Endomicroscopic optical coherence tomography for cellular resolution imaging of gastrointestinal tracts

Our ability to detect neoplastic changes in gastrointestinal (GI) tracts is limited by the lack of an endomicroscopic imaging tool that provides cellular‐level structural details of GI mucosa over a large tissue area. In this article, we report a fiber‐optic‐based micro‐optical coherence tomography (μOCT) system and demonstrate its capability to acquire cellular‐level details of GI tissue through circumferential scanning. The system achieves an axial resolution of 2.48 μm in air and a transverse resolution of 4.8 μm with a depth‐of‐focus (DOF) of ~150 μm. To mitigate the issue of limited DOF, we used a rigid sheath to maintain a circular lumen and center the distal‐end optics. The sensitivity is tested to be 98.8 dB with an illumination power of 15.6 mW on the sample. With fresh swine colon tissues imaged ex vivo, detailed structures such as crypt lumens and goblet cells can be clearly resolved, demonstrating that this fiber‐optic μOCT system is capable of visualizing cellular‐level morphological features. We also demonstrate that time‐lapsed frame averaging and imaging speckle reduction are essential for clearly visualizing cellular‐level details. Further development of a clinically viable μOCT endomicroscope is likely to improve the diagnostic outcome of GI cancers.      

Optical coherence tomography for ultrahigh resolution in vivo imaging

Optical coherence tomography (OCT) is an emerging biomedical optical imaging technique that performs high-resolution, cross-sectional tomographic imaging of microstructure in biological systems. OCT can achieve image resolutions of 1-15 microm, one to two orders of magnitude finer than standard ultrasound. The image penetration depth of OCT is determined by the optical scattering and is up to 2-3 mm in tissue. OCT functions as a type of 'optical biopsy' to provide cross-sectional images of tissue structure on the micron scale. It is a promising imaging technology because it can provide images of tissue in situ and in real time, without the need for excision and processing of specimens.     

Gingivitis resolution followed by optical coherence tomography and fluorescence imaging: A case study

Gingivitis is highly prevalent in adults, and if left untreated, can progress to periodontitis. In this article, we present an interesting case study where the resolution of gingivitis was followed over a period of 10 days using optical coherence tomography (OCT) and light-induced autofluorescence (LIAF). We demonstrate that OCT and its functional angiography can distinctively capture the changes during the resolution of gingivitis; while LIAF can detect red-fluorescent signals associated with mature plaque present at the inflamed site. The acute inflammatory region showed evidence of angiogenesis based on the quantification of vessel density and number; while no angiogenesis was detected within the less inflamed region. Gingival thickness showed a reduction of 140 ± 26 μm on average, measured between the peak gingivitis event and the period wherein the inflammation was resolved. Vessels in the angiogenesis site was found to reduce exponentially. The mildly inflamed site showed a decreasing trend in the vessel size, which however was within the error of the measurement.     

Super‐achromatic optical coherence tomography capsule for ultrahigh‐resolution imaging of esophagus

Endoscopic optical coherence tomography (OCT) is a noninvasive technology allowing for imaging of tissue microanatomies of luminal organs in real time. Conventional endoscopic OCT operates at 1300 nm wavelength region with a suboptimal axial resolution limited to 8‐20 μm. In this paper, we present the first ultrahigh‐resolution tethered OCT capsule operating at 800 nm and offering about 3‐ to 4‐fold improvement of axial resolution (plus enhanced imaging contrast). The capsule uses diffractive optics to manage chromatic aberration over a full ~200 nm spectral bandwidth centering around 830 nm, enabling to achieve super‐achromaticity and an axial resolution of ~2.6 μm in air. The performance of the OCT capsule is demonstrated by volumetric imaging of swine esophagus ex vivo and sheep esophagus in vivo, where fine anatomic structures including the sub‐epithelial layers are clearly identified. The ultrahigh resolution and excellent imaging contrast at 800 nm of the tethered capsule suggest the potential of the technology as an enabling tool for surveillance of early esophageal diseases on awake patients without the need for sedation.      

