Search

When comparing the performance of different industrial X-ray computed tomography (CT) systems, reconstruction algorithms, or scan protocols, it is important to assess how well the required inspection and measurement tasks can be performed. Furthermore, it can be very informative to quantify image quality (IQ) metrics that can provide insight into the IQ characteristics that lead to the resulting inspection or measurement task performance. Inspection and measurement task performance is determined by basic characteristics such as spatial resolution; feature contrast, size, and shape; random noise (noise due to statistical uncertainty in measurements); and image artifacts. In this report, we describe a modular phantom set that enables robustly quantifying these characteristics and also enables assessing the performance of the inspection or measurement tasks themselves. The phantom set includes two phantom bodies and several insert types that can be optionally installed in the bodies. Phantom body extensions can be optionally included to increase scatter. The phantom bodies combined with the available insert types can comprehensively evaluate all important IQ metrics and inspection or measurement tasks. The precisely-known phantom body geometry and insert location, geometry, and orientation supports automatic analysis of large, complex experiments of multiple variables. This phantom set, with the associated image analysis software, could potentially serve as a general evaluation method for non-destructive testing (NDT) CT.

Objective: The objective is enhanced ophthalmic ultrasound imaging to monitor ocular structure and intracranial dynamics changes related to visual impairment and intracranial pressure (ICP) induced by microgravity. The goals are to improve the ease of use and reduce operator variability by automatically rendering improved views of the anatomy and deriving new metrics of the morphology and dynamics.

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.

Minimally invasive catheter-based electrophysiological (EP) interventions are becoming a standard procedure in diagnosis and treatment of cardiac arrhythmias. As a result of technological advances that enable small feature sizes and a high level of integration, nonfluoroscopic intracardiac echocardiography (ICE) imaging catheters are attracting increasing attention. ICE catheters improve EP procedural guidance while reducing the undesirable use of fluoroscopy, which is currently the common catheter guidance method. Phased-array ICE catheters have been in use for several years now, although only for side-looking imaging. We are developing a forward-looking ICE catheter for improved visualization. In this effort, we fabricate a 24-element, fine-pitch 1-D array of capacitive micromachined ultrasonic transducers (CMUT), with a total footprint of 1.73 mm x 1.27 mm. We also design a custom integrated circuit (IC) composed of 24 identical blocks of transmit/ receive circuitry, measuring 2.1 mm x 2.1 mm. The transmit circuitry is capable of delivering 25-V unipolar pulses, and the receive circuitry includes a transimpedance preamplifier followed by an output buffer. The CMUT array and the custom IC are designed to be mounted at the tip of a 10-Fr catheter for high-frame-rate forward-looking intracardiac imaging. Through-wafer vias incorporated in the CMUT array provide access to individual array elements from the back side of the array. We successfully flip-chip bond a CMUT array to the custom IC with 100% yield. We coat the device with a layer of polydimethylsiloxane (PDMS) to electrically isolate the device for imaging in water and tissue. The pulse-echo in water from a total plane reflector has a center frequency of 9.2 MHz with a 96% fractional bandwidth. Finally, we demonstrate the imaging capability of the integrated device on commercial phantoms and on a beating ex vivo rabbit heart (Langendorff model) using a commercial ultrasound imaging system.

