Warren Lee

A miniaturized catheter 2-D array for real-time, 3-D intracardiac echocardiography

The design, fabrication, and characterization of a 112 channel, 5 MHz, two-dimensional (2-D) array transducer constructed on a six layer flexible polyimide interconnect circuit is described. The transducer was mounted in a 7 Fr (2.33 mm outside diameter) catheter for use in real-time intracardiac volumetric imaging. Two transducers were constructed: one with a single silver epoxy matching layer and the other without a matching layer. The center frequency and -6 dB fractional bandwidth of the transducer with a matching layer were 4.9 MHz and 31%, respectively. The 50 /spl Omega/ pitch-catch insertion loss was 80 dB, and the typical interelement crosstalk was -30 dB. The final element yield was greater than 97% for both transducers. The transducers were used to acquire real-time, 3-D images in an in vivo sheep model. We present in vivo images of cardiac anatomy obtained from within the coronary sinus, including the left and right atria, aorta, coronary arteries, and pulmonary veins. We also present images showing the manipulation of a separate electrophysiological catheter into the coronary sinus.

High-density flexible interconnect for two-dimensional ultrasound arrays

We present a method for fabricating flexible multilayer circuits for interconnection to 2-D array ultrasound transducers. In addition, we describe four 2-D arrays in which such flexible interconnect is implemented, including transthoracic arrays with 438 channels operating at up to 7 MHz and intracardiac catheter arrays with 70 channels operating at up to 7 MHz. We employ thin and thick film microfabrication techniques to batch produce the interconnect circuits with minimum dimensions of 12-/spl mu/m lines, 40-/spl mu/m vias, and 150-/spl mu/m array pitch. The arrays show 50-/spl Omega/ insertion loss of -60 to -84 dB and a fractional bandwidth of 27 to 67%. The arrays are used to obtain real time, in vivo volumetric scans.

Dual lumen transducer probes for real-time 3-D interventional cardiac ultrasound.

We have developed dual lumen probes incorporating a forward-viewing matrix array transducer with an integrated working lumen for delivery of tools in real-time 3-D (RT3-D) interventional echocardiography. The probes are of 14 Fr and 22 Fr sizes, with 112 channel 2-D arrays operating at 5 MHz. We obtained images of cardiac anatomy and simultaneous interventional device delivery with an in vivo sheep model, including: manipulation of a 0.36-mm diameter guidewire into the coronary sinus, guidance of a transseptal puncture using a 1.2-mm diameter Brockenbrough needle, and guidance of a right ventricular biopsy using 3 Fr biopsy forceps. We have also incorporated the 22 Fr probe within a 6-mm surgical trocar to obtain apical four-chamber ultrasound (US) scans from a subcostal position. Combining the imaging catheter with a working lumen in a single device may simplify cardiac interventional procedures by allowing clinicians to easily visualize cardiac structures and simultaneously direct interventional tools in a RT3-D image.

Real-Time 3D Color Flow Doppler for Guidance of Vibrating Interventional Devices:

The goal of this investigation was to examine the feasibility of guiding interventional devices using piezoelectric buzzers to create velocity sources, which were imaged and tracked with real-time 3D color flow Doppler. The interventional devices examined in this study included a pacemaker lead, Brockenbrough needle for cardiac septal puncture, cardiac guidewire and radiofrequency ablation needles for cancer therapy. Each was mechanically coupled to a piezoelectric buzzer and was imaged using a commercial real-time 3D ultrasound system with either a 2.5 MHz matrix array transducer or a 5 MHz, 22 F catheter transducer equipped with a tool port. In vitro images acquired in tissue phantoms, excised liver with a ‘tumor’ target and an excised sheep heart show strong vibration signals in 3D color flow Doppler, enabling real-time tracking and guidance of all the devices in three dimensions. In a sheep model, in vivo tracking of the pacing lead was performed in the superior vena cava as well as the right atrium using RT3D color flow Doppler images. The vibrating rf ablation needles were guided through the liver toward “tumor” targets in vivo with real-time 3D color flow Doppler images.

