Optical coherence tomography (OCT) has been widely used to study mammalian embryonic development with the advantages of high spatial and temporal resolutions and without the need for any contrast enhancement probes. However, the limited imaging depth of traditional OCT might prohibit visualization of the full embryonic body. To overcome this limitation, we have developed a new methodology to enhance the imaging range of OCT in embryonic day (E) 9.5 and 10.5 mouse embryos using rotational imaging. Rotational imaging OCT (RI-OCT) enables full-body imaging of mouse embryos by performing multiangle imaging. A series of postprocessing procedures was performed on each cross-section image, resulting in the final composited image. The results demonstrate that RI-OCT is able to improve the visualization of internal mouse embryo structures as compared to conventional OCT.
We tested and compared the capability of multiple optical coherence tomography (OCT) angiography methods: phase variance, amplitude decorrelation and speckle variance, with application of the split spectrum technique, to image the choroiretinal complex of the human eye. To test the possibility of OCT imaging stability improvement we utilized a real-time tracking scanning laser ophthalmoscopy (TSLO) system combined with a swept source OCT setup. In addition, we implemented a post- processing volume averaging method for improved angiographic image quality and reduction of motion artifacts. The OCT system operated at the central wavelength of 1040nm to enable sufficient depth penetration into the choroid. Imaging was performed in the eyes of healthy volunteers and patients diagnosed with age-related macular degeneration.
A systematic investigation was conducted on the accuracies of four analytical methods for obtaining the elasticity of soft samples by using optical coherence elastography (OCE). The results were compared to the elasticity measured by uniaxial mechanical testing. OCE has emerged as a noninvasive method for quantifying tissue biomechanical properties with spatial resolution of a few micrometers. A proper mechanical model is required for extracting the biomechanical parameters accurately from OCE measurements. In this work, tissuemimicking agar phantoms were utilized to analyze the accuracy and feasibility of four methods for reconstructing the Young’s modulus from OCE-measured elastic wave which were induced by a focused airpulse. These reconstruction methods are: the shear wave equation (SWE), the surface wave equation (SuWE), the Rayleigh-Lamb frequency equation (RLFE), and the finite element method (FEM). The reconstructed elasticity values were also compared with uniaxial mechanical testing results. It was shown that the RLFE and the FEM are more robust in quantifying elasticity than the other simplified models. This work may provide a reference for reconstructing the biomechanical properties of tissues based on OCE measurements. Accurate reconstruction of biomechanical properties is an important issue for further developing noninvasive elastography methods.
Optical coherence tomography (OCT) provides significant advantages of high-resolution (approaching the histopathology level) real-time imaging of tissues without use of contrast agents. Based on these advantages, the microstructural features of tumors can be visualized and detected intra-operatively. However, it is still not clinically accepted for tumor margin delineation due to poor specificity and accuracy. In contrast, Raman spectroscopy (RS) can obtain tissue information at the molecular level, but does not provide real-time imaging capability. Therefore, combining OCT and RS could provide synergy. To this end, we present a tissue analysis and classification method using both the slope of OCT intensity signal versus depth and the principle components from the RS spectrum as the indicators for tissue characterization. Our pilot experiments were performed on mouse kidneys, livers, and small intestines. The prediction accuracy with five-fold cross validation of the method has been evaluated by support vector machine method. The results demonstrate that RS can effectively improve tissue classification compared to OCT alone. Next, we demonstrate that the boundary between myxoid liposarcoma and normal fat which is easily identifiable both Raman and OCT. In cases where structural images are indistinguishable, for example, in normal fat and well differentiated liposarcoma (WDLS) or gastrointestinal sarcoma tumor (GIST) and Myxoma, distinct molecular spectra have been obtained. The results suggest RS can effectively complement OCT to tumor boundary demarcation with high specificity.
