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The Journal of the Acoustical Society of America 08/2012; 132(2):1247. · 1.55 Impact Factor
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ABSTRACT: A ring array provides a very suitable geometry for forward-looking volumetric intracardiac and intravascular ultrasound imaging. We fabricated an annular 64-element capacitive micromachined ultrasonic transducer (CMUT) array featuring a 10-MHz operating frequency and a 1.27-mm outer radius. A custom software suite was developed to run on a PC-based imaging system for real-time imaging using this device. This paper presents simulated and experimental imaging results for the described CMUT ring array. Three different imaging methods--flash, classic phased array (CPA), and synthetic phased array (SPA)--were used in the study. For SPA imaging, two techniques to improve the image quality--Hadamard coding and aperture weighting--were also applied. The results show that SPA with Hadamard coding and aperture weighting is a good option for ring-array imaging. Compared with CPA, it achieves better image resolution and comparable signal-to-noise ratio at a much faster image acquisition rate. Using this method, a fast frame rate of up to 463 volumes per second is achievable if limited only by the ultrasound time of flight; with the described system we reconstructed three cross-sectional images in real-time at 10 frames per second, which was limited by the computation time in synthetic beamforming.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control 06/2012; 59(6):1201-11. · 1.80 Impact Factor
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ABSTRACT: Thermal strain imaging (TSI) or temporal strain imaging is an ultrasound application that exploits the temperature dependence of sound speed to create thermal (temporal) strain images. This article provides an overview of the field of TSI for biomedical applications that have appeared in the literature over the past several years. Basic theory in thermal strain is introduced. Two major energy sources appropriate for clinical applications are discussed. Promising biomedical applications are presented throughout the paper, including non-invasive thermometry and tissue characterization. We present some of the limitations and complications of the method. The paper concludes with a discussion of competing technologies.
Interface focus: a theme supplement of Journal of the Royal Society interface 08/2011; 1(4):649-64.
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Chi Hyung Seo,
Douglas N Stephens,
Jonathan Cannata,
Aaron Dentinger,
Feng Lin,
Suhyun Park,
Douglas Wildes,
Kai E Thomenius,
Peter Chen,
Tho Nguyen,
Alan de La Rama,
Jong Seob Jeong,
Aman Mahajan,
Kalyanam Shivkumar,
Amin Nikoozadeh,
Omer Oralkan,
Uyen Truong,
David J Sahn,
Pierre T Khuri-Yakub, Matthew O'Donnell
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ABSTRACT: A method is introduced to monitor cardiac ablative therapy by examining slope changes in the thermal strain curve caused by speed of sound variations with temperature. The sound speed of water-bearing tissue such as cardiac muscle increases with temperature. However, at temperatures above about 50°C, there is no further increase in the sound speed and the temperature coefficient may become slightly negative. For ablation therapy, an irreversible injury to tissue and a complete heart block occurs in the range of 48 to 50°C for a short period in accordance with the well-known Arrhenius equation. Using these two properties, we propose a potential tool to detect the moment when tissue damage occurs by using the reduced slope in the thermal strain curve as a function of heating time. We have illustrated the feasibility of this method initially using porcine myocardium in vitro. The method was further demonstrated in vivo, using a specially equipped ablation tip and an 11-MHz microlinear intracardiac echocardiography (ICE) array mounted on the tip of a catheter. The thermal strain curves showed a plateau, strongly suggesting that the temperature reached at least 50°C.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control 07/2011; 58(7):1406-17. · 1.80 Impact Factor
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ABSTRACT: In ultrasound strain and elasticity imaging, an accurate and cost-effective sub-pixel displacement estimator is required because strain/elasticity imaging quality relies on the displacement SNR, which can often be higher if more computational resources are provided. In this paper, we introduce an autocorrelation-based method to cost-effectively improve subpixel displacement estimation quality. To quantitatively evaluate the performance of the autocorrelation method, simulated and tissue-mimicking phantom experiments were performed. The computational cost of the autocorrelation method is also discussed. The results of our study suggest the autocorrelation method can be used for a real-time elasticity imaging system.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control 04/2011; 58(4):838-43. · 1.80 Impact Factor