High‐intensity‐focused ultrasound and phase‐sensitive optical coherence tomography for high resolution surface acoustic wave elastography

Elastography has the ability of quantitatively evaluating the mechanical properties of soft tissue; thus it is helpful for diagnosis and treatment monitoring of many diseases, for example, skin diseases. Surface acoustic waves (SAWs) have been proven to be a non‐invasive, non‐destructive method for accurate characterization of tissue elastic properties. Current SAW elastography using high‐energy laser pulse or mechanical shaker still have some problems. In order to improve SAW elastography in medical application, a new technique was proposed in this paper, which combines high‐intensity‐focused ultrasound as a SAWs impulse inducer and phase‐sensitive optical coherence tomography as a SAWs detector. A 2% agar‐agar phantom and ex‐vivo porcine skin were tested. The data were processed by a new algorithm based on the Fourier analysis. The results show that the proposed method has the capability of quantifying the elastic properties of soft tissue‐mimicking materials. The lateral resolution of the elastogram has been significantly improved and the different layers in heterogeneous material could also been distinguished. Our improved technique of SAW elastography has a large potential to be widely applied in clinical use for skin disease diagnosis and treatment monitoring.      

In vivo biomicroscopy of the skin with high-resolution magnetic resonance imaging and high frequency ultrasound.

Noninvasive imaging and characterization of the skin is of great interest in dermatology. In order to get relevant diagnostic information, high-resolution imaging techniques have to be applied. Ultrasonic imaging is a potential method for this purpose where the special requirements concerning the spatial resolution make it essential to apply high frequency ultrasound (HFUS). Alternatively, magnetic resonance imaging (MRI), being a very promising imaging modality, also shows the perspective of becoming a valuable diagnostic tool in dermatology. However, to account for the small dimensions of the structures under observation, very specialized system designs have to be developed. In this paper, a HFUS imaging system working in the 50 MHz and 100 MHz range is applied for high-resolution skin imaging. Furthermore, a commercial MRI-system was equipped with specially designed low noise rf (radio frequency) coils with minimized volume, and customized imaging sequences were applied to optimize the signal-to-noise ratio. With HFUS and high-resolution magnetic resonance (HR-MR) imaging complementary imaging techniques for in vivo biomicroscopy of the skin are available.     

Comparison of pulsed photothermal radiometry,optical coherence tomography and ultrasound for melanoma thickness measurement in PDMS tissue phantoms

Melanoma accounts for 75% of all skin cancer deaths. Pulsed photothermal radiometry (PPTR), optical coherence tomography (OCT) and ultrasound (US) are non‐invasive imaging techniques that may be used to measure melanoma thickness, thus, determining surgical margins. We constructed a series of PDMS tissue phantoms simulating melanomas of different thicknesses. PPTR, OCT and US measurements were recorded from PDMS tissue phantoms and results were compared in terms of axial imaging range, axial resolution and imaging time. A Monte Carlo simulation and three‐dimensional heat transfer model was constructed to simulate PPTR measurement. Experimental results show that PPTR and US can provide a wide axial imaging range (75 μm–1.7 mm and 120–910 μm respectively) but poor axial resolution (75 and 120 μm respectively) in PDMS tissue phantoms, while OCT has the most superficial axial imaging range (14–450 μm) but highest axial resolution (14 μm). The Monte Carlo simulation and three‐dimensional heat transfer model give good agreement with PPTR measurement. PPTR and US are suited to measure thicker melanoma lesions (<$>><$>400 μm), while OCT is better to measure thin melanoma lesions (<$><<$>400 μm). (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparative study of optical coherence tomography angiography algorithms for rodent retinal imaging

Optical coherence tomography angiography (OCTA) is a functional extension of optical coherence tomography for non-invasive in vivo three-dimensional imaging of the microvasculature of biological tissues. Several algorithms have been developed to construct OCTA images from the measured optical coherence tomography signals. In this study, we compared the performance of three OCTA algorithms that are based on the variance of phase, amplitude, and the complex representations of the optical coherence tomography signals for rodent retinal imaging, namely the phase variance, improved speckle contrast, and optical microangiography. The performance of the different algorithms was evaluated by comparing the quality of the OCTA images regarding how well the vasculature network can be resolved. Quantities that are widely used in ophthalmic studies including blood vessel density, vessel diameter index, vessel perimeter index, vessel complexity index were also compared. Results showed that both the improved speckle contrast and optical microangiography algorithms are more robust than phase variance, and they can reveal similar vasculature features while there are statistical differences in the calculated quantities.     

