Intravital microscopy (IVM) is a well-established imaging technique for real-time monitoring of microscale lung tissue dynamics. Although accepted as a gold standard in respiratory research, its characteristic image features are scarcely understood, especially when trying to determine the actual position of alveolar walls. To allow correct interpretation of these images with respect to the true geometry of the lung parenchyma, we analyzed IVM data of alveoli in a mouse model in comparison with simultaneously acquired optical coherence tomography images. Several IVM characteristics, such as double ring structures or disappearing alveoli in regions of liquid filling, could be identified and related to the position of alveoli relative to each other. Utilizing a ray tracing approach based on an idealized geometry of the mouse lung parenchyma, two major reflection processes could be attributed to the IVM image formation: partial reflection and total internal reflection between adjacent alveoli. Considering the origin of the reflexes, a model was developed to determine the true position of alveolar walls within IVM images. These results allow thorough understanding of IVM data and may serve as a basis for the correction of alveolar sizes for more accurate quantitative analysis within future studies of lung tissue dynamics.
In the course of pulmonary research, understanding alveolar tissue dynamics plays a critical role in the treatment of
patients suffering from acute lung diseases. As a gold standard technique for monitoring micro scale changes of lung
tissue, real-time intra-vital microscopy (IVM) has been established to evaluate the behavior of the alveolar tissue. To
allow profound qualitative and quantitative conclusions, characteristic features of the obtained images have to be
thoroughly understood. These factors are strongly influenced by the imaging setup and physiological condition of the
lung. To circumvent misinterpretations, a ray-tracing approach has been applied in this study using an idealized
geometry of the mouse lung parenchyma deduced from optical coherence tomography (OCT) as a complementary
imaging technique. Basic features of IVM images are double ring structures and disappearing of alveoli related to liquid
infiltration. Ray propagation analysis reveals the formation of these features by two major reflection processes: partial
reflection and total internal reflection. The results give rise to quantification errors of the alveolar area related to reflexes
misinterpreted as alveolar borders and should further be used to yield a correction factor for future IVM lung tissue
studies.
KEYWORDS: Optical coherence tomography, Biometrics, Scanners, 3D image processing, Skin, Control systems, Image acquisition, Image analysis, Information security, 3D acquisition
The most established technique for the identification at biometric access control systems is the human fingerprint. While every human fingerprint is unique, fingerprints can be faked very easily by using thin layer fakes. Because commercial fingerprint scanners use only a two-dimensional image acquisition of the finger surface, they can only hardly differentiate between real fingerprints and fingerprint fakes applied on thin layer materials. A Swept Source OCT system with an A-line rate of 20 kHz and a lateral and axial resolution of approximately 13 μm, a centre wavelength of 1320 nm and a band width of 120 nm (FWHM) was used to acquire fingerprints and finger tips with overlying fakes. Three-dimensional volume stacks with dimensions of 4.5 mm x 4 mm x 2 mm were acquired. The layering arrangement of the imaged finger tips and faked finger tips was analyzed and subsequently classified into real and faked fingerprints. Additionally, sweat gland ducts were detected and consulted for the classification. The manual classification between real fingerprints and faked fingerprints results in almost 100 % correctness. The outer as well as the internal fingerprint can be recognized in all real human fingers, whereby this was not possible in the image stacks of the faked fingerprints. Furthermore, in all image stacks of real human fingers the sweat gland ducts were detected. The number of sweat gland ducts differs between the test persons. The typical helix shape of the ducts was observed. In contrast, in images of faked fingerprints we observe abnormal layer arrangements and no sweat gland ducts connecting the papillae of the outer fingerprint and the internal fingerprint. We demonstrated that OCT is a very useful tool to enhance the performance of biometric control systems concerning attacks by thin layer fingerprint fakes.
Broadband light sources provide a significant benefit for optical coherence tomography (OCT) imaging
concerning the axial resolution. Light sources with bandwidths over 200 nm result in an axial resolution up to 2
microns. Such broad band OCT imaging can be achieved utilizing super continuum (SC) light sources. The main
important disadvantage of commercial SC light sources is the overall size and the high costs. Therefore, the use
of SC light sources in small OCT setups and applications is limited. We present a new small housing and costeffective
light source, which is suitable for OCT imaging. The used light source has dimensions of 110 x 160 x
60 mm and covers a wavelength range from 390 nm up to 2500 nm.
