Measuring changes in blood volume fraction during induced gingivitis of healthy and unhealthy populations using hyperspectral spatial frequency domain imaging: a clinical study.

This investigation aimed to quantitatively measure the changes in inflammation of subjects with healthy and unhealthy gums during a period of induced gingivitis. A total of 30 subjects (15 healthy, 15 with gum inflammation) were enlisted and given oral exams by a dental hygienist. Baseline measurements were acquired before a 3-week period of oral hygiene abstinence. The lobene modified gingival index scoring was used for inflammation scoring and hyperspectral spatial frequency domain imaging was used to quantitatively measure oxy- and deoxygenated blood volume fraction at two time points: at Baseline and after 3 weeks of oral hygiene abstinence. We found that abstaining from oral hygiene causes a near proportional increase in oxygenated and deoxygenated blood volume fraction for healthy individuals. For individuals who started the study with mild to moderate gingivitis, increases in blood volume were mainly due to deoxygenated blood.

Spectral imaging of normal, hydrated, and desiccated porcine skin using polarized light.

Significance: Spectroscopic and structural imaging of tissue layers is important for investigating tissue health. However, investigating superficial tissue is difficult using optical imaging, due to the convolved absorption and backscatter of light from deeper layers. Aim: This report investigates the effects of hydration and desiccation of ex vivo porcine skin on the reflectance of polarized light at different wavelengths (light-emitting diodes). Approach: We developed a spectroscopic polarized imaging system to investigate submicron changes in tissue structures. By separating polarized from depolarized backscattered light, submicron structural changes in subsurface and deeper tissue layers can be separated and monitored. Results: The results demonstrate that (1) polarized light reflectance is about 2%, consistent with ∼6 scattering events, on average; (2) there was little wavelength dependence to the reflectance of polarized light; (3) increased hydration leads to a modest increase in total reflectance (from 0.8 to 0.9), whereas desiccation had little effect; however, hydration did not affect polarized reflectance, but desiccation slightly lowered polarized reflectance. Conclusions: Higher scattering from the reticular dermis was likely due to swelling of collagen fiber bundles in the dermal layers, which increased fibril spacing. The epidermal skin surface showed little change due to the stratum corneum resisting desiccation and maintaining hydration.

Noninvasive multimodal imaging by integrating optical coherence tomography with autofluorescence imaging for dental applications.

We report the development of an integrated multifunctional imaging system capable of providing anatomical (optical coherence tomography, OCT), functional (OCT angiography, OCTA) and molecular imaging (light-induced autofluorescence, LIAF) for in vivo dental applications. Blue excitation light (405 nm) was used for LIAF imaging, while the OCT was powered by a 1310 nm swept laser source. A red-green-blue digital camera, with a 450 nm cut-on broadband optical filter, was used for LIAF detection. The exciting light source and camera were integrated directly with the OCT scanning probe. The integrated system used two noninvasive imaging modalities to improve the speed of in vivo OCT data collection and to better target the regions of interest. The newly designed system maintained the ability to detect differences between healthy and hypomineralized teeth, identify dental biofilm and visualize the microvasculature of gingival tissue. The development of the integrated OCT-LIAF system provides an opportunity to conduct clinical studies more efficiently, examining changes in oral conditions over time.

An Experimental Review of Optical Coherence Tomography Systems for Noninvasive Assessment of Hard Dental Tissues.

Optical coherence tomography (OCT) is a noninvasive, high-resolution, cross-sectional imaging technique. To date, OCT has been demonstrated in several areas of dentistry, primarily using wavelengths around 1,300 nm, low numerical aperture (NA) imaging lenses, and detectors insensitive to the polarization of light. The objective of this study is to compare the performance of three commercially available OCT systems operating with alternative wavelengths, imaging lenses, and detectors for OCT imaging of dental enamel. Spectral-domain (SD) OCT systems with (i) 840 nm (Lumedica, OQ LabScope 1.0), (ii) 1,300 nm (Thorlabs, Tel320) center wavelengths, and (iii) a swept-source (SS) OCT system (Thorlabs OCS1300SS) centered at 1,325 nm with optional polarization-sensitive detection were used. Low NA (0.04) and high NA (0.15) imaging lenses were used with system (iii). Healthy in vivo and in vitrohuman enamel and eroded in vitro bovine enamel specimens were imaged. The Tel320 system achieved greater imaging depth than the OQ LabScope 1.0, on average imaging 2.6 times deeper into the tooth (n = 10). The low NA lens provided a larger field of view and depth of focus, while the high NA lens provided higher lateral resolution and greater contrast. Polarization-sensitive imaging eliminated birefringent banding artifacts that can appear in conventional OCT scans. In summary, this study illustrates the performance of three commercially available OCT systems, objective lenses, and imaging modes and how these can affect imaging depth, resolution, field of view, and contrast in enamel. Users investigating OCT for dental applications should consider these factors when selecting an OCT system for clinical or basic science studies.

