An Automatic 3-D Ultrasound and Photoacoustic Combined Imaging System for Human Inflammatory Arthritis.

Aiming at a point-of-care device for rheumatology clinics, we developed an automatic 3-D imaging system combining the emerging photoacoustic (PA) imaging with conventional Doppler ultrasound (US) for detecting human inflammatory arthritis. This system is based on a commercial-grade GE HealthCare (GEHC, Chicago, IL, USA) Vivid E95 US machine and a Universal Robot UR3 robotic arm. This system automatically locates the patient's finger joints from a photograph taken by an overhead camera powered by an automatic hand joint identification method, followed by the robotic arm moving the imaging probe to the targeted joint to scan and obtain 3-D PA and Doppler US images. The GEHC US machine was modified to enable high-speed, high-resolution PA imaging while maintaining the features available on the system. The commercial-grade image quality and the high sensitivity in detecting inflammation in peripheral joints via PA technology hold great potential to significantly benefit clinical care of inflammatory arthritis in a novel way.

Longitudinal volumetric assessment of inflammatory arthritis via photoacoustic imaging and Doppler ultrasound imaging.

Aiming at clinical translation, we developed an automatic 3D imaging system combining the emerging photoacoustic imaging with conventional Doppler ultrasound for detecting inflammatory arthritis. This system was built with a GE HealthCare (GEHC) Vivid™ E95 ultrasound system and a Universal Robot UR3 robotic arm. In this work, the performance of this system was examined with a longitudinal study utilizing a clinically relevant adjuvant induced arthritis (AIA) murine model. After adjuvant injection, daily imaging of the rat ankle joints was conducted until joint inflammation was obvious based on visual inspection. Processed imaging results and statistical analyses indicated that both the hyperemia (enhanced blood volume) detected by photoacoustic imaging and the enhanced blood flow detected by Doppler ultrasound reflected the progress of joint inflammation. However, photoacoustic imaging, by leveraging the highly sensitive optical contrast, detected inflammation earlier than Doppler ultrasound, and also showed changes that are more statistically significant. This side-by-side comparison between photoacoustic imaging and Doppler ultrasound using the same commercial grade GEHC ultrasound machine demonstrates the advantage and potential value of the emerging photoacoustic imaging for rheumatology clinical care of arthritis.

Photoacoustic Imaging of COVID-19 Vaccine Site Inflammation of Autoimmune Disease Patients.

Based on the observations made in rheumatology clinics, autoimmune disease (AD) patients on immunosuppressive (IS) medications have variable vaccine site inflammation responses, whose study may help predict the long-term efficacy of the vaccine in this at-risk population. However, the quantitative assessment of the inflammation of the vaccine site is technically challenging. In this study analyzing AD patients on IS medications and normal control subjects, we imaged the inflammation of the vaccine site 24 h after mRNA COVID-19 vaccinations were administered using both the emerging photoacoustic imaging (PAI) method and the established Doppler ultrasound (US) method. A total of 15 subjects were involved, including 6 AD patients on IS and 9 normal control subjects, and the results from the two groups were compared. Compared to the results obtained from the control subjects, the AD patients on IS medications showed statistically significant reductions in vaccine site inflammation, indicating that immunosuppressed AD patients also experience local inflammation after mRNA vaccination but not in as clinically apparent of a manner when compared to non-immunosuppressed non-AD individuals. Both PAI and Doppler US were able to detect mRNA COVID-19 vaccine-induced local inflammation. PAI, based on the optical absorption contrast, shows better sensitivity in assessing and quantifying the spatially distributed inflammation in soft tissues at the vaccine site.

Volumetric Ophthalmic Ultrasound for Inflight Monitoring of Visual Impairment and Intracranial Pressure.

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. MATERIALS AND METHODS: A prototype three-dimensional (3-D) probe was integrated onto a portable ultrasound scanner. Image analysis algorithms were developed to automatically detect the ocular anatomy and simultaneously render views of the optic nerve with improved sheath definition. Curvature metrics were calculated from 3-D retinal surfaces to quantify posterior globe flattening, and tissue velocity waveforms of the optic nerve were analyzed to assess intracranial dynamics. RESULTS: New 3-D structural measurements were evaluated in a head-down tilt study. The response of optic nerve sheath and globe flattening metrics were quantified in 11 healthy volunteers from baseline to moderately elevated ICP. The optic nerve measurements showed good correlation with existing two-dimensional (2-D) methods and an acute response to increased ICP, while globe flattening did not show an acute response. The tissue velocities were evaluated in a porcine model from baseline to significantly elevated ICP and correlated with invasive ICP readings in four animals. CONCLUSIONS: Volumetric ophthalmic imaging was demonstrated on a portable ultrasound system and structural measurements validated with existing methods. New 3-D structural measurements and dynamic measurements were evaluation during in vivo studies. Further investigations are needed to evaluate improvements in performance for non-experts and application to clinically relevant conditions.

