Douglas Glenn Wildes

Improved in vivo abdominal image quality using real-time estimation and correction of wavefront arrival time errors

The speed of sound varies with tissue type, yet commercial ultrasound imagers assume it is constant. Sound speed variation in abdominal fat and muscle layers is widely believed to be largely responsible for poor image contrast and resolution in some patients. The simplest model of the abdominal wall assumes that it adds a spatially varying time delay to the ultrasound wavefront. We describe an adaptive imaging system consisting of a GE LOGIQ 700 imager connected to a multi-processor computer. Arrival time errors for each beamforming channel, estimated by correlating each channel signal with the beamsum signal, are used to correct the imagers transmit and receive beamforming time delays at the image frame rate. A multi-row transducer provides two dimensional sampling of wavefront arrival time errors. After beamforming time delay correction, we observe significant improvement in abdominal images of healthy male volunteers, including increased contrast of blood vessels, increased brightness of liver tissue, and improved definition of the renal capsule and splenic boundary.

Forward-looking volumetric intracardiac imaging using a fully integrated CMUT ring array

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.

Prospects for in-process diagnosis of metal cutting by monitoring vibration signals

Vibration signals from various metal cutting processes in e frequency range of a few Hz to several MHz have been investigated by many researchers for their possible application to an in-process cutting condition monitoring system and some remarkable laboratory results have been reported. In spite of many very interesting demonstrations of feasibility in laboratories, numerous attempts to apply the technology to manufacturing conditions have not been very successful. The main objectives of this brief review are to summarize the key points of various published reports and to discuss the critical technical issues which are hindering transformation of the laboratory results to more broadly applicable technology. The vibration signals from metal cutting processes contain very useful information and offer excellent possibilities for in-process diagnosis of many critical metal cutting problems including tool wear. But the current state of knowledge still consists mainly of empirical observations, many of which need further clarification. Sonna of these key issues requiring future studies, particularly those issues related to in-process monitoring of tool wear, are discussed in this review.

High-density cable and method therefor

A high-density cable of a type suitable for transmitting ultrasound signals from an ultrasonic probe to multiplexing circuitry during a medical ultrasound procedure is provided. The cable includes one or more flexible circuits arranged within a flexible sheath that surrounds and confines the flexible circuits. Each flexible circuit includes an elongate flexible substrate with oppositely-disposed surfaces and multiple conductors on at least one of these surfaces. The opposing longitudinal ends of the substrate define integral connectors for connecting with respective output connectors and/or electronic devices, such as an ultrasonic probe or multiplexing circuitry.

Forward-looking intracardiac ultrasound imaging using a 1-D CMUT array integrated with custom front-end electronics

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 forwardlooking 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.

Forward-looking intracardiac imaging catheters using fully integrated CMUT arrays

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 ICs that are integrated with the CMUT arrays at the tip of the catheters. The integration of the ICs with the CMUT arrays was accomplished using custom flexible PCBs. 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.

A 1.5D transducer for medical ultrasound

The current shift to digital beamforming technology holds promise for regular and rapid increases in the number of channels in a medical imager. A 1D transducer typically utilizes 125 elements, while a fully sampled two-dimensional aperture requires of order 10000 elements. Currently, channels are still expensive, so it is of interest to evaluate how much performance can be improved with a moderate increment in channel count. How may we maximize the impact on voxel size? The number of elevational elements is constrained by how complex the interconnections can become. It is impractical to significantly degrade the azimuthal resolution from the 1D case. We present beam profiles and images from a first attempt at judicious use of a 256 channel imager. Simulations and experiments allow us to explore compromises among a number of design goals. We have fabricated a transducer with several elevational rows which reduces the slice thickness of the image while maintaining full azimuthal resolution

The feasibility of using thermal strain imaging to regulate energy delivery during intracardiac radio-frequency ablation

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.

Experimental Studies With a 9F Forward-Looking Intracardiac Imaging and Ablation Catheter

Objective. 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. Methods. 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. Results. 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. Conclusions. 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 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.