Catheter-based electrophysiology (EP) testing and transcatheter radio frequency (RF) ablation are well-established modalities for the diagnosis and treatment of many types of arrhythmias.1–6 Catheter ablation can be performed in any chamber of the heart and in patients with diverse structural cardiac abnormalities,7 including infants and children.8,9 Catheter ablation requires precise localization of structures within the heart, real-time intracardiac hemodynamics, and accurate identification of important anatomic landmarks and the catheter position. Currently available approaches to spatial guidance and anatomic localization of the ablation are electroanatomic (EA) mapping,10,11 fluoroscopy,11,12 and echocardiography. Preliminary reports have shown the use of intracardiac imaging during catheter ablation to assist in identifying endocardial contact and lesion formation.13,14 Intracardiac echocardiography (ICE) has allowed imaging from the right side of the heart for imaging both right- and left-sided cardiac chambers and structures.15–23 Although the earlier devices were lower-frequency versions of intracoronary intravascular ultrasound devices (often mechanically driven), later devices also provided color and spectral Doppler imaging. In 1995, a 10F steerable (±25°–30°) side-looking AcuNav catheter device (Acuson; Siemens Medical Solutions, Mountain View, CA) was approved for intracardiac imaging from the right side of the heart in patients. It functions as a vector array with a 5.5- to 10-MHz frequency. Although animal studies have suggested very high-quality imaging and ease of use, human studies have identified problems related to near-field resolution and color Doppler quality as well as difficulty in imaging larger abnormal structures at a distance of greater than 8 cm from the probe.24 In addition, the cost of these devices as single-use products has spurred the formation of a network of secondary vendors that provide resterilization of AcuNav catheters with varying levels of performance verification. With our 2001 National Institutes of Health Bioengineering Research Partnership grant, funded for 5 years by the National Heart, Lung, and Blood Institute, we proposed to build an advanced imaging device that combines the advantages of electrical mapping and ablation with 2-dimensional (2D) echocardiography, tissue velocity imaging (TVI), and strain rate imaging (SRI). The ICE device was designed to provide ultrasound imaging and procedural guidance for EP-based rhythm analysis, ablation, and resynchronization. This report details the development and initial experimental animal studies of the applicability of our 9F side-looking ultrasound array catheter, which, because of its substantial flexibility of steering, we have dubbed the hockey stick (HS). It is electrode equipped for EP recording and 3-dimensional (3D) NavX guidance integration (St Jude Medical Corp, Minneapolis, MN), and its development was supported by the National Institutes of Health Bioengineering Research Partnership cited above. The study tested the hypothesis that this new device could be built to run on a Vivid 7 scanner (GE Healthcare, Milwaukee, WI) and could image cardiac anatomy to locate landmarks, visualize ablation performed with other devices, and, using online strain and tissue Doppler methods, show the changes in regional mechanics or the propagation of contraction occurring after ablation- or pacing-induced changes in regional synchrony. We also evaluated the integration of 3D electrofield fusion mapping and display of our devices with the NavX system.

The detection and quantification of carotid artery stenosis guides the decision of the need for surgical intervention such as endarterectomy or stenting of a patient. Contrast enhanced ultrasound highlights detailed information on hemodynam-ics and even on pathophysiology, and 3D scans yield full in-situ information of the complete anatomy. We introduce 3D image analysis algorithms that enable quantification and visualization of the carotid lumen in these scans. Our method enhances the lumen intensity contrast, extracts lumen centerlines using a gradient concentration calculation, and then uses a graph search method to obtain a coarse lumen segmentation, which is refined through a level set method applied on an intensity-corrected image. We processed 35 images acquired from 7 patients, and demonstrated quantitative comparisons with MR/CT lumen segmentations. We obtained a segmentation correlation score of R2 = 0.94 and a coefficient of 0.99 for US versus MR/CT through a linear regression on effective diameters extracted from slices in the XY-plane.

