Kyle Cheng, Adrian Mariampillai, Kenneth Lee, Barry Vuong, Timothy Luk, Joel Ramjist, M. Anne Curtis, Henry Jakubovic, Peter Kertes, Michelle Letarte, Marie Faughnan, Victor Yang
Speckle statistics of flowing scatterers have been well documented in the literature. Speckle variance optical coherence tomography exploits the large variance values of intensity changes in time caused mainly by the random backscattering of light resulting from translational activity of red blood cells to map out the microvascular networks. A method to map out the microvasculature malformation of skin based on the time-domain histograms of individual pixels is presented with results obtained from both normal skin and skin containing vascular malformation. Results demonstrated that this method can potentially map out deeper blood vessels and enhance the visualization of microvasculature in low signal regions, while being resistant against motion (e.g., patient tremor or internal reflex movements). The overall results are manifested as more uniform en face projection maps of microvessels. Potential applications include clinical imaging of skin vascular abnormalities and wide-field skin angiography for the study of complex vascular networks.
We present an in vivo implementation of a multi-parametric technique for detecting apoptosis using optical coherence tomography in a mouse tumor model. Solid tumors were grown from acute myeloid leukemia cells in the hind leg of SCID mice and treated with a single dose of cisplatin and dexamethasone to induce apoptosis. Both spectral features and speckle decorrelation times indicated good consistency between control mice and reasonable agreement with in vitro measurements. The integrated backscatter increased significantly in tumors responding to treatment while the spectral slope and decorrelation time did not show significant changes. This study demonstrates the feasibility of using spectroscopic OCT and dynamic light scattering for treatment monitoring in vivo.
A fiber-optic 3D shape, position and temperature sensor is demonstrated with femtosecond laser direct-written optical and Bragg grating waveguides that were distributed axially and radially inside a single coreless optical fiber. Efficient light coupling between the laser-written optical circuit elements and a standard single-mode optical fiber was obtained by 3D laser writing of a 1 × 3 directional coupler and fusion splicing. Coupler optimization by real-time monitoring of Bragg grating strengths is discussed. Simultaneous interrogation of nine Bragg gratings is presented through a single waveguide port to follow the Bragg wavelength shifts and thereby infer shape and temperature profile along the fiber length.
In this work, we explored the potential of measuring shear wave propagation using Optical Coherence Elastography (OCE) in MCF7 cell modules (comprised of MCF7 cells and collagen) and based on a swept-source optical coherence tomography (OCT) system. Shear waves were generated using a piezoelectric transducer transmitting sine-wave bursts of 400 μs, synchronized with an OCT swept source wavelength sweep imaging system. Acoustic radiation force was applied to the MCF7 cell constructs. Differential OCT phase maps, measured with and without the acoustic radiation force, demonstrate microscopic displacement generated by shear wave propagation in these modules. The OCT phase maps are acquired with a swept-source OCT (SS-OCT) system. We also calculated the tissue mechanical properties based on the propagating shear waves in the MCF7 + collagen phantoms using the Acoustic Radiation Force (ARF) of an ultrasound transducer, and measured the shear wave speed with the OCT phase maps. This method lays the foundation for future studies of mechanical property measurements of breast cancer structures, with applications in the study of breast cancer pathologies.
High-resolution mapping of microvasculature has been applied to diverse body systems, including the retinal and choroidal vasculature, cardiac vasculature, the central nervous system, and various tumor models. Many imaging techniques have been developed to address specific research questions, and each has its own merits and drawbacks. Understanding, optimization, and proper implementation of these imaging techniques can significantly improve the data obtained along the spectrum of unique research projects to obtain diagnostic clinical information. We describe the recently developed algorithms and applications of two general classes of microvascular imaging techniques: speckle-variance and phase-variance optical coherence tomography (OCT). We compare and contrast their performance with Doppler OCT and optical microangiography. In addition, we highlight ongoing work in the development of variance-based techniques to further refine the characterization of microvascular networks.
In this work, we explored the potential of measuring shear wave propagation using Optical Coherence Elastography (OCE) in a layered phantom and based on a swept-source optical coherence tomography (OCT) system. Shear waves were generated using a piezoelectric transducer transmitting sine-wave bursts of 400 μs, synchronized with an OCT swept source wavelength sweep imaging system. The acoustic radiation force was applied to layered phantoms. The phantoms were composed of gelatin and titanium dioxide. Differential OCT phase maps, measured with and without the acoustic radiation force, demonstrate microscopic displacement generated by shear wave propagation in these phantoms of different stiffness. The OCT phase maps are acquired with a swept-source OCT (SS-OCT) system. We present a technique for calculating tissue mechanical properties by propagating shear waves in inhomogeneous tissue equivalent phantoms using the Acoustic Radiation Force (ARF) of an ultrasound transducer, and measuring the shear wave speed and its associated properties in the different layers with OCT phase maps. This method lays the foundation for future studies of mechanical property measurements of heterogeneous tissue structures, with applications in the study of aneurysms and other intravascular pathologies.
