Analysis of intravascular optical coherence tomography (IVOCT) data has potential for real-time in vivo plaque classification. We developed a processing pipeline on a three-dimensional local region of support for estimation of optical properties of atherosclerotic plaques from coronary artery, IVOCT pullbacks. Using realistic coronary artery disease phantoms, we determined insignificant differences in mean and standard deviation estimates between our pullback analyses and more conventional processing of stationary acquisitions with frame averaging. There was no effect of tissue depth or oblique imaging on pullback parameter estimates. The method’s performance was assessed in comparison with observer-defined standards using clinical pullback data. Values (calcium 3.58±1.74 mm−1, lipid 9.93±2.44 mm−1, and fibrous 1.96±1.11 mm−1) were consistent with previous measurements obtained by other means. Using optical parameters (μt, 〈I〉, I0), we achieved feature space separation of plaque types and classification accuracy of 92.5±3%. Despite the rapid z motion and varying incidence angle in pullbacks, the proposed computational pipeline appears to work as well as a more standard “stationary” approach.
We propose and test various strategies for the creation of artery phantoms mimicking different kinds of diseased arteries when imaged by intravascular optical coherence tomography (IVOCT). We first review the method for making healthy artery phantoms. We then describe the procedure to fabricate diseased artery phantoms with intima thickening, lipid pool, thin-capped fibroatheroma, calcification, and restenosis (homogeneous and layered) after stent apposition. For each case, a phantom is fabricated, an IVOCT image is obtained, and the image is compared to that of a real artery.
We explored the potential of intravascular optical coherence tomography (IVOCT) to assess deformation during angioplasty balloon inflation. Using a semi-compliant balloon and artery phantoms, we considered two experimental scenarios. The goal for the first scenario was to investigate if variation in the elasticity of the structure surrounding the balloon could be sensed by IVOCT monitoring. In this scenario, we used three single-layer phantoms with various mechanical properties. Image analysis was performed to extract the inner and outer diameters of the phantoms at various pressures. The goal for the second scenario was twofold. First, we investigated the IVOCT capability to monitor a more complex balloon inflation process. The balloon was in a folded state prior to inflation. This allowed studying two stages of deformation: during balloon unfolding and during balloon expansion. Second, we investigated IVOCT capability to monitor the deformation in a three-layer phantom used to better mimic a true artery. So, not only were the IVOCT images processed to provide the inner and outer diameters of the phantom, but the layer thicknesses were also determined. In both scenarios, IVOCT monitoring revealed to be very efficient in providing relevant information about the phantom deformation during balloon inflation.
The Industrial Material Institute (IMI) together with the Institute for Biodiagnostic (IBD) has developed its own optical
catheters for cardiovascular imaging applications. Those catheters have been used experimentally in the in vitro coronary
artery model of the Langendorff beating heart and in a percutaneous coronary intervention procedure in a porcine model.
For some catheter designs, non-uniform rotational distortion (NURD) can be observed as expected from past experience
with intra-vascular ultrasound (IVUS) catheters.
A two-dimensional (2D) coronary artery test bench that simulates the path into the coronary arteries has been developed.
The presence or absence of NURD can be assessed with the test bench using a custom-built cardiovascular Optical
Coherence Tomography (OCT) imaging system. A square geometry instead of the circular shape of an artery is used to
simulate the coronary arteries. Thereby, it is easier to visualize NURD when it is present. The accumulated torsion
induced by the friction on the catheter is measured along the artery path.
NURD is induced by the varying friction force that is balanced by the accumulated torsion force. The pullback force is
measured and correlated with NURD observed in the 2D test bench. Finally, a model is presented to help understanding
the mechanical constraint that leads to the friction force variations.
We explore the potential of intravascular or endoscopic optical coherence tomography (OCT) to extract relevant
mechanical properties of a tissue deformed by an inflating balloon. Tubular OCT phantoms with different mechanical
properties are fabricated. The phantoms are deformed by an inflating balloon, and the deformation is monitored with
OCT. A quantitative description of the phantom deformation is obtained by segmenting the OCT images. Two strategies
to extract the mechanical properties from this quantitative data are presented: by comparing to a finite-element
simulation and by performing a mechanical analysis.
In this paper, we present recent development of phantoms of coronary arteries with representative
mechanical properties. The phantoms were made of poly(vinyl alcohol) cryogel (PVA-C).
Multilayer phantoms were fabricated by an overmoulding process. The optical properties are
adjusted in each layer by the different number of freeze-thaw cycles in combination with additives.
The mechanical properties of the multilayer phantoms are characterized, and various means for
improving the strain hardening are investigated.
The advantages and limitations of using a beating heart model in the development of intravascular optical coherence tomography are discussed. The model fills the gap between bench experiments, performed on phantoms and excised arteries, and whole animal in-vivo preparations. The beating heart model is stable for many hours, allowing for extended measurement times and multiple imaging sessions under in-vivo conditions without the complications of maintaining whole-animal preparation. The perfusate supplying the heart with nutrients can be switched between light scattering blood to a nonscattering perfusate to allow the optical system to be optimized without the need of an efficient blood displacement strategy. Direct access to the coronary vessels means that there is no need for x-ray fluoroscopic guidance of the catheter to the heart, as is the case in whole animal preparation. The model proves to be a valuable asset in the development of our intravascular optical coherence tomography technology.
We previously presented a method to fabricate phantoms of normal coronary arteries. This method allows the
deposition of multiple layers on a tubular structure, each layer replicating optical and mechanical properties
of coronary artery layers. We now present an improved method to produce phantoms of arteries affected by
atherosclerosis. The method now includes techniques to introduce structures that mimics the OCT signature of
a calcification and of a lipid pool.
