bluuebunny/crossref_metadata_2025 huggingface dataset:
Single-Element Focused Ultrasound Transducer Method for Harmonic Motion Imaging
Authors: Maleke Caroline , Pernot Mathieu , Konofagou Elisa E.
Published: March 2013

The harmonic motion imaging (HMI) technique for simultaneous monitoring and generation of ultrasound therapy using two separate focused ultrasound transducer elements was previously demonstrated. In this study, a new HMI technique is described that images tissue displacement induced by a harmonic radiation force using a single focused-ultrasound element. A wave propagation simulation model first indicated that, unlike in the two-beam configuration, the amplitude-modulated beam produced a stable focal zone for the applied harmonic radiation force. The AM beam thus offered the unique advantage of sustaining the application of the spatially-invariant radiation force. Experiments were performed on gelatin phantoms and ex vivo tissues. The radiation force was generated by a 4.68 MHz focused ultrasound (FUS) transducer using a 50 Hz amplitude-modulated wave. A 7.5 MHz pulse-echo transducer was used to acquire rf echoes during the application of the harmonic radiation force. Consecutive rf echoes were acquired with a pulse repetition frequency (PRF) of 6.5 kHz and 1D cross-correlation was performed to estimate the resulting axial tissue displacement. The HMI technique was shown capable of estimating stiffness-dependent displacement amplitudes. Finally, taking advantage of the real-time capability of the HMI technique, temperature-dependent measurements enabled monitoring of HIFU sonication in ex vivo tissues. The new HMI method may thus enable a highly-localized force and stiffness-dependent measurements as well as real-time and low-cost HIFU monitoring.
Distorted Born Diffraction Tomography Applied to Inverting Ultrasonic Field Scattered by Noncircular Infinite Elastic Tube
Authors: Lasaygues Philippe , Guillermin Régine , Lefebvre Jean-Pierre
Published: March 2013

This study focuses on the application of ultrasonic diffraction tomography to noncircular 2D-cylindrical objects immersed in an infinite fluid. The distorted Born iterative method used to solve the inverse scattering problem belongs to the class of algebraic reconstruction algorithms. This method was developed to increase the order of application of the Born approximation (in the case of weakly-contrasted media) to higher orders. This yields quantitative information about the scatterer, such as the speed of sound and the attenuation. Quantitative ultrasonic imaging techniques of this kind are of great potential value in fields such as medicine, underwater acoustics and nondestructive testing.
Spectral and Scatterer-Size Correlation during Angular Compounding: Simulations and Experimental Studies
Authors: Liu W. , Zagzebski J.A. , Varghese T. , Gerig A.L. , Hall T.J.
Published: March 2013

In a previous study, theoretical expressions were derived for the correlation between ultrasonic scatterer-size estimates and their associated spectral measures when echo data are acquired from the same location but at different angles. The results were verified using simulations. In the present work, we further analyze simulation data for these conditions; in addition, we measure the correlations using a cylindrical tissue-mimicking phantom. Experimental and theoretical results show that the relationship of scatterer-size correlation to insonification angle depends on gate duration, gate type and beam profile. Some discrepancies are noted between experimental results and theoretical predictions, particularly when using smaller gated windows. The sources of the discrepancies are discussed. Experimental results using a 6-MHz linear array suggest that, to save acquisition and processing time while reducing variance, a 2°–3° angular increment step provides efficient angular compounding for scatterer-size imaging with this array. Theoretical predictions can provide estimates of expected correlations between angular acquisitions when compounding with other transducers.
Real-Time Stereo 3D Ultrasound
Authors: Noble Joanna R. , Fronheiser Matthew P. , Smith Stephen W.
Published: March 2013

Real-time 3D ultrasound was developed at Duke University in 1991 and has since been used with a variety of transducers and shown effectiveness in clinical applications and in vivo animal imaging studies. Methods for displaying the 3D pyramid of data acquired by the system include selecting 2D image slices or integrating data into a volume rendered view. A third method, real-time stereo 3D imaging, is discussed here. The clinical commercial 3D system has been modified in our laboratory to display a real-time stereo image pair on the scanner display to be viewed through a stereoscope. This merges the pair into a single image, with a sensation of depth. Stereoscopic displays have previously been demonstrated to provide benefits, including improved depth judgments and increased perception of image quality in other applications. Previously-saved volumes of ultrasound data are shown in stereo 3D using the new system.
Integrated Endoscope for Real-Time 3D Ultrasound Imaging and Hyperthermia: Feasibility Study
Authors: Pua Eric C. , Qiu Yupeng , Smith S.W.
Published: March 2013

