[Show abstract][Hide abstract] ABSTRACT: We report on a new articular cartilage imaging technique with potential for clinical arthroscopic use, by supplementing the variable-incidence-angle polarization-sensitive optical coherence tomography method previously developed by us with a conical beam scan protocol. The technique is validated on bovine tendon by comparing experimental data with simulated data generated using the extended Jones matrix calculus. A unique capability of this new optical technique is that it can locate the "brushing direction" of collagen fibers in articular cartilage, which is structural information that extends beyond established methods such as split-line photography or birefringent fast-axis measurement in that it is uniquely defined over the full azimuthal-angle range of (-π, + π). The mapping of this direction over the cartilage surface may offer insights into the optimal design of tissue-engineering scaffolds for cartilage repair.
[Show abstract][Hide abstract] ABSTRACT: A new imaging technique is presented by introducing the concept of conical scan to the variable-incidenc-angle polarimetry (VIA) previously developed by our group. The technique would facilitate the translating of the VIA technique to the clinic by simplifying the requirements of measurements in two orthogonal planes by using a conical scan protocol. Conical scan PS-OCT images could illustrate directly the azimuthal angle of the collage fibers in birefringent tissue, which was validated by measurements on a bovine tendon. We have showed the unique technique can be used to locate the "brushing direction" of collagen fibers in articular cartilage. Measuring this direction over the cartilage surface could potentially help designing of tissue-engineering scaffolds for cartilage repair.
[Show abstract][Hide abstract] ABSTRACT: The biological and mechanical function of connective tissues is largely determined by controlled cellular alignment and therefore it seems appropriate that tissue-engineered constructs should be architecturally similar to the in vivo tissue targeted for repair or replacement. Collagen organisation dictates the tensile properties of most tissues and so monitoring the deposition of cell-secreted collagen as the construct develops is essential for understanding tissue formation. In this study, electrospun fibres with a random or high degree of orientation, mimicking two types of tissue architecture found in the body, were used to culture human fibroblasts for controlling cell alignment. The minimally-invasive technique of second harmonic generation was used with the aim of monitoring and profiling the deposition and organisation of collagen at different construct depths over time while construct mechanical properties were also determined over the culture period. It was seen that scaffold fibre organisation affected cell migration and orientation up to 21 days which in turn had an effect on collagen organisation. Collagen in random fibrous constructs was deposited in alternating configurations at different depths however a high degree of organisation was observed throughout aligned fibrous constructs orientated in the scaffold fibre direction. Three-dimensional second harmonic generation images showed that deposited collagen was more uniformly distributed in random constructs but aligned constructs were more organised and had higher intensities. The tensile properties of all constructs increased with increasing collagen deposition and were ultimately dictated by collagen organisation. This study highlights the importance of scaffold architecture for controlling the development of well-organised tissue engineered constructs and the usefulness of second harmonic generation imaging for monitoring collagen maturation in a minimally invasive manner.
PLoS ONE 01/2014; 9(2):e89761. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Optical coherence tomography (OCT) is a modern high resolution subsurface medical imaging technique. Herein we describe: (i) the synthesis of a thiophene-functionalized oligo(ethylene glycol) methacrylate (OEGMA)-based statistical copolymer, denoted poly(2TMOI-OEGMA); (ii) the preparation of sterically-stabilized polypyrrole (PPy) nanoparticles of approximately 60 nm diameter; (iii) the evaluation of these nanoparticles as a NIR-absorbing optical contrast agent for high-resolution OCT imaging. We show that poly(2TMOI-OEGMA)-stabilized PPy nanoparticles exhibit similar optical properties to poly(vinyl alcohol) (PVA)-stabilized PPy nanoparticles of comparable size prepared using commercially available PVA. Spectroscopic measurements and Mie calculations indicate that both types of PPy nanoparticles strongly absorb NIR radiation above 1000 nm, suggesting their potential use as OCT contrast agents. In vitro OCT studies indicate that both types of PPy nanoparticles reduce NIR backscattering within homogeneous intralipid tissue phantoms, offering almost identical contrast performance in this medium. However, PVA-stabilized PPy nanoparticles became colloidally unstable when dispersed in physiological buffer and immersed in a solid biotissue phantom and hence failed to generate a strong contrast effect. In contrast, the poly(2TMOI-OEGMA)-stabilized PPy nanoparticles remained well-dispersed and hence exhibited a strong rapid onset contrast effect within the biotissue phantom under identical physiological conditions. Ex vivo studies performed on excised chicken and porcine skin tissue demonstrated that topical administration of a low concentration of poly(2TMOI-OEGMA)-stabilized PPy nanoparticles rapidly enhances OCT image contrast in both cases, allowing key tissue features to be readily identified.