Introduction: Vulnerable plaque is marked by increased intra-plaque vascularity, hemorrhage and is associated with cerebrovascular (CV) events. Current use of 2D CEUS carotid imaging does not provide a true volumetric representation of the intra-plaque angiogenesis. Therefore, this is the first clinical trial using 3D CEUS to assess intra-plaque angiogenesis, in patients with clinically significant plaques prior to carotid endarterectomy (CEA). Methods: Data were acquired on 11 patients that were asked to participate in this pilot study prior to CEA. All patients had MR and/or CT angiogram as part of their standard care and all carotid artery plaque specimens were collected and sent for histologic evaluation. CEUS volumes were acquired using a GE LOGIQ E9, RSP6-16 4D probe and Optison. In order to assess plaque vulnerability, semi-automatic image analysis algorithms were developed to segment the lumen, plaque, and intra-plaque vascularity. Measurements derived from 3D CEUS images were validated against CT, MR, and histology. Results: Preliminary results from 3 patients were analyzed and lumen volumes were segmented from all available modalities (figure shows CEUS example). Lumen measurements of the CCA, ICA, and ECA from 3D CEUS were compared to MR or CT. High correlation is shown in the figure for these patients (R 2 =0.95). Further analysis of the 3D CEUS images demonstrates that we can identify intra-plaque vascularity (see segmentation from one patient). These CEUS results estimated an average cross-sectional vascular density of 7-11% in the plaque, matching histology estimates of 10% from a single slice. Conclusion: These results demonstrate that it is feasible to use 3D CEUS for quantitative, volumetric imaging of the carotid artery and intra-plaque angiogenesis in patients scheduled for CEA. Future work will extend this analysis to all patients and make a quantitative comparison of intra-plaque vascular density from 3D CEUS vs. multiple histology slices.

In this paper we describe a fast method to segment and track a vessel of interest in 4D (i.e. 3D + time) Ultrasound images. An initial 2D seed is used to initialize a single spatial Kalman-Filter tracker which tracks the vessel center-line in 3D. The 3D vessel is then segmented using a fast area weighted active contour method. This segmented 3D vessel is then tracked across multiple time-points using a set of temporal Kalman- Filters which track the movement of the center of the vessel in each 2D slice. The vessel boundaries are estimated by growing an area weighted active contour outward from the centerline. Based on qualitative as well as quantitative performance measures, the proposed method shows promising tracking results on numerous phantom as well as patient datasets.

Electrophysiologic interventions have had increasing popularity as treatment options for arrhythmias, particularly atrial fibrillation.1 Atrial fibrillation is the most common arrhythmia, with an incidence of 2 to 3 per 1000 people aged 55 to 64 years annually,2 and is associated with considerable morbidity and mortality.3,4 There are at least 3 techniques available to interventionalists that can accurately locate intracardiac regions of interest, with fluoroscopy being the most established technique. However, the exposure to ionizing radiation, as well as the inability of fluoroscopy to clearly delineate subsurface intracardiac regions and confirm catheter contact with the endocardium, has made echocardiography and electroanatomic mapping (EAM) the most attractive as adjunct modalities.5–9 Intracardiac echocardiography (ICE), in particular, has found multiple uses in the electrophysiology laboratory, providing real-time display of intracardiac structures.6–8 The use of ultrasound image guidance for interventional radiofrequency ablation (RFA) procedures in the heart has begun to play a more important role in the minimization of fluoroscopic radiation exposure to the patient while imaging important intracardiac features, eg, the membranous fossa of the interatrial septum for puncture access to the left atrium, the pulmonary veins, and Doppler blood velocities associated with pulmonary vein stenosis.10 Important considerations in the design of ICE catheters are the (1) imaging and handling performance features, (2), compatibility with current interventional practice, and (3) cost in both procedural time and purchasing expense. Overall, a catheter that can be itself guided into place with EAM, perform high-quality image guidance of RFA therapy, and improve procedural throughput at a lower cost is a worthwhile goal. As a general guide, Table 1 compares the common RFA catheter with an “ideal” catheter and with the initial features of a proposed progenitor, a microlinear capacitive micromachined ultrasound transducer (ML-CMUT) catheter. Table 1 Performance Parameter Objectives for Catheters Used in Radiofrequency Ablation Procedures The miniaturization of ICE catheters has revolutionized interventional procedures by integrating ultrasound transducers onto flexible, low-profile catheters, which allow imaging in the restricted spaces of vascular and cardiac structures.11–13 Two distinctly different ICE catheter prototypes, descriptively referred as ML catheters because of their small ultrasonic array designs, have been developed within a program to build a series of miniaturized high-frequency forward-looking transducer arrays.14 Piezoceramic arrays, namely those made with lead zirconate titanate (PZT), are considered standard design types for most ultrasound applications. Currently in their third generation of development, our early ML devices are called ML-PZT array catheters. The second array transducer type is the CMUT, now in its second generation of development15; these CMUT arrays are used in the assembly of the ML-CMUT array catheter (Figure 1). By comparison to PZT, the CMUT as an acoustic transducer is relatively new as an ultrasound transceiver. This silicon-based array, however, has several design aspects that may yield a considerable advantage over the PZT array type, especially at small sizes. The small-element CMUT array in combination with a local buffer-preamplifier offers excellent transmit and receive sensitivity with a wide bandwidth, allows special element shaping, does not require acoustic matching layers, and may be considerably less expensive in large-scale manufacturing. Figure 1 Prefinished distal tip (a) of the 9F microlinear capacitive micromachined ultrasound transducer (CMUT) intracardiac imaging catheter with a metal radiofrequency ablation tip electrode, and the 24-element CMUT array (b) with silicon die dimensions of 1.9 ... The principal objective of this work is to describe the first in vivo use of a forward-looking ML-CMUT array catheter in a true 9F profile, the catheter compatibility with EAM guidance, and the use of a specially integrated RFA tip capable of both monitoring and delivery of intracardiac ablation. This work represents the first in vivo ablation and direct simultaneous collection of tissue echo data for the thermal strain temperature at the exact ablation site. In addition, we describe the initial use of the ML-CMUT catheter in exploratory cardiac imaging from the perspective of the epicardial surface from within the pericardium.

