[Show abstract][Hide abstract] ABSTRACT: Our long-term goal is the detection and characterization of vulnerable plaque in the coronary arteries of the heart using intravascular ultrasound (IVUS) catheters. Vulnerable plaque, characterized by a thin fibrous cap and a soft, lipid-rich necrotic core is a precursor to heart attack and stroke. Early detection of such plaques may potentially alter the course of treatment of the patient to prevent ischemic events. We have previously described the characterization of carotid plaques using external linear arrays operating at 9 MHz. In addition, we previously modified circular array IVUS catheters by short-circuiting several neighboring elements to produce fixed beamwidths for intravascular hyperthermia applications. In this paper, we modified Volcano Visions 8.2 French, 9 MHz catheters and Volcano Platinum 3.5 French, 20 MHz catheters by short-circuiting portions of the array for acoustic radiation force impulse imaging (ARFI) applications. The catheters had an effective transmit aperture size of 2 mm and 1.5 mm, respectively. The catheters were connected to a Verasonics scanner and driven with pushing pulses of 180 V p-p to acquire ARFI data from a soft gel phantom with a Young's modulus of 2.9 kPa. The dynamic response of the tissue-mimicking material demonstrates a typical ARFI motion of 1 to 2 microns as the gel phantom displaces away and recovers back to its normal position. The hardware modifications applied to our IVUS catheters mimic potential beamforming modifications that could be implemented on IVUS scanners. Our results demonstrate that the generation of radiation force from IVUS catheters and the development of intravascular ARFI may be feasible.
[Show abstract][Hide abstract] ABSTRACT: We developed new forward-viewing matrix transducers consisting of double ring arrays of 118 total PZT elements integrated into catheters used to deploy medical interventional devices. Our goal is 3D ultrasound guidance of medical device implantation to reduce x-ray fluoroscopy exposure. The double ring arrays were fabricated on inner and outer custom polyimide flexible circuits with inter-element spacing of 0.20 mm and then wrapped around an 11 French (Fr) catheter to produce a 15 Fr catheter (outer diameter [O.D.]). We used a braided cabling technology to connect the elements to the Volumetrics Medical Imaging (VMI) real-time 3D ultrasound scanner. Transducer performance yielded an average -6 dB fractional bandwidth of 49% ± 11% centered at 4.4 MHz for 118 elements. Real-time 3D cardiac scans of the in vivo pig model yielded good image quality including en face views of the tricuspid valve and real-time 3D guidance of an endo-myocardial biopsy catheter introduced into the left ventricle.
[Show abstract][Hide abstract] ABSTRACT: We present the first correction of refraction in three-dimensional (3D) ultrasound imaging using an iterative approach that traces propagation paths through a two-layer planar tissue model, applying Snell's law in 3D. This approach is applied to real-time 3D transcranial ultrasound imaging by precomputing delays offline for several skull thicknesses, allowing the user to switch between three sets of delays for phased array imaging at the push of a button. Simulations indicate that refraction correction may be expected to increase sensitivity, reduce beam steering errors, and partially restore lost spatial resolution, with the greatest improvements occurring at the largest steering angles. Distorted images of cylindrical lesions were created by imaging through an acrylic plate in a tissue-mimicking phantom. As a result of correcting for refraction, lesions were restored to 93.6% of their original diameter in the lateral direction and 98.1% of their original shape along the long axis of the cylinders. In imaging two healthy volunteers, the mean brightness increased by 8.3% and showed no spatial dependency.
[Show abstract][Hide abstract] ABSTRACT: With stroke currently the second-leading cause of death globally, and 87% of all strokes classified as ischemic, the development of a fast, accessible, cost-effective approach for imaging occlusive stroke could have a significant impact on health care outcomes and costs. Although clinical examination and standard computed tomography alone do not provide adequate information for understanding the complex temporal events that occur during an ischemic stroke, ultrasound imaging is well suited to the task of examining blood flow dynamics in real time and may allow for localization of a clot. A prototype bilateral 3-D ultrasound imaging system using two matrix array probes on either side of the head allows for correction of skull-induced aberration throughout two entire phased array imaging volumes. We investigated the feasibility of applying this custom correction technique in five healthy volunteers with Definity microbubble contrast enhancement. Subjects were scanned simultaneously via both temporal acoustic windows in 3-D color flow mode. The number of color flow voxels above a common threshold increased as a result of aberration correction in five of five subjects, with a mean increase of 33.9%. The percentage of large arteries visualized by 3-D color Doppler imaging increased from 46% without aberration correction to 60% with aberration correction.
