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D.J. Sahn,
D.N. Stephens,
J.M. Cannata,
K. Kirk Shung,
O. Oralkan,
A. Nikoozadeh,
B.T. Khuri-Yakub, H. Nguyen,
P. Chen,
A.M. Dentinger,
D. Wildes,
K.E. Thomenius,
A. Mahajan,
K. Shivkumar,
M. O'Donnell
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ABSTRACT: Our Bioengineering Research Partnership grant, ldquoHigh Frequency Ultrasound Arrays for Cardiac Imagingrdquo, 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 capacitive 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.
Engineering in Medicine and Biology Society, 2009. EMBC 2009. Annual International Conference of the IEEE; 10/2009
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ABSTRACT: Lipid-encapsulated microbubbles have demonstrated utility in biomedical applications as ultrasound contrast agents and drug delivery vehicles. Current production methods of these microbubbles result in distributions with a large size variance. The size and monodispersity of ultrasound contrast agents are fundamentally important due to the relationship between bubble diameter and resonant frequency, destruction threshold, and susceptibility to radiation force. Several groups have recently developed microfluidic technologies for generation of microbubbles, but to date no group has demonstrated the production of shell-stabilized monodisperse contrast agents using these techniques. In this work, we use microfluidic-based flow focusing methods to produce monodisperse microbubbles in the diameter range required for in-vivo imaging. The diameter of the bubbles produced using this technique can be precisely tailored by adjusting the gas and liquid flow rate parameters. In order to stabilize the microbubbles for use as ultrasound contrast agents, we examine aqueous mixtures of glycerol/propylene glycol as well as stabilizing lipids. The effect of the lipid, emulsifier and viscosity agent concentration was found to be critical to stabilize the microbubbles. High-speed camera images and particle sizing analysis were combined to study the coalescence and dissolution phenomena as well as the size distribution. The concentration of the PEG-emulsifier and the existence of the viscosity agents determined the microbubble coalescence rate. Our experiments show that an optimum concentration of glycerol and propylene glycol in the liquid phase mixture reduces coalescence. Monodisperse microbubbles coated with a lipid-shell in a viscous solution were found to be stable up to three months
Ultrasonics Symposium, 2006. IEEE; 11/2006
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D.N. Stephens,
J. Cannata,
Ruibin Liu,
K.K. Shung,
O. Oralkan,
A. Nikoozadeh,
P. Khuri-Yakub, H. Nguyen,
R. Chia,
A. Dentinger,
D. Wildes,
K.E. Thomenius,
A. Mahajan,
K. Shivkumar,
K. Kim,
M. O'Donnell,
D. Sahn
[show abstract]
[hide abstract]
ABSTRACT: Minimally invasive electrophysiology interventions to treat cardiac arrhythmias are increasing worldwide due to advances in technologies that enable more effective clinical procedures. A forward imaging ultrasound catheter design has been developed and tested to advance the methods of integration of intracardiac imaging and electrophysiology sensing. The first catheters built have been constructed with a 9F (3 mm) shaft and a large (15F) tip to support experimental wire ports adjacent to a 24 element phased array operating at 14 MHz. The final tip design construction size will be 9F and possess an integrated metal electrode at the catheter distal end. Two forward looking array designs have been developed in parallel to produce two contrasting fine pitch (65 microns) 24 element phased array construction approaches. The first array has been assembled with a standard 2-2 composite PZT technology with the flex circuit mounted on the front facing side, and the second design is a cMUT version with a flip-chip bonded silicon die bonded to a backside flex circuit. The cMUT design requires a special interface to assure a safe element biasing scheme while enhancing the array's linearity and sensitivity. The first PZT array prototypes, built without explicit matching layers, have been characterized and agree with FEA and KLM analyses in operation at 14 MHz. Matching layer variations have been used on the front layer flex circuit to optimize the sensitivity and bandwidth of the PZT arrays while minimizing the thermal boundary layer. Specially designed assembly approaches addressed the challenging forward looking array configurations that utilize interconnection flex circuits with bend radii at 250 microns. Animal studies have been performed utilizing beam forming adaptations for the forward looking imaging catheter operation on a Vingmed Vivid-7 system. The first piezoceramic array devices were used successfully to image the myocardium of the right atrium of a pig while simult-
aneous tissue ablation was performed
Ultrasonics Symposium, 2006. IEEE; 11/2006
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ABSTRACT: Lubricant molecules on carbon surfaces are typically present in two distinctive chemical-physical environments, conventionally referred to as bonded and free lubricant. We observe and analyze the spectral shift in the lubricant FTIR spectrum using principal component analysis (PCA) to quantify and understand the bonded and free lubricant states for the lubricant systems Zdol, AM, and ZTetraol. In addition, we performed extended PCA to elucidate lubricant interactions with phosphazene additives. PCA of FTIR spectra is found to be a viable method in quantifying bonded lube ratio as well as in studying the mechanism of lubricant and phosphazene additive-carbon interactions.