The light source was coupled in a dual band OCT system. The light is guided into the interferometer and split in
reference and sample beam. The superimposed signal is guided to the spectrometer unit, which consists of two
spectrometers. This spectrometer system separates the light. One band centered at 800 nm with a full bandwidth
of 176 nm and a second band centered at 1250 nm with a full spectral width of 300 nm was extracted. The 800
nm interference signal is detected by a silicon line scan camera and the 1250 nm signal by an indium gallium
arsenide linear image sensor.
In this test measurement a plastic foil was used as a sample, which is composed of several plastic film layers.
Three dimensional images were acquired simultaneous with the dual band OCT setup. The images were acquired
at an A-scan rate of 1 kHz. The 1 kHz A-line rate was chosen because so far the optical power of the light source
is not optimal for high speed OCT imaging. The source provides 2 mW in the range of 390 nm to 800 nm and 25
mW in the range from 390 nm to 1650 nm. Furthermore, we coupled the light source by a 50:50 optical fiber
coupler, which also reduces the overall optical power of the light source within the OCT setup.
Nevertheless, we demonstrated that this new small-package and cost-effective light source is very suitable to
carry out OCT imaging. The use of this light source can open up new OCT applications, which require OCT
setups with very high axial resolution and small footprint.
The most established technique for the identification at biometric access control systems is the human fingerprint. While every human fingerprint is unique, fingerprints can be faked very easily by using thin layer fakes. Because commercial fingerprint scanners use only a two-dimensional image acquisition of the finger surface, they can only hardly differentiate between real fingerprints and fingerprint fakes applied on thin layer materials. A Swept Source OCT system with an A-line rate of 20 kHz and a lateral and axial resolution of approximately 13 μm, a centre wavelength of 1320 nm and a band width of 120 nm (FWHM) was used to acquire fingerprints and finger tips with overlying fakes. Three-dimensional volume stacks with dimensions of 4.5 mm x 4 mm x 2 mm were acquired. The layering arrangement of the imaged finger tips and faked finger tips was analyzed and subsequently classified into real and faked fingerprints. Additionally, sweat gland ducts were detected and consulted for the classification. The manual classification between real fingerprints and faked fingerprints results in almost 100 % correctness. The outer as well as the internal fingerprint can be recognized in all real human fingers, whereby this was not possible in the image stacks of the faked fingerprints. Furthermore, in all image stacks of real human fingers the sweat gland ducts were detected. The number of sweat gland ducts differs between the test persons. The typical helix shape of the ducts was observed. In contrast, in images of faked fingerprints we observe abnormal layer arrangements and no sweat gland ducts connecting the papillae of the outer fingerprint and the internal fingerprint. We demonstrated that OCT is a very useful tool to enhance the performance of biometric control systems concerning attacks by thin layer fingerprint fakes.
Although several strategies exist for a minimal-invasive treatment of patients with lung failure, the mortality rate of acute respiratory distress syndrome still reaches 30% at minimum. This striking number indicates the necessity of understanding lung dynamics on an alveolar level. To investigate the dynamical behavior on a microscale, we used three-dimensional geometrical and functional imaging to observe tissue parameters including alveolar size and length of embedded elastic fibers during ventilation. We established a combined optical coherence tomography (OCT) and confocal fluorescence microscopy system that is able to monitor the distension of alveolar tissue and elastin fibers simultaneously within three dimensions. The OCT system can laterally resolve a 4.9 μm line pair feature and has an approximately 11 μm full-width-half-maximum axial resolution in air. confocal fluorescence microscopy visualizes molecular properties of the tissue with a resolution of 0.75 μm (laterally), and 5.9 μm (axially) via fluorescence detection of the dye sulforhodamine B specifically binding to elastin. For system evaluation, we used a mouse model in situ to perform lung distension by application of different constant pressure values within the physiological regime. Our method enables the investigation of alveolar dynamics by helping to reveal basic processes emerging during artificial ventilation and breathing.