Precision depth control of bone resection is necessary for safe surgical procedures in the spine. In this paper, we compare the control and quality of cutting bovine tail bone, as an ex vivo model of laminectomy and bony resection simulating spinal surgery, planned with micro-CT data and executed using two approaches: (a) mechanical milling guided by optical topographical imaging (OTI) and (b) optical milling using closed-loop inline coherent imaging (ICI) to monitor and control the incision depth of a high-power 1070 nm fiber laser in situ. OTI provides the in situ topology of the 2-dimensional surface of the bone orientation in the mechanical mill which is registered with the treatment plan derived from the micro-CT data. The coregistration allows the plan to be programmed into the mill which is then used as a benchmark of current surgical techniques. For laser cutting, 3D optical land marking with coaxial camera vision and the ICI system is used to coregister the treatment plan. The unstable, carbonization-mediated ablation behaviour of 1070 nm light and the unknown initial geometry of bone leads to unpredictable ablation which substantially limits the depth accuracy of open-loop cutting. However, even with such a non-ideal cutting laser, we demonstrate that ICI provides in situ high-speed feedback that automatically and accurately limits the laser’s cut depth to effectively create an all-optical analogue to the mechanical mill.
Optical Coherence Tomography (OCT) provides images at near histological resolution, which allows for the identification
of micron sized morphological tissue structures. Optical coherence elastography (OCE) measures tissue displacement
and utilizes the high resolution of OCT to generate high-resolution stiffness maps. In this work, we explored the
potential of measuring shear wave propagation using OCE. A swept-source OCT system was used in this study. The laser
had a center wavelength of 1310 nm and a bandwidth of ~110 nm. The lateral resolution was approximately 13 μm in
the samples. Acoustic radiation force was applied to two different phantoms using a 20 MHz circular 8.5 mm diameter
piezoelectric transducer element (PZT, f-number 2.35) transmitting sine-wave bursts of 400 μs. The first phantom consisted
of a 355 μm glass sphere (dark) embedded in gelatin that was used to characterize the ultrasound pushing beam.
The second consisted of gelatin mixed with titanium dioxide, which provided uniform acoustic and optical scattering.
The OCT signal from this second set of phantoms was used for the measurement of the shear wave speed and viscosity.
For both sets of experiments phase analysis was applied to B-mode and M-mode OCT images which were obtained
while the ultrasound transducer was generating the "push" in the phantom. The experiments are the first step towards
imaging shear wave propagation in tissue and characterization of tissue mechanical properties using OCE, with the eventual
goal of developing OCE as a diagnostic tool for the assessment of pathological lesions with different mechanical
tissue property.
A prototype neurosurgical hand-held optical coherence tomography (OCT) imaging probe has been developed to provide
micron resolution cross-sectional images of subsurface tissue during open surgery. This new ergonomic hand-held probe
has been designed based on our group's previous work on electrostatically driven optical fibers. It has been packaged
into a catheter probe in the familiar form factor of the clinically accepted Bayonet shaped neurosurgical non-imaging
Doppler ultrasound probes. The optical design was optimized using ZEMAX simulation. Optical properties of the probe
were tested to yield an ~20 um spot size, 5 mm working distance and a 3.5 mm field of view. The scan frequency can be
increased or decreased by changing the applied voltage. Typically a scan frequency of less than 60Hz is chosen to keep
the applied voltage to less than 2000V. The axial resolution of the probe was ~15 um (in air) as determined by the OCT
system. A custom-triggering methodology has been developed to provide continuous stable imaging, which is crucial for
clinical utility. Feasibility of this probe, in combination with a 1310 nm swept source OCT system was tested and images
are presented to highlight the usefulness of such a forward viewing handheld OCT imaging probe. Knowledge gained
from this research will lay the foundation for developing new OCT technologies for endovascular management of
cerebral aneurysms and transsphenoidal neuroendoscopic treatment of pituitary tumors.
We present, for the first time an in vivo implementation of dynamic light scattering (DLS) adapted to optical coherence
tomography (OCT). Human bladder carcinoma tumors were grown in dorsal skin-fold window chambers fitted to male
nude mice and imaged at a rate of 200 Hz using OCT. Maps of speckle decorrelation times (DT) were generated for
regions of skin from individual mice as well as for regions containing tumor tissue before and after treatment with
chemotherapy. Variations in DT were found between individual mice exhibiting different skin anatomy (primarily due to
deterioration from the window chamber implantation). A significant difference in DT was also observed between tumor
regions and surrounding normal tissue. Finally, maps of DT generated for tumor tissue treated with chemotherapy
indicated a drop in DT at 24 and 48 hours after treatment. These preliminary results suggest the feasibility of using DLSOCT
to measure intracellular motion as an endogenous contrast mechanism in vivo.