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.     

High‐definition optical coherence tomography of melanocytic skin lesions

High‐definition optical coherence tomography (HD‐OCT) scanners have recently been developed. We assessed micromorphological HD‐OCT correlates of benign naevi (BN) and malignant melanoma (MM). 28 BN and 20 MM were studied using HD‐OCT and histology. Epidermal honeycomb/cobblestone pattern, regular junctional cell nests, and edged papillae are more often observed in BN, whereas fusion of rete ridges, pagetoid cells and junctional and/or dermal nests with atypical cells are more frequently seen in MM. A high overlap of HD‐OCT features in BN and MM was observed and in 20% of MM we did not find evidence for malignancy in OCT images at all. Using HD‐OCT it is possible to visualize architectural and cellular alterations of melanocytic skin lesions. The overlap of HD‐OCT features seen in BN and MM and the absence of suspicious HD‐OCT features in some MM represents an important limitation of HD‐OCT affecting the sensitivity of HD‐OCT in diagnosing MM.

High‐definition optical coherence tomography and the corresponding vertically sectioned histology of a compound naevus.     

Preclinical mouse model of optical coherence tomography for subcortical brain imaging without dissection

The purpose of this study was to investigate the feasibility of using optical coherence tomography (OCT) to identify internal brain lesions, specifically intracerebral hemorrhage, without dissection. Mice with artificially injected brain hematomas were used to test the OCT system, and the recorded images were compared with microscopic images of the same mouse brains after hematoxylin and eosin staining. The intracranial structures surrounding the hematomas were clearly visualized by the OCT system without dissection. These images reflect the ability of OCT to determine the extent of a lesion in several planes. OCT is a useful technology, and these findings could be used as a starting point for future research in intraoperative imaging.     

Static and dynamic imaging of alveoli using optical coherence tomography needle probes

Imaging of alveoli in situ has for the most part been infeasible due to the high resolution required to discern individual alveoli and limited access to alveoli beneath the lung surface. In this study, we present a novel technique to image alveoli using optical coherence tomography (OCT). We propose the use of OCT needle probes, where the distal imaging probe has been miniaturized and encased within a hypodermic needle (as small as 30-gauge, outer diameter 310 μm), allowing insertion deep within the lung tissue with minimal tissue distortion. Such probes enable imaging at a resolution of ～12 μm within a three-dimensional cylindrical field of view with diameter ～1.5 mm centered on the needle tip. The imaging technique is demonstrated on excised lungs from three different species: adult rats, fetal sheep, and adult pigs. OCT needle probes were used to image alveoli, small bronchioles, and blood vessels, and results were matched to histological sections. We also present the first dynamic OCT images acquired with an OCT needle probe, allowing tracking of individual alveoli during simulated cyclical lung inflation and deflation.     

Delineating papillary dermis around basal cell carcinomas by high and ultrahigh resolution optical coherence tomography—A pilot study

Bedside diagnosis of skin cancer remains a challenging task. The real-time noninvasive technology of optical coherence tomography (OCT) masters a high diagnostic accuracy in basal cell carcinoma (BCC) but a lower specificity in recognizing imitators and other carcinomas. We investigate the delicate signal of papillary dermis using an in-house developed ultrahigh resolution OCT (UHR-OCT) system with shadow compensation and a commercial multi-focus high resolution OCT (HR-OCT) system for clinical BCC imaging. We find that the HR-OCT system struggled to resolve the dark band signal of papillary dermis where the UHR-OCT located this in all cases and detected changes in signal width. UHR-OCT is able to monitor extension and position of papillary dermis suggesting a novel feature for delineating superficial BCCs in pursuit of a fast accurate diagnosis. Comprehensive studies involving more patients are imperative in order to corroborate results.     