Ultrasound in medicine & biology 11/2013; · 2.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ultrasound imaging has been proposed as a rapid, portable alternative imaging modality to examine stroke patients in pre-hospital or emergency room settings. However, in performing transcranial ultrasound examinations, 8%-29% of patients in a general population may present with window failure, in which case it is not possible to acquire clinically useful sonographic information through the temporal bone acoustic window. In this work, we describe the technical considerations, design and fabrication of low-frequency (1.2 MHz), large aperture (25.3 mm) sparse matrix array transducers for 3-D imaging in the event of window failure. These transducers are integrated into a system for real-time 3-D bilateral transcranial imaging-the ultrasound brain helmet-and color flow imaging capabilities at 1.2 MHz are directly compared with arrays operating at 1.8 MHz in a flow phantom with attenuation comparable to the in vivo case. Contrast-enhanced imaging allowed visualization of arteries of the Circle of Willis in 5 of 5 subjects and 8 of 10 sides of the head despite probe placement outside of the acoustic window. Results suggest that this type of transducer may allow acquisition of useful images either in individuals with poor windows or outside of the temporal acoustic window in the field.
Ultrasound in medicine & biology 02/2013; · 2.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present an approach for correcting multiple distinct aberrators within a single transcranial imaging volume, i.e. several isoplanatic patches. Aberration is estimated using cross-correlation of RF channel signals followed by least mean squares solution of the resulting overdetermined system. Delay maps are updated and real-time 3D scanning resumes. This adaptive imaging technique, which uses steered unfocused waves transmitted by the "beacon" array on the opposite side of the head, updates the transmit and receive delays of 5 isoplanatic patches within a 64°×64° volume. In phantom experiments, color flow voxels above a common threshold have increased by an average of 92%, while color flow variance decreased by an average of 10%. This approach has been applied to bilateral temporal acoustic windows of two human subjects, yielding increases in echo brightness in 5 isoplanatic patches, with a mean value of 24.3 ± 9.1%.
2012 IEEE International Ultrasonics Symposium (IUS), Dresden, Germany; 10/2012
[Show abstract][Hide abstract] ABSTRACT: We developed new miniature ring array transducers integrated into interventional device catheters such as used to deploy atrial septal occluders. Each ring array consisted of 55 elements operating near 5 MHz with interelement spacing of 0.20 mm. It was constructed on a flat piece of copper-clad polyimide and then wrapped around an 11 French O.D. catheter. We used a braided cabling technology from Tyco Electronics Corporation to connect the elements to the Volumetric Medical Imaging (VMI) real-time 3-D ultrasound scanner. Transducer performance yielded a -6 dB fractional bandwidth of 20% centered at 4.7 MHz without a matching layer vs. average bandwidth of 60% centered at 4.4 MHz with a matching layer. Real-time 3-D rendered images of an en face view of a Gore Helex septal occluder in a water tank showed a finer texture of the device surface from the ring array with the matching layer.
Ultrasound in medicine & biology 06/2012; 38(8):1483-7. · 2.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Having previously presented a system for simultaneous 3D ultrasound imaging via both temporal bone acoustic windows, we take advantage of this system's scanning geometry to allow each matrix array to serve as a correction source for the opposing array. Aberration is estimated using cross-correlation of RF channel signals followed by least squares solution of the resulting overdetermined system. Delay maps are updated and real-time 3D scanning resumes. Saved volumes are also registered and fused offline. Mean residual error for this technique is 11.2 ns for 75 ns electronic aberrators. We also present results showing the efficacy of this technique for correcting physical and in vivo aberration.