A dynamic light scattering technique is implemented using optical coherence tomography (OCT) to measure the change in intracellular motion as cells undergo apoptosis. Acute myeloid leukemia cells were treated with cisplatin and imaged at a frame rate of 166 Hz using a 1300 nm swept-source OCT system at various times over a period of 48 h. Time correlation analysis of the speckle intensities indicated a significant increase in intracellular motion 24 h after treatment. This rise in intracellular motion correlated with histological findings of irregularly shaped and fragmented cells indicative of cell membrane blebbing and fragmentation.
We present a dynamic light scattering technique applied to optical coherence tomography (OCT) for detecting changes
in intracellular motion caused by cellular reorganization during apoptosis. We have validated our method by measuring
Brownian motion in microsphere suspensions and comparing the measured values to those derived based on particle
diffusion calculated using the Einstein-Stokes equation. Autocorrelations of OCT signal intensities acquired from acute
myeloid leukemia cells as a function of treatment time demonstrated a significant drop in the decorrelation time after 24
hours of cisplatin treatment. This corresponded with nuclear fragmentation and irregular cell shape observed in
histological sections. A similar analysis conducted with multicellular tumor spheroids indicated a shorter decorrelation
time in the spheroid core relative to its edges. The spheroid core corresponded to a region exhibiting signs of cell death
in histological sections and increased backscatter intensity in OCT images.
Multichannel optical coherence tomography (MOCT) imaging is demonstrated using a high-power wavelength-swept
laser source. The main benefit of MOCT is faster image acquisition rates without a corresponding increase in the laser
tuning speed. The wavelength-swept laser was constructed using a compact telescope-less polygon-based filter in
Littman arrangement. High output power, necessary for MOCT, was achieved by incorporating two serial
semiconductor optical amplifiers in a ring laser cavity in Fourier domain mode-locked configuration. The laser has a
measured wavelength tuning range of 111 nm centered at 1329 nm, coherence length of 5.5 mm, and total average
output power of 131 mW at 43 kHz sweeping rate. Using this laser, a six-channel imaging system was constructed. The
imaging arm consisted of a multi-fiber push-on connector mounted on a galvanometer-based scanner. All channels,
spaced 250 μm apart, were focused at the same depth. Six-channel OCT imaging to achieve 258 kHz scan rate is
demonstrated. The increase in effective frame rate using multichannel acquisition may be beneficial for 3-dimensional
in-vivo imaging where bulk tissue motion can adversely affect the image quality.
We demonstrate high efficiency and wide bandwidth gain in a Ytterbium doped fiber amplifier. The highpowered
amplifier has potential applications for use with a swept-source fiber ring laser in multi-channel optical
coherence tomography (OCT) system. The ring cavity design includes a 976nm pumped dual core Yb doped fiber as the
gain medium, where a rotating polygon mirror is used as a wavelength-sweeping filter for this source. The amplified
spontaneous emission (ASE) had a spectral bandwidth of 1037-1145nm at -60dBm, where a tunable lasing bandwidth of
the ring cavity ranged from 1057-1115nm. The highest output power, for both the ASE and lasing spectrum, with this
configuration was ~200mW, however it is possible to have a larger bandwidth and a larger output power. Higher power,
in the wattage range is achievable if free space components are employed. Pumped with 976nm light at 1.27W, the use
of this novel dual core Yb doped fiber as an amplifier has been successfully demonstrated, as it provided a small signal
gain of 29.6 dB at 1085nm, where the gain medium was successfully saturated during operation. This is important for the
spectral shaping requirements of OCT to improve image quality. The gain was demonstrated for several different
wavelengths and for several pumping powers at a 1085nm wavelength. Fourier domain mode locked operation (FDML)
was achieved with a bandwidth of 15nm and a sweep rate of 51.4kHz. This laser source offers a low-cost, high power
alternative for biomedical imaging with multi-channel optical coherence tomography.
We demonstrate the potential of a forward-looking Doppler optical coherence tomography (OCT) probe for color flow imaging in several commonly seen narrowed artery morphologies. As a proof of concept, we present imaging results of a surgically exposed thrombotic occlusion model that was imaged superficially to demonstrate that Doppler OCT can identify flow within the recanalization channels of a blocked artery. We present Doppler OCT images in which the flow is nearly antiparallel to the imaging direction. These images are acquired using a flexible 2.2-mm-diam catheter that used electrostatic actuation to scan up to 30 deg ahead of the distal end. Doppler OCT images of physiologically relevant flow phantoms consisting of small channels and tapered entrance geometries are demonstrated.