Optimized skin optical clearing for optical coherence tomography monitoring of encapsulated drug delivery through the hair follicles

Hair follicles (HF) represent a drug delivery reservoir for improved treatment of skin disorders. Although various particulate systems play an important role in HF‐targeting, their optical monitoring in skin is challenging due to strong light scattering. Optical clearing is an effective approach allowing the increasing of particle detection depth in skin. The enhancement of optical probing depth (OPD) and optical detection depth (ODD) of particle localization using optical coherence tomography (OCT) was evaluated under application of various optical clearing agents (OCAs) together with skin permeability enhancers ex vivo in rats. Efficient OPD increasing was demonstrated for all investigated OCAs. However, skin dehydration under action of hyperosmotic agents led to the worsening of OCT‐contrast in dermis decreasing the ODD. Lipophilic agents provided optical clearing of epidermis without its dehydration. The highest ODD was obtained at application of a PEG‐400/oleic acid mixture. This OCA was tested in vivo showing beneficial ODD and OPD enhancement.     

Investigation of optical attenuation imaging using optical coherence tomography for monitoring of scars undergoing fractional laser treatment

We demonstrate the use of the near‐infrared attenuation coefficient, measured using optical coherence tomography (OCT), in longitudinal assessment of hypertrophic burn scars undergoing fractional laser treatment. The measurement method incorporates blood vessel detection by speckle decorrelation and masking, and a robust regression estimator to produce 2D en face parametric images of the attenuation coefficient of the dermis. Through reliable co‐location of the field of view across pre‐ and post‐treatment imaging sessions, the study was able to quantify changes in the attenuation coefficient of the dermis over a period of ～20 weeks in seven patients. Minimal variation was observed in the mean attenuation coefficient of normal skin and control (untreated) mature scars, as expected. However, a significant decrease (13 ± 5%, mean ± standard deviation) was observed in the treated mature scars, resulting in a greater distinction from normal skin in response to localized damage from the laser treatment. By contrast, we observed an increase in the mean attenuation coefficient of treated (31 ± 27%) and control (27 ± 20%) immature scars, with numerical values incrementally approaching normal skin as the healing progressed. This pilot study supports conducting a more extensive investigation of OCT attenuation imaging for quantitative longitudinal monitoring of scars.

En face 2D OCT attenuation coefficient map of a treated immature scar derived from the pre‐treatment (top) and the post‐treatment (bottom) scans. (Vasculature (black) is masked out.) The scale bars are 0.5 mm.     

Multicontrast endomyocardial imaging by single‐channel high‐resolution cross‐polarization optical coherence tomography

A single‐channel high‐resolution cross‐polarization (CP) optical coherence tomography (OCT) system is presented for multicontrast imaging of human myocardium in one‐shot measurement. The intensity and functional contrasts, including the ratio between the cross‐ and co‐polarization channels as well as the cumulative retardation, are reconstructed from the CP‐OCT readout. By comparing the CP‐OCT results with histological analysis, it is shown that the system can successfully delineate microstructures in the myocardium and differentiate the fibrotic myocardium from normal or ablated myocardium based on the functional contrasts provided by the CP‐OCT system. The feasibility of using A‐line profiles from the 2 orthogonal polarization channels to identify fibrotic myocardium, normal myocardium and ablated lesion is also discussed.      

Clinical assessment of non carious cervical lesion using swept‐source optical coherence tomography

Non‐carious cervical lesions (NCCLs) involve various forms of tooth loss with different etiologies. This study aimed to utilize swept‐source optical coherence tomography (SS‐OCT) at 1300 nm wavelength range in vitro and in vivo to evaluate and clarify the mechanism of NCCLs. In the in vitro phase, a dentin attenuation coefficient (μ_t) derived from the SS‐OCT signal at NCCL was compared with mineral loss obtained from transverse microradiography (TMR) to determine a μ_t threshold to discriminate demineralization of cervical dentin in vivo. In the clinical study, 242 buccal surfaces were investigated in 35 subjects. Presence and dimensions of NCCLs, cervical cracking and the degree of demineralization at the exposed cervical dentin were determined using SS‐OCT. Dentin demineralization was observed in 69% of NCCLs. SS‐OCT results confirm that dentin mineral loss and occlusal attrition were associated with larger NCCLs, and can be considered as an etiological factor in formation and progress of these lesions.