A noninvasive imaging and measurement using optical coherence tomography angiography for the assessment of gingiva: An in vivo study.

Gingiva is the soft tissue that surrounds and protects the teeth. Healthy gingiva provides an effective barrier to periodontal insults to deeper tissue, thus is an important indicator to a patient's periodontal health. Current methods in assessing gingival tissue health, including visual observation and physical examination with probing on the gingiva, are qualitative and subjective. They may become cumbersome when more complex cases are involved, such as variations in gingival biotypes where feature and thickness of the gingiva are considered. A noninvasive imaging technique providing depth-resolved structural and vascular information is necessary for an improved assessment of gingival tissue and more accurate diagnosis of periodontal status. We propose a three-dimensional (3D) imaging technique, optical coherence tomography (OCT), to perform in situ imaging on human gingiva. Ten volunteers (five male, five female, age 25-35) were recruited; and the labial gingival tissues of upper incisors were scanned using the combined use of state-of-the-art swept-source OCT and OCT angiography (OCTA). Information was collected describing the 3D tissue microstructure and capillary vasculature of the gingiva within a penetration depth of up to 2 mm. Results indicate significant structural and vascular differences between the two extreme gingival biotypes (ie, thick and thin gingiva), and demonstrate special features of vascular arrangement and characteristics in gingival inflammation. Within the limit of this study, the OCT/OCTA technique is feasible in quantifying different attributes of gingival biotypes and the severity of gingival inflammation.

Feasibility of correlation mapping optical coherence tomography angiographic technique using a 200 kHz vertical-cavity surface-emitting laser source for in vivo microcirculation imaging applications.

Optical coherence tomography (OCT) angiography is a well-established in vivo imaging technique to assess the overall vascular morphology of tissues and is an emerging field of research for the assessment of blood flow dynamics and functional parameters such as oxygen saturation. In this study, we present a modified scanning-based correlation mapping OCT using a 200 kHz high-speed swept-source OCT system operating at 1300 nm and demonstrate its wide field-imaging capability in ocular angiographic studies.

3D nondestructive testing system with an affordable multiple reference optical-delay-based optical coherence tomography.

Optical coherence tomography (OCT) is emerging as a powerful noncontact imaging technique, allowing high-quality cross-sectional imaging of scattering specimens nondestructively. However, the complexity and cost of current embodiments of an OCT system limit its use in various nondestructive testing (NDT) applications at resource-limited settings. In this paper, we demonstrate the feasibility of a novel low-cost OCT system for a range of nondestructive testing (NDT) applications. The proposed imaging system is based on an enhanced time-domain OCT system with a low cost and small form factor reference arm optical delay, called multiple reference OCT (MR-OCT), which uses a miniature voice coil actuator and a partial mirror for extending the axial scan range. The proposed approach is potentially a low-cost, compact, and unique optical imaging modality for a range of NDT applications in a low-resource setting. Using this method, we demonstrated the capability of MR-OCT to perform cross-sectional and volumetric imaging at 1200 A-scans per second.

Developing cross-correlation as a method for microvessel imaging using clinical intravascular optical coherence tomography systems.

Current clinical intravascular optical coherence tomography (IV-OCT) imaging systems have limited in-vivo flow imaging capability because of non-uniform catheter rotation and inadequate A-line scan density. Thus any flow-localisation method that seeks to identify sites of variation within the OCT image data-sets, whether that is in amplitude or phase, produces non-representative correlation (or variance) maps. In this study, both mean and the variation within a set of cross-correlation maps, for static OCT imaging was used to differentiate flow from nonflow regions. Variation was quantified by use of standard deviation. The advantage of this approach is its ability to image flow, even in the presence of motion artifacts. The ability of this technique to suppress noise and capture flow maps was demonstrated by imaging microflow in an ex-vivo porcine coronary artery model, by nailfold capillary imaging and in-vivo microvessel imaging from within the human coronary sinus.

Linear-array-based photoacoustic imaging of human microcirculation with a range of high frequency transducer probes.

Photoacoustic imaging (PAI) with a linear-array-based probe can provide a convenient means of imaging the human microcirculation within its native structural context and adds functional information. PAI using a multielement linear transducer array combined with multichannel collecting system was used for in vivo volumetric imaging of the blood microcirculation, the total concentration of hemoglobin (HbT), and the hemoglobin oxygen saturation (sO2) within human tissue. Three-dimensional (3-D) PA and ultrasound (US) volumetric scans were acquired from the forearm skin by linearly translating the transducer with a stepper motor over a region of interest, while capturing two-dimensional images using 15, 21, and 40 MHz frequency transducer probes. For the microvasculature imaging, PA images were acquired at 800- and 1064-nm wavelengths. For the HbT and sO2 estimates, PA images were collected at 750- and 850-nm wavelengths. 3-D microcirculation, HbT, and sO2 maps of the forearm skin were obtained from normal subjects. The linear-array-based PAI has been found promising in terms of resolution, imaging depth, and imaging speed for in vivo microcirculation imaging within human skin. We believe that a reflection type probe, similar to existing clinical US probes, is most likely to succeed in real clinical applications. Its advantages include ease of use, speed, and familiarity for radiographers and clinicians.