Atrial fibrillation, the most common type of cardiac arrhythmia, now affects more than 2.2 million adults in the US alone. Currently, electrophysiological interventions are performed under fluoroscopy guidance, a procedure that introduces harmful ionizing radiation without providing adequate soft-tissue resolution. Intracardiac echocardiography (ICE) provides real-time, high-resolution anatomical information, reduces fluoroscopy time, and enhances procedural success. We have previously developed a forward-looking, volumetric ICE catheter using a ring-shaped, 64-element capacitive micromachined ultrasonic transducer (CMUT) array with a 10MHz center frequency. The Ring array was flip-chip bonded to a flexible PCB along with 8 identical custom ASICs providing a total of 64 dedicated preamplifiers. The flex was then reshaped for integration with the catheter shaft. In the second-generation catheter, 72 micro-coaxial cables (reduced from 100) are terminated on a newly designed flex to provide the connection between the array electronics and the imaging system. The reduced number of cables enhances the catheter’s steerability. Furthermore, the new flex allows grounding of the top CMUT electrode through proper level-shifting of the ASIC supplies without additional circuitry. This feature enables complete ground shielding of the catheter, which improves its noise susceptibility and is an important safety measure for its clinical use. Beyond real-time, forward-looking imaging capability, the Ring catheter provides a continuous central lumen, enabling convenient delivery of other devices such as HIFU transducers, RF ablation catheters, etc. Using a PC-based imaging platform from Verasonics and a commercial Vivid7 imaging system from GE, we have demonstrated the in vivo, volumetric, real-time imaging capability of the finalized Ring catheter in a pig heart.

Atrial fibrillation is the most common sustained arrhythmia that now affects approximately 2.2 million adults in the United States alone. Minimally invasive catheter-based electrophysiological interventions have revolutionized the management of cardiac arrhythmias. We are developing forward-viewing ultrasound imaging catheters based on two types of transducer arrays using the capacitive micromachined ultrasonic transducer technology: A 10-MHz, 24-element MicroLinear (ML) array with a footprint of 1.7 mm × 1.3 mm, and a 10-MHz, 64-element annular ring array with an outside diameter of 2.6 mm and inner diameter of 1.6 mm. Both arrays are integrated with custom-designed front-end electronic circuitry to overcome the performance degradation associated with long cables in the catheter. The ML and ring arrays provide real-time 2-D and 3-D images, respectively, in front of the catheter tip. Using the ML array, we demonstrated ex-vivo images of the left atrial appendage in an isolated Langendorff-perfused rabbit heart model and in-vivo images of heart through the open chest in a porcine animal model. We used the ring array to demonstrate 3-D images of coronary stents and an anatomic cast of a left atrial model.

