This PDF file contains the front matter associated with SPIE Proceedings Volume 7265, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Computer Assisted Orthopaedic Surgery (CAOS) systems improve the results and the standardization of surgical interventions. Anatomical landmarks and bone surface detection is straightforward to either register the surgical space with the pre-operative imaging space and to compute biomechanical parameters for prosthesis alignment. Surface points acquisition increases the intervention invasiveness and can be influenced by the soft tissue layer interposition (7-15mm localization errors). This study is aimed at evaluating the accuracy of a custom-made A-mode ultrasound (US) system for non invasive detection of anatomical landmarks and surfaces. A-mode solutions eliminate the necessity of US images segmentation, offers real-time signal processing and requires less invasive equipment. The system consists in a single transducer US probe optically tracked, a pulser/receiver and an FPGA-based board, which is responsible for logic control command generation and for real-time signal processing and three custom-made board (signal acquisition, blanking and synchronization). We propose a new calibration method of the US system. The experimental validation was then performed measuring the length of known-shape polymethylmethacrylate boxes filled with pure water and acquiring bone surface points on a bovine bone phantom covered with soft-tissue mimicking materials. Measurement errors were computed through MR and CT images acquisitions of the phantom. Points acquisition on bone surface with the US system demonstrated lower errors (1.2mm) than standard pointer acquisition (4.2mm).

We describe early stage experiments to test the feasibility of an ultrasound brain helmet to produce multiple simultaneous real-time 3D scans of the cerebral vasculature from temporal and suboccipital acoustic windows of the skull. The transducer hardware and software of the Volumetrics Medical Imaging real-time 3D scanner were modified to support dual 2.5 MHz matrix arrays of 256 transmit elements and 128 receive elements which produce two simultaneous 64° pyramidal scans. The real-time display format consists of two coronal B-mode images merged into a 128° sector, two simultaneous parasagittal images merged into a 128° × 64° C-mode plane, and a simultaneous 64° axial image. Real-time 3D color Doppler images acquired in initial clinical studies after contrast injection demonstrate flow in several representative blood vessels. An offline Doppler rendering of data from two transducers simultaneously scanning via the temporal windows provides an early visualization of the flow in vessels on both sides of the brain. The long-term goal is to produce real-time 3D ultrasound images of the cerebral vasculature from a portable unit capable of internet transmission, thus enabling interactive 3D imaging, remote diagnosis and earlier therapeutic intervention. We are motivated by the urgency for rapid diagnosis of stroke due to the short time window of effective therapeutic intervention.

The use of ultrasound in dentistry is still an open growing area of research. Currently, there is a lack of imaging modalities to accurately predict minute structures and defects in the jawbone. In particular, the inability of 2D radiographic images to detect bony periodontal defects resulted from infection of the periodontium. This study investigates the feasibility of high frequency ultrasound to reconstruct high resolution 3D surface images of human jawbone. Methods: A dentate and non-dentate mandibles were used in this study. The system employs high frequency single-element ultrasound focused transducers (15-30 MHz) for scanning. Continuous acquisition using a 1 GHz data acquisition card is synchronized with a high precision two-dimensional stage positioning system of ±1 μm resolution for acquiring accurate and quantitative measurements of the mandible in vitro. Radio frequency (RF) signals are acquired laterally 44-45.5 μm apart for each frame. Different frames are reconstructed 500 μm apart for the 3D reconstruction. Signal processing algorithms are applied on the received ultrasound signals for filtering, focusing, and envelope detection before frame reconstruction. Furthermore, an edge detection technique is adopted to detect the bone surface in each frame. Finally, all edges are combined together in order to render a 3D surface image of the jawbone. Major anatomical landmarks on the resultant images were confirmed with the anatomical structures on the mandibles to show the efficacy of the system. Comparison were also made with conventional 2D radiographs to show the superiority of the ultrasound imaging system in diagnosing small defects in the lateral, axial and elevation planes of space. Results: The landmarks on all ultrasound images matched with those on the mandible, indicating the efficacy of the system in detecting small structures in human jaw bones. Comparison with conventional 2D radiographic images of the same mandible showed superiority of the 3D ultrasound images in detecting defects in the elevation plane of space. These results suggest that the high frequency ultrasound system shows great potential in providing a non-invasive method to characterize the jawbone and detect periodontal diseases at earlier stages.

Ultrasound can be used to study tendon and muscle movement. However, quantization is mostly based on manual tracking of anatomical landmarks such as the musculotendinous junction, limiting the applicability to a small number of muscle-tendon units. The aim of this study is to quantify tendon displacement without employing anatomical landmarks, using dedicated speckle tracking in long B-mode image sequences. We devised a dedicated two-dimensional multikernel block-matching scheme with subpixel accuracy to handle large displacements over long sequences. Images were acquired with a Philips iE33 with a 7 MHz linear array and a VisualSonics Vevo 770 using a 40 MHz mechanical probe. We displaced the flexor digitorum superficialis of two pig cadaver forelegs with three different velocities (4,10 and 16 mm/s) over 3 distances (5, 10, 15 mm). As a reference, we manually determined the total displacement of an injected hyperechogenic bullet in the tendons. We automatically tracked tendon parts with and without markers and compared results to the true displacement. Using the iE33, mean tissue displacement underestimations for the three different velocities were 2.5 ± 1.0%, 1.7 ± 1.1% and 0.7 ± 0.4%. Using the Vevo770, mean tissue displacement underestimations were 0.8 ± 1.3%, 0.6 ± 0.3% and 0.6 ± 0.3%. Marker tracking displacement underestimations were only slightly smaller, showing limited tracking drift for non-marker tendon tissue as well as for markers. This study showed that our dedicated speckle tracking can quantify extensive tendon displacement with physiological velocities without anatomical landmarks with good accuracy for different types of ultrasound configurations. This technique allows tracking of a much larger range of muscle-tendon units than by using anatomical landmarks.

Breast ultrasound tomography is a rapidly developing imaging modality that that has the potential to impact breast cancer screening and diagnosis. A new ultrasound breast imaging device (CURE) with a ring array of transducers has been designed and built at Karmanos Cancer Institute, which acquires both reflection and transmission ultrasound signals. To extract the sound-speed information from the breast data acquired by CURE, we have developed an iterative sound-speed image reconstruction algorithm for breast ultrasound transmission tomography based on total-variation (TV) minimization. We investigate applicability of the TV tomography algorithm using in vivo ultrasound breast data from 61 patients, and compare the results with those obtained using the Tikhonov regularization method. We demonstrate that, compared to the Tikhonov regularization scheme, the TV regularization method significantly improves image quality, resulting in sound-speed tomography images with sharp (preserved) edges of abnormalities and few artifacts.