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ABSTRACT: Ultrasound strain imaging has been proposed to quantitatively assess myocardial contractility. Cross-correlation-based 2-D speckle tracking (ST) and auto-correlation-based tissue Doppler imaging (TDI) [often called Doppler tissue imaging (DTI)] are competitive ultrasound techniques for this application. Compared with 2-D ST, TDI, as a 1-D method, is sensitive to beam angle and suffers from low strain signal-to-noise ratio because a high pulse repetition frequency is required to avoid aliasing in velocity estimation. In addition, ST and TDI are fundamentally different in the way that physical parameters such as the mechanical strain are derived, resulting in different estimation accuracy and interpretation. In this study, we directly compared the accuracy of TDI and 2-D ST estimates of instantaneous axial normal strain and accumulated axial normal strain using a simulated heart. We then used an isolated rabbit heart model of acute ischemia produced by left descending anterior artery ligation to evaluate the performance of the two methods in detecting abnormal motion. Results showed that instantaneous axial normal strains derived using TDI (0.36% error) were less accurate with larger variance than those derived from 2-D ST (0.08% error) given the same spatial resolution. In addition to poorer accuracy, accumulated axial normal strain estimates derived using TDI suffered from bias, because the accumulation method for TDI cannot trace along the actual tissue displacement path. Finally, we demonstrated the advantage 2-D ST has over TDI to reduce dependency on beam angle for lesion detection by estimating strains based on the principal stretches and their corresponding principal axes.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control 11/2010; 57(11):2491-502. · 1.80 Impact Factor
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ABSTRACT: Enhanced optical breakdown of KB tumor cells folate-targeted with silver-dendrimer composite nanodevices (CNDs) is described. CNDs [(Ag(0))(25)-PAMAM_E5.(NH(2))(42)(NGly)(74)(NFA)(2.7)] were fabricated by reactive encapsulation, using a biocompatible template of dendrimer-folic acid (FA) conjugates. Preferential uptake of the folate-targeted CNDs (of various treatment concentrations and surface functionality) by KB cells was visualized with confocal microscopy and transmission electron microscopy. Intracellular laser-induced optical breakdown threshold and dynamics were detected and characterized by high-frequency ultrasonic monitoring of resulting transient bubble events. When irradiated with a near-infrared, femtosecond laser, the CND-targeted KB cells acted as well-confined activators of laser energy, enhancing nonlinear energy absorption, exhibiting a significant reduction in breakdown threshold and thus selectively promoting intracellular laser-induced optical breakdown. FROM THE CLINICAL EDITOR: This study presents a novel method to selectively destroy cancer cells by combining biochemical targeting with topical laser irradiation. A human epidermoid cancer cell line was targeted with folated silver-dendrimer composite nanodevices and the labeled cancer cells were subsequently destroyed by the microbubbles generated due the enhanced energy uptake of the silver nanoparticles from the laser irradiation, as compared to unlabeled cells.
Nanomedicine: nanotechnology, biology, and medicine 09/2010; 7(1):97-106. · 5.44 Impact Factor
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ABSTRACT: Engineering compact imaging probes with highly integrated modalities is a key focus in bionanotechnology and will have profound impact on molecular diagnostics, imaging and therapeutics. However, combining multiple components on a nanometre scale to create new imaging modalities unavailable from individual components has proven to be challenging. In this paper, we demonstrate iron oxide and gold-coupled core-shell nanoparticles (NPs) with well-defined structural characteristics (for example, size, shell thickness and core-shell separation) and physical properties (for example, electronic, magnetic, optical, thermal and acoustic). The resulting multifunctional nanoprobes not only offer contrast for electron microscopy, magnetic resonance imaging and scattering-based imaging but, more importantly, enable a new imaging mode, magnetomotive photoacoustic imaging, with remarkable contrast enhancement compared with photoacoustic images using conventional NP contrast agents.