Nano-sensitive optical coherence tomography.

Depth resolved label-free detection of structural changes with nanoscale sensitivity is an outstanding problem in the biological and physical sciences and has significant applications in both the fundamental research and healthcare diagnostics arenas. Here we experimentally demonstrate a novel label-free depth resolved sensing technique based on optical coherence tomography (OCT) to detect structural changes at the nanoscale. Structural components of the 3D object, spectrally encoded in the remitted light, are transformed from the Fourier domain into each voxel of the 3D OCT image without compromising sensitivity. Spatial distribution of the nanoscale structural changes in the depth direction is visualized in just a single OCT scan. This label free approach provides new possibilities for depth resolved study of pathogenic and physiologically relevant molecules in the body with high sensitivity and specificity. It offers a powerful opportunity for early diagnosis and treatment of diseases. Experimental results show the ability of the approach to differentiate structural changes of 30 nm in nanosphere aggregates, located at different depths, from a single OCT scan, and structural changes less than 30 nm in time from two OCT scans. Application for visualization of the structure of human skin in vivo is also demonstrated.

Microcirculation imaging based on full-range high-speed spectral domain correlation mapping optical coherence tomography.

Microcirculation imaging is a key parameter for studying the pathophysiological processes of various disease conditions, in both clinical and fundamental research. A full-range spectral-domain correlation mapping optical coherence tomography (cm-OCT) method to obtain a complex-conjugate-free, full-range depth-resolved microcirculation map is presented. The proposed system is based on a high-speed spectrometer at 91 kHz with a modified scanning protocol to achieve higher acquisition speed to render cm-OCT images with high-speed and wide scan range. The mirror image elimination is based on linear phase modulation of B-frames by introducing a slight off-set of the probe beam with respect to the lateral scanning fast mirror's pivot axis. An algorithm that exploits the Hilbert transform to obtain a complex-conjugate-free image in conjunction with the cm-OCT algorithm is used to obtain full-range imaging of microcirculation within tissue beds in vivo. The estimated sensitivity of the system was around 105 dB near the zero-delay line with ∼20 dB roll-off from ±0.5 to ±3 mm imaging-depth position. The estimated axial and lateral resolutions are ∼12 and ∼30 µm, respectively. A direct consequence of this complex conjugate artifact elimination is the enhanced flow imaging sensitivity for deep tissue imaging application by imaging through the most sensitive zero-delay line and doubling the imaging range.

In vivo full-field en face correlation mapping optical coherence tomography.

A full-field optical coherence tomography (OCT) system has been developed for the purpose of performing nonscanning en face flow imaging. The light source is centered at 840 nm with a bandwidth of 50 nm resulting in an axial resolution of 8 µm in air. Microscope objectives with a numerical aperture of 0.1 were incorporated giving a transverse resolution of 5 µm. A magnification of 5.65 was measured, resulting in a field of view of 1260×945 µm. Pairs of interference fringe images are captured with opposing phase and a two-step phase image reconstruction method is applied to reconstruct each en face image. The OCT frame rate is 10 Hz. A two-dimensional cross-correlation technique is applied to pairs of consecutive en face images in order to distinguish dynamic from static light-scatterers. The feasibility of the method was examined by simulating blood flow by creating a phantom with 5% intralipid solution. In vivo imaging of a Xenopus laevis tadpole was also performed in order to investigate the feasibility of imaging the vascular system. We present for what we believe to be the first time, the application of correlation mapping optical coherence tomography to full-field OCT to provide in vivo functional imaging of blood vessels.

Feasibility of correlation mapping optical coherence tomography (cmOCT) for anti-spoof sub-surface fingerprinting.

We propose the use of correlation mapping optical coherence tomography (cmOCT) to deliver additional biometrics associated with the finger that could complement existing fingerprint technology for law enforcement applications. The current study extends the existing fingerprint paradigm by measuring additional biometrics associated with sub-surface finger tissue such as sub-surface fingerprints, sweat glands, and the pattern of the capillary bed to yield a user-friendly cost effective and anti-spoof multi-mode biometric solution associated with the finger. To our knowledge no other method has been able to capture sub-surface fingerprint, papillary pattern and horizontal vessel pattern in a single scan or to show the correspondence between these patterns in live adult human fingertip. Unlike many current technologies this approach incorporates 'liveness' testing by default. The ultimate output is a biometric module which is difficult to defeat and complements fingerprint scanners that currently are used in border control and law enforcement applications.

