Preparation and imaging of intravascular high-frequency transducer

Intravascular ultrasound (IVUS) imaging is by far the most favorable imaging modality for coronary artery evaluation. IVUS transducer design and fabrication, a key technology for intravascular ultrasound imaging, has a significant impact on the performance of the imaging results. Herein, a 35-MHz side-looking IVUS transducer probe was developed. With a small aperture of 0.40 mm × 0.40 mm, the transducer exhibited a very wide -6 dB bandwidth of 85% and a very low insertion loss of -12 dB. Further, the in vitro IVUS imaging of a porcine coronary artery was performed to clearly display the vessel wall structure while the corresponding color-coded graph was constructed successfully to distinguish necrotic core and fibrous plaque via image processing. The results demonstrated that the imaging performance of the optimized design transducer performs favorably

An open system for intravascular ultrasound imaging

Author name used in this publication: Cheng, Wang FaiInvited conference paper2011-2012 > Academic research: refereed > Invited conference paperVersion of RecordPublishe

In-Vitro MPI-Guided IVOCT Catheter Tracking in Real Time for Motion Artifact Compensation

Purpose: Using 4D magnetic particle imaging (MPI), intravascular optical coherence tomography (IVOCT) catheters are tracked in real time in order to compensate for image artifacts related to relative motion. Our approach demonstrates the feasibility for bimodal IVOCT and MPI in-vitro experiments. Material and Methods: During IVOCT imaging of a stenosis phantom the catheter is tracked using MPI. A 4D trajectory of the catheter tip is determined from the MPI data using center of mass sub-voxel strategies. A custom built IVOCT imaging adapter is used to perform different catheter motion profiles: no motion artifacts, motion artifacts due to catheter bending, and heart beat motion artifacts. Two IVOCT volume reconstruction methods are compared qualitatively and quantitatively using the DICE metric and the known stenosis length. Results: The MPI-tracked trajectory of the IVOCT catheter is validated in multiple repeated measurements calculating the absolute mean error and standard deviation. Both volume reconstruction methods are compared and analyzed whether they are capable of compensating the motion artifacts. The novel approach of MPI-guided catheter tracking corrects motion artifacts leading to a DICE coefficient with a minimum of 86% in comparison to 58% for a standard reconstruction approach. Conclusions: IVOCT catheter tracking with MPI in real time is an auspicious method for radiation free MPI-guided IVOCT interventions. The combination of MPI and IVOCT can help to reduce motion artifacts due to catheter bending and heart beat for optimized IVOCT volume reconstructions.Comment: 19 pages, 11 figure

Simultaneous Morphological and Flow Imaging Enabled by Megahertz Intravascular Doppler Optical Coherence Tomography

We demonstrate three-dimensional intravascular flow imaging compatible with routine clinical image acquisition workflow by means of megahertz (MHz) intravascular Doppler Optical Coherence Tomography (OCT). The OCT system relies on a 1.1 mm diameter motorized imaging catheter and a 1.5 MHz Fourier Domain Mode Locked (FDML) laser. Using a post processing method to compensate the drift of the FDML laser output, we can resolve the Doppler phase shift between two adjoining OCT A-line datasets. By interpretation of the velocity field as measured around the zero phase shift, the flow direction at specific angles can be qualitatively estimated. Imaging experiments were carried out in phantoms, micro channels, and swine coronary artery in vitro at a speed of 600 frames/s. The MHz wavelength sweep rate of the OCT system allows us to directly investigate flow velocity of up to 37.5 cm/s while computationally expensive phase-unwrapping has to be applied to measure such high speed using conventional OCT system. The MHz sweep rate also enables a volumetric Doppler imaging even with a fast pullback at 40 mm/s. We present the first simultaneously recorded 3D morphological images and Doppler flow profiles. Flow pattern estimation and three-dimensional structural reconstruction of entire coronary artery are achieved using a single OCT pullback dataset