Hemodynamic monitoring provides vital information for diagnosing and treating patients in acute clinical settings. A method is investigated to non-invasively monitor changes in the hemodynamic state. The approach utilizes short-axis ultrasound color flow imaging and processing methods to produce simultaneous waveforms for the arterial area and flow. Beat-to-beat measurements of the mean area, peak volumetric flow rate, and heart rate are extracted, and the distribution of these parameters is used to define the hemodynamic state. Changes in the hemodynamic state are detected by calculating a distance between new measurements and the current hemodynamic state, and then comparing this distance to an adaptive threshold. The distribution was modeled as a multivariate normal distribution characterized by a mean vector and a covariance matrix, and the Mahalanobis distance was used as the distance metric. The threshold level was adapted to produce a constant probability of false positives based on the current distribution. The method was evaluated by observing pharmacologically induced changes in the hemodynamic state during an in vivo animal experiment. The ultrasound-based measurements provided sufficient accuracy to discriminate between the hemodynamic states before, during and after infusion of a vasodilator. The ability to detect an acute change in the hemodynamic state was demonstrated in the transient period at the start of the infusion.

Currently the feedback guidance of intracardiac radiofrequency ablation (RFA) is very limited, offering only a catheter electrode (not tissue) temperature estimation and a means to titrate radiofrequency (RF) power delivery to the tissue. Our “MicroLinear” (ML) forward imaging ultrasound catheter design, now at a true 9F (3mm) in size, has been optimized with several features to simultaneously permit a) high quality intracardiac steering and imaging, b) tracking of 3D position with electroanatomical mapping, c) RF ablation, and d) tissue thermal strain (TS) estimation for direct tissue temperature feedback. Two types of ML catheters have been built and tested in 3 porcine animal models. The first type, in its third generation, is based on a PZT transducer array; the second type, in its second generation, is based on a CMUT array with custom integrated interface circuitry. Both types of devices are true 9F in size and performed well in imaging tests in recent in vivo studies. Both the ML-PZT and ML-CMUT arrays, as described previously, have a fine pitch (65 and 63 micron respectively) 24 element phased arrays operating at 14 MHz which project a B-mode plane directly out from the tip of the catheter. Intracardiac imaging performance was documented to show that the very small array apertures of the ML design (1.2mm × 1.58mm, and 1.1mm × 1.4mm) permit good, high resolution imaging to depths as great as 4 cm. The ML-PZT catheter was equipped with a special low profile ablation tip which allowed simultaneous imaging and ablation at the distal end of the catheter. TS data were acquired during tissue ablations in right atrium (RA) and right ventricle (RV). The TS data of the RF ablations were processed off line. In vivo use of this new technology has shown for the first time the very substantial potential for a single, low profile catheter to simultaneously image within the heart and perform intracardiac ablation therapy with tissue temperature guidance produced from the incorporation of TS imaging. Work is underway to further assess the temperature estimation accuracy and to integrate the TS processing for real time displays.

A method to monitor ablative therapy by examining slope changes in the thermal strain curve caused by speed of sound with temperature is introduced. The variation of sound speed with temperature rise for most soft tissue follows a similar pattern to that of water. Unlike most liquids, the sound speed of tissue 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 48–50 °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 using the reduced slope in the thermal strain curve as a function of heating time. Using a prototype intracardiac echocardiography (ICE) array for imaging and a catheter for RF ablation, we were able to observe an obvious slope change in the thermal strain curve in an excised tissue sample. The method was further tested in-vivo, using a specially equipped ablation tip and an 11 MHz microlinear (ML) ICE array mounted on the tip of a catheter. As with in-vitro experiments, the thermal strain curve showed a plateau and a change in the sign of the slope.