[Show abstract][Hide abstract] ABSTRACT: We report on a photothermal modulation detection scheme developed using a swept source-based optical coherence tomography (OCT) system centred at 1300nm. Photothermal detection is an improved technique for studying the contrast properties of exogenous contrast agents such as highly absorbing polypyrrole (PPy) nanoparticles used for OCT imaging. The swept source based OCT system has a wavelength sweep rate of 10 kHz which is used for the phase modulation detection of various concentrations of PPy nanoparticles. PPy nanoparticles have been recently reported to be a promising candidate for OCT imaging owing to their strong NIR absorption from 700–1300nm. Phase-sensitive detection of the photothermal modulation signal is achieved using a pumped 975 nm laser beam at 80Hz and 160Hz for varying concentrations of PPy nanoparticles dispersed in 2% Intralipid phantom. A phase-sensitive detection system is realised by carrying out the phase calibration using the back reflections obtained from the coverslip used with the sample. This study provides quantitative support for the use of PPy nanoparticles as a potential biocompatible contrast agent in OCT imaging.
[Show abstract][Hide abstract] ABSTRACT: This paper highlights the extended Jones matrix calculus based
multi-angle study carried out to understand the depth dependent
structural orientation of the collagen fibers in articular cartilage
using polarization-sensitive optical coherence tomography (PS-OCT). A 3D
lamellar model for the collagen fiber orientation, with a quadratic
profile for the arching of the collagen fibers in transitional zone
which points towards an ordered arrangement of fibers in that zone is
the basis of the organization architecture of collagen fibers in
articular cartilage. Experimental data for both ex-vivo bovine fetlock
and human patellar cartilage samples are compared with theoretical
predictions, with a good quantitative agreement for bovine and a
reasonable qualitative agreement for human articular cartilage samples
[Show abstract][Hide abstract] ABSTRACT: We report on a new calibration technique that permits the accurate
extraction of sample Jones matrix and hence fast-axis orientation by
using fiber-based polarization-sensitive optical coherence tomography
(PS-OCT) that is completely based on non polarization maintaining fiber
such as SMF-28. In this technique, two quarter waveplates are used to
completely specify the parameters of the system fibers in the sample arm
so that the Jones matrix of the sample can be determined directly. The
device was validated on measurements of a quarter waveplate and an
equine tendon sample by a single-mode fiber-based swept-source PS-OCT
[Show abstract][Hide abstract] ABSTRACT: We report on a new calibration technique that permits the accurate extraction of sample Jones matrix and hence fast-axis orientation by using fiber-based polarization-sensitive optical coherence tomography (PS-OCT) that is completely based on non-polarization-maintaining fiber such as SMF-28. In this technique, two quarter-wave plates (QWPs) are used to completely specify the parameters of the system fibers in the sample arm so that the Jones matrix of the sample can be determined directly. The device was validated on measurements of a QWP and an equine tendon sample by a single-mode fiber-based swept-source PS-OCT system.
[Show abstract][Hide abstract] ABSTRACT: We report results to verify a theoretical framework to analyze the 3D depth-wise structural organization of collagen fibers in articular cartilage using polarization-sensitive optical coherence tomography. Apparent birefringence data obtained from multi-angle measurements using a time domain polarization-sensitive optical coherence tomography system has been compared with simulated data based on the extended Jones matrix calculus. Experimental data has been shown to agree with the lamellar model previously proposed for the cartilage microstructure based on scanning electron microscopy data. This tool could have potential application in mapping the collagen structural orientation information of cartilage non-invasively during arthroscopy.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate theoretically and experimentally that the phase retardance and relative optic-axis orientation of a sample can be calculated without prior knowledge of the actual value of the phase modulation amplitude when using a polarization-sensitive optical coherence tomography system based on continuous polarization modulation (CPM-PS-OCT). We also demonstrate that the sample Jones matrix can be calculated at any values of the phase modulation amplitude in a reasonable range depending on the system effective signal-to-noise ratio. This has fundamental importance for the development of clinical systems by simplifying the polarization modulator drive instrumentation and eliminating its calibration procedure. This was validated on measurements of a three-quarter waveplate and an equine tendon sample by a fiber-based swept-source CPM-PS-OCT system.