It is demonstrated that distortion of a non-linearly generated first harmonic transmit beam due to a near-field aberrator is reduced as transmit pressure is increased. The first harmonic transmit beam is then used as a source for correction of aberration. In the first experiment, pieces of Lucite 11 mm and 24 mm thick were used as near-field aberrators. Beam plots of the fundamental and first harmonic were measured in a water tank with and without the aberrators present at multiple transmit voltages. The Lucite aberrator was then removed and an electronic aberrator with RMS delay error of 138 ns was applied to the transmit and receive apertures. The first harmonic reflected from the tip of a hydrophone was measured, and correcting delays were determined using a multi-lag least-means-squares cross-correlation method. Corrections were applied to an imaging beam transmitted at twice the frequency of the fundamental beam, the same frequency as the generated first-harmonic. Results from the Lucite experiments showed a -6 dB beam width improvement of 1.8 degrees when transmit voltage was increased from 20 volts to 80 volts. Results from first harmonic based correction of the electronic aberrator resulted in significant improvement in beam width and showed an average improvement of 16.8 dB in transmit beam signal level and 31.9 dB improvement in transmit-receive beam signal level.

Two types of signal acquisition methods using CMOS sensor array coated with piezoelectric material (PE-CMOS) were studied. The laboratory projection-reflection ultrasound prototypes featuring a PE-CMOS ultrasound sensing array and an acoustic compound lens were employed to image pork bones with fractures in vitro. We found that the projection-reflection ultrasound prototypes are capable of revealing hairline bone fractures with skin in tact. However, the image characteristics generated from these C-scan prototypes are somewhat different because they were equipped with two different senor array models. The signal acquired by the first sensor model is based on an integrated signal (IS) at a given time interval. But the signal acquired by the second sensor model is based on peak signal (PS) with a time gating function controllable by the user. We found that both systems can detect bone fracture as small as 0.5mm shown as a strip of ultrasound signal. However, images obtained from the IS sensor show more speckles with a greater blooming effect on the fractures. On the other hand, images obtained from the PS sensor show less contrast with less speckles. When the beam position is slightly tilted from the normal direction, the blooming effect of the ultrasound image would become dark on the fracture region with both acquisition modes.

Harmonic imaging has been shown to yield significant improvements in image quality over conventional ultrasound imaging. It has been proposed that harmonic imaging generates these improvements by the reduction in clutter from reverberation in the tissue layers underlying the transducer, a reduction in beam distortion from aberration, and a reduction in clutter due to suppressed sidelobes. There is little research indicating the exact sources of clutter and how they may relate to the improvements observed with in vivo harmonic imaging. We describe simulation and experimental studies in human bladders describing the sources and characteristics of clutter and discuss their relationship to the above proposed mechanisms. The results indicate that a large source of clutter is the product of reverberation in the abdominal layers. Experimental and simulated harmonic images indicate a 3-5 and 3-8 dB reduction in clutter over fundamental images, respectively, in the upper bladder cavity, lending support for the first mechanism described above. Scattering was also observed from off-axis sources in both the fundamental and harmonic images. Simulations of the fundamental point-spread-function (PSF) showed clutter magnitudes of -43 dB in the isochronous volume. Harmonic imaging marginally improved clutter magnitude to -47 dB in this same region. When aberration was removed from the simulation while keeping the impedance constant, the isochronous volume in the fundamental PSF marginally improved to -47 dB, while harmonic imaging improved this region to -58 dB, a reduction of 11 dB. This indicates that the image quality improvements seen with harmonic imaging are more dependent on the reduction in clutter from near-field layers than with reductions in clutter due to aberration.

First-principle approaches to the design of medical ultrasonic imaging systems for specific visual tasks are being explored in this paper. Our study focuses on breast cancer diagnosis and is based on the ideal observer concept for visual discrimination tasks, whereby tasks based on five clinical features are expressed mathematically as likelihood functions. Realistic approximations to the ideal strategy for each task are proposed as additional beamforming to maximize diagnostic image information content available to readers. Our previous study showed that a spatial Wiener filter (SWF) beamformer, derived as a stationary approximation of the ideal observer and operating on RF echo data, generally improved discriminability except for one case involving high-contrast lesions. This study explores an adaptive, iterative spatial Wiener filter (ISWF) beamformer that includes a lesion segmentation algorithm to overcome the stationarity assumption and improve discriminability for highcontrast lesions. Predicted performance is compared with that measured from trained human observers using psychophysical methods. We found the greatest feature enhancement of the delay-and-sum beamformer followed by SWF occurs at the image formation step where RF data are converted into B-mode data. The Smith-Wagner computational observer, which operates on the B-mode instead of RF data, was applied to indicate performance lost by envelope detection. ISWF was found to match the performance of SWF for low-contrast lesions and increase the performance for the high-contrast tasks. The ISWF beamforming approach offers greater diagnostic performance for discriminating malignant and benign breast lesions, and it provides a rational basis for further task-specific imaging system design.

DSP chips are gaining importance in ultrasound applications as the need for portability and low power grows. One of the more computationally demanding applications for ultrasound involves estimating blood flow characteristics using Doppler techniques. This ultrasound mode, called color Doppler ultrasound, is used to diagnose many conditions like blood clots, valve defects and blocked arteries. This work looks at mapping some typical color Doppler algorithms onto Texas Instruments' (TI's) high performance C64x+^(TM) core. The algorithms include RF demodulation, wall filtering and flow power, velocity and turbulence estimation. This paper starts with a general technique for analyzing algorithm complexity in terms of CPU instruction cycles on VLIW architectures like the C64x+^(TM). It then applies this technique to Doppler processing algorithms, explains their mapping to the C64x+^(TM) architecture and derives lower bounds for the computational complexity for these algorithm kernels. For each of these algorithms, these estimates are finally compared to actual implementations, and various implementation tradeoffs will be illustrated. Based on these implementations, it will be shown that these algorithms can run on TI's C64x+^(TM) based DSPs using a fraction of the available processing power.