Atrial fibrillation, the most common type of cardiac arrhythmia, now affects more than 2.2 million adults in the US alone. Currently, electrophysiological interventions are performed under fluoroscopy guidance, which besides its harmful ionizing radiation does not provide adequate soft-tissue resolution. Intracardiac echocardiography (ICE) provides realtime anatomical information that has proven valuable in reducing the fluoroscopy time and enhancing procedural success. We developed two types of forward-looking ICE catheters using capacitive micromachined ultrasonic transducer (CMUT) technology: MicroLinear (ML) and ring catheters. The ML catheter enables real-time forward-looking 2-D imaging using a 24-element 1-D CMUT phased-array that is designed for a center frequency of 10 MHz. The ring catheter uses a 64-element ring CMUT array that is also designed for a center frequency of 10 MHz. However, this ring-shaped 2-D array enables real-time forward-looking volumetric imaging. In addition, this catheter provides a continuous central lumen that enables convenient delivery of other devices such as RF ablation catheter, EP diagnostic catheter, biopsy devices, etc. Both catheters are equipped with custom front-end IC's that are integrated with the CMUT arrays at the tip of the catheters. The integration of the IC's with the CMUT arrays was accomplished using custom flexible PCB's. We also developed several image reconstruction schemes for the ring catheter on a PC-based imaging platform from VeraSonics. We performed a variety of bench-top characterizations to validate the functionality and performance of our fully integrated CMUT arrays. Using both catheters, we demonstrated in vivo images of the heart in a porcine animal model. We have successfully prototyped the first CMUT-based ICE catheters and proven the capabilities of the CMUT technology for implementing high-frequency miniature transducer arrays with integrated electronics.

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.

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.

Atrial fibrillation is the most common type of cardiac arrhythmia that now affects over 2.2 million adults in the United States alone. Currently fluoroscopy is the most common method for guiding interventional electrophysiological procedures. We are developing a 9-F forward-looking intracardiac ultrasound catheter for real-time volumetric imaging. We designed and fabricated a 64-element 10-MHz CMUT ring array with through-wafer via interconnects. We also designed custom front-end electronics to be closely integrated with the CMUT array at the tip of the catheter for improved SNR. This integrated circuit (IC) is composed of preamplifiers and protection circuitry, and can directly interface a standard imaging system. This multi-channel IC is capable of passing up to ±50-V bipolar pulses. An 8-channel front-end IC was fabricated based on this circuit topology. Additionally, a flexible PCB was designed for the integration of ring array with front-end electronics. We have acquired a PC-based real-time imaging platform and demonstrated real-time imaging with the ring array. We have also shown volume images using off-line full synthetic aperture image reconstruction method. The presented experimental results demonstrate the performance of our forward-looking volumetric intracardiac imaging approach. We are currently working on the final catheter integration and further development of our real-time imaging methods.

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.

A family of 3 multifunctional intracardiac imaging and electrophysiology (EP) mapping catheters has been in development to help guide diagnostic and therapeutic intracardiac EP procedures. The catheter tip on the first device includes a 7.5 MHz, 64-element, side-looking phased array for high resolution sector scanning. The second device is a forward-looking catheter with a 24-element 14 MHz phased array. Both of these catheters operate on a commercial imaging system with standard software. Multiple EP mapping sensors were mounted as ring electrodes near the arrays for electrocardiographic synchronization of ultrasound images and used for unique integration with EP mapping technologies. To help establish the catheters' ability for integration with EP interventional procedures, tests were performed in vivo in a porcine animal model to demonstrate both useful intracardiac echocardiographic (ICE) visualization and simultaneous 3-D positional information using integrated electroanatomical mapping techniques. The catheters also performed well in high frame rate imaging, color flow imaging, and strain rate imaging of atrial and ventricular structures. The companion paper of this work discusses the catheter design of the side-looking catheter with special attention to acoustic lens design. The third device in development is a 10 MHz forward-looking ring array that is to be mounted at the distal tip of a 9F catheter to permit use of the available catheter lumen for adjunctive therapy tools.

