The natural history of atherosclerosis is marked by changes in the lipid biochemistry in the diseased arterial wall. As lesions become more vulnerable, different cholesterol species accumulate in the plaque. Understanding unstable atherosclerosis as a pharmacological and interventional therapeutic target requires chemically specific imaging of disease foci. In this study, we aim to image atherosclerotic plaque lipids and other vessel wall constituents with spectroscopic intravascular photoacoustics (sIVPA). sIVPA imaging can identify lipids in human coronary atherosclerotic plaque by relying on contrast in the near-infrared absorption spectra of the arterial wall components. Using reference spectra acquired on pure compounds, we analyzed sIVPA data from human coronary plaques ex vivo, to image plaque composition in terms of cholesterol and cholesterol ester content. In addition, we visualized the deeper lying connective tissue layers of the adventitia, as well as the fatty acid containing adipose cells in the peri-adventitial tissue. We performed simultaneous coregistered IVUS imaging to obtain complementary morphological information. Results were corroborated by histopathology. sIVPA imaging can distinguish the most prevalent lipid components of human atherosclerotic plaques and also visualize the connective tissue layers of the adventitia and the fatty acid containing adipose cells in the peri-adventitial tissue.
The catheter-based intravascular photoacoustic (IVPA) imaging for diagnosing atherosclerosis, which can provide optical absorption contrast of the arterial wall besides acoustic scattering contrast from the conventional intravascular ultrasound (IVUS) imaging, has been intensively researched recently. The resolution of IVPA is determined by the frequency bandwidth of an ultrasonic transducer. Higher resolution can be achieved by increasing the transducer's working frequency and bandwidth. We introduce IVPA imaging at 35 and 80 MHz by using newly designed integrated IVUS/IVPA probes. This is the first time IVPA has been achieved as high as 80 MHz. Six-micrometer tungsten wires were imaged to evaluate the probes' spatial resolutions and beam patterns. Healthy rabbit aorta was imaged in vitro. Imaging results show that IVPA has superior contrast over IVUS in identifying the arterial wall, and IVPA at 80 MHz demonstrates extraordinary resolution (35 μm) compared to 35 MHz.
Intravascular ultrasound (IVUS) is mature imaging modality to diagnose blood vessel disease, especially for calcification characterization. Based on the intrinsic optical absorption, intravascular photoacoustic (IVPA) works as a complementary method to IVUS. In this paper, we develop a miniature intravascular probe combined photoacoustic and ultrasound imaging. The optical components and ultrasound transducer were integrated to achieve internal illumination. Atherosclerotic human artery was imaged ex vivo, which demonstrates the imaging ability of the multi-functional probe and illustrate its clinical potential.
Intracoronary optical coherence tomography (OCT) and intravascular ultrasound (IVUS) are two popular
techniques for the detection and determination of atherosclerosis. IVUS allows visualization of plaques while also
providing a large penetration depth to determine plaque volume. Intracoronary OCT provides the ability to capture
microscopic features associated with high risk plaque. Traditionally to utilize the benefits of both modalities, separate
probes and systems had to be used one at a time to image a vessel. We present work required to create a combined OCT
IVUS system capable of simultaneous imaging to detect atherosclerotic plaques. A novel integrated probe of size 0.69
mm OD featuring sequential placement of components was created to acquire co-registered images within small
coronary vessels. By utilizing commercial graphics processing units (GPUs) real time visualization of acquired data is
possible up to a maximum 48 frames per second per channel. In vitro studies on human coronary artery samples as well
as in vivo studies in rabbits and pigs show various plaque buildups in both OCT and IVUS images which match
histology results, demonstrating the capabilities of the system.
Arterial wall is composed of three layers: intima, media and adventitia. Intima-media thickness (IMT) is an important
prognostic indicator of atherosclerotic diseases. Although intravascular ultrasound (IVUS) imaging is a commonly used
method for delineation of the layered structures, it is inferior to the optical absorption contrast offered by intravascular
photoacoustic (IVPA) imaging. We introduce an integrated miniature probe that combines the capabilities of IVUS and
IVPA imaging for the evaluation of arterial wall layered structures. Healthy rabbit aorta was imaged ex vivo. IVPA
results showed superior contrast over IVUS in identifying the layered structures of arterial wall.
A miniature integrated optical coherence tomography (OCT) - ultrasound (US) probing system for real-time
intravascular imaging has been developed. The outer diameter of the integrated probe is 0.69 mm, which is small enough
for imaging in human coronary arteries. This probe, which has high resolution and deep tissue penetration, is designed to
identify vulnerable atherosclerotic plaques in coronary arteries. The first in vivo images of a rabbit abdominal aorta
obtained by the integrated OCT-US probe are presented.
We report on the synergy of an integrated ultrasound (US) and photoacoustic (PA) probe system for intravascular imaging. The combined dual-modality probe is based on a 39 MHz ring-shaped US transducer which detects both US echoes and laser-generated PA signals. By combining optical fiber, US transducer, and micromirror, we can obtain intravascular cross-sectional B-scan images by internal illumination of the sample. The performance of the probe is evaluated in a phantom study. Moreover, the coaxially designed probe also provides co-registered US and PA images of a normal rabbit aorta, which demonstrates the imaging ability of the dual-functional system, implying future clinical applications.