First in vivo use of a capacitive micromachined ultrasound transducer array-based imaging and ablation catheter.

OBJECTIVES: The primary objective was to test in vivo for the first time the general operation of a new multifunctional intracardiac echocardiography (ICE) catheter constructed with a microlinear capacitive micromachined ultrasound transducer (ML-CMUT) imaging array. Secondarily, we examined the compatibility of this catheter with electroanatomic mapping (EAM) guidance and also as a radiofrequency ablation (RFA) catheter. Preliminary thermal strain imaging (TSI)-derived temperature data were obtained from within the endocardium simultaneously during RFA to show the feasibility of direct ablation guidance procedures. METHODS: The new 9F forward-looking ICE catheter was constructed with 3 complementary technologies: a CMUT imaging array with a custom electronic array buffer, catheter surface electrodes for EAM guidance, and a special ablation tip, that permits simultaneous TSI and RFA. In vivo imaging studies of 5 anesthetized porcine models with 5 CMUT catheters were performed. RESULTS: The ML-CMUT ICE catheter provided high-resolution real-time wideband 2-dimensional (2D) images at greater than 8 MHz and is capable of both RFA and EAM guidance. Although the 24-element array aperture dimension is only 1.5 mm, the imaging depth of penetration is greater than 30 mm. The specially designed ultrasound-compatible metalized plastic tip allowed simultaneous imaging during ablation and direct acquisition of TSI data for tissue ablation temperatures. Postprocessing analysis showed a first-order correlation between TSI and temperature, permitting early development temperature-time relationships at specific myocardial ablation sites. CONCLUSIONS: Multifunctional forward-looking ML-CMUT ICE catheters, with simultaneous intracardiac guidance, ultrasound imaging, and RFA, may offer a new means to improve interventional ablation procedures.

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.

Miniaturized ultrasound imaging probes enabled by CMUT arrays with integrated frontend electronic circuits.

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.

Non-invasive hemodynamic state monitoring using ultrasound.

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.

A family of intracardiac ultrasound imaging devices designed for guidance of electrophysiology ablation procedures.

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.

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.

The acoustic lens design and in vivo use of a multifunctional catheter combining intracardiac ultrasound imaging and electrophysiology sensing.

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.

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 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.

Development of an electrophysiology (EP)-enabled intracardiac ultrasound catheter integrated with NavX 3-dimensional electrofield mapping for guiding cardiac EP interventions: experimental studies.

OBJECTIVE: We have developed an integrated high-resolution intracardiac echocardiography (ICE) catheter for electrophysiology (EP) testing, which can be coregistered in 3-dimensional space with EP testing and ablation catheters using electrofield sensing. METHODS: Twelve open-chest pigs (34-55 kg) and 3 closed-chest pigs were studied. After introduction from the jugular or femoral venous locations, the 9F side-looking, highly steerable (0 degrees -180 degrees), 64-element array catheters could be manipulated easily throughout the right side of the heart. Multisite cardiac pacing was performed for assessing left ventricular (LV) synchrony using tissue Doppler methods. Also, in the open-chest pigs, right atrial (RA) and right ventricular (RV) ablations were performed with a separate radio frequency catheter under fluoroscopic guidance and visualized with ICE to characterize the changes. In the 3 closed-chest pigs, electrofield NavX 3-dimensional coregistration (St Jude Medical Corp, Minneapolis, MN) allowed us to test whether this additional feature could shorten the time necessary to perform 4 targeted ablations in each animal while imaging the ablation catheter and the adjacent region by ICE. RESULTS: Intracardiac anatomy, tricuspid, aortic, pulmonary, and mitral valve function, and pulmonary vein flow were all imaged reproducibly from scanning locations in the RA or RV in all animals, along with assessment of cardiac motion and the effects of multisite pacing. Three-dimensional electrofield displays detailed the spatial relationship between the ICE catheter and ablation catheters such that the time to visualize and ablate 4 sites in each of the 3 closed-chest animals was reduced. CONCLUSIONS: This new technology is a first step in the integration of ICE with EP procedures.

Array signal processing for local arterial pulse wave velocity measurement using ultrasound.

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.