As part of an ongoing program to develop two-photon (2-) photodynamic therapy (PDT) for treatment of wet-form age-related macular degeneration (AMD) and other vascular pathologies, we have evaluated the reciprocity of drug-light doses in focal-PDT. We targeted individual arteries in a murine window chamber model, using primarily the clinical photosensitizer Visudyne/liposomal-verteporfin. Shortly after administration of the photosensitizer, a small region including an arteriole was selected and irradiated with varying light doses. Targeted and nearby vessels were observed for a maximum of 17 to 25 h to assess vascular shutdown, tapering, and dye leakage/occlusion. For a given end-point metric, there was reciprocity between the drug and light doses, i.e., the response correlated with the drug-light product (DLP). These results provide the first quantification of photosensitizer and light dose relationships for localized irradiation of a single blood vessel and are compared to the DLP required for vessel closure between 1- and 2- activation, between focal and broad-beam irradiation, and between verteporfin and a porphyrin dimer with high 2- cross section. Demonstration of reciprocity over a wide range of DLP is important for further development of focal PDT treatments, such as the targeting of feeder vessels in 2- PDT of AMD.
Intravital imaging using confocal microscopy facilitates high-resolution studies of cellular and molecular events in vivo. We use this, complemented by Doppler optical coherence tomography (OCT), to assess blood flow in a mouse dorsal skin-fold window chamber model to image the response of individual blood vessels to localized photodynamic therapy (PDT). Specific fluorescent cell markers were used to assess the effect on the vascular endothelial cell lining of the treated vessels. A fluorescently tagged antibody against an endothelial transmembrane glycoprotein (CD31) was used to image endothelial cell integrity in the targeted blood vessel. A cell permeability (viability) indicator, SYTOX Orange, was also used to further assess damage to endothelial cells. A fluorescently labeled anti-CD41 antibody that binds to platelets was used to confirm platelet aggregation in the treated vessel. These optical techniques enable dynamic assessment of responses to PDT in vivo, at both the vascular endothelial cell and whole vessel levels.
We measure the tumor vascular response to varying irradiance rates during photodynamic therapy (PDT) in a Dunning rat prostate model with interstitial Doppler optical coherence tomography (IS-DOCT). Rats are given a photosensitizer drug, Photofrin, and the tumors are exposed to light (635 nm) with irradiance rates ranging from 8 to 133 mW/cm2 for 25 min, corresponding to total irradiance of 12 to 200 J/cm2 (measured at surface). The vascular index computed from IS-DOCT results shows the irradiance rate and total irradiance dependent microvascular shutdown in the tumor tissue during PDT. While faster rates of vascular shutdown were associated with increasing PDT irradiance rate and total irradiance, a threshold effect was observed as irradiance rates above 66 mW/cm2 (surface), where no further increase in vascular shutdown rate was detected. The maximum post-treatment vascular shutdown (81%) without immediate microcirculatory recovery was reached with the PDT condition of 33 mW/cm2 and 50 J/cm2. Control groups without Photofrin show no significant microvascular changes. Microvascular shutdown occurs at different rates and shows correlation with PDT total irradiance and irradiance rates. These dependencies may play an important role in PDT treatment planning, feedback control for treatment optimization, and post-treatment assessment.
Microcirculatory changes, such as vascular shutdown, may be a predictor to the therapeutic efficacy of
photodynamic therapy (PDT). The aim of this study was to measure the tumour vascular response to varying irradiance
rates during PDT deep within prostate tumour xenograft, via interstitial Doppler optical coherence tomography
(DOCT).
DOCT provides micron-scale spatial resolution allowing visualization of structures at near histological levels,
and yields flow velocity resolution of ~20 μm/s. Current in vivo DOCT imaging probes are limited to intraluminal and
near-surface sites. To improve the accessibility of DOCT to anatomically relevant sites deep within the body (e.g.,
prostate), an interstitial (IS) needle (~700μm diameter) probe was developed for minimally invasive monitoring of the
microvascular response to PDT (irradiance administered superficially) within tumour tissue. Rats were given a
photosensitizer drug, Photofrin, and 20-24 h later the tumours were exposed to light (635nm) with an irradiance rate of
8-133 mW/cm2 for 25 minutes to a total irradiance of 12-200 J/cm2. Results illustrated different rates of vascular
shutdown within the tumour as imaged by IS-DOCT, related to the administered PDT irradiance rate and total
irradiance. Controls (probe only, probe + light) showed no significant microvascular changes.
IS-DOCT was able to detect and monitor microvascular changes during PDT. Microvascular shutdown
occurred at different rates and showed correlation with PDT light dose and irradiance rate. These dependencies may
play an important role in PDT treatment planning, feedback control for treatment optimization, and post treatment
assessment.
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