The goal of this research is to determine the feasibility of using a single endoscopic probe for the combined purpose of real-time 3D (RT3D) ultrasound imaging of a target organ and the delivery of ultrasound therapy to facilitate the absorption of compounds for cancer treatment. Recent research in ultrasound therapy has shown that ultrasound-mediated drug delivery improves absorption of treatments for prostate, cervical and esophageal cancer. The ability to combine ultrasound hyperthermia and 3D imaging could improve visualization and targeting of cancerous tissues. In this study, numerical modeling and experimental measurements were developed to determine the feasibility of combined therapy and imaging with a 1cm diameter endoscopic RT3D probe with 504 transmitters and 252 receive channels. This device operates at 5 MHz and has a 6.3 mm × 6.3 mm aperture to produce real time 3D pyramidal scans of 60–120 degrees incorporating 64 × 64 = 4,096 image lines at 30 volumes/sec interleaved with a 3D steerable therapy beam. A finite-element mesh was constructed with over 128,000 elements in LS-DYNA to simulate the induced temperature rise from our transducer with a 3 cm deep focus in tissue. Quarter-symmetry of the transducer was used to reduce mesh size and computation time. Based on intensity values calculated in Field II using the transducer's array geometry, a minimum ISPTA of 3.6 W/cm2 is required from our endoscope probe in order to induce a temperature rise of 4°C within five minutes. Experimental measurements of the array's power output capabilities were conducted using a PVDF hydrophone placed 3 cm away from the face of the transducer in a watertank. Using a PDA14 Signatec data acquisition board to capture full volumes of transmitted ultrasound data, it was determined that the probe can presently maintain intensity values up to 2.4 W/cm2 over indefinite times for therapeutic applications combined with intermittent 3D scanning to maintain targeting. These values were acquired using 8 cycle bursts at a prf of 6 kHz. Ex vivo heating experiments of excised pork tissue yielded a maximum temperature rises of 2.3°C over 5 minutes of ultrasound exposure with an average rise of 1.8 ± 0.2°C over 5 trials. Modifications to the power supply and transducer array may enable us to reach the higher intensities required to facilitate drug delivery therapy.
A Novel Noninvasive Technique for Pulse-Wave Imaging and Characterization of Clinically-Significant Vascular Mechanical Properties In Vivo
Authors: Fujikura Kana , Luo Jianwen , Gamarnik Viktor , Pernot Mathieu , Fukumoto Royd , Tilson Martin David , Konofagou Elisa E.
Published: March 2013

The pulse-wave velocity (PWV) has been used as an indicator of vascular stiffness, which can be an early predictor of cardiovascular mortality. A noninvasive, easily applicable method for detecting the regional pulse wave (PW) may contribute as a future modality for risk assessment. The purpose of this study was to demonstrate the feasibility and reproducibility of PW imaging (PWI) during propagation along the abdominal aortic wall by acquiring electrocardiography-gated (ECG-gated) radiofrequency (rf) signals noninvasively. An abdominal aortic aneurysm (AAA) was induced using a CaCl2 model in order to investigate the utility of this novel method for detecting disease. The abdominal aortas of twelve normal and five CaCl2, mice were scanned at 30 MHz and electrocardiography (ECG) was acquired simultaneously. The radial wall velocities were mapped with 8000 frames/s. Propagation of the PW was demonstrated in a color-coded ciné-loop format in all cases. In the normal mice, the wave propagated in linear fashion from a proximal to a distal region. However, in CaCl2 mice, multiple waves were initiated from several regions (i.e., most likely initiated from various calcified regions within the aortic wall). The regional PWV in normal aortas was 2.70 ± 0.54 m/s ( r2 = 0.85 ± 0.06, n = 12), which was in agreement with previous reports using conventional techniques. Although there was no statistical difference in the regional PWV between the normal and CaCl2-treated aortas (2.95 ± 0.90 m/s ( r2 = 0.51 ± 0.22, n = 5)), the correlation coefficient was found to be significantly lower in the CaCl2-treated aortas ( p<0.01). This state-of-the-art technique allows noninvasive mapping of vascular disease in vivo. In future clinical applications, it may contribute to the detection of early stages of cardiovascular disease, which may decrease mortality among high-risk patients.
A Three-Dimensional Registration Method for MicroUS/MicroPET Multimodality Small-Animal Imaging
Authors: Liao Ai-Ho , Chen Li-Yen , Cheng Wen-Fang , Li Pai-Chi
Published: March 2013

Small-animal models are used extensively in disease research, genomics research, drug development and developmental biology. The development of noninvasive small-animal imaging techniques with adequate spatial resolution and sensitivity is therefore of prime importance. In particular, multimodality small-animal imaging can provide complementary information. This paper presents a method for registering high-frequency ultrasonic (microUS) images with small-animal positron-emission tomography (microPET) images. Registration is performed using six external multimodality markers, each being a glass bead with a diameter of 0.43–0.60 mm, with 0.1 μl of [18F]FDG placed in each marker holder. A small-animal holder is used to transfer mice between the microPET and microUS systems. Multimodality imaging was performed on C57BL/6J black mice bearing WF-3 ovary cancer cells in the second week after tumor implantation and rigid-body image registration of the six markers was also performed. The average registration error was 0.31 mm when all six markers were used and increased as the number of markers decreased. After image registration, image segmentation and fusion are performed on the tumor. Our multimodality small-animal imaging method allows structural information from microUS to be combined with functional information from microPET, with the preliminary results showing it to be an effective tool for cancer research.
Investigation of Micro-Ultrasound for Microvessel Imaging in a Model of Chronic Total Occlusion
Authors: Thind Amandeep S. , Leung General , Munce Nigel R. , Graham John J. , Anderson Kevan J.T. , Dick Alexander J. , Strauss Bradley H. , Wright Graham A. , Foster F. Stuart
Published: March 2013