Optical coherence tomography (OCT) has proved to be an effective tool to study the development of mammalian
embryos due to its high resolution and contrast. However, light attenuation is an important factor which constrains the imaging depth of OCT. Limitation of imaging depth will inhibit us to better study the structural characteristics of
mouse embryos. Here we propose a new method, rotational imaging OCT (riOCT), to improve the imaging depth and provide full-body embryonic imaging. The experimental setup comprises the swept source OCT system and the square glass tube mounted on a rotational stage. The E10.5 mouse embryos are dissected and immersed in the glass
tube using 0.9% saline solution. 3D structural imaging is performed at four different angles with the interval of 90 degrees. The OCT image records the optical distances of different components such as glass, gelatin and tissue. The position of rotation center is determined by the track of the glass tube center at different angles. The final image is acquired by rotating the images at different angles according to the rotation center. Results indicate that this method is able to improve the visualization of structural information of mouse embryo compared to conventional OCT.
Because of the ease in generating transgenic/gene knock out models and accessibility to early stages of embryogenesis, mouse and rat models have become invaluable to studying the mechanisms that underlie human birth defects. To study precisely how structural birth defects arise, Ultrasound, MRI, microCT, Optical Projection Tomography (OPT), Optical Coherence Tomography (OCT) and histological methods have all been used for imaging mouse/rat embryos. However, of these methods, only OCT enables live, functional imaging with high spatial and temporal resolution. However, one of the major limitations of conventional OCT imaging is the light depth penetration, which limits acquisition of structural information from the whole embryo. Here we introduce new imaging scheme by OCT imaging from different sides of the embryos that extend the depth penetration of OCT to permit high-resolution imaging of 3D and 4D volumes.
Consumption of alcohol during pregnancy can be severely detrimental to the development of the brain in fetuses. This study explores the usage of optical coherence tomography (OCT) to the study the effects of maternal consumption of ethanol on brain development in mouse fetuses. On gestational day 14.5, fetuses were collected and fixed in 4% paraformaldehyde. A swept-source OCT (SSOCT) system was used to acquire 3D images of the brain of ethanol-exposed and control fetuses. The volume of right and left brain ventricles were measured and used to compare between ethanol-exposed and control fetuses. A total of 5 fetuses were used for each of the two groups. The average volumes of the right and left ventricles were measured to be 0.35 and 0.15 mm3 for ethanol-exposed and control fetuses, respectively. The results demonstrated that there is an alcohol-induced developmental delay in mouse fetal brains.
Alcohol consumption during pregnancy can be severely damage to the brain development in fetuses. This study
investigates the effects of maternal ethanol consumption on brain development in mice embryos. Pregnant mice at
gestational day 12.5 were intragastrically gavaged with ethanol (3g/Kg bwt) twice daily for three consecutive days.
On gestational day 14.5, fetuses were collected and fixed in 4% paraformaldehyde and imaged using a swept-source
optical coherence tomography (SSOCT) system. 3D images of the mice embryo brain were obtained and the
volumes of the left and right ventricles of the brain were measured. The average volumes of the left and the right
volumes of 5 embryos each alcohol-exposed and control embryos were measured to be 0.35 and 0.15 mm3,
respectively. The results suggest that the left and right ventricle volumes of brain are much larger in the alcohol-exposed
embryos as compared to control embryos indicating alcohol-induced developmental delay.
We have used a swept-source optical coherence tomography (OCT) system to study the development of eyes in mice embryo in utero at different development stages from E13.5 - 18.5. Obtained results demonstrate capability of OCT technology for high-resolution imaging of ocular tissues in utero and capability of assessing key developmental characteristics of the eye during embryonic development.
We present a computational method for the analysis of optical coherence tomography (OCT) images to detect
soft tissue sarcomas. The method combines the quantitative analysis of two aspects of information from the
intensity A-lines of OCT images; one is the slope of the intensity A-line with dB unit, which is determined by
the optical attenuation characteristics of tissue; the other is the standard deviation (SD) of the slope-removed
intensity A-line, which is dependent on the tissue structural features. The method is tested with pilot
experiments on ex vivo tissue samples of human fat, muscle, well differentiated liposarcoma (WDLS) and
leiomyosarcoma. Our results demonstrate the feasibility of this quantitative method in the differentiation of soft
tissue sarcomas from normal tissues. This study indicates that OCT can be a potential computer-aided means of
automatically and accurately identifying resection margins of soft tissues sarcomas during surgical treatment.