2011 IEEE International Ultrasonics Symposium (IUS), Orlando, FL; 10/2011
[Show abstract][Hide abstract] ABSTRACT: We developed new miniature 2D array ring transducers integrated into interventional device catheters such as deploy atrial septal occluders. One transducer consisted of 55 elements operating near 5 MHz. The interelement spacing is 0.20 mm. It was constructed on a flat piece of copper-clad polyimide and then wrapped around an 11 French catheter. We used a braided wiring technology from Tyco Electronics Corp to connect the elements to our real-time 3D ultrasound scanner. Typical measured transducer element bandwidth was 20% centered at 4.7 MHz. We built another 55 element transducer with a single matching layer. The matching layer is from EBL Products, Inc. and is the #107 matching layer, .19 mm thick. The matching layer plate was metallized on both sides with 500 Å of nickel and 1000 Å of gold prior to bonding to the PZT layer with Epotek 301 Epoxy. The resulting average bandwidth was 60% centered at 4.4 MHz Keywords – 2D array transducer, real-time 3D imaging, septal occluder
2011 IEEE International Ultrasonics Symposium (IUS), Orlando, FL; 10/2011
[Show abstract][Hide abstract] ABSTRACT: In this study, we investigated the feasibility of using 3.5-Fr intravascular ultrasound (IVUS) catheters for minimally-invasive, image-guided hyperthermia treatment of tumors in the brain. Feasibility was demonstrated by: (1) retro-fitting a commercial 3.5-Fr IVUS catheter with a 5 × 0.5 × 0.22 mm PZT-4 transducer for 9-MHz imaging and (2) testing an identical transducer for therapy potential with 3.3-MHz continuous-wave excitation. The imaging transducer was compared with a 9-Fr, 9-MHz ICE catheter when visualizing the post-mortem ovine brain and was also used to attempt vascular access to an in vivo porcine brain. A net average electrical power input of 700 mW was applied to the therapy transducer, producing a temperature rise of +13.5°C at a depth of 1.5 mm in live brain tumor tissue in the mouse model. These results suggest that it may be feasible to combine the imaging and therapeutic capabilities into a single device as a clinically-viable instrument.
Ultrasound in medicine & biology 08/2011; 37(10):1667-76. · 2.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: As a treatment for aortic stenosis, several companies have recently introduced prosthetic heart valves designed to be deployed through a catheter using an intravenous or transapical approach. This procedure can either take the place of open heart surgery with some ofthe devices or delay it with others. Real-time 3D ultrasound could enable continuous monitoring of these structures before, during and after deployment. We have developed a 2D ring array integrated with a 30 French catheter that is used for transapical prosthetic heart valve implantation. The transducer array was built using three 46 cm long flex circuits from MicroConnex (Snoqualmie, WA) which terminate in an interconnect that plugs directly into our system cable; thus, no cable soldering is required. This transducer consists of 210 elements at 0.157 mm interelement spacing and operates at 5 MHz. Average measured element bandwidth was 26% and average round-trip 50 ohm insertion loss was -58.1 dB after correcting for diffractive losses. The transducer was wrapped around the 1 cm diameter lumen of a heart-valve deployment catheter. Prosthetic heart valve images were obtained in water-tank studies.
[Show abstract][Hide abstract] ABSTRACT: Because stroke remains an important and time-sensitive health concern in developed nations, we present a system capable of fusing 3-D transcranial ultrasound volumes acquired from two sides of the head. This system uses custom sparse array transducers built on flexible multilayer circuits that can be positioned for simultaneous imaging through both temporal acoustic windows, allowing for potential registration of multiple real-time 3-D scans of cerebral vasculature. We examine hardware considerations for new matrix arrays-transducer design and interconnects-in this application. Specifically, it is proposed that SNR may be increased by reducing the length of probe cables. This claim is evaluated as part of the presented system through simulation, experimental data, and in vivo imaging. Ultimately, gains in SNR of 7 dB are realized by replacing a standard probe cable with a much shorter flex interconnect; higher gains may be possible using ribbon-based probe cables. In vivo images are presented, showing cerebral arteries with and without the use of microbubble contrast agent; they have been registered and fused using a simple algorithm which maximizes normalized cross-correlation.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control 06/2011; 58(6):1189-202. · 1.80 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An autonomous multiple-core biopsy system guided by real-time 3D ultrasound and operated by a robotic arm with 6+1 degrees of freedom has been developed. Using a specimen of turkey breast as a tissue phantom, our system was able to first autonomously locate the phantom in the image volume and then perform needle sticks in each of eight sectors in the phantom in a single session, with no human intervention required. Based on the fraction of eight sectors successfully sampled in an experiment of five trials, a success rate of 93% was recorded. This system could have relevance in clinical procedures that involve multiple needle-core sampling such as prostate or breast biopsy.
[Show abstract][Hide abstract] ABSTRACT: Our laboratory previously conducted feasibility studies of autonomous robotic breast biopsy guided by 4D ultrasound. Using a complete 3D image volume, processed by elementary thresholding algorithms with no human intervention, the robot was able to successfully target bright voxels representing micro-calcifications and dark regions representing cysts in turkey breast tissue. We now describe a clinical prototype of a computer-controlled single arm robot guided by 4D ultrasound which can autonomously locate a breast lesion and then fire a spring-loaded biopsy needle into the lesion. RMS error in a water tank experiment locating a bright point target was 2.82 mm.