The aim of the current study is to investigate the ability of micro-ultrasound (μUS) to identify microvasculature in CTOs in vivo. Results are compared with MRI studies. CTOs were developed in nine porcine superficial femoral arteries (SFA) by percutaneous insertion of a dissolvable polymer plug. This model is characterized by acute thrombosis that later organizes into a fibrotic CTO containing abundant microchannels. 3D μUS images with Power Doppler (PD) overlays from the arteries were acquired at two timepoints: one and eight weeks after placement of the polymer plug. Phase contrast MRI and contrast enhanced MRI was also performed. Imaging was performed transcutaneously. Microvessels were identified in vivo in six of eight CTOs using μUS, and in three of seven CTO vessels with MRI, compared with five of seven seen histologically. PW Doppler profiles showed pulsatile blood velocities of ∼2 cm/s. Intraluminal microvessels within CTOs can be consistently identified by 3D μUS. This technique appears to be more sensitive than MRI. μUS may play a role in guiding CTO interventions.
Real-Time Three-Dimensional Transesophageal Echocardiography for Guiding Interventional Electrophysiology: Feasibility Study
Authors: Pua Eric C. , Idriss Salim F. , Wolf Patrick D. , Smith S.W.
Published: March 2013

At present, there are limited methods of acquiring three-dimensional visualization of cardiac structure and function in real-time during interventional electrophysiology procedures. Images acquired for integration of computerized tomography and magnetic resonance imaging with electroanatomic mapping systems are static and are obtained earlier in time. The purpose of this study was to test the feasibility of real-time three-dimensional transesophageal echocardiography for the guidance of interventional electrophysiological studies. A matrix array transducer with 504 channels operating at 5 MHz in a 1 cm diameter steerable esophageal probe was used in conjunction with a scanner capable of real-time 3D scanning of pyramidal volumes from 65° to 120° at rates up to 30 volumes per second. This device has a spatial resolution of approximately 3 mm at 5 cm depth. The authors acquired real-time three-dimensional images of anatomic landmarks of value for electrophysiological procedures in five closed chest canines. Real-time, three-dimensional ultrasound imaging was also used for visualization and guidance of interventional catheter devices within the canine heart. Real-time three-dimensional images of the atria, pulmonary veins, and coronary sinus were acquired. Real-time 3-D color flow Doppler was employed to confirm patency. Multiple image planes of image volumes and rendered views were used to track catheter position and orientation. Images of left veno-atrial junctions have been confirmed by dissection.

This study has demonstrated the feasiblity of using real-time three-dimensional transesophageal echocardiography for guiding interventional electrophysiology. The technology has the potential to fill a niche as an adjunct modality for cost-effective real-time interventional guidance and assessment, providing catheter and pacing lead visualization simultaneously with functional volumetric cardiac imaging.
Noninvasive Tumor Imaging with High-Frequency Ultrasound and MicroPET in Small Animals
Authors: Liao Ai-Ho , Hwang Jeng-Jong , Li Chen-Han , Cheng Wen-Fang , Li Pai-Chi
Published: March 2013

In this study, we used a micro-ultrasound (microUS) system that we developed in-house as an alternative method for tumor growth calipers. In addition, microUS was combined with small-animal positron-emission tomography (microPET) for tumor metastatic assessment. MicroUS provides anatomical information that can be used for tumor volume measurements while microPET is a functional imaging method with positron-emitting radiophamaceuticals, such as 18F-labeled deoxyglucose, [18F]FDG. In this study, microUS and microPET were performed in a mouse tumor longitudinal study (2–8 weeks), both with 3D tumor segmentation and volume measurements. Compared with vernier calipers, microPET generally overestimated tumor volumes during weeks 2–4 due to its inadequate spatial resolution. During weeks 5–8, standard deviations of microPET results were large due to tumor hypoxia or necrosis. On the contrary, microUS tumor volume measurements were more reliable as they were less affected by these factors. Nonetheless, microUS is not able to provide functional information similar to that provided by microPET. Therefore, microUS and microPET are complementary to each other as microUS has superior spatial resolution and microPET provides functional information, such as hypoxia or necrosis in the progression of the tumor. With image registration and fusion, the combination can be a valuable tool for cancer research.
Autonomous Surgical Robotics Using 3-D Ultrasound Guidance: Feasibility Study
Authors: Whitman John , Fronheiser Matthew P. , Ivancevich Nikolas M. , Smith Stephen W.
Published: March 2013

The goal of this study was to test the feasibility of using a real-time 3D (RT3D) ultrasound scanner with a transthoracic matrix array transducer probe to guide an autonomous surgical robot. Employing a fiducial alignment mark on the transducer to orient the robot's frame of reference and using simple thresholding algorithms to segment the 3D images, we tested the accuracy of using the scanner to automatically direct a robot arm that touched two needle tips together within a water tank. RMS measurement error was 3.8% or 1.58 mm for an average path length of 41 mm. Using these same techniques, the autonomous robot also performed simulated needle biopsies of a cyst-like lesion in a tissue phantom. This feasibility study shows the potential for 3D ultrasound guidance of an autonomous surgical robot for simple interventional tasks, including lesion biopsy and foreign body removal.
3D Strain Imaging Using a Rectilinear 2D Array
Authors: Awad Samer I. , Yen Jesse T.
Published: March 2013

Under mechanical compression, tissue movements are inherently three-dimensional. 2-D strain imaging can suffer from decorrelation noise caused by out-of-plane tissue movement in elevation. With 3-D strain imaging, all tissue movements can be estimated and compensated, hence minimizing out-of-plane decorrelation noise. Promising 3-D strain imaging results have been shown using 1 -D arrays with mechanical translation in elevation. However, the relatively large slice thickness and mechanical translation can degrade image quality. Using 2-D arrays, an improved elevational resolution can be achieved with electronic focusing. Furthermore, scanning with 2-D arrays is also done electronically, which eliminates the need for mechanical translation.