A multifunctional 9F intracardiac imaging and electrophysiology mapping catheter was developed and tested to help guide diagnostic and therapeutic intracardiac electrophysiology (EP) procedures. The catheter tip includes a 7.25-MHz, 64-element, side-looking phased array for high resolution sector scanning. Multiple electrophysiology mapping sensors were mounted as ring electrodes near the array for electrocardiographic synchronization of ultrasound images. The catheter array elevation beam performance in particular was investigated. An acoustic lens for the distal tip array designed with a round cross section can produce an acceptable elevation beam shape; however, the velocity of sound in the lens material should be approximately 155 m/s slower than in tissue for the best beam shape and wide bandwidth performance. To help establish the catheter's unique ability for integration with electrophysiology interventional procedures, it was used in vivo in a porcine animal model, and demonstrated both useful intracardiac echocardiographic visualization and simultaneous 3- D positional information using integrated electroanatomical mapping techniques. The catheter also performed well in high frame rate imaging, color flow imaging, and strain rate imaging of atrial and ventricular structures.

Background: We have developed the first forward-looking highly steerable intracardiac echo probe developed for ultrasound visualization of ablation. It is a 24-element forward-looking microlinear array on a 9 Fr catheter that has additional electrodes so it can be localized compared to separate ablation catheters through electrofield navigation by NavX. Methods: In 4 studies of closed-chest pigs, we have imaged ablation locations in the right atrium and the isthmus and on the right side of the septum and at the right ventricular apex, and also imaged across the septum at ablations in the left ventricle along the septum with this device. Results: Images at 150–170 frames/sec at 12–15 MHz give very high detail of the changes occurring during ablation, including liquefaction, heating changes, brightening and thickening of tissue, and thrombus formation in the adjacent region in unheparinized pigs. The devices are well enough shielded from RF energy that there is little interference, and yet an ablation is being performed. A catheter tip artifact makes it easy to see the actual location of the ablation catheter tip with the microlinear array. Tissue Doppler/strain rate imaging also yields the possibility of determining mechanical changes occurring in ablation where brightening of tissue associated with stiffening diminished mechanical strain deformations in ablated lesions, especially in the ventricles. Conclusions: This new technology provides a new method for guidance and, more importantly, a method for understanding the changes that occur with RF ablations in experimental animals and, eventually, in patients.

A new signal processing approach to estimation of local arterial pulse wave velocity (PWV) in superficial arterial segments using long-axis ultrasound measurements is proposed. The method is designed to be resistant to estimation bias due to pulse wave reflections. It is evaluated using a laboratory test tank, and it appears to estimate local PWV with less bias than previously accepted methods, and with similar estimation variance to those methods.

Assessment of the arterial pulse wave velocity (PWV) has long been an area of interest in physiology, and ultrasound has long been used to provide measurements for such assessments. Recently, new signal processing approaches for ultrasound data have emerged. However, these methods suffer from inaccuracies due to pulse wave reflections, which are always present and can strongly bias the PWV estimates away from the true velocity. Recently the authors (Hoctor et al. (2004)) showed that pulse wave velocity estimation from several ultrasound measurements taken along a short uniform arterial segment is equivalent to the broadband directional of arrival problem with coherent multipath found in radar and sonar. This tutorial paper reviews the physiological and ultrasound-systems aspects of the PWV estimation problem, and examines its relationship to the direction-of-arrival estimation problem. The paper also demonstrates why nonlinear, high-resolution methods are needed and outlines the application of several such estimators to the problem.