Depth-resolved dual-beamlet vibrometry based on Fourier domain low coherence interferometry.

We present an optical vibrometer based on delay-encoded, dual-beamlet phase-sensitive Fourier domain interferometric system to provide depth-resolved subnanometer scale vibration information from scattering biological specimens. System characterization, calibration, and preliminary vibrometry with biological specimens were performed. The proposed system has the potential to provide both amplitude and direction of vibration of tissue microstructures on a single two-dimensional plane.

Feasibility of spectral-domain phase-sensitive optical coherence tomography for middle ear vibrometry.

We describe a novel application of spectral-domain phase-sensitive optical coherence tomography (SD PS-OCT) to detect the tiny motions of the middle ear structures, such as the tympanic membrane and ossicular chain, and their morphological features for differential diagnosis of CHL. This technique has the potential to provide meaningful vibration of ossicles with a vibration sensitivity of ≈ 0.5 nm at 1 kHz of acoustic stimulation. To the best of our knowledge, this is the first demonstration of depth-resolved vibration imaging of ossicles with a PS-OCT system at a nanometer scale.

Optical detection of indocyanine green encapsulated biocompatible poly (lactic-co-glycolic) acid nanoparticles with photothermal optical coherence tomography.

We describe a functional imaging paradigm that uses photothermal optical coherence tomography (PT-OCT) to detect indocyanine green (ICG)-encapsulated biocompatible poly(lactic-co-glycolic) acid (PLGA) nanoparticles embedded in highly scattering tissue phantoms with high resolution and sensitivity. The ICG-loaded PLGA nanoparticles were fabricated using a modified emulsification solvent diffusion method. With a 20 kHz axial scan rate, PT-OCT based on spectral-domain interferometric configuration at 1310 nm was used to detect phase changes induced by a 808 nm photothermal excitation of ICG-encapsulated PLGA nanoparticles. An algorithm based on Fourier transform analysis of differential phase of the spectral interferogram was developed for detecting the depth resolved localized photothermal signal. Excellent contrast difference was observed with PT-OCT between phantoms containing different concentrations of ICG-encapsulated PLGA nanoparticles. This technique has the potential to provide simultaneous structural and molecular-targeted imaging with excellent signal-to-noise for various clinical applications.

Volumetric in vivo imaging of microvascular perfusion within the intact cochlea in mice using ultra-high sensitive optical microangiography.

Studying the inner ear microvascular dynamics is extremely important to understand the cochlear function and to further advance the diagnosis, prevention, and treatment of many otologic disorders. However, there is currently no effective imaging tool available that is able to access the blood flow within the intact cochlea. In this paper, we report the use of an ultrahigh sensitive optical micro-angiography (UHS-OMAG) imaging system to image 3-D microvascular perfusion within the intact cochlea in living mice. The UHS-OMAG image system used in this study is based on spectral domain optical coherence tomography, which uses a broadband light source centered at 1300 nm with an imaging rate of 47[Formula: see text] 000 A-scans/s, capable of acquiring high-resolution B scans at 300 frames/s. The technique is sensitive enough to image very slow blood flow velocities, such as those found in capillary networks. The 3-D imaging acquisition time for a whole cochlea is  âˆ¼ 4.1 s. We demonstrate that volumetric reconstruction of microvascular flow obtained by UHS-OMAG provides a comprehensive perfusion map of several regions of the cochlea, including the otic capsule, the stria vascularis of the apical and middle turns and the radiating arterioles that emanate from the modiolus.

Volumetric in vivo imaging of intracochlear microstructures in mice by high-speed spectral domain optical coherence tomography.

There is considerable interest in developing new methods for in vivo imaging of the complex anatomy of the mammalian cochlea for clinical as well as fundamental studies. In this study, we explored, the feasibility of spectral domain optical coherence tomography (SD-OCT) for 3-D in vivo imaging of the cochlea in mice. The SD-OCT system employed in this study used a broadband light source centered at 1300 nm, and the imaging speed of the system was 47,000 A-scans per second using the InGaAs camera. The system was capable of providing fully processed, high-resolution B-scan images [512 (axial) x 128 (lateral) pixels] at 280 frames per sec. The 3-D imaging acquisition time for a whole cochlea was approximately 0.45 sec. The traditional SD-OCT structural imaging algorithm was used to reconstruct 3-D cochlear morphology. We demonstrated that SD-OCT can be successfully used for in vivo imaging of important morphological features within the mouse cochlea, such as the otic capsule and structures within, including Reissner's membrane, the basilar membrane, tectorial membrane, organ of Corti, and modiolus of the apical and middle turns.