In this paper, we demonstrate the feasibility of 3-D strain imaging using a 4 cm × 4 cm ultrasonic sparse rectilinear 2-D array operating at 5MHz. The signal processing combinations of 2-D or 3-D beamforming followed by 2-D or 3-D strain imaging are studied and compared to each other to evaluate the performance of our 3-D strain imaging system. 3-D beamforming followed by 3-D strain imaging showed best performance in all experiments.
A Scalable Architecture for Real-Time Synthetic-Focus Imaging
Authors: Richard William D.
Published: March 2013

A scalable architecture for forming real-time synthetic focus images is described, and the design of a 256-channel system using currently available technology is presented as an example implementation of the architecture. The parallelism of the system scales directly with the number of array elements, and the image computation rate for a given image size (in pixels) stays constant as the number of array elements is increased. The system leverages earlier work in the real-time generation of the required time-of-flight surfaces and allows either real-time image generation or iterative adaptive image generation from a single complete dataset.
Ultrasonic Reflection Tomography vs. Canonical Body Approximation: Experimental Assessment of an Infinite Elastic Cylindrical Tube
Authors: Lasaygues Philippe , Marrec Loïc Le
Published: March 2013

Comparisons were made between the results obtained using two quantitative ultrasound imaging methods on the solid cross section of a cylindrical tube that is infinite in the axial direction. The first method tested was the classical reflection tomography method based on the first-order Born approximation, which can only be used under conditions to obtain limited reconstruction of the external boundaries of the high contrast scatterer. The results were compared with those obtained using another inversion scheme based on the Intercepting Canonical Body Approximation (ICBA) in a large frequency range, which gives accurate complete geometrical information about the tube (thickness measurements). The numerical and experimental results obtained show the feasibility of the latter approach.
Modeling of Shock Wave Propagation in Large Amplitude Ultrasound
Authors: Pinton Gianmarco F. , Trahey Gregg E.
Published: March 2013

The Rankine-Hugoniot relation for shock wave propagation describes the shock speed of a nonlinear wave. This paper investigates time-domain numerical methods that solve the nonlinear parabolic wave equation, or the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation, and the conditions they require to satisfy the Rankine-Hugoniot relation. Two numerical methods commonly used in hyperbolic conservation laws are adapted to solve the KZK equation: Godunov's method and the monotonic upwind scheme for conservation laws (MUSCL). It is shown that they satisfy the Rankine-Hugoniot relation regardless of attenuation. These two methods are compared with the current implicit solution based method. When the attenuation is small, such as in water, the current method requires a degree of grid refinement that is computationally impractical. All three numerical methods are compared in simulations for lithotripters and high intensity focused ultrasound (HIFU) where the attenuation is small compared to the non-linearity because much of the propagation occurs in water. The simulations are performed on grid sizes that are consistent with present-day computational resources but are not sufficiently refined for the current method to satisfy the Rankine-Hugoniot condition. It is shown that satisfying the Rankine-Hugoniot conditions has a significant impact on metrics relevant to lithotripsy (such as peak pressures) and HIFU (intensity). Because the Godunov and MUSCL schemes satisfy the Rankine-Hugoniot conditions on coarse grids, they are particularly advantageous for three-dimensional simulations.
Feasibility Exploration of Blood Flow Estimation by Contrast-Assisted Nakagami Imaging
Authors: Tsui Po-Hsiang , Yeh Chih-Kuang , Chang Chien-Cheng
Published: March 2013

The microbubble contrast agent destruction/replenishment technique has been widely applied to ultrasound-based blood flow estimation. The rate of increase of the time-intensity curve (TIC) due to microbubbles flowing into the region of interest as measured from B-mode images closely reflects the flow velocity. In this study, we monitored microbubble replenishment by a proposed new approach called the time-Nakagami-parameter curve (TNC) obtained from Nakagami-parameter images for quantifying the flow velocity. The feasibility of using the TNC to estimate the flow was evaluated in computer simulations of the TIC and TNC for flow velocities from 10 to 30 cm/s under an ultrasound frequency of 5 MHz. The clutter effects on the TIC and TNC were explored in a more realistic situation by carrying out phantom measurements of 25 MHz. The rates of increase of the TIC and TNC were expressed by the rate constants βI and βN of a monoexponential model, respectively. The average βI increased from 38 to 110 s–1 as the flow velocity increased from 10to30cm/s( r = 0.98), and the average βN increased from approximately 40 to 120 s–1 for the same increase in flow velocity ( r = 0.98). The p-value between the results of βI and βN as a function of flow velocity was 0.77. These results represent that βN quantifies the flow velocity similarly to the conventional βI. In particular, both the simulation and experimental results revealed that the TNC method conditionally tolerates the presence of nonperfused areas (e.g., surrounding tissues or vessel walls) in the region of interest without requiring application of an additional wall filter to cancel the influences of clutter echoes on the flow estimation. These findings suggest that the TNC-based technique may be a potential method as a complementary tool for the conventional TIC technique to improve the estimation of blood flow.
Quantitative Assessment of the Magnitude, Impact and Spatial Extent of Ultrasonic Clutter
Authors: Lediju Muyinatu A. , Pihl Michael J. , Dahl Jeremy J. , Trahey Gregg E.
Published: March 2013