To develop new treatment possibilities for patients with severe lung diseases it is crucial to understand the lung function
on an alveolar level. Optical coherence tomography (OCT) in combination with intravital microscopy (IVM) are used for
imaging subpleural alveoli in animal models to gain information about dynamic and morphological changes of lung
tissue during mechanical ventilation. The image content suitable for further analysis is influenced by image artifacts
caused by scattering, refraction, reflection, and absorbance. Because the refractive index varies with each air-tissue
interface in lung tissue, these effects decrease OCT image quality exceedingly. The quality of OCT images can be
increased when the refractive index inside the alveoli is matched to the one of tissue via liquid-filling. Thereby,
scattering loss can be decreased and higher penetration depth and tissue contrast can be achieved. To use the advantages
of liquid-filling for in vivo imaging of small rodent lungs, a suitable breathing fluid (perfluorodecalin) and a special
liquid respirator are necessary. Here we show the effect of liquid-filling on OCT and IVM image quality of subpleural
alveoli in a mouse model.
In the context of protective artificial ventilation strategies for patients with severe lung diseases, the contribution
of ventilator settings to tissue changes on the alveolar level of the lung is still a question under debate. To
understand the impact of respiratory settings as well as the dynamic process of respiration, high-resolution
monitoring and visualization of the dynamics of lung alveoli are essential. An instrument allowing 3D imaging of
lung tissue as well as imaging of functional constituents, such as elastin fibers, in in situ experimental conditions
is presented in this study using a combination of Fourier domain optical coherence tomography (FD-OCT) and
fiber-guided two photon microscopy. In a comparative study, fixed lung tissue, stained with sulforhodamine B for
elastin fibers, was used to illustrate the ability of fiber-guided two photon excitation and single photon excitation
for the visualization of elastin fibers within the tissue. Together with the fast 3D imaging capability of OCT, a
new tool is given for the monitoring of alveolar lung dynamics in future in vivo experiments.
KEYWORDS: Optical coherence tomography, Lung, Signal to noise ratio, Mode locking, In vivo imaging, Tissues, Coherence imaging, Single mode fibers, Visualization, Biomedical optics
Optical coherence tomography (OCT) is a noninvasive imaging modality generating cross sectional and volumetric
images of translucent samples. In Fourier domain OCT (FD OCT), the depth profile is calculated by a fast Fourier
transformation of the interference spectrum, providing speed and SNR advantage and thus making FD OCT well suitable
in biomedical applications. The interference spectrum can be acquired spectrally resolved in spectral domain OCT or
time-resolved in optical frequency domain imaging (OFDI). Since OCT images still suffer from motion artifacts,
especially under in vivo conditions, increased depth scan rates are required. Therefor, the principle of Fourier domain
mode locking has been presented by R. Huber et al. circumventing the speed limitations of conventional FD OCT
systems. In FDML lasers, a long single mode fiber is inserted in the ring resonator of the laser resulting in an optical
round trip time of a few microseconds. Sweeping the wavelength synchronously by a tunable Fabry-Perot filter can
provide wavelength sweeps with repetition rates up to a few MHz used for OFDI. Imaging of subpleural lung tissue for
investigation of lung dynamics and its elastic properties is a further biomedical application demanding high-speed OCT
imaging techniques. For the first time, the visualization of subpleural alveolar structures of a rabbit lung is presented by
the use of an FDML-based OCT system enabling repetition rates of 49.5 kHz and 122.6 kHz, respectively.
KEYWORDS: Lung, Optical coherence tomography, Liquids, Tissues, In vivo imaging, Animal model studies, Tissue optics, Prototyping, Oxygen, Refractive index
Optical coherence tomography (OCT) is used for imaging subpleural alveoli in animal models to gain information about
dynamic and morphological changes of lung tissue during mechanical ventilation. The quality of OCT images can be
increased if the refraction index inside the alveoli is matched to the one of tissue via liquid-filling. Thereby, scattering
loss can be decreased and higher penetration depth and tissue contrast can be achieved. Until now, images of liquid-filled
lungs were acquired in isolated and fixated lungs only, so that an in vivo measurement situation is not present. To use the
advantages of liquid-filling for in vivo imaging of small rodent lungs, it was necessary to develop a liquid ventilator.
Perfluorodecalin, a perfluorocarbon, was selected as breathing fluid because of its refraction index being similar to the
one of water and the high transport capacity for carbon dioxide and oxygen. The setup is characterized by two
independent syringe pumps to insert and withdraw the fluid into and from the lung and a custom-made control program
for volume- or pressure-controlled ventilation modes. The presented results demonstrate the liquid-filling verified by
optical coherence tomography and intravital microscopy (IVM) and the advantages of liquid-filling to OCT imaging of
subpleural alveoli.