Update of two dimensional arrays for real time volumetric and real time intracardiac imaging

The authors have previously described 2-D array transducers with up to several thousand elements operating at frequencies between 2.5 and 5.0 MHz for real time volumetric imaging. Lately, there has been interest in developing catheter based intracardiac imaging systems to aid in the precise tracking of anatomical features and intracardiac devices for improved diagnoses and therapies. The authors constructed several arrays for real time intracardiac volumetric imaging based upon 2 different designs; a 13/spl times/11=143 element 5.0 MHz 2-D array for side scanning applications, and a 10/spl times/10=100 element 7.0 MHz 2-D array for side scanning applications. The 5.0 MHz array fits into a 12 French (3.8 mm OD) catheter and the 7.0 MHz transducer is designed to fit into a 9 French (2.9 mm OD) catheter. The authors also constructed 2 transducers for transthoracic imaging; a 40/spl times/40 5.0 MHz 2-D array, and a 40/spl times/40 7.0 MHz 2-D array. The -6 dB fractional bandwidths for the transducers varied from 27% to 67%. All the transducers were constructed on a 6 layer polyimide interconnect. Both transthoracic and intracardiac volumetric images of ultrasound phantoms and animal models have been obtained using the Duke University real time volumetric imaging system which is capable of generating multiple planes at any desired angle and depth within a pyramidal volume.

Intracardiac catheter 2-D arrays on a silicon substrate

The design, fabrication, and characterization of a 7 MHz, two-dimensional (2-D) array transducer built on a silicon substrate is described. The array fits inside a 9-French (2.9 mm O.D.) catheter for use in real-time intracardiac volumetric imaging. The -6 dB fractional bandwidth of the transducer is 30%, the 50 /spl Omega/ pitch-catch insertion loss is 78 dB, and the interelement crosstalk is -25 dB. Realtime volumetric images in phantoms and in-vitro images of a sheep heart have been acquired yielding measured spatial resolution of 2 mm at a depth of 1 cm. The cardiac structures imaged include ventricular chambers, interventricular septum, mitral and tricuspid valves and real-time 3-D rendered volumes of the tricuspid valve in the open and closed position.

Two dimensional arrays for real time volumetric and intracardiac imaging with simultaneous electrocardiogram

The authors have previously described 2D arrays operating up to 7.0 MHz consisting of several thousand elements for transthoracic cardiac imaging and up to 200 elements for intracardiac imaging. Most recently, the authors have constructed a 10.0 MHz array that includes 120/spl times/120=14,400 elements for real time transthoracic volumetric imaging. The resulting bandwidth is 27% and the 50 Ohm insertion loss is -68 dB. Real time volumetric images in phantoms have been made. There is interest in developing catheter based intracardiac imaging systems to aid in the precise tracking of anatomical features and interventional devices for improved diagnoses and therapies. Potential clinical applications include guidance of cardiac electrophysiological mapping and ablation procedures, long term monitoring of ventricular volumes in intensive care units and guidance of cardiac revascularization procedures using laser and drug angiogenic agents. The authors have constructed catheter array transducers with ECG electrodes for collecting electrophysiological data simultaneously with their images. There are 5 ring electrodes and 1 tip electrode for each transducer. The transducers consist of a 13/spl times/11=143 element array operating at 5.0 MHz and fits into a 12 French catheter (OD=3.8 mm). The first transducer array design is for side scanning applications. The second transducer layout has been inclined to a 20/spl deg/ bevel to improve image acquisition. The -6 dB fractional bandwidths for the different arrays varied from 40% to 63%, and the 50 Ohm insertion loss for the transducers was approximately -64 dB. Both the transducers were constructed on a 6 layer flexible polyimide interconnect Real time phantom images and intracardiac volumetric images in animal models have been obtained using the Duke University real time volumetric imaging system, which is capable of generating multiple planes at any desired angle and depth within a pyramidal volume. The authors obtained in vivo images of the ventricles and atria as well as simultaneous acquisition of 3 bipolar intracardiac ECG signals. With the real time volumetric scanner, the authors also guided and monitored the RF ablation of an excised sheep left ventricle. Cross section and face on images show excellent contrast between ablated versus normal myocardium.