Nature Communications 07/2010; 1:41. · 7.40 Impact Factor
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Article:
BiOS
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ABSTRACT: Ultrasonic (US) imaging is the most common real-time modality, providing multiple dimensional changes in morphology for clinical practice. Photoacoustic (PA) imaging has demonstrated great promise as a new functional and molecular imaging tool. However, absorption in background tissue also generates a PA signal and limits the specific contrast of molecular contrast agents. To increase the linear range of these agents, the background must be suppressed. Magnetic nanoparticles provide a new possibility to increase contrast by magnetomotive manipulation during imaging. A multi-functional imaging system integrating US and PA imaging with magnetic manipulation can take advantage of each single modality by providing anatomical images and molecular function with greater contrast. However, one key issue for multi-functional imaging is how to spatially combine and temporarily synchronize US and PA imaging with magnetomotive instrumentation. In this study, we built a simple system to integrate US and PA imaging with magnetomotive capability. We evaluated this system by measuring the motion of a phantom including magnetic nanoparticles (MNPs) using US when these particles were subjected to a time-varying magnetic field.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
02/2010;
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B T Khuri-Yakub,
Omer Oralkan,
Amin Nikoozadeh,
Ira O Wygant,
Steve Zhuang,
Mustafa Gencel,
Jung Woo Choe,
Douglas N Stephens,
Alan de la Rama,
Peter Chen,
Feng Lin,
Aaron Dentinger,
Douglas Wildes,
Kai Thomenius,
Kalyanam Shivkumar,
Aman Mahajan,
Chi Hyung Seo, Matthew O'Donnell,
Uyen Truong,
David J Sahn
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ABSTRACT: Capacitive micromachined ultrasonic transducer (CMUT) arrays are conveniently integrated with frontend integrated circuits either monolithically or in a hybrid multichip form. This integration helps with reducing the number of active data processing channels for 2D arrays. This approach also preserves the signal integrity for arrays with small elements. Therefore CMUT arrays integrated with electronic circuits are most suitable to implement miniaturized probes required for many intravascular, intracardiac, and endoscopic applications. This paper presents examples of miniaturized CMUT probes utilizing 1D, 2D, and ring arrays with integrated electronics.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2010; 2010:5987-90.
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ABSTRACT: We present differential-absorption photoacoustic imaging, which detects the difference between transient and ground-state absorption, for contrast enhancement based on suppressing undesired objects. Two tubes were imaged. One contains a Pt(II) octaethylporphine (PtOEP) dye solution and serves as an object of interest, while the other contains an IR-783 (from Sigma-Aldrich) dye solution and serves as an object to suppress. Although the IR-783 tube dominates the conventional photoacoustic image, it is suppressed by 43 dB and consequently significantly overwhelmed by the PtOEP tube in the differential-absorption photoacoustic image. Imaging depth in this mode is also discussed.
Optics Letters 09/2009; 34(16):2393-5. · 3.40 Impact Factor
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Congxian Jia,
Ragnar Olafsson,
Kang Kim,
Theodore J Kolias,
Jonathan M Rubin,
William F Weitzel,
Russell S Witte,
Sheng-Wen Huang,
Michael S Richards,
Cheri X Deng, Matthew O'Donnell
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ABSTRACT: Ultrasound strain imaging using 2-D speckle tracking has been proposed to quantitatively assess changes in myocardial contractility caused by ischemia. Its performance must be demonstrated in a controlled model system as a step toward routine clinical application. In this study, a well-controlled 2-D cardiac elasticity imaging technique was developed using two coplanar and orthogonal linear probes simultaneously imaging an isolated retroperfused rabbit heart. Acute ischemia was generated by left anterior descending (LAD) artery ligation. An excitation-contraction decoupler, 2,3-butanedione monoxime, was applied at a 4-mM concentration to reversibly reduce myocardial contractility. Results using a single probe demonstrate that directional changes in the in-plane principal deformation axes can help locate the bulging area as a result of LAD ligation, which matched well with corresponding Evans Blue staining, and strains or strain magnitude, based on principal stretches, can characterize heart muscle contractility. These two findings using asymmetric displacement accuracy (i.e., normal single-probe measurements with good axial but poor lateral estimates) were further validated using symmetric displacement accuracy (i.e., dual-probe measurements using only accurate axial tracking estimates from each). However, the accuracy of 2-D cardiac strain imaging using a single probe depends on the probe's orientation because of the large variance in lateral displacement estimates.