In critical care medicine, artificial ventilation is a life saving tool providing sufficient blood oxygenation to patients
suffering from respiratory failure. Essential for their survival is the use of protective ventilation strategies to
prevent further lung damage due to ventilator induced lung injury (VILI). Since there is only little known about
implications of lung tissue overdistension on the alveolar level, especially in the case of diseased lungs, this
research deals with the investigation of lung tissue deformation on a microscale. A combined setup utilizing
optical coherence tomography (OCT) and confocal fluorescence microscopy, is used to study the elastic behavior
of the alveolar tissue. Three-dimensional geometrical information with voxel sizes of 6 μm × 6 μm × 11 μm
(in air) is provided by OCT, structural information about localization of elastin fibers is elucidated via confocal
fluorescence microscopy with a lateral resolution of around 1 μm. Imaging depths of 90 μm for OCT and
20 μm for confocal fluorescence microscopy were obtained. Dynamic studies of subpleural tissue were carried
out on the basis of an in vivo mouse model post mortem, mimicking the physiological environment of an intact
thorax and facilitating a window for the application of optical methods. Morphological changes were recorded by
applying constant positive airway pressures of different values. With this, alveolar volume changes could clearly
be recognized and quantified to form a compliance value of 3.5 • 10-6(see manuscript). The distribution of elastin fibers
was detected and will be subject to further elasticity analysis.
Transfer of too high mechanical energy from the ventilator to the lung's alveolar tissue is the main cause for ventilator-induced lung injury (VILI). To investigate the effects of cyclic energy transfer to the alveoli, we introduce a new method of transthoracic endoscopy that provides morphological as well as functional information about alveolar geometry and mechanics. We evaluate the new endoscopic method to continuously record images of focused subpleural alveoli. The method is evaluated by using finite element modeling techniques and by direct observation of subpleural alveoli both in isolated rat lungs as well as in intact animals (rats). The results confirm the overall low invasiveness of the endoscopic method insofar as the mechanical influences on the recorded alveoli are only marginal. It is, hence, a suited method for intravital microscopy in the rat model as well as in larger animals.
Acute lung injury (ALI) is a severe pulmonary disease leading to hypoxemia accompanied by a reduced compliance
and partial edema of the lung. Most of the patients have to be ventilated to compensate for the lack of oxygen.
The treatment is strongly connected with ventilator induced lung injury (VILI), which is believed to introduce
further stress to the lung and changes in its elastic performance. A thorough understanding of the organs
micro-structure is crucial to gain more insight into the course of the disease. Due to backscattering of near-infrared
light, detailed description of lung morphology can be obtained using optical coherence tomography
(OCT), a non-invasive, non-contact, high resolution and fast three-dimensional imaging technique. One of its
drawbacks lies in the non-specificity of light distribution in relation to defined substances, like elastic biomolecules.
Using fluorescence detection, these chemical components can be visualized by introducing specifically binding
fluorophores. This study presents a combined setup for studying alveolar compliance depending on volume
changes and elastic fiber distributions. Simultaneously acquired OCT and confocal fluorescence images allow an
entire view into morphological rearrangements during ventilation for an ex vivo mouse model using continuous
pulmonary airway pressure at different values.
Optical coherence tomography (OCT), as a non-invasive technique for studying tissue morphology, is widely
used in in vivo studies, requiring high resolution and fast three-dimensional imaging. Based on light scattering
it reveals micrometer sized substructures of the samples due to changes in their optical properties and therefore
allows quantification of the specimen's geometry. Utilizing fluorescence microscopy further information can be
obtained from molecular compositions embedded in the investigated object. Fluorescent markers, specifically
binding to the substance of interest, reveal the sample's chemical structure and give rise to functional studies.
This research presents the application of a combined OCT and laser scanning confocal microscopy (LSCM)
system to investigate structural details in lung tissue. OCT reveals the three-dimensional morphology of the
alveoli whereas fluorescence detection, arising from the fluorophore Sulforhodamin B (SRB) which is binding
to elastin, shows the elastic meshwork of the organs extracellular matrix. Different plains of fluorescence can
be obtained by using a piezo driven objective and exploiting the confocal functionality of the setup. Both
techniques combined in one optical system not only ease the experimental procedure but also contribute to a
thorough description of tissue's morphology and chemical composition.