Clutter is a noise artifact in ultrasound images that appears as diffuse echoes overlying signals of interest. It is most easily observed in anechoic or hypoechoic regions, such as in cysts, blood vessels, amniotic fluid, and urine-filled bladders. Clutter often obscures targets of interest and complicates anatomical measurements. An analytical expression that characterizes the extent to which clutter degrades lesion contrast was derived and compared to the measured contrast loss due to clutter in a bladder phantom. Simulation and phantom studies were performed to determine ideal and achievable signal-to-clutter ratios. In vivo clutter magnitudes were quantified in simultaneously-acquired fundamental and harmonic bladder images from five volunteers. Clutter magnitudes ranged from −30 dB to 0 dB, relative to the mean signal of the bladder wall. For this range of clutter magnitudes, the analytical expression predicts a contrast loss of 0–45 dB for lesions with clutter-free contrasts of 6–48 dB. A pixel-wise comparison of simultaneously-acquired fundamental and harmonic bladder images from each volunteer revealed an overall signal reduction in harmonic images, with average reductions ranging from 11–18 dB in the bladder interior and 9–11 dB in the tissue surrounding the bladder. Harmonic imaging did not reduce clutter in all volunteers.
Design, Fabrication and Testing of a Dual-Band Photoacoustic Transducer
Authors: Liu Jian-Hung , Wei Chen-Wei , Sheu Yae-Lin , Tasi Yu-Tsung , Wang Yu-Hsin , Li Pai-Chi
Published: March 2013

Combining photoacoustic and ultrasonic imaging allows both optical and acoustic properties to be displayed simultaneously. In this paper, we describe a dual-band transducer for implementing such a multimodality imaging setup. The transducer exhibits two frequency bands so that it matches the frequency of interest in both imaging methods. An optical fiber is included in the center so that it is inherently coregistered. The transducer was fabricated from lithium niobate and comprises two concentric rings whose center frequencies are 4.9 MHz and 14.8 MHz. Pulse-echo measurements and phantom imaging were performed to demonstrate its performance characteristics.
Monitoring Angiogenesis in Human Melanoma Xenograft Model Using Contrast-Enhanced Ultrasound Imaging
Authors: Forsberg F. , Ro R.J. , Liu J.B. , Lipcan K.J. , Potoczek M. , Nazarian L.N.
Published: March 2013

The potential for noninvasive monitoring and quantification of tumor angiogenesis with contrast-enhanced ultrasound imaging has been investigated in a murine cancer model. Seventy athymic nude mice were implanted with the human melanoma cell line DB-1 but only 30 of these were available for the final study. The 30 mice were divided into three groups (10 mice/group), which were studied with contrast-enhanced ultrasound imaging 4, 5 or 6 weeks post-implantation. Power Doppler and pulse inversion harmonic imaging (PIHI) were performed (in real time and intermittently) with a Sonoline Elegra scanner (Siemens Medical Solutions, Issaquah, WA) following injection of Optison (dose: 0.4–0.6 ml/kg; GE Healthcare, Princeton, NJ). Ultrasound results were compared to immunohistochemical stains for endothelial cells (CD31), vascular endothelial growth factor (VEGF) and cyclooxygenase-2 (COX-2). Linear regression analysis indicated statistically significant correlations between the percent area stained with VEGF and ultrasound measures of tumor neovascularity obtained with all three techniques ( p < 0.01). Contrast-enhanced ultrasound imaging of tumor neovascularity appears to provide a noninvasive marker of angiogenesis corresponding to the expression of VEGF in the DB-1 model and may become a useful tool for monitoring clinical anti-angiogenic therapies.
Color Doppler Imaging of Cardiac Catheters Using Vibrating Motors
Authors: Reddy Kalyan E. , Light Edward D. , Rivera Danny J. , Kisslo Joseph A. , Smith Stephen W.
Published: March 2013

A miniature motor rotating at 11,000 rpm was attached onto the proximal end of cardiac electrophysiological (EP) catheters in order to produce vibrations at the tip that were then visualized by color Doppler on ultrasound scanners. The catheter tip was imaged within a vascular graft submerged in a water tank using the Volumetrics Medical Imaging 3D scanner, the Siemens Sonoline Antares 2D scanner and the Philips ie33 3D ultrasound scanner with TEE probe. The vibrating catheter tip was visualized in each case, although results varied with the color Doppler properties of the individual scanner.
Dual-Mode Intracranial Catheter Integrating 3D Ultrasound Imaging and Hyperthermia for Neuro-oncology: Feasibility Study
Authors: Herickhoff Carl D. , Light Edward D. , Bing Kristin F. , Mukundan Srinivasan , Grant Gerald A. , Wolf Patrick D. , Smith Stephen W.
Published: March 2013