Ultrasound in medicine & biology 08/2009; 35(9):1488-501. · 2.02 Impact Factor
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ABSTRACT: Sound waves generated by light are the basis of a sensitive medical imaging technique with applications to cancer diagnosis and treatment.
Physics Today 05/2009; 62(8):34-39. · 5.65 Impact Factor
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ABSTRACT: We describe the first mapping of biological current in a live heart using ultrasound current source density imaging (UCSDI). Ablation procedures that treat severe heart arrhythmias require detailed maps of the cardiac activation wave. The conventional procedure is time-consuming and limited by its poor spatial resolution (5-10 mm). UCSDI can potentially improve on existing mapping procedures. It is based on a pressure-induced change in resistivity known as the acousto-electric (AE) effect, which is spatially confined to the ultrasound focus. Data from 2 experiments are presented. A 540 kHz ultrasonic transducer (f/# = 1, focal length = 90 mm, pulse repetition frequency = 1600 Hz) was scanned over an isolated rabbit heart perfused with an excitation-contraction decoupler to reduce motion significantly while retaining electric function. Tungsten electrodes inserted in the left ventricle recorded simultaneously the AE signal and the low-frequency electrocardiogram (ECG). UCSDI displayed spatial and temporal patterns consistent with the spreading activation wave. The propagation velocity estimated from UCSDI was 0.25 +/- 0.05 mm/ms, comparable to the values obtained with the ECG signals. The maximum AE signal-to-noise ratio after filtering was 18 dB, with an equivalent detection threshold of 0.1 mA/ cm(2). This study demonstrates that UCSDI is a potentially powerful technique for mapping current flow and biopotentials in the heart.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control 04/2009; 56(3):565-74. · 1.80 Impact Factor
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Douglas N Stephens, Matthew O'Donnell,
Kai Thomenius,
Aaron Dentinger,
Douglas Wildes,
Peter Chen,
K Kirk Shung,
Jonathan Cannata,
Pierre Khuri-Yakub,
Omer Oralkan,
Aman Mahajan,
Kalyanam Shivkumar,
David J Sahn
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ABSTRACT: The purpose of this study was to develop a high-resolution, near-field-optimized 14-MHz, 24-element broad-bandwidth forward-looking array for integration on a steerable 9F electrophysiology (EP) catheter.
Several generations of prototype imaging catheters with bidirectional steering, termed microlinear (ML), were built and tested as integrated catheter designs with EP sensing electrodes near the tip. The wide-bandwidth ultrasound array was mounted on the very tip, equipped with an aperture of only 1.2 by 1.58 mm. The array pulse echo performance was fully simulated, and its construction offered shielding from ablation noise. Both ex vivo and in vivo imaging with a porcine animal model were performed.
The array pulse echo performance was concordant with Krimholtz-Leedom-Matthaei model simulation. Three generations of prototype devices were tested in the right atrium and ventricle in 4 acute pig studies for the following characteristics: (1) image quality, (2) anatomic identification, (3) visualization of other catheter devices, and (4) for a mechanism for stabilization when imaging ablation. The ML catheter is capable of both low-artifact ablation imaging on a standard clinical imaging system and high-frame rate myocardial wall strain rate imaging for detecting changes in cardiac mechanics associated with ablation.
The imaging resolution performance of this very small array device, together with its penetration beyond 2 cm, is excellent considering its very small array aperture. The forward-looking intracardiac catheter has been adapted to work easily on an existing commercial imaging platform with very minor software modifications.