Optical coherence tomography (OCT) is a technique, capable of high resolution and non-invasive 3D imaging
in vivo by detection of backscattered light from cellular and sub cellular structures. Due to visualization of
micrometer sized tissue constituents and high penetration depths of up to 2 mm, it is already well established in
medical fields like ophthalmology and dermatology. Laser scanning confocal microscopy (LSCM), on the contrary,
gives further information on structural tissue components stained with suitable dyes. In combination, these two
methods yield three dimensional and high resolution data providing geometrical and structural details of tissue.
In this study, we present simultaneous OCT and LSCM image acquisition resulting in a lateral resolution of
better than 6.2 μm for OCT and 0.8 μm for LSCM, respectively. The axial resolution of the OCT amounts to
8 μm. Two laser lines, 488 nm and 561 nm, are combined to provide fluorescence excitation of green and red
dyes. By using a long working distance objective, it is possible to perform experiments on bulky specimens like
isolated organs or animal models in vivo. First studies indicate the ability to identify strains of elastic fibers
within lung tissue in combination with the three dimensional morphology of the lung.
KEYWORDS: Lung, Optical coherence tomography, 3D acquisition, In vivo imaging, 3D image processing, Tissues, Data acquisition, Injuries, Stereoscopy, Image acquisition
In this feasibility study, we present a method for virtual 4-D imaging of healthy and injured subpleural lung tissue in the ventilated mouse. We use triggered swept source optical coherence tomography (OCT) with an A-scan frequency of 20 kHz to image murine subpleural alveoli during the inspiratory phase. The data acquisition is gated to the ventilation pressure to take single B-scans in each respiration cycle for different pressure levels. The acquired B-scans are combined off-line into one volume scan for each pressure level. The air fraction in healthy lungs and injured lungs is measured using 2-D OCT en-face images. Upon lung inspiration from 2 to 12 cmH2O ventilation pressure, the air fraction increases in healthy lungs by up to 11% and in injured lungs by 8%. This expansion correlates well with results of previous studies, reporting increased alveolar area with increased ventilation pressures. We demonstrate that OCT is a useful tool to investigate alveolar dynamics in spatial dimensions.
KEYWORDS: Lung, 3D modeling, Optical coherence tomography, In vivo imaging, Tissues, 3D image processing, Microscopy, Animal model studies, Scanners, Injuries
In vivo determination of three-dimensional and dynamic geometries of alveolar structures with adequate resolution is
essential to develop numerical models of the lung. To gain insight into the dynamics of alveoli a thorax window was
prepared in anesthetized rabbits by removal of muscle tissue between 3rd and 4th rib without harming the parietal pleura.
The transparent parietal pleura allows contact-free imaging by intra-vital microscopy (IVM) and 3D optical coherence
tomography (3D-OCT). We have demonstrated that it is possible to acquire the identical region in the inspiratory and
expiratory phase, and that OCT in this animal model is suitable for generating 3D geometry of in vivo lung parenchyma.
The 3D data sets of the fine structure of the lung beneath the pleura could provide a basis for the development of threedimensional
numerical models of the lung.
KEYWORDS: Optical coherence tomography, 3D modeling, Lung, 3D image processing, In vivo imaging, Tissues, Data modeling, Tissue optics, Animal model studies, Stereoscopy
In vivo determination of 3-D and dynamic geometries of alveolar structures with adequate resolution is essential for developing numerical models of the lung. A thorax window is prepared in anesthetized rabbits by removal of muscle tissue between the third and fourth rib without harming the parietal pleura. The transparent parietal pleura allows contact-free imaging by intravital microscopy (IVM) and 3-D optical coherence tomography (3-D OCT). We demonstrate that dislocation of the lung surface is small enough to observe identical regions in the expiratory and inspiratory plateau phase, and that OCT in this animal model is suitable for generating 3-D geometry of in vivo lung parenchyma. To our knowledge, we present a novel thorax window preparation technique for 3-D imaging of alveolar dynamics for the first time. The 3-D datasets of the fine structure of the lung beneath the pleura could provide a basis for the development of 3-D numerical models of the lung.