In this paper we evaluate an improved version of a signal processing approach recently proposed by the authors for estimating arterial pulse wave velocity (PWV) in a uniform arterial segment based on ultrasound measurements. The modifications are described, along with the experimental set-up for their evaluation. In general, results of physical experiments and simulations indicate that the new modifications provide a robust approach to PWV estimation. Non-invasive, in vivo assessment of the local elastic properties of an artery is a desirable capability, both in experimental physiology and in medicine. The arterial pulse wave velocity (PWV) in a short uniform segment of an artery is indicative of the local elastic state of the segment, but pulse wave reflections are always present throughout the arterial system and are a well-recognized source of error in PWV measurement (1). Elimination of estimation bias due to reflections is required if the PWV is to be used to compute parameters such as the compliance of the artery. Ultrasound is a suitable modality for the local PWV estimation problem, as it is for many problems of noninvasive, in vivo biomechanical assessment. Recently the authors (2) showed that pulse wave velocity estimation from several ultrasound measurements taken along a uniform arterial segment is mathematically equivalent to the broadband directional of arrival problem found in radar and sonar. The presence of a reflection wave traveling at the PWV, but in the opposite direction from the forward wave makes the PWV problem similar to the symmetric multipath case in the direction-of-arrival problem (3). Consequently, there is a great deal of work in signal processing literature dealing with the direction-of-arrival estimation problem in this form that can be applied the arterial PWV estimation using ultrasound by way of the problem formulation given in (2). In (4), a method for the PWV problem based on a least squares approach was presented and results of application to in vivo were presented for data taken using a 10 MHz linear probe positioned to acquire 8 beams spaced by 5.6 mm along the flow axis of the left common carotid artery (CCA). The technique of (4) produced estimates in a realistic range, but with large estimation variance on the order of 30-40%. This paper seeks to provide a more detailed evaluation of the general method, using new signal processing approaches for reduction of estimation bias. This evaluation is done by simulation, test tank experiments and further data from the CCAs of healthy volunteers.

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 simultaneous tissue ablation was performed

A 9F combination intracardiac imaging and electrophysiology mapping catheter has been developed and tested to help guide diagnostic and therapeutic intracardiac electrophysiology procedures. A 7.5 MHz, 64 element, side looking phased array was used for sector scanning from the tip of the catheter. Multiple electrophysiology (EP) mapping sensors were mounted as ring electrodes just proximal to the array for electrocardiographic synchronization of ultrasound images. The catheter has been used in vivo in a porcine animal model and has demonstrated useful intracardiac echocardiographic (ICE) visualization of both cardiac tissue and electrophysiology catheters in the right atrium. The catheter performed well in high frame rate imaging, color flow imaging, and strain rate imaging of atrial and ventricular structures.

In this paper we propose a new signal processing approach for estimating arterial pulse wave velocity (PWV) in a uniform arterial segment based on ultrasound measurements. The new approach compensates for whatever pulse wave reflections are present in the observation. We show that the long-axis PWV estimation problem with reflections is similar to that of direction-of-arrival (DOA) estimation for two far-field, narrowband, coherent sources. A high-SNR simulation is performed to compare the performance of the new method to that of three existing methods in the presence of reflections. A limited amount of in vivo data is processed and the resulting estimates, although superior to those obtained from existing methods, are seen to be noisy. Finally, further research directions are outlined.

This paper describes the experimental hardware design and implementation for a delay hopped transmitted reference communication system. The hardware is designed to generate the delay hopped transmitted reference signal for a number of experimental conditions. It can be used either in an ultra wideband pulse mode, ultra wideband noise mode, or in a narrowband mode. We use the experimental hardware setup to conduct link experiments with a delay hopped transmitted reference communication system. Experiments were conducted in an indoor multipath environment to test the viability of delay hopped transmitted reference for short-range indoor communications. The experimental results presented demonstrate that this modulation format is capable of transmitting data short range indoors without line of sight transmission path with minimal transmitted RF power.