In this study, we investigated the feasibility of an intracranial catheter transducer with dual-mode capability of real-time 3D (RT3D) imaging and ultrasound hyperthermia, for application in the visualization and treatment of tumors in the brain. Feasibility is demonstrated in two ways: first by using a 50-element linear array transducer (17 mm × 3.1 mm aperture) operating at 4.4 MHz with our Volumetrics diagnostic scanner and custom, electrical impedance-matching circuits to achieve a temperature rise over 4°C in excised pork muscle, and second, by designing and constructing a 12 Fr, integrated matrix and linear-array catheter transducer prototype for combined RT3D imaging and heating capability. This dual-mode catheter incorporated 153 matrix array elements and 11 linear array elements diced on a 0.2 mm pitch, with a total aperture size of 8.4 mm × 2.3 mm. This 3.64 MHz array achieved a 3.5°C in vitro temperature rise at a 2 cm focal distance in tissue-mimicking material. The dual-mode catheter prototype was compared with a Siemens 10 Fr AcuNav™ catheter as a gold standard in experiments assessing image quality and therapeutic potential and both probes were used in an in vivo canine brain model to image anatomical structures and color Doppler blood flow and to attempt in vivo heating.
Hardware-Efficient Methods for Elimination of Signal Distortion in Sigma-Delta-Based Ultrasound Beamforming
Authors: Han Ho-San , Kim Jung-Jun , Song Tai-Kyong
Published: March 2013

An efficient ultrasound beamforming algorithm based on sigma-delta modulation (SDM) is proposed, which performs dynamic focusing at the Nyquist rate as in conventional delay-sum beamformers. Specifically, a block of consecutive SDM samples for each focal point is selected on each channel according to the focusing delay. The data blocks for all channels are then added up on a bit-to-bit basis and the resulting block of multibit samples is fed to the demodulation filter to produce the focused signal. Since the SDM samples in each data block are not altered at all, the proposed method does not cause any signal distortion. Two hardware structures are also proposed for minimum hardware implementation of the proposed error-free SDM beamforming method. It is verified that compared to the delay-sum beamformer using 10-bit ADCs, the proposed algorithm provides almost the same image quality with a greatly reduced hardware complexity. In addition, it can be implemented with a lower hardware complexity than that of the conventional SDM beamformer when the number of channels is 64 or less.
ARFI Ultrasound for In Vivo Hemostasis Assessment Postcardiac Catheterization, Part I: Preclinical Studies
Authors: Behler Russell H. , Scola Mallory R. , Nichols Timothy C. , Bellinger Dwight A. , Gallippi Caterina M.
Published: March 2013

The world wide prevalence of cardiovascular disease leads to over seven million annual percutaneous coronary catheterization procedures, the majority of which exploit femoral artery access. Femoral puncture sites (‘arteriotomies’) can be associated with severe vessel complications after sheath removal if hemostasis is not properly achieved. Hemostasis onset is routinely determined by examination for bleeding at the skin puncture; however, clotting along the puncture path can obscure subcutaneous bleeding, and therefore hemostasis is blindly assessed. We hypothesize that hemostasis assessment can be un-blinded by Acoustic Radiation Force Impulse (ARFI) ultrasound. In this first of a two-part series, we present in vivo ARFI hemostasis imaging data obtained in relevant canine models of femoral artery puncture. Above arteriotomies, ARFI-induced displacements were large (3.5 to>5.0 μm) relative to surrounding soft tissue soon after needle removal, which was consistent with our expectation for pooled extravasated blood. ARFI-induced displacements above arteriotomies decreased in magnitude (to ∼ 2μm) some time after needle removal and suggested the onset of hemostasis. This preclinical investigation served as proof of concept and justification for a pilot human study, which is presented in part two of this series.
In Vivo Cardiac, Acoustic-Radiation-Force-Driven, Shear Wave Velocimetry
Authors: Bouchard Richard R. , Hsu Stephen J. , Wolf Patrick D. , Trahey Gregg E.
Published: March 2013

Shear wave elasticity imaging (SWEI) was employed to track acoustic radiation force impulse (ARFI)-induced shear waves in the mid-myocardium of the left ventricular free wall (LVFW) of a beating canine heart. Shear waves were generated and tracked with a linear ultrasound transducer that was placed directly on the exposed epicardium. Acquisition was ECG-gated and coincided with the mid-diastolic portion of the cardiac cycle. Axial displacement profiles consistent with shear wave propagation were clearly evident in all SWEI acquisitions (i.e., those including an ARFI excitation); displacement data from control cases (i.e., sequences lacking an ARFI excitation) offered no evidence of shear wave propagation and yielded a peak absolute mean displacement below 0.31 μm after motion filtering. Shear wave velocity estimates ranged from 0.82 to 2.65 m/s and were stable across multiple heartbeats for the same interrogation region, with coefficients of variation less than 19% for all matched acquisitions. Variations in velocity estimates suggest a spatial dependence of shear wave velocity through the mid-myocardium of the LVFW, with velocity estimates changing, in limited cases, through depth and lateral position.
New Fabrication Techniques for Ring-Array Transducers for Real-Time 3D Intravascular Ultrasound
Authors: Light Edward D. , Lieu Victor , Smith Stephen W.
Published: March 2013

We have previously described miniature 2D array transducers integrated into a Cook Medical, Inc. vena cava filter deployment device. While functional, the fabrication technique was very labor intensive and did not lend itself well to efficient fabrication of large numbers of devices. We developed two new fabrication methods that we believe can be used to efficiently manufacture these types of devices in greater than prototype numbers. One transducer consisted of 55 elements operating near 5 MHz. The interelement spacing is 0.20 mm. It was constructed on a flat piece of copper-clad polyimide and then wrapped around an 11 French catheter of a Cook Medical, Inc. inferior vena cava (IVC) filter deployment device. We used a braided wiring technology from Tyco Electronics Corp. to connect the elements to our real-time 3D ultrasound scanner. Typical measured transducer element bandwidth was 20% centered at 4.7 MHz and the 50 Ω round trip insertion loss was −82 dB. The mean of the nearest neighbor cross talk was −37.0 dB.