Intravascular Fluorescence lifetime characterization of Atherosclerosis

Fluorescence lifetime imaging (FLIm) provides a biochemical signature of tissue based on autofluorescence properties. Here, we developed an integrated FLIm-IVUS imaging catheter system, suitable for the interrogation of coronary arteries in vivo. This includes adapting a pulse sampling acquisition scheme to enable co-registered FLIm-IVUS acquisition and designing, fabricating and testing a motor drive unit and low profile FLIm-IVUS catheter. The ability of this instrument to acquire robust FLIm data in coronary arteries in vivo using conventional percutaneous coronary intervention techniques was evaluated in swine model. Imaging of ex vivo human samples confirmed the benefit of additional accurately co-registered spectroscopic data to IVUS for improved lesion characterization. Optimization of optical and mechanical performance of the catheter was achieved with the development of a monolithic freeform reflective optics that enables improvements in collection efficiency, and lateral resolution in a compact, fluorescence background free element [P2]. Finally, a pilot comparative imaging study of ex vivo human artery samples was performed using the pulse sampling FLIm data acquisition technique, combined with Raman spectroscopy, by means of a bimodal forward-viewing optical probe. Methods were developed for the automated analysis of FLIm contrast sources using Raman spectroscopy data. The development of dedicated intravascular instrumentation combined with further understanding of the information provided by FLIm will improve the relevance of FLIm as a practical tool for the investigation of atherosclerosis. Future work will focus on regulatory activities to enable studies in human subjects, where the ability of FLIm to provide the biochemical signature of lesions in vivo may be leveraged to improve understanding of the disease natural history, develop new drugs, and possibly be used in clinical settings to improve patient treatment

Ultrasound Probe Calibration Method of Single-Wire Phantom Using Levenberg-Marquardt Algorithm

A freehand three-dimensional (3D) ultrasound system is a method of acquiring images using a 3D ultrasound probe or conventional two-dimensional (2D) ultrasound probe to give a 3D visualization of an object inside the body. Ultrasounds are used extensively in clinical applications since they are advantageous in that they do not bring dangerous radiation effects and have a low cost. However, a probe calibration method is needed to transform the coordinate position into a 3D visualization display, especially for image-guided intervention. The current ultrasound probe calibration system usually uses the numerical regression method for the N-wire phantom, which has problems in accuracy and reliability due to nonlinear point scattered ultrasound image data. Hence, a method for ultrasound probe positional calibration of single-wire phantom using the Levenberg-Marquardt algorithm (LMA) was proposed to overcome this weakness. This experiment consisted of an optical tracking system setup, a 2D ultrasound probe with marker, an ultrasound machine, and a single-wire object in a water container equipped with a marker. The position and orientation of the marker in a 2D ultrasound probe and the marker in the water container were tracked using the optical tracking system. A 2D ultrasound probe was equipped with a marker connected wirelessly using an optical tracking system to capture the single-wire object. The resulting sequences of 2D ultrasound images were reconstructed and visualized into 3D ultrasound images using three transformations, ultrasound beam to ultrasound probe’s marker, single-wire phantom position to container’s marker, and the 3D visualization transformation. The LMA was used to determine the best optimization parameters for determining the exact position and representing that 3D visualization. The experiment result showed that the lowest mean square error (MSE), rotation error, and translation error were 0.45 mm, 0.25°, and 0.3828 mm, respectively