[Show abstract][Hide abstract] ABSTRACT: Feasibility studies of autonomous robot biopsies in tissue have been conducted using real-time three-dimensional (3-D) ultrasound combined with simple thresholding algorithms. The robot first autonomously processed 3-D image volumes received from the ultrasound scanner to locate a metal rod target embedded in turkey breast tissue simulating a calcification, and in a separate experiment, the center of a water-filled void in the breast tissue simulating a cyst. In both experiments the robot then directed a needle to the desired target, with no user input required. Separate needle-touch experiments performed by the image-guided robot in a water tank yielded an rms error of 1.15 mm. (E-mail: email@example.com).
Ultrasound in medicine & biology 11/2009; 36(1):173-7. · 2.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have previously described miniature 2D array transducers integrated into a Cook Medical, Inc. vena cava filter deployment device. While functional, the fabrication technique was very labor intensive and did not lend itself well to efficient fabrication of large numbers of devices. We developed two new fabrication methods that we believe can be used to efficiently manufacture these types of devices in greater than prototype numbers. One transducer consisted of 55 elements operating near 5 MHz. The interelement spacing is 0.20 mm. It was constructed on a flat piece of copper-clad polyimide and then wrapped around an 11 French catheter of a Cook Medical, Inc. inferior vena cava (IVC) filter deployment device. We used a braided wiring technology from Tyco Electronics Corp. to connect the elements to our real-time 3D ultrasound scanner. Typical measured transducer element bandwidth was 20% centered at 4.7 MHz and the 50 Omega round trip insertion loss was --82 dB. The mean of the nearest neighbor cross talk was -37.0 dB. The second method consisted of a 46-cm long single layer flex circuit from MicroConnex that terminates in an interconnect that plugs directly into our system cable. This transducer had 70 elements at 0.157 mm interelement spacing operating at 4.8 MHz. Typical measured transducer element bandwidth was 29% and the 50 Omega round trip insertion loss was -83 dB. The mean of the nearest neighbor cross talk was -33.0 dB.
[Show abstract][Hide abstract] ABSTRACT: Phase correction has the potential to increase the image quality of 3-D ultrasound, especially transcranial ultrasound. We implemented and compared 2 algorithms for aberration correction, multi-lag cross-correlation and speckle brightness, using static and moving targets. We corrected three 75-ns rms electronic aberrators with full-width at half-maximum (FWHM) auto-correlation lengths of 1.35, 2.7, and 5.4 mm. Cross-correlation proved the better algorithm at 2.7 and 5.4 mm correlation lengths (P < 0.05). Static cross-correlation performed better than moving-target cross-correlation at the 2.7 mm correlation length (P < 0.05). Finally, we compared the static and moving-target cross-correlation on a flow phantom with a skull casting aberrator. Using signal from static targets, the correction resulted in an average contrast increase of 22.2%, compared with 13.2% using signal from moving targets. The contrast-to-noise ratio (CNR) increased by 20.5% and 12.8% using static and moving targets, respectively. Doppler signal strength increased by 5.6% and 4.9% for the static and moving-targets methods, respectively.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control 10/2009; 56(10):2157-66. · 1.80 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, we investigated the feasibility of an intracranial catheter transducer with dual-mode capability of real-time 3D (RT3D) imaging and ultrasound hyperthermia, for application in the visualization and treatment of tumors in the brain. Feasibility is demonstrated in two ways: first by using a 50-element linear array transducer (17 mm x 3.1 mm aperture) operating at 4.4 MHz with our Volumetrics diagnostic scanner and custom, electrical impedance-matching circuits to achieve a temperature rise over 4 degrees C in excised pork muscle, and second, by designing and constructing a 12 Fr, integrated matrix and linear-array catheter transducer prototype for combined RT3D imaging and heating capability. This dual-mode catheter incorporated 153 matrix array elements and 11 linear array elements diced on a 0.2 mm pitch, with a total aperture size of 8.4 mm x 2.3 mm. This 3.64 MHz array achieved a 3.5 degrees C in vitro temperature rise at a 2 cm focal distance in tissue-mimicking material. The dual-mode catheter prototype was compared with a Siemens 10 Fr AcuNav catheter as a gold standard in experiments assessing image quality and therapeutic potential and both probes were used in an in vivo canine brain model to image anatomical structures and color Doppler blood flow and to attempt in vivo heating.
[Show abstract][Hide abstract] ABSTRACT: Vibrations can be induced in ferromagnetic shrapnel by a variable electromagnet. Real time 3-D color Doppler ultrasound located the induced motion in a needle fragment and determined its 3-D position in the scanner coordinates. This information was used to guide a robot which moved a probe to touch the shrapnel fragment.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control 02/2009; 56(7):1301-3. · 1.80 Impact Factor