The second method consisted of a 46-cm long single layer flex circuit from MicroConnex that terminates in an interconnect that plugs directly into our system cable. This transducer had 70 elements at 0.157 mm interelement spacing operating at 4.8 MHz. Typical measured transducer element bandwidth was 29% and the 50 Ω round trip insertion loss was −83 dB. The mean of the nearest neighbor cross talk was −33.0 dB.
Optimal Transmit Phasing for Harmonic-Background Suppression with Bipolar Square-Wave Pulser
Authors: Shen Che-Chou , Yang Yun-Chian , Chen Wen-Shiang
Published: March 2013

Optimal transmit phasing has been proposed to increase contrast-to-tissue ratio (CTR) by relatively phasing the tissue and leakage harmonic components to cancel each other out for tissue-background suppression in harmonic imaging. Since most clinical systems are only equipped with a bipolar square-wave pulser, effective procedures for binary conversion of continuous transmit signals become essential in optimal transmit phasing to generate arbitrarily-phased bipolar waveforms. In this study, sigma-delta modulation is combined with code tuning to achieve this goal. Measurements of echoes from a wire phantom were performed to investigate the difference in harmonic suppression between the original transmit waveform and its bipolar counterpart. In-vivo cardiac imaging of a rabbit model was also established in the clinical ultrasound system to test the efficacy of a bipolar waveform in optimal transmit phasing. Our results indicate that although the harmonic magnitude becomes abrupt with the transmit phasing when a bipolar waveform is utilized in optimal transmit phasing, effective harmonic suppression is still achievable in the tissue background. Based on in-vivo images of seven consecutive cardiac cycles, a bipolar transmit waveform with the optimal suppression phase generally improves the CTR by 4.9 dB ( p<10−8). It should be noted, however, that the abrupt harmonic magnitude with transmit phasing could pose difficulties in the selection of the optimal suppression phase and thus limit the clinical applicability of optimal transmit phasing.
Effects of Ultrasound-Induced Inertial Cavitation on Enzymatic Thrombolysis
Authors: Chuang Yueh-Hsun , Cheng Po-Wen , Chen Szu-Chia , Ruan Jia-Ling , Li Pai-Chi
Published: March 2013

Cavitation induced by ultrasound enhances enzymatic fibrinolysis by increasing the transport of reactants. However, the effects of cavitation need to be fully understood before sonothrombolysis can be applied clinically. In order to understand the underlying mechanisms, we examined the effects of combining ultrasound, microbubbles and thrombolytic enzymes on thrombolysis. First, we evaluated the relations between inertial cavitation and the reduction in the weight of a blood clot. Inertial cavitation was varied by changing the amplitude and duration of the transmitted acoustic wave as well as the concentration of microbubbles used to induce cavitation. Second, we studied the combined effects of streptokinase and inertial cavitation on thrombolysis. The results show that inertial cavitation increases the weight reduction of a blood clot by up to 33.9%. With linear regression fitting, the measured differential inertial cavitation dose and the weight reduction had a correlation coefficient of 0.66. Microscopically, enzymatic thrombolysis effects manifest as multiple large cavities within the clot that are uniformly distributed on the side exposed to ultrasound. This suggests that inertial cavitation plays an important role in producing cavities, while microjetting of the microbubbles induces pits on the clot surface. These observations preliminarily demonstrate the clinical potential of sonothrombolysis. The use of the differential inertial cavitation dose as an indicator of blood clot weight loss for controlled sonothrombolysis is also possible and will be further explored.
Compression-Dependent Viscoelastic Behavior of Human Cervix Tissue
Authors: DeWall Ryan J. , Varghese Tomy , Kliewer Mark A. , Harter Josephine M. , Hartenbach Ellen M.
Published: March 2013

We have characterized the viscoelastic properties of human cervical tissue through a range of pre-compressional loads and testing frequencies. Mechanical testing is necessary to develop robust elasticity-based techniques for the diagnosis of cervical abnormalities. The storage modulus ( E′) and material damping (tan δ) were measured in 13 patients, 40 to 76 years old. Our results showed that E′ increased monotonically from approximately 4.7 to 6.3 kPa over the precompression range (1–6%) for a testing frequency of 1 Hz. Increases in precompressions of 4% or greater significantly increased E′ obtained after dynamic compression testing when data were normalized to 1% precompression. Tan δ remained fairly constant (∼0.35) and was not significantly affected by changes in precompression. E′ and tan δ increased significantly with frequency. E′ monotonically increased from 4.7 to 7.9 kPa for the 1–3% compression range (lowest precompression for 2% amplitude) and from 6.3 to 10.3 kPa for the 6–8% range (highest precompression for 2% amplitude) when increasing frequency from 1 to 30 Hz. Tan δ increased montonically from 0.35 to 0.45 for 2% amplitude compressions from 1 to 30 Hz regardless of initial precompression. Our results show that precompression and testing frequency must be taken into account in orderto obtain consistent measurements in mechanical diagnostic tests developed for cervical abnormalities.
Effect of Adaptive Threshold Filtering on Ultrasonic Nakagami Parameter to Detect Variation in Scatterer Concentration
Authors: Tsui Po-Hsiang , Wan Yung-Liang , Huang Chih-Chung , Wang Ming-Chen
Published: March 2013