In this paper, we present the image reconstruction algorithm developed for a conformal ultrasound array imaging system operating in the step frequency-modulated continuous wave (FMCW) mode. The image formation procedure is based on a key relationship that establishes the equivalence between pulse-echo and step FMCW modalities, and thus permits conversion between the data types. Prior step FMCW simulation work could then be merged with pulse-echo data collected experimentally to achieve full-scale synthesis between laboratory data and a structured theoretical framework. We describe how an experimentally acquired pulse-echo waveform was extracted and incorporated into a step FMCW imaging simulation to increase image accuracy and improve visualization of physical effects. With knowledge of the transducer element positions in a multistatic configuration, image reconstruction was achieved by mapping the complex range profiles over to a target region. Included in this paper are images reconstructed after waveform synthesis, which feature transducer elements uniformly spaced around a circular aperture imaging several enclosed targets with different bandwidths.

In this paper, we present an automatic approach for alignment of standard apical and short-axis slices, and correcting them for out-of-plane motion in 3D echocardiography. This is enabled by using real-time Kalman tracking to perform automatic left ventricle segmentation using a coupled deformable model, consisting of a left ventricle model, as well as structures for the right ventricle and left ventricle outflow tract. Landmark points from the segmented model are then used to generate standard apical and short-axis slices. The slices are automatically updated after tracking in each frame to correct for out-of-plane motion caused by longitudinal shortening of the left ventricle. Results from a dataset of 35 recordings demonstrate the potential for automating apical slice initialization and dynamic short-axis slices. Apical 4-chamber, 2-chamber and long-axis slices are generated based on an assumption of fixed angle between the slices, and short-axis slices are generated so that they follow the same myocardial tissue over the entire cardiac cycle. The error compared to manual annotation was 8.4 ± 3.5 mm for apex, 3.6 ± 1.8 mm for mitral valve and 8.4 ± 7.4 for apical 4-chamber view. The high computational efficiency and automatic behavior of the method enables it to operate in real-time, potentially during image acquisition.

Segmentation of ultrasound kidney images represents a challenge due to low quality data. Speckle, shadows, signal dropout and low contrast make segmentation a harsh task. In addition, kidney ultrasound imaging presents a great variability concerning the organ's shape on the image. This characteristic makes learning methods hard to use. The aim of this study is to develop a real time kidney ultrasound image segmentation method usable during surgical operations such as punctures. To deal with real time constraints, we decided to focus on region based methods and particularly split and merge algorithm. In this prospective study, the selection of the interesting area in the initial image is made by the physician, drawing a coarse bounding box around the organ. A pre-processing phase is first performed to correct image's artefacts. This phase is composed of three major steps. First, an image specification is made between the image to segment and a reference one. Then, a Haar wavelet filtering method is applied on the resulting image and finally an anisotropic diffusion filter is applied to smooth the result. Then, a split and merge algorithm is applied on the resulting image. Both split and merge criteria are based on regions statistics. Our method has been successfully applied on a set of 22 clinical images coming from 10 different patients and presenting different points of view regarding kidney's shape. We obtained very good results, for an average computational time of 8.5 seconds per image.

Analysis of ultrasound fetal head images is a daily routine for medical professionals in obstetrics. The contours of fetal skulls often appear discontinuous and irregular in clinical ultrasound images, making it difficult to measure the fetal head size automatically. In addition, the presence of heavy noise in ultrasound images is another challenge for computer aided automatic fetal head detection. In this paper, we first utilize the stick method to suppress the noise and compute an adaptive threshold for fetal skull segmentation. Morphological thinning is then performed to obtain a skeleton image, which is used as an input to the Hough transform. Finally, automatic fetal skull detection is realized by Iterative Randomized Hough Transform (IRHT). The elliptic eccentricity is used in the IRHT to reduce the number of invalid accumulations in the parameter space, improving the detection accuracy. Furthermore, the target region is adaptively adjusted in the IRHT. To evaluate the performance of IRHT, we also developed a simulation user interface for comparing results produced by the conventional randomized Hough transform (RHT) and the IRHT. Experimental results showed that the proposed method is effective for automatic fetal head detection in ultrasound images.

Measuring the artery thickness can detect potential blockages in blood flow. Automating parts of the measurement could improve both the accuracy and repeatability, leading to more consistent treatment. We develop a process for extracting the artery boundaries from an ultrasound image, then consistently measuring the artery thickness. The measurements result in excellent agreement between computer-calculated values and expert measurements.­

The coherent nature of ultrasound imaging inherently produces the notorious signal-dependent speckle noise. Recently, a novel approach based upon embedding the statistical and physical properties of speckle patterns into a Markov-random-field (MRF) framework was developed and demonstrated by the authors in the context of synthetic-aperture radar imaging. The contributions of this work are twofold. First, the MRF approach is extended to include a pseudo maximum-likelihood estimator of a key model parameter, making the approach fully autonomous. Second, the capability of the extended approach, called the modified MRF-based conditional-expectation approach (MRFCEA), in denoising real ultrasound imagery is demonstrated. The proposed MRFCEA approach offers superior performance over existing methods by reducing speckle noise without compromising the spatial resolution. In addition, MRFCEA is autonomous, contrary to existing methods such as the enhanced-Frost or the modified-Lee, which require user's input.

Photoacoustic imaging is a relatively new medical imaging modality. In principle it can be used to image the optical absorption distribution of an object by measurements of optically induced acoustic signals. Recently we have developed a modified photoacoustic measurement system which can be used to simultaneously image the ultrasound propagation parameters as well. By proper placement of a passive element we obtain isolated measurements of the object's ultrasound propagation parameters, independent of the optical absorption inside the object. This passive element acts as a photoacoustic source and measurements are obtained by allowing the generated ultrasound signal to propagate through the object. Images of the ultrasound propagation parameters, being the attenuation and speed of sound, can then be reconstructed by inversion of a measurement model. This measurement model relates the projections non-linearly to the unknown images, due to ray refraction effects. After estimating the speed of sound and attenuation distribution, the optical absorption distribution is reconstructed. In this reconstruction problem we take into account the previously estimated speed of sound distribution. So far, the reconstruction algorithms have been tested using computer simulations. The method has been compared with existing algorithms and good results have been obtained.