Journal of Biomedical Optics 03/2012; 17(3):030504. · 2.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The difference in the genetic make up of the constituent molecules in
collagen fibers in tendon and articular cartilage is what makes them
mechanically and functionally different. A comparative study carried out
on the differences in the angle-resolved back-scattering properties
obtained from optical coherence tomography based studies on the two
different types of scatterers: collagen I and collagen II fibers in
bovine tendon and bovine articular cartilage sample, respectively, is
reported here. Tendon sample shows greater anisotropy in the
angle-resolved scattering profile compared to that obtained from
articular cartilage sample. Rayleigh-Gans scattering approximation is
used to provide the qualitative support needed to substantiate
differences in the light scattering profiles obtained from the two
tissues based on the size and type of the scatterers involved.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate theoretically and experimentally that the phase
retardance and relative optic-axis orientation of a sample can be
calculated without prior knowledge of the actual value of the phase
modulation amplitude when using a polarization-sensitive optical
coherence tomography system based on continuous polarization modulation
(CPM-PS-OCT). We also demonstrate that the sample Jones matrix can be
calculated at any values of the phase modulation amplitude in a
reasonable range depending on the system effective signal-to-noise
ratio. This has fundamental importance for the development of clinical
systems by simplifying the polarization modulator drive instrumentation
and eliminating its calibration procedure. This was validated on
measurements of a three-quarter waveplate and an equine tendon sample by
a fiber-based swept-source CPM-PS-OCT system.
[Show abstract][Hide abstract] ABSTRACT: A near-infrared (NIR) absorbing contrast agent based on polypyrrole nanoparticles is described. Quantitative optical coherence tomography studies on tissue phantoms and Mie scattering calculations indicate their potential application for early-stage cancer diagnosis.
[Show abstract][Hide abstract] ABSTRACT: Optical coherence tomography (OCT) is a noninvasive imaging methodology that is able to image tissue to depths of over 1 mm. Many epithelial conditions, such as melanoma and oral cancers, require an invasive biopsy for diagnosis. A noninvasive, real-time, point of care method of imaging depth-resolved epithelial structure could greatly improve early diagnosis and long-term monitoring in patients. Here, we have used tissue-engineered (TE) models of normal skin and oral mucosa to generate models of melanoma and oral cancer. We have used these to determine the ability of OCT to image epithelial differences in vitro. We report that while in vivo OCT gives reasonable depth information for both skin and oral mucosa, in vitro the information provided is less detailed but still useful. OCT can provide reassurance on the development of TE models of skin and oral mucosa as they develop in vitro. OCT was able to detect the gross alteration in the epithelium of skin and mucosal models generated with malignant cell lines but was less able to detect alteration in the epithelium of TE models that mimicked oral dysplasia or, in models where tumor cells had penetrated into the dermis.
Journal of Biomedical Optics 11/2011; 16(11):116015. · 2.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In a biological tissue, light scattering is based on the size and type of scatterers seen as refractive index variations that describe the optical properties shown. In this paper, we have implemented the variable incidence angle technique of multiple angle of illumination experiment on tendon and cartilage samples whose dominant constituents are genetically different types of collagen fibers, type I and type II, respectively. It is found that tendon displays a much greater angular anisotropy in its optical backscattering coefficient than the healthy cartilage. We propose that this is due to a more uniform distribution of fine fibrils than is found in tendon. Rayleigh-Gans approximation is used to give qualitative support to this idea.
Journal of Biomedical Optics 08/2011; 16(8):080501. · 2.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a phase fluctuation calibration method for polarization-sensitive swept-source optical coherence tomography (PS-SS-OCT) using continuous polarization modulation. The method uses a low-voltage broadband polarization modulator driven by a synchronized sinusoidal burst waveform rather than an asynchronous waveform, together with the removal of the global phases of the measured Jones matrices by the use of matrix normalization. This makes it possible to average the measured Jones matrices to remove the artifact due to the speckle noise of the signal in the sample without introducing auxiliary optical components into the sample arm. This method was validated on measurements of an equine tendon sample by the PS-SS-OCT system.