The developing fetal brain is vulnerable to a variety of environmental agents including maternal ethanol consumption. Preclinical studies on the development and amelioration of fetal teratology would be significantly facilitated by the application of high resolution imaging technologies like optical coherence tomography (OCT) and high-frequency ultrasound (US). This study investigates the ability of these imaging technologies to measure the effects of maternal ethanol exposure on brain development, ex vivo, in fetal mice. Pregnant mice at gestational day 12.5 were administered ethanol (3 g/Kg b.wt.) or water by intragastric gavage, twice daily for three consecutive days. On gestational day 14.5, fetuses were collected and imaged. Three-dimensional images of the mice fetus brains were obtained by OCT and high-resolution US, and the volumes of the left and right ventricles of the brain were measured. Ethanol-exposed fetuses exhibited a statistically significant, 2-fold increase in average left and right ventricular volumes compared with the ventricular volume of control fetuses, with OCT-derived measures of 0.38 and 0.18 mm 3 , respectively, whereas the boundaries of the fetal mouse lateral ventricles were not clearly definable with US imaging. Our results indicate that OCT is a useful technology for assessing ventriculomegaly accompanying alcohol-induced developmental delay. This study clearly demonstrated advantages of using OCT for quantitative assessment of embryonic development compared with US imaging.
Mouse models of ocular diseases provide a powerful resource for exploration of molecular regulation of eye development and pre-clinical studies. Availability of a live high-resolution imaging method for mouse embryonic eyes would significantly enhance longitudinal analyses and high-throughput morphological screening. We demonstrate that optical coherence tomography (OCT) can be used for live embryonic ocular imaging throughout gestation. At all studied stages, the whole eye is within the imaging distance of the system and there is a good optical contrast between the structures. We also performed OCT eye imaging in the embryonic retinoblastoma mouse model Pax6-SV40 T-antigen, which spontaneously forms lens and retinal lesions, and demonstrate that OCT allows us to clearly differentiate between the mutant and wild type phenotypes. These results demonstrate that OCTin utero imaging is a potentially useful tool to study embryonic ocular diseases in mouse models.
In imaging of turbid biological samples using optical techniques, optical clearing methods can compensate for the lack of
light penetration due to strong attenuation. The addition of optical clearing agents into scattering media increases the
optical homogeneity of the sample and reduces its turbidity, allowing for the increased light penetration. In this study we
investigated the extent of optical clearing in porcine skin by utilizing various concentrations of glucose solution. A goldplated
mirror was fixed beneath the tissue and percentage clearing was determined by measuring the change in intensity
of optical coherence tomography light returning from the mirror over time. A ratio of percentage clearing per tissue
thickness for 10%, 30%, and 50% glucose was determined to be to be (4.7 ± 1.6%) mm-1 (n = 6), (10.6 ± 2.0%) mm-1 (n
= 7), and (21.8 ± 2.2%) mm-1 (n = 5), respectively. Although the extent of optical clearing in porcine skin was more
significant for 50% glucose, the osmotic stress on the sample can cause considerable morphology change, thus a suitable
concentration must be chosen for particular circumstances.
The stiffness of biological tissues could be assessed by measuring the propagation of mechanically induced waves on its
surfaces that could help identifying various tissue pathologies. Here we present results for the volumetric assessment of
mechanical waves propagating on both surfaces of the crystalline lens measured with the Phase-Sensitive Swept Source
Optical Coherence Tomography (PhS-SSOCT) technique. The results indicate that the system could detect vibrations of
as small as 0.03 μm in amplitude induced on the surface of crystalline lens, and hence, PhS-SSOCT could potentially be
used to assess stiffness of a crystalline lens.