Photoacoustic Tomography is an emerging imaging technology mainly for medical and biological applications. A sample is illuminated by a short laser pulse. Depending on the optical properties the electromagnetic radiation is distributed and absorbed. Thereby local temperature increase generates thermal expansion and broadband ultrasonic signals, also called photoacoustic signals. Unlike conventional ultrasound in photoacoustic imaging the contrast depends on the optical properties of the sample which provides not only morphologic information but also functional information. This way photoacoustic imaging combines the advantages of optical imaging (high contrast) and ultrasonic imaging (high spatial resolution) and is particularly suited for medical applications like mammography or skin cancer detection. Our group uses integrating line detectors instead of ultrasonic point receivers. Line detectors integrate the pressure along one dimension whereby the 3D problem is reduced to a 2D problem and enables a tomography setup that requires only a single axis of rotation. Implementations of line detectors use optical interferometers, e.g. a Fabry-Perot interferometer or a Mach-Zehnder interferometer. We use free-beam interferometers as well as fiber-based interferometers for collecting photoacoustic signals. The latter are somewhat easier to handle because they require fewer optical components. Finally, the advantages of optical detection methods over piezoelectric detection methods are the better frequency response and the resistance against electrical interference from the environment. First measurements on phantoms and image reconstruction using a time reversal method demonstrated the capability of integrating line detectors for collecting broadband ultrasonic signals for photoacoustic tomography.

Optoacoustic (OA) imaging allows optical absorption contrast to be visualised using thermoelastically generated ultrasound. To date, optoacoustic theory has been applied to homogeneously absorbing tissue models that may describe, for example, large vessels filled with blood, where the whole target will act as a coherent source of sound. Here we describe a new model in which the optical absorbers are distributed inhomogeneously, as appropriate to describe microvasculature, or perhaps the distribution of molecularly targeted OA contrast agents inside a tumour. The degree of coherence over the resulting distributed acoustic source is influenced by parameters that describe the scale of the inhomogeneity, such as the sizes of the absorbers and the distances between them. To investigate the influence of these parameters on OA image appearance, phantoms with homogeneously and imhomogeneously absorbing regions were built and imaged. Simulations of the same situation were conducted using a time domain acoustic propagation method. Both simulations and experiments showed that introducing inhomogeneity of absorption produces more complete images of macroscopic targets than are obtained with a homogeneous absorption. Image improvement and target detectability were found to reach a maximum at an intermediate value of the length-scale of the inhomogeneity that was similar to the axial resolution of the acoustic receiver employed. As the scale of inhomogeneity became finer than this the target's detectability and appearance began to revert to that for homogeneous absorption. Further understanding of this topic is believed to be important for optimising the design of clinical optoacoustic imaging systems.

We have investigated the application of acousto-optic sensing for quantitative imaging of tissue-mimicking phantoms. An Intralipid phantom, which contains a turbid absorber, confined in a silicone tube, was used. Scattered pulsed laser light was modulated by ultrasonic bursts focused in a predefined volume in the medium. By varying the delay time between ultrasound burst initiation and light pulse firing we could perform a scan in the ultrasound-propagation plane. The use of calibration procedures allowed us to establish a quantitative correlation between local absorbances in the phantom and the measured signal and to obtain information on the ratios of dye concentrations inside the tube.

We describe catheter ring arrays for real-time 3D ultrasound guidance of devices such as vascular grafts, heart valves and vena cava filters. We have constructed several prototypes operating at 5 MHz and consisting of 54 elements using the W.L. Gore & Associates, Inc. micro-miniature ribbon cables. We have recently constructed a new transducer using a braided wiring technology from Precision Interconnect. This transducer consists of 54 elements at 4.8 MHz with pitch of 0.20 mm and typical -6 dB bandwidth of 22%. In all cases, the transducer and wiring assembly were integrated with an 11 French catheter of a Cook Medical deployment device for vena cava filters. Preliminary in vivo and in vitro testing is ongoing including simultaneous 3D ultrasound and x-ray fluoroscopy.

Two studies have been conducted using real time 3D ultrasound and an automated robot system for carrying out surgical tasks. The first task is to perform a breast lesion biopsy automatically after detection by ultrasound. Combining 3D ultrasound with traditional mammography allows real time guidance of the biopsy needle. Image processing techniques analyze volumes to calculate the location of a target lesion. This position was converted into the coordinate system of a three axis robot which moved a needle probe to touch the lesion. The second task is to remove shrapnel from a tissue phantom autonomously. In some emergency situations, shrapnel detection in the body is necessary for quick treatment. Furthermore, small or uneven shrapnel geometry may hinder location by typical ultrasound imaging methods. Vibrations and small displacements can be induced in ferromagnetic shrapnel by a variable electromagnet. We used real time 3D color Doppler to locate this motion for 2 mm long needle fragments and determined the 3D position of the fragment in the scanner coordinates. The rms error of the image guided robot for 5 trials was 1.06 mm for this task which was accomplished in 76 seconds.

A major limitation of thermal therapies is the lack of detailed thermal information needed to monitor the therapy. Temperatures are routinely measured invasively with thermocouples, but only sparse measurements can be made. Ultrasound tomography is an attractive modality for temperature monitoring because it is noninvasive, non-ionizing, convenient and inexpensive. It capitalizes on the fact that the changes in temperature cause the changes in sound speed. In this work we investigate the possibility of monitoring large temperature changes, in the interval from body temperature to -40°C. The ability to estimate temperature in this interval is of a great importance in cryosurgery, where freezing is used to destroy abnormal tissue. In our experiment, we freeze locally a tissue-mimicking phantom using a combination of one, two or three cryoprobes. The estimation of sound speed is a difficult task because, first, the sound is highly attenuated when traversing the frozen tissue; and second, the sound speed to be reconstructed has a high spatial bandwidth, due to the dramatic change in speed between the frozen and unfrozen tissue. We show that the first problem can be overcome using a beamforming technique. As the classical reconstruction algorithms inherently smooth the reconstruction, we propose to solve the second problem by applying reconstruction techniques based on sparsity.

Three dimensional heat-induced echo-strain imaging is a potentially useful tool for monitoring the formation of thermal lesions during ablative therapy. Heat-induced echo-strain, known as thermal strain, is due to the changes in the speed of propagating ultrasound signals and to tissue expansion during heat deposition. This paper presents a complete system for targeting and intraoperative monitoring of thermal ablation by high intensity focused acoustic applicators. A special software interface has been developed to enable motor motion control of 3D mechanical probes and rapid acquisition of 3D-RF data (ultrasound raw data after the beam-forming unit). Ex-vivo phantom and tissue studies were performed in a controlled laboratory environment. While B-mode ultrasound does not clearly identify the development of either necrotic lesions or the deposited thermal dose, the proposed 3D echo-strain imaging can visualize these changes, demonstrating agreement with temperature sensor readings and gross-pathology. Current results also demonstrate feasibility for realtime computation through a parallelized implementation for the algorithm used. Typically, 125 frames per volume can be processed in less than a second. We also demonstrate motion compensation that can account for shift within frames due to either tissue movement or positional error in the US 3D imaging probe.