Journal of Biomedical Optics 07/2011; 16(7):070502. · 2.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Polarization-sensitive optical coherence tomography (PSOCT) has established itself as an important non-invasive optical imaging tool to study the birefringent biological tissues. The complex D structure architecture of the collagen fibers in articular cartilage is investigated using a time domain PSOCT (TD-PSOCT) system and the depth-wise cumulative retardance profiles obtained are compared with a three layer cartilage model. The PSOCT result obtained from the variable incidence angle (VIA) experiment of bovine cartilage sample is found to be consistent with the proposed lamellar cartilage model based on scanning electron microscope studies. This shows potential use of PSOCT -VIA technique to obtain depth-wise information about the complex 3D architecture of collagen fibers in the cartilage. Further studies would have to be carried out to map out depth wise retardance information at different sites of the cartilage, which could establish the general validity of this approach.
[Show abstract][Hide abstract] ABSTRACT: We describe a simple swept-laser design that characterizes the emission bandwidth, linewidth, spectral shape and output noise. A short cavity Littmann configuration is used in which the semiconductor optical amplifier (SOA) lasing wavelength is tuned by a galvanometer with an 830 grooves per mm diffraction grating. A 3dB coupler extracts light from the cavity formed by the grating and end-mirror and the optical output uses to illuminate a balanced swept source optical coherence tomography (SS-OCT) interferometer incorporating a circulator, 3dB coupler, dispersion compensator and balanced detector. The SOA (SOA-1200-70-PM-20sB, Innolume GmbH) uses a novel III-V semiconductor quantum-dot gain medium. ASE is emitted between 1150nm and 1300nm at a drive current of 700mA. When used in the Littmann cavity laser a coherence length of about 10mm is produced, which is tunable over 60nm. The peak output power is 12mW. The swept-laser has been incorporated into a fiber-based SS-OCT system and used to image biological tissues. Axial resolution in air is 12 microns. Images of human palmar skin in-vivo are demonstrated, showing good resolution and contrast, with the stratum corneum, epidermis, rete ridges and epidermal-dermal junction visualized.
[Show abstract][Hide abstract] ABSTRACT: We describe a fibre-based variable-incidence angle (VIA) polarization-sensitive swept-source optical coherence tomography (PS-SS-OCT) system to determine the 3D optical axis of birefringent biological tissues. Single-plane VIA-PS-OCT is also explored which requires measurement of the absolute fast-axis orientation. A state-of-the-art PS-SS-OCT system with some improvements both in hardware and software was used to determine the apparent optical birefringence of equine tendon for a number of different illumination directions. Polar and azimuthal angles of cut equine tendon were produced by the VIA method and compared with the nominal values. A quarter waveplate (QWP) and equine tendon were used as test targets to validate the fast-axis measurements using the system. Polar and azimuthal angles of cut equine tendon broadly agreed with the expected values within about 8% of the nominal values. A theoretical and experimental analysis of the effect of the sample arm fibre on determination of optical axis orientation using a proposed definition based on the orientation of the eigenpolarization ellipse experimentally confirms that this algorithm only works correctly for special settings of the sample arm fibre. A proposed algorithm based on the angle between Stokes vectors on the Poincaré sphere is confirmed to work for all settings of the sample arm fibre. A calibration procedure is proposed to remove the sign ambiguity of the measured orientation and was confirmed experimentally by using the QWP.
Physics in Medicine and Biology 02/2011; 56(4):1105-22. · 2.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a common path Fourier domain optical coherence tomography (FDOCT) setup where the reference signal arises from multiple reflections within the sample arm. Two configurations are demonstrated. The first is based on a reflective microscope objective while the second is based on a normal (refractive) microscope objective. The second configuration is effectively a Mireau interferometer. We present sensitivity analysis of these setups and images of in vivo skin. Advantages of both common path arrangements include: 1) the reference surface is not close to the sample surface while keeping the optical path lengths matched (so the additional interferometer is not needed) and 2) the user can independently control reference and sample arm power. Additionally, the configuration using the refractive objective ensures that the coherence gate and focus gate always match. A disadvantage is that the reference arm power in certain circumstances is not optimal (i.e. is not close to saturating the CCD). However, this issue can be removed by a light source of sufficient output power. We believe the idea is scalable and therefore of interest to endoscopy applications.