IEEE Transactions on Magnetics 08/2004; · 1.36 Impact Factor
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ABSTRACT: We have explored the feasibility of an alternative strategy using biological signals such as sEMG of the sternocleidomastoid muscle (SCM) for variable control of our head movement system. Seven volunteers were instrumented with bilateral sEMG sensors on the SCM. Basic neck movements of lateral tilts and graded head rotations were performed. Data were normalized as a percentage of maximum voluntary contractions (MVC) for right and left sides, respectively. The contribution from ipsilateral sEMG signal as percentage of full-range was ∼75% for left and 55% for right head tilts. During head rotations at 30, 45, and 60° to both sides, results for sEMG signal amplitude as a percentage of MVC showed excellent reproducibility of the contralateral SCM at approximately 10%, 18%, and 32% on both sides. Despite the small number of subjects for a thorough statistical analysis, no differences exist in t-tests between sEMG (as % of MVC) right and left sides during head rotation; however, differences do exist for each level of rotation (p<0.01). Head rotation provided the most consistent sEMG signal correlation with the degree of motion in all subjects, allowing for reproducible proportional control for our head movement technology.
Engineering in Medicine and Biology Society, 2003. Proceedings of the 25th Annual International Conference of the IEEE; 10/2003
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ABSTRACT: Wafer level-chip scale packaging (WL-CSP) has become a popular packaging option in recent years due to its lower profile, faster signal transfer, and smaller size. These features represent the current industry trend toward high performance and miniaturization. Encapsulant materials are usually required to enhance CSP package reliability for thermal cycling and drop resistance. In addition, the encapsulant also provides a certain measure of environmental protection. Among current CSP packaging options such as standard underfill wicking and the so-called no-flow process, the wafer pre-apply process is the most cost-effective packaging method. The wafer level process increases production output and reduces the overall assembly cost significantly, while achieving comparable or better reliability. This paper provides details on the requirements of underfills applied to WL-CSPs, the properties of the new class of materials developed, the optimal wafer process and assembly conditions, and the reliability data obtained to date on WL-CSPs.
Electronic Components and Technology Conference, 2002. Proceedings. 52nd; 02/2002
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[show abstract]
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ABSTRACT: Underfill materials play a major role in the reliability of flip chip packages. These adhesives have been the subject of much research and development in the last few years, and improvement in material performance has been obtained. However, the assembly method still remains unchanged, with the underfill being dispensed at the individual die level after flip chip reflow. Even with the arrival of "no-flow" underfills, assembly still requires depositing the underfill material onto the flip chip site prior to positioning the flip chip die. Processing underfill at the wafer level brings in a new paradigm shift to the area of flip chip packaging. Precoating the wafer with the underfill. will create significant savings in both time and money. The application cycle time of the wafer level process becomes equivalent to one single dispensing operation. This paper will present and discuss the latest results obtained with stencil printing used as the application method for the wafer level process. Several experimental underfill formulations were tested as a function of various printing conditions. With the optimal process conditions, the desired coating thickness can be applied without damage to bumped wafers. Assembly challenges together with reliability data are presented.
Electronics Manufacturing Technology Symposium, 2002. IEMT 2002. 27th Annual IEEE/SEMI International; 02/2002