Ultrasound elastography (UE) is a promising imaging modality [1]. In vascular applications it uses ultrasound images of arteries in motion to assess their mechanical parameters and stress distributions in physiological or interventional loading conditions [2]. However some simplifying assumptions adopted classically in UE image processing methods restrict this modality to strain imaging. This work presents a new UE image processing method based on differential optical flow. The method constrains the solution of the optical flow problem to minimize a mechanical potential energy. In other words, from all possible solutions of the optical flow problem, it determines the one that minimizes strain energy density of the tissue. In addition, in order to estimate concurrently the stiffness parameter of the tissue with its optical flow (or apparent displacement field); we constrain them to verify the tissue mechanical equilibrium equations. In principle, with this approach we can assess the strain field and map the stiffness parameter for an elastic tissue. Finally our approach also allows us to estimate mechanical parameters of strained phantoms, from their RF or B-mode ultrasound images, considering not only the usual linear elastic mechanical law but also hyperelastic ones.

Measurement of flow-mediated vasodilatation (FMD) in brachial and other conduit arteries has become a common method to asses the status of endothelial function in vivo. In spite of the direct relationship between the arterial wall multi-component strains and FMD responses, direct measurement of wall strain tensor due to FMD has not yet been reported in the literature. In this work, a noninvasive direct ultrasound-based strain tensor measuring (STM) technique is presented to assess changes in the mechanical parameters of the vascular wall during FMD. The STM technique utilizes only sequences of B-mode ultrasound images, and starts with segmenting a region of interest within the artery and providing the acquisition parameters. Then a block matching technique is employed to measure the frame to frame local velocities. Displacements, diameter change, multi-component strain tensor and strain rates are then calculated by integrating or differentiating velocity components. The accuracy of the STM algorithm was assessed using a phantom study, and was further validated using in vivo data from human subjects. Results indicate the validity and versatility of the STM algorithm, and describe how parameters other than the diameter change are sensitive to pre- and post-occlusion, which can then be used for accurate assessment of atherosclerosis.

High-frequency power Doppler imaging of angiogenesis can be challenging given the presence of small blood vessels and slow flow velocities. In the presence of substantial Doppler artifacts such as false-positive color pixels or undetected vessels, color pixel density (CPD) and related vascularity metrics do not provide accurate estimates of vascular volume fraction. As a step towards improved microvascular quantification, flow-phantom experiments were performed to establish relationships between CPD and wall filter cut-off velocity for various combinations of vessel size (160, 200, 250, 300, and 360 μm), flow velocity (4, 3, 2, 1, and 0.5 mm/s), and transducer frequency (30 and 40 MHz). Three distinct regions were observed in plots of CPD versus wall filter cut-off velocity: overestimation of CPD at low cut-offs, underestimation of CPD at high cut-offs, and a plateau at intermediate cut-offs. The CPD at the plateau closely matched the phantom's actual vascular volume fraction. The length of the plateau corresponded with the flow-detection performance of the Doppler system, which was assessed using receiver operating characteristic analysis. Color pixel density versus wall filter cut-off curves from analogous in vivo experiments exhibited the same shape, including a distinct CPD plateau. The similar shape of the flow-phantom and in vivo curves suggests that the presence of a plateau can be used to identify the best-estimate CPD value in an in vivo experiment. The ability to identify the best CPD estimate is expected to improve quantification of angiogenesis and anti-angiogenic treatment responses with power Doppler.

In color flow imaging (CFI), blood flow is estimated from a sequence of 8 to 32 temporal samples using Doppler effects. Most existing techniques are local in that the flow at a spatial location is estimated using its own and, possibly, neighboring temporal samples. As a result, the estimates can often be severely affected by background clutter (e.g., tissue and tissue motion), leading to fragmented/spotty color flow. In this work, we developed a more global technique that segments the temporal samples into connected and smooth spatial regions of blood flow and tissue, thereby improving flow visualization and potentially, flow estimates.

The resolution of ultrasound imaging is restricted primarily by the blurring process of the imaging system embedded in the point spread function (PSF). Supercompounding has been found to be a highly effective way to enhance the resolution of ultrasound imaging. Here we utilize a spatial ultrasound compounding technique using a B-mode array rotated around a target in a range encompassing 180° or greater which we term "supercompounding." For some ultrasound imaging modalities, the PSF is unknown and is space variant, caused by a mono-focus imaging device. To use linear algorithms to enhance the resolution, images must be assumed to have a uniform PSF which is space invariant; otherwise, it is necessary to use complicated non-linear algorithms. Under the above circumstances, an image with a uniform PSF is the key element to more effective resolution enhancement. The supercompounding technique as here can create an image with a uniform PSF from 214 B-scan images thus allowing the use of linear algorithm enhancement. Once a supercompound image with a uniform PSF is constructed, the resolution of the image was further improved with Weiner deconvolution. The processing technique was demonstrated on imaging a dissected porcine aortic root at 5 different critical height levels both with and without inflated pressure into to the sinus. The results can be analyzed to acquire the mechanical properties and geometry of the aortic valve for future use. The resolution as measured by -6dB width of the sinus wall shows a 14% improvement.

Image-based intravascular ultrasound (IVUS) cardiac phase detection allows coronary volume reconstruction in different phases. Consecutive volumes are not necessarily spatially aligned due to longitudinal movement of the catheter. Besides ordinary pullback velocity, there is a relative longitudinal movement of the heart vessel walls and the transducer, due to myocardial contraction. In this manuscript, we aim to spatially align cardiac phase coronary IVUS volumes. In addition, we want to investigate this non-linear longitudinal catheter movement. With this purpose, we have analyzed 120 simulated IVUS images and 10 real IVUS pullbacks. We implemented the following methodology. Firstly, we built IVUS volume for each distinct phase. Secondly, each IVUS volume was transformed into a parametric signal of average frame intensity. We have used these signals to make correlation in space with a reference one. Then we estimated the spatial distance between the distinct IVUS volumes and the reference. We have tested in simulated images and real examinations. We have also observed similar pattern in real IVUS examinations. This spatial alignment method is feasible and useful as a step towards dynamic studies of IVUS examination.

Ultrasound is commonly used as an adjunct to mammography for diagnostic evaluation of suspicions arising from breast cancer screening. As an alternative to conventional sonography that uses hand-held transducers, toroidal array probes that encircle the breast immersed in a water bath have been investigated for ultrasound tomography. This paper introduces a new method for three-dimensional synthetic aperture diffraction tomography that maximizes the resolution in the scanning direction and provides quantitative reconstructions of the acoustic properties of the object. The method is validated by means of numerical simulations.