The Nakagami parameter is associated with the Nakagami distribution estimated from ultrasonic backscattered signals and closely reflects the scatterer concentrations in tissues. There is an interest in exploring the possibility of enhancing the ability of the Nakagami parameter to characterize tissues. In this paper, we explore the effect of adaptive threshold filtering based on the noise-assisted empirical mode decomposition of the ultrasonic backscattered signals on the Nakagami parameter as a function of scatterer concentration for improving the Nakagami parameter performance. We carried out phantom experiments using 5 MHz focused and nonfocused transducers. Before filtering, the dynamic ranges of the Nakagami parameter, estimated using focused and nonfocused transducers between the scatterer concentrations of 2 and 32 scatterers/mm3, were 0.44 and 0.1, respectively. After filtering, the dynamic ranges of the Nakagami parameter, using the focused and nonfocused transducers, were 0.71 and 0.79, respectively. The experimental results showed that the adaptive threshold filter makes the Nakagami parameter measured by a focused transducer more sensitive to the variation in the scatterer concentration. The proposed method also endows the Nakagami parameter measured by a nonfocused transducer with the ability to differentiate various scatterer concentrations. However, the Nakagami parameters estimated by focused and nonfocused transducers after adaptive threshold filtering have different physical meanings: the former represents the statistics of signals backscattered from unresolvable scatterers while the latter is associated with stronger resolvable scatterers or local inhomogeneity due to scatterer aggregation.
Lesion Detectability in Diagnostic Ultrasound with Short-Lag Spatial Coherence Imaging
Authors: Dahl Jeremy J. , Hyun Dongwoon , Lediju Muyinatu , Trahey Gregg E.
Published: March 2013

We demonstrate a novel imaging technique, named short-lag spatial coherence (SLSC) imaging, which uses short distance (or lag) values of the coherence function of backscattered ultrasound to create images. Simulations using Field II are used to demonstrate the detection of lesions of varying sizes and contrasts with and without acoustical clutter in the backscattered data. B-mode and SLSC imaging are shown to be nearly equivalent in lesion detection, based on the contrast-to-noise ratio (CNR) of the lesion, in noise-free conditions. The CNR of the SLSC image, however, can be adjusted to achieve an optimal value at the expense of image smoothness and resolution. In the presence of acoustic clutter, SLSC imaging yields significantly higher CNR than B-mode imaging and maintains higher image quality than B-mode with increasing noise. Compression of SLSC images is shown to be required under high-noise conditions but is unnecessary under no- and low-noise conditions. SLSC imaging is applied to in vivo imaging of the carotid sheath and demonstrates significant gains in CNR as well as visualization of arterioles in the carotid sheath. SLSC imaging has a potential application to clutter rejection in ultrasonic imaging.
Ultrafast Photoacoustic Imaging and its Application to Real-Time 3D Imaging with Improved Focusing
Authors: Wang Yu-Hsin , Li Pai-Chi
Published: March 2013

The restricted temporal resolution of photoacoustic imaging due to limited frame rates often prohibits its applications in areas such as real-time 3D imaging. This paper presents an ultrasound/photoacoustic multimodality imaging system that provides an ultrafast frame rate and consists of an ultrasound transducer array with plane wave excitation and a laser with pulse repetition frequency up to 2,000 Hz. Its application to real-time 3D photoacoustic imaging is demonstrated and a synthetic-aperture focusing technique is applied to improve the elevational focusing quality of the mechanically-scanned 1D array. A 3D frame rate of 12 Hz in a volume covering a 19.2 mm × 19.2 mm scanning surface is demonstrated.
Progress in Ring Array Transducers for Real-Time 3D Ultrasound Guidance of Cardiac Interventional Devices
Authors: Light Edward D. , Lieu Victor , Smith Stephen W.
Published: March 2013

As a treatment for aortic stenosis, several companies have recently introduced prosthetic heart valves designed to be deployed through a catheter using an intravenous or transapical approach. This procedure can either take the place of open heart surgery with some of the devices or delay it with others. Real-time 3D ultrasound could enable continuous monitoring of these structures before, during and after deployment. We have developed a 2D ring array integrated with a 30 French catheter that is used for transapical prosthetic heart valve implantation. The transducer array was built using three 46 cm long flex circuits from MicroConnex (Snoqualmie, WA) which terminate in an interconnect that plugs directly into our system cable; thus, no cable soldering is required. This transducer consists of 210 elements at 0.157 mm interelement spacing and operates at 5 MHz. Average measured element bandwidth was 26% and average round-trip 50 ohm insertion loss was −58.1 dB after correcting for diffractive losses. The transducer was wrapped around the 1 cm diameter lumen of a heart-valve deployment catheter. Prosthetic heart valve images were obtained in water-tank studies.