Three-dimensional Fourier domain optical coherence tomography (3-D FDOCT) is used to demonstrate that perfusion fixation with a mixture of glutaraldehyde and paraformaldehyde does not alter the geometry of subpleural lung parenchyma in isolated and perfused rabbit lungs. This is confirmed by simultaneous imaging of lung parenchyma with intravital microscopy. To eliminate the diffraction index interfaces between alveolar pockets and walls, we fill the fixed lungs with ethanol by perfusing with gradually increasing concentrations. This bottom-up filling process leaves no remaining air bubbles in the alveolar structures, thus drastically improving the resolution and penetration depth of 3-D FDOCT imaging. We observe an approximately 18% increase in alveolar area after ethanol filling, likely due in large part to elimination of the air/tissue interfaces. 3-D OCT datasets acquired from ethanol-filled lungs allow segmentation of the ethanol-filled structures, which were formerly air-filled, and 3-D reconstruction of larger areas of subpleural alveolar structures. Our innovative process of filling the lungs with ethanol postperfusion fixation thus enables more accurate quantification of alveolar geometries, a critical component of modeling lung function.
KEYWORDS: Optical coherence tomography, Lung, 3D image processing, Mechanics, Microscopy, Image segmentation, Tissues, In vivo imaging, 3D modeling, Imaging systems
There is a growing interest in analyzing lung mechanics at the level of the alveoli in order to understand stress-related pathogenesis and possibly avoid ventilator associated lung injury. Emerging quantitative models to simulate fluid mechanics and the associated stresses and strains on delicate alveolar walls require realistic quantitative input on alveolar geometry and its dynamics during ventilation. Here, three-dimensional optical coherence tomography (OCT) and conventional intravital microscopy are joined in one setup to investigate the geometric changes of subpleural alveoli during stepwise pressure increase and release in an isolated and perfused rabbit lung model. We describe good qualitative agreement and quantitative correlation between the OCT data and video micrographs. Our main finding is the inflation and deflation of individual alveoli with noticeable hysteresis. Importantly, this three-dimensional geometry data can be extracted and converted into input data for numerical simulations.
In this study, we demonstrate that phase-resolved Doppler optical frequency domain imaging (OFDI) is very suitable to
quantify the pulsatile blood flow within a vasodynamic measurement in the in vivo mouse model. For this, an OFDI-system
with a read-out rate of 20 kHz and a center wavelength of 1320 nm has been used to image the time-resolved
murine blood flow in 300 μμm vessels. Because OFDI is less sensitive to fringe washout due to axial sample motion, it is
applied to analyze the blood flow velocities and the vascular dynamics in six-week-old C57BL/6 mice compared to one
of the LDLR knockout strain kept under sedentary conditions or with access to voluntary wheel running. We have shown
that the systolic as well as the diastolic phase of the pulsatile arterial blood flow can be well identified at each
vasodynamic state. Furthermore, the changes of the flow velocities after vasoconstriction and -dilation were presented
and interpreted in the entire physiological context. With this, the combined measurement of time-resolved blood flow
and vessel diameter provides the basis to analyze the vascular function and its influence on the blood flow of small
arteries of different mouse strains in response to different life styles.
KEYWORDS: Lung, Optical coherence tomography, 3D modeling, Tissues, Bioalcohols, Image segmentation, In vivo imaging, Image resolution, 3D image processing, Imaging systems
Three dimensional alveolar geometry of subpleural lung parenchyma is of high interest for respiratory research
exemplary for the development of numerical models of the lung for simulating alveolar mechanics. We present a method
for 3D imaging lung tissue up to a depth of 800 μm beneath the pleura by optical coherence tomography with a
resolution of less than 10 μm. Isolated and fixated rabbit lungs were perfused with a series of ethanol with increasing
concentration (20 % - 50 % - 70 % - 95 % - 100 %; 100 ml of each concentration). The alveolar space, normally air
filled, is flooded by the ethanol. The ethanol filling provides an adaptation of the refraction index and therefore imaging
artifacts caused by differences in diffraction index between air and tissue are minimized. We improved the penetration
depth from 200 μm up to 800 μm for subpleural lung parenchyma and we demonstrated that the acquired 3D data sets
are suitable for 3D reconstruction of alveolar tissue.