Compound ultrasound (US) images benefit from reduced speckle noise, at the expense of blurring. The purpose of this work was to evaluate several different methods for reducing the effects of blurring on compounded ultrasound images. We evaluated 3 different approaches: unsharp masking (USM), Gaussian deconvolution (GD), and system measured point-spread-function (PSF) deconvolution (PD). The compounded images are created from summation of approximately 300 B-Mode US images. We applied the different de-blurring methods to these images and examined the images subjectively as well as measured resolution with an autocorrelation metric. Overall, these methods improved resolution by 1.25 (USM), 1.09 (GD), and 1.27 (PD). Unsharp masking was the best trade-off between runtime performance and image quality.

The objective of this study is to investigate a potential low-cost-alternative to MRI, based on acoustic tomography. Using MRI as the gold standard, our goals are to assess the performance of acoustic tomography in (i) depicting normal breast anatomy, (ii) imaging cancerous lesions and (iii) accentuating lesions relative to background tissue using thresholding techniques. Fifteen patients were imaged with MRI and with an acoustic tomography prototype. A qualitative visual comparison of the MRI and prototype images was used to verify anatomical similarities. These similarities suggest that the prototype can image fibrous stroma, parenchyma and fatty tissues, with similar sensitivity to MRI. The prototype was also shown to be able to image masses but equivalency in mass sensitivity with MRI could not be established because of the small numbers of patients and the prototype's limited scanning range. The range of thresholds required to establish tumor volume equivalency suggests that a universal threshold for isolating masses relative to background tissue is possible with acoustic tomography. Thresholding techniques promise to accentuate masses relative to background anatomy which may prove clinically useful in potential screening applications. Future work will utilize larger trials to verify these preliminary conclusions.

Vibro-acoustography is a speckle-free ultrasound based imaging modality that can visualize normal and abnormal soft tissue through mapping stimulated acoustic emission. The acoustic emission is generated by focusing two ultrasound beams of slightly different frequencies (Δf = f₁-f₂) to the same spatial location and vibrating the tissue as a result of ultrasound radiation force. Reverberation of the acoustic emission can create dark and bright areas in the image that affect overall image contrast and detectability of abnormal tissue. Using finite length tonebursts yields acoustic emission at Δf and at sidebands centered about Δf that originate from the temporal toneburst gating. Separate images are formed by bandpass filtering the acoustic emission at Δf and the associated sidebands. The data at these multiple frequencies are compounded through coherent or incoherent processes to reduce the artifacts associated with reverberation of the acoustic emission. Experimental results from a urethane breast phantom and in vivo human breast scans are shown. The reduction in reverberation artifacts are analyzed using a smoothness metric which uses the variances of the gray levels of the original images and those formed through coherent and incoherent compounding of image data. This smoothness metric is minimized when the overall image background is smooth while image features are still preserved. The smoothness metric indicates that the images improved by factors from 1.23-4.33 and 1.09-2.68 in phantom and in vivo studies, respectively. The coherent and incoherent compounding of multifrequency data demonstrate, both qualitatively and quantitatively, the efficacy of this method for reduction of reverberation artifacts.

Shear wave elasticity imaging (SWEI) was employed to track acoustic radiation force (ARF)-induced shear waves in the myocardium of a beating heart. Shear waves were generated in and tracked through the myocardium of the left ventricular free wall (LVFW) in an in vivo heart that was exposed through a thoracotomy; matched studies were also preformed on an ex vivo myocardial specimen. Average shear wave velocities ranged from 2.22 to 2.53 m/s for the ex vivo specimen and 1.5 to 2.9 m/s (1.5-2.09 m/s during diastole; 2.9 m/s during systole) for in vivo specimens. Despite the known rotation of myocardial fiber orientation with tissue depth, there was no statistically significant shear wave velocity depth dependence observed in any of the experimental trials.

Crawling wave (CrW) sonoelastography is an elasticity imaging technique capable of estimating the localized shear wave speed in tissue and, therefore, can provide a quantitative estimation of the Young's modulus for a given vibration frequency. In this paper, this technique is used to detect cancer in excised human prostates and to provide quantitative estimations of the viscoelastic properties of cancerous and normal tissues. Image processing techniques are introduced to compensate for attenuation and reflection artifacts of the CrW images. Preliminary results were obtained with fifteen prostate glands after radical prostatectomy. The glands were vibrated at 100, 120 and 140Hz. At each frequency, three cross-sections of the gland (apex, mid-gland and base) were imaged using CrW Sonoelastography and compared to corresponding histological slices. Results showed good spatial correspondence with histology and an 80% accuracy in cancer detection. In addition, shear velocities for cancerous and normal tissues were estimated as 4.75±0.97 m/s and 3.26±0.87 m/s, respectively.

The determination of elasticity of living soft tissues is of interest in medical diagnostics since the tissue elasticity is usually related to some abnormal, pathological process. Internal tissue deformation induced by externally applied mechanical forces has been evaluated to characterize tissue elasticity. For a quantitative elasticity imaging, material parameter such as shear modulus must be reconstructed from the measurement of internal displacement. A method to estimate the elastic modulus of an isotropic, inhomogeneous, incompressible elastic medium using measured displacement data is formulated by inversely solving the forward problem for static deformation. A finite-element based model for static deformation is proposed and then rearranged for solving the distribution of the shear modulus of the soft tissue from a knowledge of the displacement within the tissue. When the force boundary condition is unknown, it reconstructs the relative value of the elastic modulus of the tissue. The feasibility of the proposed method is demonstrated and the performance of the algorithm with noise in the displacement data is tested using the simulated deformation data of the simple two-dimensional inclusion problem. The results show that the relative shear modulus may be reconstructed from the displacement data measured locally in the region of interest, and that the relative shear modulus can be recovered to some degree of accuracy from only one-dimensional displacement data.

We present novel methodologies for compounding large numbers of 3D echocardiography volumes. Our aim is to investigate the effect of using an increased number of images, and to compare the performance of different compounding methods on image quality. Three sets of 3D echocardiography images were acquired from three volunteers. Each set of data (containing 10+ images) were registered using external tracking followed by state-of-the-art image registration. Four compounding methods were investigated, mean, maximum, and two methods derived from phase-based compounding. The compounded images were compared by calculating signal-to-noise ratios and contrast at manually identified anatomical positions within the images, and by visual inspection by experienced echocardiographers. Our results indicate that signal-to-noise ratio and contrast can be improved using increased number of images, and that a coherent compounded image can be produced using large (10+) numbers of 3D volumes.