Two dimensional arrays for 3-D ultrasound imaging

Phased array ultrasound transducers have been fabricated in our laboratories at Duke University since 1970. In 1986, we began the development of 2-D arrays with a 20 /spl times/ 20 element Mills cross array including 64 active channels operating at 1 MHz which produced the first real time 3-D ultrasound images. In our more recent arrays we have progressed to 108 /spl times/ 108 = 11,664 elements in a series of transducers operating from 2.5 - 10 MHz. These were used in a commercial version of our Duke 3-D system developed by Volumetrics Medical Imaging for cardiac applications. The system scans a 65/spl deg/ 3-D pyramid at up to 60 volumes/sec and features five simultaneous slice images at any desired angle and depth as well as real time 3-D rendering, 3-D pulsed and color flow Doppler. We have also modified this scanner to produce the first real time 3-D rectilinear and curvilinear images using arrays of 256 /spl times/ 256 = 65,536 elements operating at 5 MHz for vascular and small parts applications. Finally, we have developed catheter 2-D arrays for intra-cardiac 3-D ultrasound including 112 channels in a 2.2 mm lumen (7 French) operating at 5-7 MHz. In animal studies, these transducers have been applied to the guidance of cardiac interventional procedures including RF ablation, ECG mapping, surgical biopsy and atrial septal puncture.

A 10 Fr ultrasound catheter with integrated micromotor for 4D intracardiac echocardiography

We developed prototype catheters for real-time three-dimensional intracardiac echo (4D ICE) imaging. The catheter tips contained a low profile 64-element, 6.2 MHz phased array transducer and integrated micromotor, allowing oscillation of the transducer in the elevation direction. The tips were integrated with two-way deflectable 10 Fr catheters and used in in-vivo animal testing at multiple facilities. The 4D ICE catheters were capable of imaging a 90° azimuth by up to 180° elevation field of view. Volume rates ranged from 1 vol/sec (180° elevation) to approximately 10 vol/sec (45° elevation). We successfully imaged electrophysiology catheters, atrial septal puncture procedures, and detailed cardiac anatomy. The elevation oscillation enabled 3D visualization of devices and anatomy providing new clinical information and perspective not possible with current 2D imaging catheters.

4-D ICE: A 2-D Array Transducer With Integrated ASIC in a 10-Fr Catheter for Real-Time 3-D Intracardiac Echocardiography

We developed a 2.5×6.6 mm2 2-D array transducer with integrated transmit/receive application-specific integrated circuit (ASIC) for real-time 3-D intracardiac echocardiography (4-D ICE) applications. The ASIC and transducer design were optimized so that the high-voltage transmit, low-voltage time-gain control and preamp, subaperture beamformer, and digital control circuits for each transducer element all fit within the 0.019-mm2 area of the element. The transducer assembly was deployed in a 10-Fr (3.3-mm diameter) catheter, integrated with a GE Vivid E9 ultrasound imaging system, and evaluated in three preclinical studies. The 2-D image quality and imaging modes were comparable to commercial 2-D ICE catheters. The 4-D field of view was at least 90° × 60° × 8 cm and could be imaged at 30 vol/s, sufficient to visualize cardiac anatomy and other diagnostic and therapy catheters. 4-D ICE should significantly reduce X-ray fluoroscopy use and dose during electrophysiology ablation procedures. 4-D ICE may be able to replace transesophageal echocardiography (TEE), and the associated risks and costs of general anesthesia, for guidance of some structural heart procedures.We developed a 2.5 x 6.6 mm 2D array transducer with integrated transmit/receive ASIC for 4D ICE (real-time 3D IntraCardiac Echocardiography) applications. The ASIC and transducer design were optimized so that the high voltage transmit, low-voltage TGC (time-gain control) and preamp, subaperture beamformer, and digital control circuits for each transducer element all fit within the 0.019 mm2 area of the element. The transducer assembly was deployed in a 10 Fr (3.3 mm diameter) catheter, integrated with a GE Vivid1 E9 ultrasound imaging system, and evaluated in three pre-clinical studies. 2D image quality and imaging modes were comparable to commercial 2D ICE catheters. The 4D field of view was at least 90° x 60° x 8 cm and could be imaged at 30 volumes/sec, sufficient to visualize cardiac anatomy and other diagnostic and therapy catheters. 4D ICE should significantly reduce X-ray fluoroscopy use and dose during electrophysiology (EP) ablation procedures. 4D ICE may be able to replace trans-esophageal echocardiography (TEE), and the associated risks and costs of general anesthesia, for guidance of some structural heart procedures.