, we propose a new method of replace-approximation based on apex-seeking for ambiguous FADS solutions. Due to a partial overlap of different structures, factor curves are assumed to be approximately replaced by the curves existing in medical image sequences. Therefore, how to find optimal curves is the key point of the technique. No matter how many structures are assumed, our method always starts to seek apexes from one-dimensional space where the original high-dimensional data is mapped. By finding two stable apexes from one dimensional space, the method can ascertain the third one. The process can be continued until all structures are found. This technique were tested on two phantoms of blood perfusion and compared to the two variants of apex-seeking method. The results showed that the technique outperformed two variants in comparison of region of interest measurements from phantom data. It can be applied to the estimation of TICs derived from CEUS images and separation of different physiological regions in hepatic perfusion.

Monitoring the ablation process in order to document the adequacy of margins during treatment is of significant importance. Observing that the ablation lesion is harder than normal tissue, it has been proposed to monitor the ablation using ultrasound elastography. Furthermore, it has been reported that the ablated cancer tumor is harder than ablated normal tissue. In this paper we propose an ultrasound elastography technique for visualizing the ablation lesion and the ablated cancerous tumor in Hepatocellular carcinoma (HCC). This work focuses on devising techniques to generate elasticity images which distinguish the ablated cancerous tumor and the ablated normal lesion. We first calculate the displacement field between two ultrasound images acquired before and after some compression. We then use the displacement field to calculate the correlation coefficient between the two images. Parts of the tissue that undergo large deformation give small correlation coefficient due to decorrelation within each window, and parts of the tissue that undergo small deformation give large correlation coefficient. Simulating phantoms with two lesions, a harder tumor inside a hard lesion, using finite element and Field II, we show that this method enables delineating the tumor from the lesion.

EM algorithm for the reconstruction of freehand B-Scan ultrasound image was developed by Joao M. Sanches et al. The reconstruction has a parameter K which can be adjusted so that the results can be smoother or sharper depending to the value of K. In order to make the image smoother inside the organs but sharper in their boundaries simultaneously, we introduced a improved EM algorithm: EM algorithm with a diffusion filer or is referred as EMD algorithm. There was a cubic average filter inside the loop of the iteration of the EM algorithm. This average filter is replaced by a diffusion filter in the EMD algorithm. The diffusion filter offers an additional parameter K_d which can be used to adjust the reconstructed image with better optimization in both smoothness insider the human organ and sharpness in its boundary. Two above mentioned reconstruction algorithms for the freehand B-scan ultrasound image are compared through the simulation and the phantom measurements. In the simulation, strong noises are added to the ultrasound frame data. The parameters of two algorithms are optimized to get smallest errors. The errors are compared between two algorithms with optimized parameters. For the measurement with phantom, the Eigen's tracker system is used to continuously measure the coordinates of the ultrasound probe. The ultrasound B-scan frame is synchronously recorded with the probe coordinates. Zonare ultrasound machine is used to acquire the 2D frame images. The segmentation of the reconstruction results is done. The segmentation volumes of the prostate phantoms are compared. The results shows that EMD algorithm is better at reducing the noises and keeping the image edge comparing to EM algorithm. Eigen's tracker is cacaple to acquire freehand ultrasound data for a 3D image reconstruction with high quality.

Intravascular ultrasound (IVUS) examination offers a tomographic view of the vessel, having the catheter tip as reference. During examination, the catheter is pulled back with a constant speed (0.5 or 1.0 mm/s) and the ultrasound transducer captures cross-sectional slices of the coronary. Currently, 3D IVUS reconstruction is based on single-plane or biplane angiography together with IVUS images. In this work, we present a preliminary approach to reconstruct tridimensionally the catheter path and coronary, based only on IVUS sequence. We have proposed a numeric phantom framework: coronary simulation, catheter dynamic path simulation, IVUS acquisition, reconstruction and validation. Our method infers the catheter path inside the coronary, based on shortest path graph algorithm. To reconstruct morphology, we have associated the catheter path and the position of the frame with smoothness costs, and solved it as a minimization problem. In this experiment we have used three different morphologies (straight, one curve and two curves) and 60 random initializations each for the initial point and angle of catheter insertion. The results for the plane containing the centerline of the catheter were 95.8% true positive and 8.5% false positive rates.

Sonography performed in high frame rate aims to achieve high temporal resolution. Echocardiography and fetal echocardiography are typical examinations performed in this manner. In general, image quality of sonograms acquired by high frame rate mode is poorer compared to that acquired by low frame rate mode. Poor definition and rich of noises are drawbacks usually found in the images obtained in high frame rate. We propose an approach to improve image quality of the sonograms, in which the noises can effectively be removed from the corrupted images and the definition of textures can also be enhanced. Three techniques are involved in the approach: image interpolation, addition of spatial information and averaging image by cycle spinning. The first technique is employed to generate extra spatial information. The second one intends to extract high frequency information from the original image and add the information to the high frequency subbands so that the image can further be enhanced. The last technique aims to remove noises by averaging images which have been undergone frame shifting and coefficient addition. Our experimental results show that noises randomly scattered in the images, not speckles, are effectively removed, and the definition of texture is further reinforced.