We report phantom studies on a new approach to ultrasound-based tissue typing. In the proposed approach, we continuously record RF echo signals backscattered from tissue, while the imaging probe and the tissue are fixed in position. The continuously recorded RF data generates a time series of echoes for each spatial sample of the RF signal. We use the spectral and fractal features of ultrasound RF time series averaged over a region of interest, along with support vector machine classifiers, for tissue typing. In this paper, the effects of two properties of tissue on RF time series are investigated: cell size and elasticity. We show that RF time series acquired from agar-gelatin based tissue mimicking phantoms, with difference only in the size of cell-mimicking glass beads, are distinguishable with statistically reliable accuracies up to 82.2%. Similar experiments using phantoms with different elastic properties did not result in consistently high classification accuracies. The results of this study confirm that the evident differences in microstructure of the cancerous versus normal tissue could play a role in the success of the proposed tissue typing method in detection of prostate cancer.

As part of an ongoing assessment of the in-vivo performance of a operator independent breast imaging device, based on acoustic tomography, we report on new results obtained with patients undergoing neoadjuvant chemotherapy. Five patients were examined with the prototype on multiple occasions corresponding in time to their chemotherapy sessions. 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 acoustic properties of the tumors could be measured directly from the images. The measured properties include reflectivity, sound speed and attenuation, leading to measurable changes in the volume, shape and internal attributes of the tumors. These measurements were used to monitor the response of the tumors to the therapy with the long term goal of correlating results with pathological and clinical outcomes. Comparisons with tumor size changes based on traditional US and MRI indicates potential for accurate, quantifiable tracking of tumor volume. Furthermore, our tentative results also show declines in internal properties of the tumors, possibly relating to a reduction in tissue stiffness and/or density. Future work will include an expansion of the study to a larger cohort of patients for determining the statistical significance of our findings.

Ubiquitous use of 2D ultrasound (US) is limited by the difficulty in interpretation of images for an untrained operator. We present a solution for operator guidance through visual cues via registration of US to a 3D model. The method is demonstrated on 2D echocardiography data, where we are able to localize the scan plane in relation to the standard planes on the 3D model. Our algorithm operates by pre-processing both the US and CT images to the most basic information- muscle, blood pool - using classification. Subsequently, these labels are registered using the match cardinality metric for binary labeled images. We evaluated our method on four parasternal long-axis and three parasternal short-axis images from different patients. Results show that our system is able to correctly distinguish between the different US standard views and is able to localize the scan on the 3D model, correctly on five out of seven cases.

Ultrasound is a widely used medical imaging methodology because it is safe and relatively inexpensive. However, the quality of the images is affected by the point spread function of the system and coherent wave interference or speckle. The present research studies the averaging of images that have been displaced laterally and displays them using an interlaced grid. The main goals are to reduce speckle and improve contrast and resolution. The point spread function of the ultrasound scanner was estimated using a thin nylon thread within a water bath. Then, a set of eight images of a breast phantom (having lateral displacements smaller than the width of the point spread function) were averaged and interlaced. The results show a total improvement of 4% in signal to noise ratio and 7% in contrast to noise ratio.

Freehand 3D ultrasound (US) using a 2D US probe has the advantage over conventional 3D probes of being able to collect arbitrary 3D volumes at a lower cost. Conventionally, optical and electromagnetic (EM) sensors are used to keep track of the US probe position. Optical tracking provides more accuracy but requires line-of-sight which can be a problem for many applications. Conversely, EM tracking does not have any line-of-sight restrictions, but it has lower accuracy and measurement jitter, and is susceptible to metallic distortions. Ultrasound imaging has the advantage that the speckle inherent in all images contains relative position information due to the decorrelation of speckle over distance. However, tracking the position of US images using speckle information alone suffers from drifts caused by tissue inconsistencies, and overall lack of accuracy. In our work, we examine the possibility for overcoming the limitations of both EM US tracking and freehand, speckle-based US image tracking, through the fusion of these techniques. Even though positions found through speckle-based tracking have very little jitter, the overall error is large, due to drifts in position estimation. By combining the EM and speckle-based tracking information using an Unscented Kalman Filter, we are able to reduce the drift errors as well as to eliminate high-frequency jitter noise from the EM tracker positions. Such fusion produces a smooth and accurate 3D reconstruction superior to those using the EM tracker alone. In addition, we look at the effect of metallic distortions on our fusion and demonstrate improvements over the EM tracker reconstruction.

Breast irradiation significantly reduces the risk of recurrence of cancer. There is growing evidence suggesting that irradiation of only the involved area of the breast, partial breast irradiation (PBI), is as effective as whole breast irradiation. Benefits of PBI include shortened treatment time, and perhaps fewer side effects as less tissue is treated. However, these benefits cannot be realized without precise and accurate localization of the lumpectomy cavity. Several studies have shown that accurate delineation of the cavity in CT scans is very challenging and the delineated volumes differ dramatically over time and among users. In this paper, we propose utilizing 3D ultrasound (3D-US) and tracked strain images as complementary modalities to reduce uncertainties associated with current CT planning workflow. We present the early version of an integrated system that fuses 3D-US and real-time strain images. For the first time, we employ tracking information to reduce the noise in calculation of strain image by choosing the properly compressed frames and to position the strain image within the ultrasound volume. Using this system, we provide the tools to retrieve additional information from 3D-US and strain image alongside the CT scan. We have preliminarily evaluated our proposed system in a step-by-step fashion using a breast phantom and clinical experiments.

Pulsatile tissue-motion in the B-mode ultrasonogram of neonatal cranium has been visualized in the three-dimensional (3-D) domain. A movie of 2-D ultrasonogram (640×480pixels/frame, 8bits/pixel, 33ms/frame), which was taken with a conventional ultrasonogram apparatus (ATL HDI5000) and an ultrasonic probe combined with a compact tilt-sensor, was captured and recorded together with the orientations of probe into a 2-D visualization system developed by ourselves. The pulsatile strength was evaluated from a heartbeat-frequency component calculated by Fourier transform of a series of pixel values as a function of time sampled at each pixel of the 2-D ultrasonogram. The 3-D image of pulsatile strength was obtained by projecting the pulsatile strength on the several sections at different orientations of probe. The 3-D images of pulsatile-strength clearly described characteristic 3-D structures of arteries such as the anterior, middle and posterior cerebral arteries, Willis ring and cerebellar arteries. Since our technique is completely noninvasive, it is very useful for neonates rested completely at incubators. Furthermore, it is effective approach to obtain a useful 3-D ultrasonogram even in homogeneous tissues other than brain tissues, because it is easy to recognize the tissue boundary by selective detection of special tissues with their own motion characteristics.