( A ) We determined the attenuation coeffcient (μ_t) threshold of SS‐OCT signal for the detection of demineralization (1.21) from in vitro study. DEM: demineralized dentin, sound: sound dentin. ( B ) Using the μ_t threshold, we observed NCCLs in vivo to detect the demineralization in cervical dentin. SS‐OCT scanning was performed along the red line. ( C ) SS‐OCT image obtained along the red line in B. In SS‐OCT, brightness of dentin beneath the NCCL was increased (arrow) compared with intact zone. The cervical dentin was slightly demineralized (μ_t: 1.25). e: enamel, d: dentin, g: gingiva.     

A compact high‐speed full‐field optical coherence microscope for high‐resolution in vivo skin imaging

A compact high‐speed full‐field optical coherence microscope has been developed for high‐resolution in vivo imaging of biological tissues. The interferometer, in the Linnik configuration, has a size of 11 × 11 × 5 cm³ and a weight of 210 g. Full‐field illumination with low‐coherence light is achieved with a high‐brightness broadband light‐emitting diode. High‐speed full‐field detection is achieved by using part of the image sensor of a high‐dynamic range CMOS camera. En face tomographic images are acquired at a rate of 50 Hz, with an integration time of 0.9 ms. The image spatial resolution is 0.9 μm × 1.2 μm (axial × transverse), over a field of view of 245 × 245 μm². Images of human skin, revealing in‐depth cellular‐level structures, were obtained in vivo and in real‐time without the need for stabilization of the subject. The system can image larger fields, up to 1 × 1 mm², but at a reduced depth.      

Ex vivo optical coherence tomography and laser-induced fluorescence spectroscopy imaging of murine gastrointestinal tract

Optical coherence tomography (OCT) and laser-induced fluorescence (LIF) spectroscopy each have clinical potential in identifying human gastrointestinal (GI) pathologies, yet their diagnostic capability in mouse models is unknown. In this study, we combined the 2 modalities to survey the GI tract of a variety of mouse strains and ages and to sample dysplasias and inflammatory bowel disease (IBD) of the intestines. Segments (length, 2.5 cm) of duodenum and lower colon and the entire esophagus were imaged ex-vivo with combined OCT and LIE We evaluated 30 normal mice (A/J and 10- and 21-wk-old and retired breeder C57BL/6J) and 10 mice each of 2 strains modeling colon cancer and IBD (Apc(Min) and IL2-deficient mice, respectively). Histology was used to classify tissue regions as normal, Peyer patch, dysplasia, adenoma, or IBD. Features in corresponding OCT images were analyzed. Spectra from each category were averaged and compared via Student t tests. OCT provided structural information that led to identification of the imaging characteristics of healthy mouse GI. With histology as the 'gold standard,' we developed preliminary image criteria for early disease in the form of adenomas, dysplasias, and IBD. LIF characterized the endogenous fluorescence of mouse GI tract, with spectral features corresponding to collagen, NADH, and hemoglobin. In the IBD sample, LIF emission spectra displayed potentially diagnostic peaks at 635 and 670 nm, which we attributed to increased porphyrin production by bacteria associated with IBD. OCT and LIF appear to be useful and complementary modalities for ex vivo imaging of mouse GI tissues.     

Indocyanine green-enhanced multimodal photoacoustic microscopy and optical coherence tomography molecular imaging of choroidal neovascularization

Photoacoustic microscopy (PAM) has great potential for visualization of the microvasculature with high spatial resolution and contrast. Early detection and differentiation of newly developed blood vessels named choroidal neovascularization (CNV) from normal vasculature remains a challenge in ophthalmology. Exogenous contrast agents can assist with improving PAM sensitivity, leading to differentiation of CNV. Here, an FDA-approved indocyanine green (ICG) was utilized as a PAM contrast agent. ICG was conjugated with RGD peptides, allowing the ICG to bind to the integrin expressed in CNV. Molecular PAM imaging showed that ICG-RGD can target CNV for up to 5 days post intravenous administration in living rabbits with a model of CNV. The PAM image sensitivity and image contrast were significantly enhanced by 15-fold at 24 h post-injection. Overall, the presented approach demonstrates the possibility of targeted ICG to be employed in PAM molecular imaging, allowing more precise evaluation of neovascularization.