Integrated Electronics for Wireless Imaging Microsystems with CMUT Arrays

Integration of transducer arrays with interface electronics in the form of single-chip CMUT-on-CMOS has emerged into the field of medical ultrasound imaging and is transforming this field. It has already been used in several commercial products such as handheld full-body imagers and it is being implemented by commercial and academic groups for Intravascular Ultrasound and Intracardiac Echocardiography. However, large attenuation of ultrasonic waves transmitted through the skull has prevented ultrasound imaging of the brain. This research is a prime step toward implantable wireless microsystems that use ultrasound to image the brain by bypassing the skull. These microsystems offer autonomous scanning (beam steering and focusing) of the brain and transferring data out of the brain for further processing and image reconstruction. The objective of the presented research is to develop building blocks of an integrated electronics architecture for CMUT based wireless ultrasound imaging systems while providing a fundamental study on interfacing CMUT arrays with their associated integrated electronics in terms of electrical power transfer and acoustic reflection which would potentially lead to more efficient and high-performance systems. A fully wireless architecture for ultrasound imaging is demonstrated for the first time. An on-chip programmable transmit (TX) beamformer enables phased array focusing and steering of ultrasound waves in the transmit mode while its on-chip bandpass noise shaping digitizer followed by an ultra-wideband (UWB) uplink transmitter minimizes the effect of path loss on the transmitted image data out of the brain. A single-chip application-specific integrated circuit (ASIC) is de- signed to realize the wireless architecture and interface with array elements, each of which includes a transceiver (TRX) front-end with a high-voltage (HV) pulser, a high-voltage T/R switch, and a low-noise amplifier (LNA). Novel design techniques are implemented in the system to enhance the performance of its building blocks. Apart from imaging capability, the implantable wireless microsystems can include a pressure sensing readout to measure intracranial pressure. To do so, a power-efficient readout for pressure sensing is presented. It uses pseudo-pseudo differential readout topology to cut down the static power consumption of the sensor for further power savings in wireless microsystems. In addition, the effect of matching and electrical termination on CMUT array elements is explored leading to new interface structures to improve bandwidth and sensitivity of CMUT arrays in different operation regions. Comprehensive analysis, modeling, and simulation methodologies are presented for further investigation.Ph.D

Intravascular Detection of Microvessel Infiltration in Atherosclerotic Plaques: An Intraluminal Extension of Acoustic Angiography

Cardiovascular disease is the leading cause of death worldwide, surpassing both stroke and cancer related mortality with 17.5 million deaths in 2014 alone. Atherosclerosis is the build-up of fatty deposits within arteries and is responsible for the majority of cardiovascular related deaths. Over the past decade, research in atherosclerosis has identified that a key limitation in the appropriate management of the disease is detecting and identifying dangerous fatty plaque build-ups before they dislodge and cause major cardiovascular events, such as embolisms, stroke, or myocardial infarctions. It has been noted that plaques vulnerable to rupture have several key features that may be used to distinguish them from asymptomatic plaques. One key identifier of a dangerous plaque is the presence of blood flow within the plaque itself since this is an indicator of growth and instability of the plaque. Recently, a superharmonic imaging method known as “acoustic angiography” has been shown to resolve microvasculature with unprecedented quality and could be a possible method of detecting blood vessel infiltration within these plaques. This dissertation describes the material and methods used to move the application of “acoustic angiography” to a reduced form factor typical of intravascular catheters and to demonstrate its ability to detect microvasculature. The implementation of this approach is described in terms of the contrast agents used to generate superharmonic signals, the dual-frequency transducers to image them, and the hardware needed to operate them in order to establish how these design choices can impact the quality of the images produced. Furthermore, this dissertation demonstrates how image processing methods such as adaptive windowing or automated sound speed correction can further enhance image quality of vascular targets. The results of these chapters show how acoustic angiography may be optimized using engineering considerations both in signal acquisition and post processing. Overall, these studies demonstrate that acoustic angiography can be performed using a catheter-deployable dual-frequency transducer to detect microvasculature through superharmonic imaging methods.Doctor of Philosoph

Optics and Quantum Electronics

Contains table of contents on Section 3 and reports on nineteen research projects.Defense Advanced Research Projects Agency Grant F49620-96-0126Joint Services Electronics Program Grant DAAH04-95-1-0038National Science Foundation Grant ECS 94-23737U.S. Air Force - Office of Scientific Research Contract F49620-95-1-0221U.S. Navy - Office of Naval Research Grant N00014-95-1-0715Defense Advanced Research Projects Agency/National Center for Integrated Photonics TechnologyMultidisciplinary Research InitiativeU.S. Air Force - Office of Scientific ResearchNational Science Foundation/MRSECU.S. Navy - Office of Naval Research (MFEL) Contract N00014-91-J-1956National Institutes of Health Grant R01-EY11289U.S. Navy - Office of Naval Research (MFEL) Contract N00014-94-0717Defense Advanced Research Projects Agency Contract N66001-96-C-863