Multi-volume rendering is a technique that renders and displays multiple volumes simultaneously. In ultrasound imaging, multi-volume rendering is used for mixing 3D anatomical structures from B-mode imaging with blood flow information from power Doppler imaging (PDI) or color Doppler imaging (CDI). A variety of multi-volume rendering techniques have been proposed, such as post fusion (PF), composite fusion (CF) and progressive fusion (PGF). PF, which combines independently-rendered volumes, is unable to depict a spatial relationship between B-mode images (i.e., tissue structure) and PDI/CDI images (i.e., blood flow). The CF technique suffers from color distortion due to intermixing of hue values. In our recent study, the PGF technique was found to better retain and display tissue structures, vasculature and their depth relationship. However, the disadvantages of PGF include its high computational cost due to the requirement of maintaining a separate rendering pipeline for each volume (i.e., B-mode and power/color Doppler) and potential artifacts of depth-order ambiguity. In this paper, we present a new flexible computationally efficient multivolume rendering technique, named volume fusion (VF), and compare it with existing techniques. We have evaluated the VF method and other multi-volume rendering techniques with data acquired from a commercial ultrasound machine and found that the VF technique can preserve the spatial relationships well amongst multiple volumes without color distortion while the same rendering pipeline can be used to support both PDI and CDI volume fusion.

Freehand 3D ultrasound makes use of a 2D ultrasound system and a position sensor to reconstruct 3D ultrasound images. To achieve real-time reconstruction while acquisition, the reconstruction volume must be determined in advance. In this paper, a novel technique is proposed to address the problem effectively. This technique consists of two steps: the interactive selection of the region of interest (ROI), and the automatic determination of the reconstruction volume. The tracked B-scan is used as a vivid tool to explore the target object. After the decision of the principal directions of the target object, four B-scans are designated to enclose the ROI. The reconstruction volume corresponding to the ROI is then figured out automatically according to the four tracked B-scans. The presented technique can fast predetermine a compact reconstruction volume aligned with the best viewing direction. Furthermore, the technique is convenient for the clinician and comfortable for the patient. The efficient and flexible nature of the technique is demonstrated on a real-time freehand system.

Coded excitation can improve the performance factors, such as SNR and CTR, of harmonic imaging with a low voltage transmit waveform. For these purposes, harmonic imaging methods using Golay codes with advantages in range sidelobe levels and implementation simplicity have been proposed. However, they require four transmit-receive (T/R) events to form each scan line. This work describes a new harmonic Golay coded excitation technique to overcome this problem. The proposed method can produce two scan lines through four T/R events using four pairs of codes. On the first T/R cycle, the first pair of codes is fired sequentially, one at a time, along each of the two scan lines, where the two codes are designed such that their second harmonic components are mutually orthogonal Golay codes. The same transmit sequence is carried out with the second pair of codes, each of which being 180 degrees out of phase with the corresponding one of the first pair of codes to remove the fundamental components by simply adding the two resulting received signals. The third and fourth T/R cycles are followed in the same manner, but with the codes whose harmonic components are composed of the complementary set of the mutually orthogonal Golay codes used in the first T/R cycle and their sign inverted codes, respectively. Consequently, the mutually orthogonal Golay codes and their complementary set of codes representing only the harmonic components are obtained after four T/R events. Finally, using the orthogonal and complementary properties, the coded harmonic signals along each scan line can easily be separated and compressed. Computer simulation results show that the proposed method can successfully perform pulse-inversion harmonic imaging to produce two scan lines simultaneously after four T/R events with coded sequences.

We report on a continuing assessment of the in-vivo performance of an operator independent breast imaging device based on the principles of acoustic tomography. This study highlights the feasibility of mass characterization using criteria derived from reflection, sound speed and attenuation imaging. The data were collected with a clinical prototype at the Karmanos Cancer Institute in Detroit MI from patients recruited at our breast center. Tomographic sets of images were constructed from the data and used to form 3-D image stacks corresponding to the volume of the breast. Masses were identified independently by either ultrasound or biopsy and their locations determined from conventional mammography and ultrasound exams. The nature of the mass and its location were used to assess the feasibility of our prototype to detect and characterize masses in a case-following scenario. Our techniques generated 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. The three types of images are intrinsically co-registered because the reconstructions are performed using a common data set acquired by the prototype. Fusion imaging, utilizing thresholding, is shown to visualize mass characterization and facilitates separation of cancer from benign masses. These initial results indicate that operatorindependent whole-breast imaging and the detection and a characterization of cancerous breast masses are feasible using acoustic tomography techniques.

We compare the quoted and extracted human measurements on ultrasound images in order to detect the sources of error in such measurements. We extract the measurement cursors from the captured images and compare with the stated differences and pixel resolution. We found that there is a high degree of variability in the quality of the human measurements compared to the image extracted measurements of the cursor positions, as well as a significant reduction in accuracy. As a solution, we propose improved cursor modes for ultrasound devices and improved procedures for measurements.

This work is concerned with the numerical implementation of a reconstruction algorithm developed to recover a function from its spherical means over spheres centered on a circle. The algorithm is experimentally verified by simulations using numerical phantoms. In the scheme of tomography, acoustic waves are generated by illuminating an object with a short burst of radio-frequency waves. In applications, like breast cancer imaging, which use modalities like photo-acoustic tomography (PAT) that model the acoustic pressures as spherical means, data are measured on the detectors located in a circle surrounding the object. This is then used to reconstruct the absorption density inside the object. In contrast, applications like bore hole tomography and improved Intravascular Ultra Sound (IVUS) imaging for prostate cancer, which use modalities like Radial Reflection Diffraction Tomography (RRDT), a ring of detectors placed exterior to the object, collect the acoustic waves as back-scattered field. This work uses a single algorithm to reconstruct functions from data collected using these two different techniques - one, by placing the object inside the ring of detectors, and the other, by placing the object exterior to the ring of detectors. The algorithm then draws a comparison between the two reconstructions. The case of bistatic ultrasound imaging, where the elliptical Radon transform is appropriate, is also discussed.