KEYWORDS: Optical coherence tomography, Ultrasonography, In vivo imaging, Transducers, Imaging systems, Lithium, Data acquisition, In vitro testing, Arteries, Intravascular ultrasound
We have developed a miniature integrated optical coherence tomography (OCT) ultrasound (US) probing system for intravascular imaging applications. In the OCT probe, the light coming out of a single mode fiber is focused by a gradient-index lens and then reflected by a right-angle prism from the side of the probe into the sample. It was combined with a 35 MHz PMN-PT side-viewing ultrasound transducer to obtain the ultrasound image as well. The OCT and ultrasound probes were integrated as a single probe to obtain OCT and ultrasound images simultaneously. The integrated probe has an outer diameter of 0.69 mm which, to our knowledge, is the smallest integrated OCT-US probe reported. Fast data acquisition and processing was implemented for real-time imaging. In vitro OCT and US images of human coronary artery with pathology, as well as in vivo images of normal rabbit abdominal aorta, were obtained using the integrated OCT-US probe to demonstrate its capability.
Photoacoustic imaging and optical coherence tomography are two emerging imaging modalities which provide
complementary optical absorption and scattering contrasts for biological tissues. While photoacoustic imaging provides
tissue vasculature information, optical coherence tomography offers micron-scale morphological imaging with
penetration depths of 1~3 mms. Pulse-echo ultrasound is readily available from photoacoustic system and it provides
tissue structure information at deeper depths with resolutions scalable with the transducer frequency. We present a
prototype endoscope that consists of a ball lensed optical coherence tomography probe, a right-angled multimode fiber
for delivering the laser beam for photoacoustic imaging, and a high frequency ultrasound transducer of 35 MHz center
frequency. The overall diameter is 5mms. Porcine ovaries were imaged ex vivo to demonstrate the capability of this new
combined endoscopy. The microvascular and high resolution structural images at subsurface and deeper tissue range
demonstrate the synergy of the combined endoscopy over each modality alone.
For in vivo medical applications, endoscopy shows great potential for its minimally invasive manner,
flexibility and close-up imaging characteristic. A miniaturized imaging probe combining ultrasound and
photoacoustic endoscopy has been developed. The output of a 532-nm pulse laser was coupled into and
delivered to the probe by a 200-micron-core multimode fiber. A 40 MHz ring shape ultrasound transducer
was fabricated to receive pulse echo ultrasound and photoacoustic signals as well. The light-guiding optical
fiber, the ring ultrasound transducer, and a mirror-based reflective material for the coaxial laser beam and
ultrasound signal were integrated into the probe with a final packaged diameter of 2.5 mm. The
performance of the probe was tested by imaging a graphite rod. The imaging ability of this dual-modality
system was demonstrated by imaging the cross section of a rabbit aorta.
We report on the development of a multimodal optical coherence tomography (OCT) - ultrasound (US)
system and miniaturized OCT-US probe for intravascular imaging. Both OCT optical components and a US
transducer were integrated into a single probe, enabling both OCT and US imaging at the same time. A
miniaturized OCT-US probe using a single element transducer was designed with a maximum outer diameter
of 0.8 mm, which is suitable for in vivo intravascular imaging. The integrated OCT-US imaging system
adopted a two-channel data acquisition card to digitize both OCT and US signals. Simultaneous OCT and US
data processing and image display were also achieved using our home-developed software. In vitro OCT and
US imaging of human aortic tissue was performed using this multimodal imaging system, which
demonstrated the feasibility of the OCT-US system in intravascular imaging and its potential in detection of
atherosclerotic plaques.
Optical coherence tomography (OCT) and intravascular ultrasound (IVUS) are considered two complementary imaging
techniques in the detection and diagnosis of atherosclerosis. OCT permits visualization of micron-scale features of
atherosclerosis plaque, and IVUS offers full imaging depth of vessel wall. Under the guidance of IVUS, minimal amount
of flushing agent will be needed to obtain OCT imaging of the interested area. We report on a dual-modality optical
coherence tomography (OCT) - ultrasound (US) system for intravascular imaging. To the best of our knowledge, we
have developed the first integrated OCT-US probe that combines OCT optical components with an ultrasound transducer.
The OCT optical components mainly consist of a single mode fiber, a gradient index (GRIN) lens for light beam
focusing, and a right-angled prism for reflecting light into biological tissue. A 40MHz PZT-5H side-viewing ultrasound
transducer was fabricated to obtain the ultrasound image. These components were integrated into a single probe,
enabling both OCT and ultrasound imaging at the same time. In vitro OCT and ultrasound images of a rabbit aorta were
obtained using this dual-modality imaging system. This study demonstrates the feasibility of an OCT-US system for
intravascular imaging which is expected to have a prominent impact on early detection and characterization of
atherosclerosis.
We report on a dual-modality optical coherence tomography (OCT) ultrasound (US) system for intravascular imaging. To the best of our knowledge, we have developed the first integrated OCT-US probe that combines OCT optical components with an US transducer. The OCT optical components mainly consist of a single-mode fiber, a gradient index lens for light-beam focusing, and a right-angled prism for reflecting light into biological tissue. A 40-MHz piezoelectric transducer (PZT-5H) side-viewing US transducer was fabricated to obtain the US image. These components were integrated into a single probe, enabling both OCT and US imaging at the same time. In vitro OCT and ultrasound images of a rabbit aorta were obtained using this dual-modality imaging system. This study demonstrates the feasibility of an OCT-US system for intravascular imaging, which is expected to have a prominent impact on early detection and characterization of atherosclerosis.
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