KEYWORDS: Lung, Optical coherence tomography, 3D image processing, In vivo imaging, Tissues, Injuries, Imaging systems, 3D acquisition, Doppler tomography, Scanners
In this feasibility study we present a method for 4D imaging of healthy and injured subpleural lung tissue in a mouse
model. We used triggered swept source optical coherence tomography with an A-scan frequency of 20 kHz to image
murine subpleural alveoli during the ventilation cycle. The data acquisition was gated to the pulmonary airway pressure
to take one B-scan in each ventilation cycle for different pressure levels. The acquired B-scans were combined offline to
one C-scan for each pressure level. Due to the high acquisition rate of the used optical coherence tomography system, we
are also able to perform OCT Doppler imaging of the alveolar arterioles. We demonstrated that OCT is a useful tool to
investigate the alveolar dynamics in spatial dimensions and to analyze the alveolar blood flow by using Doppler OCT.
In-vivo imaging of the vascular system can provide novel insight into the dynamics of vasoconstriction and vasodilation. Fourier domain optical coherence tomography (FD-OCT) is an optical, noncontact imaging technique based on interferometry of short-coherent near-infrared light with axial resolution of less than 10 µm. In this study, we apply FD-OCT as an in-vivo imaging technique to investigate blood vessels in their anatomical context using temporally resolved image stacks. Our chosen model system is the murine saphenous artery and vein, due to their small inner vessel diameters, sensitive response to vasoactive stimuli, and advantageous anatomical position. The vascular function of male wild-type mice (C57BL/6) is determined at the ages of 6 and 20 weeks. Vasoconstriction is analyzed in response to dermal application of potassium (K+), and vasodilation in response to sodium nitroprusside (SNP). Vasodynamics are quantified from time series (75 sec, 4 frames per sec, 330×512 pixels per frame) of cross sectional images that are analyzed by semiautomated image processing software. The morphology of the saphenous artery and vein is determined by 3-D image stacks of 512×512×512 pixels. Using the FD-OCT technique, we are able to demonstrate age-dependent differences in vascular function and vasodynamics.
Fourier domain optical coherence tomography (FD-OCT) was used to acquire three-dimensional image stacks of isolated
and perfused rabbit lungs (n = 4) at different constant pulmonary airway pressures (CPAP) and during vascular fixation.
After despeckling and applying a threshold, the images were segmented into air and tissue, and registered to each other
to compensate for movement between CPAP steps. The air-filled cross-sectional areas were quantified using a semi-automatic
algorithm. The cross-sectional area of alveolar structures taken at all three perpendicular planes increased with
increasing CPAP. Between the minimal CPAP of 3 mbar and the maximum of 25 mbar the areas increased to about
140% of their initial value. There was no systematic dependency of inflation rate on initial size of the alveolar structure.
During the perfusion fixation of the lungs with glutaraldehyde morphometric changes of the alveolar geometry measured
with FD-OCT were negligible.
KEYWORDS: Optical coherence tomography, Blood vessels, Resistance, Potassium, In vivo imaging, Scanners, Head, 3D image processing, Image analysis, Near infrared
In vivo imaging of blood vessels obtain useful insights in characterizing the dynamics of vasoconstriction and
vasodilation. Fourier domain optical Coherence Tomography (FD-OCT) imaging technique permits in vivo investigation
of blood vessels in their anatomical context without preparation traumata by temporal resolved image stacks. OCT is an
optical, contact less imaging technique based on Michelson interferometry of short coherent near infrared light.
Particularly by the possibility of a contact-less measurement and the high axial resolution up to 10 microns OCT is
superior to an investigation by ultra sound measurement. Furthermore we obtain a high time resolution of vessel dynamic
measurements with the used Fourier domain OCT-system by a high A-scan rate [1,22kHz]. In this study the model of
saphenous artery was chosen for analyzing function and dynamics. The arteria saphena in the mouse is a suitable blood
vessel due to the small inner diameter, a sensitive response to vasoactive stimuli and an advantageous anatomically
position. Male wild type mice (C57BL/6) at the age of 8 weeks were fed control or high-fat diet for 10 weeks before
analyzing the vasodynamics. The blood vessel was stimulated by dermal application of potassium to induce
vasoconstriction or Sodium-Nitroprusside (SNP) to induce vasodilation. The morphology of the a. saphena and vein was
determined by 3D image stacks. Time series (72 seconds, 300x512 pixel per frame) of cross-sectional images were
analysed using semi automatic image processing software. Time course of dynamic parameters of the vessel was
measured.
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.