The use of ultrasound imaging technology during techniques of peripheral nerve blockade offers several clinical benefits. Here we report on a new method to educate residents in ultrasound-guided regional anesthesia. The daily challenge for the anesthesiologists is the 3D angle-depending handling of the stimulation needle and the ultrasound probe while watching the 2D ultrasound image on the monitor. Purpose: Our approach describes how a computer-aided simulation and training set for ultrasound-guided regional anesthesia could be built based on wireless low-cost devices and an interactive simulation of a 2D ultrasound image. For training purposes the injection needle and the ultrasound probe are replaced by wireless Bluetooth-connected 3D tracking devices, which are embedded in WII-mote controllers (Nintendo-Brand). In correlation to the tracked 3D positions of the needle and transducer models the visibility and position of the needle should be simulated in the 2D generated ultrasound image. Conclusion: In future, this tracking and visualization software module could be integrated in a more complex training set, where complex injection paths could be trained based on a 3D segmented model and the training results could be part of a curricular e-learning module.

Conventional coronary angiography has been the current gold standard for evaluation of coronary stenosis severity. However, this is an invasive procedure, based on ionizing radiation (X-Ray) and dependent of nephrotoxic contrast agents. In the past three decades, echocardiography has emerged as an important medical image modality in Cardiology. With the advent of microbubble-based contrast agents and array transducers, 3D-echocardiography now presents itself as a relative low-cost, non invasive and non ionizing alternative method to visibilize arteries and their dynamics. This paper investigates some segmentation techniques to emphasize and isolate epicardial coronaries in tridimensional microbubblecontrasted echocardiographic images, since available computational tools do not provide adequate processing.

Ultrasound image resolution and quality need to be significantly improved for breast microcalcification detection. Super-resolution imaging with the factorization method has recently been developed as a promising tool to break through the resolution limit of conventional imaging. In addition, wave-equation reflection imaging has become an effective method to reduce image speckles by properly handling ultrasound scattering/diffraction from breast heterogeneities during image reconstruction. We explore the capabilities of a novel super-resolution ultrasound imaging method and a wave-equation reflection imaging scheme for detecting breast microcalcifications. Super-resolution imaging uses the singular value decomposition and a factorization scheme to achieve an image resolution that is not possible for conventional ultrasound imaging. Wave-equation reflection imaging employs a solution to the acoustic-wave equation in heterogeneous media to backpropagate ultrasound scattering/diffraction waves to scatters and reconstruct images of heterogeneities. We construct numerical breast phantoms using in vivo breast images, and use a finite-difference wave-equation scheme to generate ultrasound data scattered from inclusions that mimic microcalcifications. We demonstrate that microcalcifications can be detected at full spatial resolution using the super-resolution ultrasound imaging and wave-equation reflection imaging methods.

Despite the success of ultrasound elasticity imaging (USEI) in medical applications such as diagnosis and screening of breast lesions and prostate cancer, USEI has not been adopted in routine clinical procedures. This is partly caused by the difficulty in acquiring reliable images and interpreting them, the lack of consistency over time, and the dependency of image quality to the expertise of the user. We previously demonstrated the potential of exploiting an external tracker to partially alleviate these issues and enhance the quality of USEI. The tracking data enabled fast and automatic selection of pairs of RF frames used in strain calculation. Here, we expand this method by including new features. The proposed method employs image content to compensate for the limited accuracy of the tracking device. It also combines multiple strain images to improve the quality of the final image. For this purpose, It normalizes the images and determines which images can be combined relying on the tracking information. We have acquired RF frames synchronized with tracking data from livers of pig containing an ablated region and a breast phantom using two different tracking devices; an optical tracker and a less accurate electromagnetic tracker. We present the promising results of the proposed method and investigate the sensitivity of frame selection technique without using the image content to inaccuracies in tracking information.

The purpose of this study was to correlate changes in biomechanical properties of breast cancer lesions in response to neoadjuvant chemotherapy. Nine patients were examined repeatedly throughout their treatment, using an experimental prototype based on the principles of ultrasound tomography. The study was HIPAA compliant, approved by the Institutional Review Board, and performed after obtaining the requisite informed consent. Images of reflection, sound speed and attenuation, representing the entire volume of the breast, were reconstructed from the exam data and analyzed for time-dependent changes during the treatment period. It was found that changes in tumor properties could be measured in all cases. Furthermore, changes in sound speed were found to vary strongly from patient to patient. A comparison of the sound speed response curves with pathological findings suggests that complete responders exhibit distinctly different responses as measured by sound speed. These preliminary results were used to define a cut-point for predicting response. Subsequently, a prospective prediction of the treatment response of a new patient was made correctly. We hypothesize that changes in the biomechanical properties of breast cancers, as measured by sound speed, can predict response. Future studies will focus on testing this hypothesis and defining and quantifying markers of response.

Out-of-plane motion in freehand 3D ultrasound can be estimated using the correlation of corresponding patches, leading to sensorless freehand 3D ultrasound systems. The correlation between two images is related to their distance by calibrating the ultrasound probe: the probe is moved with an accurate stage (or with a robot in this work) and images of a phantom are collected, such that the position of each image is known. Since parts of the calibration curve with higher derivative gives lower displacement estimation error, previous work limits displacement estimation to parts with maximum derivative. In this paper, we first propose a novel method for exploiting the entire calibration curve by using a maximum likelihood estimator (MLE). We then propose for the first time using constrains inside the image to enhance the accuracy of out-of-plane motion estimation. We specifically use continuity constraint of a needle to reduce the variance of the estimated out-of-plane motion. Simulation and real tissue experimental results are presented.