Experimental assessment of stiffness of crystalline lens of the eye can help in understanding several ocular diseases. Studies have shown that stiffness of the eye lens increases with age that might contribute to loss of accommodation. The stiffness of the lens could be assessed by measuring mechanically induced surface waves
propagating on its surface. Here we present preliminary results on phase sensitive spectral domain optical coherence tomography (PhS-SDOCT) measurements of the vibrations induced on surface of an eye lens. The system shows an axial resolution of 8 μm, phase sensitivity of 0.01 radians, imaging depth of up to 3.4 mm in air and a scanning speed of 29 kHz for a single A-line. The results indicate that the system could detect vibrations as small as 0.45 μm induced on the surface of crystalline lens, and hence, PhS-SDOCT could be potentially used to assess stiffness of a crystalline lens.
KEYWORDS: Blood, Capillaries, Biomedical optics, Optical coherence tomography, Tissues, Diagnostics, Laser therapeutics, In vitro testing, In vivo imaging, Surgery
We have developed a phase stabilized swept source optical coherence tomography (PhS-SSOCT), that shows an
axial resolution of 10 μm, phase sensitivity of 0.04 radians, imaging depth of up to 6 mm in air and a scanning speed of
20 kHz for a single A-line. In this paper, the PhS-SSOCT is applied to quantify gas microbubbles in blood in vitro. The
results indicate that the system is able to detect bubbles of diameters greater than 10 μm using the structural image and
the microbubbles of diameter less than 10 μm could be detected using the temporal phase response. Images of the
bubbles of diameters 600 μm, 405 μm and 6 μm along with their phase responses are presented. Results indicate that the
PhS-SSOCT could be potentially used for rapid assessment of blood microbubbles in vivo that cause diseases associated
with decompression sickness, venous and arterial gas emboli and barotraumas. Eventually, PhS-SSOCT can be utilized
as an early diagnostic tool for clinical purposes.
A new method for monitoring ultra-small changes in blood hematocrit (~0.2%) based on measurement of refractive
index changes in vitro using Phase Sensitive Spectral Domain Optical Coherence Tomography modality (PhS-SDOCT)
is introduced. The developed system has an axial resolution of ~8 μm, phase sensitivity of ±0.01 radians, imaging depth
of 3.4 ± 0.01 mm in air, and image acquisition speed of 29 kHz. The experimental accuracy for monitoring refractive
index changes as a function of hematocrit level in blood is found to be ±1.5x10-4 (±0.2%). Obtained results indicate that
the PhS-SDOCT can be used to monitor ultra-small changes in the hematocrit and in vitro and, potentially, in tissue
blood vessels in vivo.
Studying hemodynamic changes during early mammalian embryonic development is critical for further advances in prevention, diagnostics, and treatment of congenital cardiovascular (CV) birth defects and diseases. Doppler optical coherence tomography (OCT) has been shown to provide sensitive measurements of blood flow in avian and amphibian embryos. We combined Doppler swept-source optical coherence tomography (DSS-OCT) and live mouse embryo culture to analyze blood flow dynamics in early embryos. SS-OCT structural imaging was used for the reconstruction of embryo morphology and the orientation of blood vessels, which is required for calculating flow velocity from the Doppler measurements. Spatially and temporally resolved blood flow profiles are presented for the dorsal aorta and a yolk sac vessel in a 9.5-day embryo. We demonstrate that DSS-OCT can be successfully used for structural analysis and spatially and temporally resolved hemodynamic measurements in developing early mammalian embryos.
The refractive index is a basic optical property of a medium which is of great importance in physics, chemistry
and most of biomedical applications. In our current study we monitor the change in refractive index for aqueous
solutions of glucose, CaCl2, MgCl2, NaCl, KCl and urea using a phase sensitive spectral domain optical coherence
tomography (ph-SOCT) system. For instance, glucose induced changes in the phase are found to be 0.079 rad/mM
in 200μm thick cuvette for clear media and that is in good agreement with literature and our previous obtained data
using phase sensitive low coherence optical reflectometry(PS-OLCR). The importance of this study is to
demonstrate the capability of ph-SOCT to monitor ultra small changes in refractive index in clear media and the
accuracy for glucose sensing is estimated to be ±2.6×10-6.
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