We report preliminary results toward making artery phantoms for Optical Coherence Tomography (OCT) that also
exhibit mechanical properties similar to arteries for large deformation regimes. A matrix of PVA cryogels is used to
obtain the strain hardening effect characteristic of arteries. Means of adjusting the optical properties of PVA
cryogels are investigated and the resulting mechanical properties are characterized.
We developed coronary artery phantoms that should be of great use for intravascular optical coherence tomography. Our phantoms mimic the OCT signal profile of coronary arteries, show mechanical properties approaching those of real tissue, and are durable.
Optical coherence tomography (OCT) is emerging as a technology that can potentially be used for the detection and monitoring of early dental enamel caries since it can provide high-resolution depth imaging of early lesions. To date, most caries detection optical technologies are well suited for examining caries at facial, lingual, incisal and occlusal surfaces. The approximal surfaces between adjacent teeth are difficult to examine due to lack of visual access and limited space for these new caries detection tools. Using a catheter-style probe developed at the NRC-Industrial Materials Institute, the probe was inserted into the interproximal space to examine the approximal surfaces with OCT imaging at 1310 nm. The probe was rotated continuously and translated axially to generate depth images in a spiral fashion. The probe was used in a mock tooth arch model consisting of extracted human teeth mounted with dental rope wax in their anatomically correct positions. With this ex vivo model, the probe provided images of the approximal surfaces revealing morphological structural details, regions of calculus, and especially regions of early dental caries (white spot lesions). Results were compared with those obtained from OCT imaging of individual samples where the approximal surfaces of extracted teeth are accessible on a lab-bench. Issues regarding access, regions of interest, and factors to be considered in an in vivo setting will be discussed. Future studies are aimed at using the probe in vivo with patient volunteers.
In this paper, we present an approach toward the creation of coronary artery phantoms for optical coherence tomography
(OCT). By mixing alumina powder in a matrix of transparent silicone, it is expected that the amplitude of the OCT
signal and the soft tissue elasticity can be reproduced. The fabrication process to produce such multiple layer phantoms
is presented along with optical and characterization experiments.
We developed optical tissue phantoms with a novel combination of matrix and scatterers. These phantoms have a well
known scattering microstructure of monodisperse silica microspheres, embedded in elastic silicone. We characterize
their mechanical properties and, some of their optical properties. We also validate the control over the density of
scatterers achieved with our proposed fabrication technique. The properties obtained are a practical combination of
deformability, durability and simplicity of the microstructure. These are illustrated by results on speckle statistics in
optical coherence tomography.
Speckle is always present in Optical Coherence Tomography (OCT) measurements. To a first approximation, the speckle size is determined by the OCT resolution length and the point spread function of the focusing optics in the sample arm. But the speckle size is also affected by the tissue microstructure. We demonstrate this phenomena by performing measurements on optical phantoms with a controlled density of scatterers using time-domain OCT. In the very low density limit, the scatterers are easily identified on the OCT cross-section and, in fact, one can hardly speak of a speckle pattern. The corresponding speckle size is the resolution length axially and the point spread function of the focusing optics transversally. As the number of scatterers increases, a true speckle field appears and the measured speckle size decreases. In the high density limit, the speckle size reaches an asymptotic value that is about 70% of its low-density regime values. In addition to experimental results, theoretical estimates of the limiting speckle size values are presented. Our work contributes to a better understanding of speckle in optical coherence tomography.
As in conventional time-domain optical coherence tomography (OCT), speckle is inherent to any Optical Fourier
Domain Imaging (OFDI) of biological tissue. OFDI is also known as swept-source OCT (SS-OCT). The axial
speckle size is mainly determined by the OCT resolution length and the transverse speckle size by the focusing
optics illuminating the sample. There is also a contribution from the sample related to the number of scatterers
contained within the probed volume. In the OFDI data processing, there is some liberty in selecting the range of
wavelengths used and this allows variation in the OCT resolution length. Consequently the probed volume can
be varied. By performing measurements on an optical phantom with a controlled density of discrete scatterers
and by changing the probed volume with different range of wavelengths in the OFDI data processing, there is an
obvious change in the axial speckle size, but we show that there is also a less obvious variation in the transverse
speckle size. This work contributes to a better understanding of speckle in OCT.
Speckle is inherent to any Optical Coherence Tomography (OCT) imaging of biological tissue. It is often seen as
degrading the signal, but it also carries information about the tissue microstructure. One parameter of interest is
the speckle size. We study the variations in speckle size on optical phantoms with different density of scatterers.
Phantoms are fabricated with a new approach by introducing silica microspheres in a curing silicon matrix,
providing phantoms with a controlled density of scatterers. These phantoms are also solid, deformable, and
conservable. Experimental results are obtained with Time-Domain OCT (TD-OCT). Modeling is performed
by simulating a phantom as a random distribution with of discrete scatterers. Both experimental results and
modeling show that the speckle size varies when there are few scatterers contained within the probed volume,
the latter being defined by the coherence length and the spot size of the focusing optics. As a criterion to
differentiate tissues, the speckle size has the same sensitivity as the contrast parameter that is studied in Ref. 1.
This work also contributes to a better understanding of speckle in OCT.
An overview of the activities in low-coherence interferometry (LCI) and optical coherence tomography (OCT) at the Industrial Materials Institute are presented. An innovative optical delay line using rhombic prisms is described. A few industrial applications are described: volume loss in a wear test, combination of LCI with laser-induced breakdown spectroscopy, and modification of an existing rheometer to increase its precision. Preliminary results related to the use of speckle to differentiate tissues and materials in OCT are presented. The speckle dimension is shown to be sensitive to low density of scatterers. An additional parameter extracted from the autocorrelation of speckle is also presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.