Journal of ultrasound in medicine: official journal of the American Institute of Ultrasound in Medicine 03/2009; 28(2):207-15. · 1.25 Impact Factor
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IEEE transactions on ultrasonics, ferroelectrics, and frequency control 01/2009; 55(12):2719-25. · 1.80 Impact Factor
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David J Sahn,
Douglas N Stephens,
Jonathan M Cannata,
K Shung,
Omer Oralkan,
Amin Nikoozadeh,
B T Pierre Khuri-Yakub,
Hien Nguyen,
Peter Chen,
Aaron M Dentinger,
Douglas Wildes,
Kai E Thomenius,
Aman Mahajan,
Kalyanam Shivkumar, Matthew O'Donnell
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ABSTRACT: Our Bioengineering Research Partnership grant, -High Frequency Ultrasound Arrays for Cardiac Imaging", including the individuals cited at the end of this paper - Douglas N. Stephens (UC Davis), Matthew O'Donnell (UW Seattle), Kai Thomenius (GE Global Research), Aaron M. Dentinger (GE Global Research), Douglas Wildes (GE Global Research), Peter Chen (St. Jude Medical), K. Kirk Shung (University of Southern California), Jonathan M. Cannata (University of Southern California), Butrus (Pierre) T. Khuri-Yakub (Stanford University), Omer Oralkan (Stanford University), Aman Mahajan (UCLA School of Medicine), Kalyanam Shivkumar (UCLA School of Medicine) and David J. Sahn (Oregon Health & Science University) - is in its sixth year of NIH funding, having proposed to develop a family of high frequency miniaturized forward and side-looking ultrasound imaging devices equipped with electrophysiology mapping and localization sensors and eventually to include a family of capactive micromachined ultrasonic transducer (cMUT) devices - a forward-looking cMUT MicroLinear array and a ring array capable of 3-dimensional imaging and a 5Fr lumen large enough to admit an electrode and ablation devices.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2009; 2009:1913-7.
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ABSTRACT: Accurate, noninvasive characterization of arterial wall mechanics and detection of fibrotic vascular lesions could vastly improve the ability to predict patient response to local treatments such as angioplasty. Current imaging and other techniques for determining wall compliance rely on imprecise or indirect estimates of wall motion. This study used high-resolution ultrasound imaging with phase-sensitive speckle tracking to obtain detailed and direct measurements of arterial stiffness in two subjects with dialysis fistula dysfunction. In both subjects, the absolute values of strain were much higher in normal regions of fistula than in regions of stenosis. The lower values of strain in stenotic fistula indicate greater stiffness of the vessel wall. The ultrasound speckle tracking technique used here may have potential to determine vascular mechanical properties noninvasively with a level of precision and accuracy not currently available.
Seminars in Dialysis 10/2008; 22(1):84-9. · 2.27 Impact Factor
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ABSTRACT: Surgery to correct severe heart arrhythmias usually requires detailed maps of the cardiac activation wave prior to ablation. The pinpoint electrical mapping procedure is laborious and limited by its spatial resolution (5-10 mm). We propose ultrasound current source density imaging (UCSDI), a direct 3-D imaging technique that potentially facilitates existing mapping procedures with superior spatial resolution. The technique is based on a pressure-induced change in resistivity known as the acoustoelectric (AE) effect, which is spatially confined to the ultrasound focus. AE-modulated voltage recordings are used to map and reconstruct current densities. In this preliminary study, we tested UCSDI under controlled conditions and compared it with conventional electrical mapping techniques. A 2-D dipole field was produced by a pair of electrodes in a bath of 0.9% NaCl solution. Boundary electrodes detected the AE signal while a 7.5-MHz focused ultrasound transducer was scanned across the bath. UCSDI located the current source and sink to within 1 mm of their actual positions. A future UCSDI system potentially provides real-time 3-D images of the cardiac activation wave coregistered with anatomical ultrasound and would greatly facilitate corrective procedures for heart abnormalities.
IEEE transactions on bio-medical engineering 08/2008; 55(7):1840-8. · 2.15 Impact Factor
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ABSTRACT: Polymer microring resonators for low-noise, wideband ultrasound detection are presented. Using a nanoimprinting technique, we fabricated polymer microring resonators with a quality factor of 6000 resulting in high sensitivity to ultrasound. A noise-equivalent pressure of 0.23 kPa over 1-75 MHz and a detection bandwidth of over 90 MHz at -3 dB were measured. These results demonstrate the potential of polymer microring resonators for high-frequency ultrasound and photoacoustic imaging. For a typical photoacoustic imaging test case, the high sensitivity demonstrated in these devices would increase imaging depth by a factor of 3 compared to state-of-the-art polyvinylidene fluoride detectors.
Applied Physics Letters 06/2008; 92(19):193509-1935093. · 3.84 Impact Factor
