Full-field Optical Coherence Tomography Research Articles

Full-depth epidermis tomography using a Mirau-based full-field optical coherence tomography.

With a Gaussian-like broadband light source from high brightness Ce(3+):YAG single-clad crystal fiber, a full-field optical coherence tomography using a home-designed Mirau objective realized high quality images of in vivo and excised skin tissues. With a 40 × silicone-oil-immersion Mirau objective, the achieved spatial resolutions in axial and lateral directions were 0.9 and 0.51 μm, respectively. Such a high spatial resolution enables the separation of lamellar structure of the full epidermis in both the cross-sectional and en face planes. The number of layers of stratum corneum and its thickness were quantitatively measured. This label free and non-invasive optical probe could be useful for evaluating the water barrier of skin tissue in clinics. As a preliminary in vivo experiment, the blood vessel in dermis was also observed, and the flowing of the red blood cells and location of the melanocyte were traced.

Optical coherence tomography today: speed, contrast, and multimodality.

In the last 25 years, optical coherence tomography (OCT) has advanced to be one of the most innovative and most successful translational optical imaging techniques, achieving substantial economic impact as well as clinical acceptance. This is largely owing to the resolution improvements by a factor of 10 to the submicron regime and to the imaging speed increase by more than half a million times to more than 5 million A-scans per second, with the latter one accomplished by the state-of-the-art swept source laser technologies that are reviewed in this article. In addition, parallelization of OCT detection, such as line-field and full-field OCT, has shortened the acquisition time even further by establishing quasi-akinetic scanning. Besides the technical improvements, several functional and contrast-enhancing OCT applications have been investigated, among which the label-free angiography shows great potential for future studies. Finally, various multimodal imaging modalities with OCT incorporated are reviewed, in that these multimodal implementations can synergistically compensate for the fundamental limitations of OCT when it is used alone.

Applying RGB LED in full-field optical coherence tomography for real-time full-color tissue imaging.

A conventional handheld skin camera is suitable for 2D inspection of shallow skin. Due to its high resolution and noninvasiveness, optical coherence tomography (OCT) has become a popular medical-imaging technology. Among OCT schemes, full-field optical coherence tomography (FF-OCT) is suitable for rapid en face imaging, as it uses a 2D imaging device for pixel processing of a sample plane. Because of its wide bandwidth and long lifetime, an RGB LED was chosen in an FF-OCT system among three source candidates in this study. A full-color tissue image and real-time video were obtained from the system to demonstrate the potential of the RGB LED FF-OCT system in medical imaging. All devices used here can be integrated by micro-optoelectromechanical technology into a handheld model. Noninvasive, real-time, full-color handheld imaging capability contributes to advance dermatology and cosmetology.

Numerical focusing methods for full field OCT: a comparison based on a common signal model.

In this paper a theoretical model of the full field swept source (FF SS) OCT signal is presented based on the angular spectrum wave propagation approach which accounts for the defocus error with imaging depth. It is shown that using the same theoretical model of the signal, numerical defocus correction methods based on a simple forward model (FM) and inverse scattering (IS), the latter being similar to interferometric synthetic aperture microscopy (ISAM), can be derived. Both FM and IS are compared quantitatively with sub-aperture based digital adaptive optics (DAO). FM has the least numerical complexity, and is the fastest in terms of computational speed among the three. SNR improvement of more than 10 dB is shown for all the three methods over a sample depth of 1.5 mm. For a sample with non-uniform refractive index with depth, FM and IS both improved the depth of focus (DOF) by a factor of 7x for an imaging NA of 0.1. DAO performs the best in case of non-uniform refractive index with respect to DOF improvement by 11x.

Diagnostic différentiel entre cicatrices chéloïdes et hypertrophiques : une nouvelle approche en tomographie par cohérence optique plein-champ

To evaluate the efficacy of full-field optical coherence tomography to differentiate hypertrophic and keloid scars on ex-vivo tissues. All patients who underwent resection of pathological scar from November 2012 to September 2013 were analyzed. The scars were fixed in formalin and analyzed by conventional histology and full-field optical coherence tomography. The criteria for evaluation were: presence of dermal nodules, presence of cells and hyalinization of collagen. Nineteen pathological scars were analyzed. Histology found 7 keloid scars, 7 mixed and 3 hypertrophic scars. The sensitivity of optical coherence tomography for the detection of dermal nodules was 100%. This technology was not helpful for detection of cells and hyalinized collagen. In the present state of technology, optical coherence tomography did not identify the presence of cells, which makes the differential diagnosis difficult in the case of hypertrophic and keloid scars.

Spectroscopic study on appearances of make‐up skins using a visible RGB‐LED OCT

Facial foundation is very effective to correct color irregularities of the skin surface and to protect the skin from harmful light. This depends strongly on both the optical properties and the coating condition of foundation on the skin surface. We constructed the full-field optical coherence tomography (OCT) (FF-OCT) microscope with visible light sources of RGB LEDs. The commercially available skin replicas were used as the model of skin in the experiment, which were composed of two layers, a thin polyurethane film transcribed from cheek surface of a female and a beige-colored silicone substrate. The foundations were applied to the skin replicas under the constant pressure. A topographic image provides spectroscopic information of reflected light and effectiveness of correction of surface irregularities by applying the foundation. A tomographic image demonstrates the spectroscopic degree of light penetration into the skin tissue. It is shown that the reflectivity increases consistently with thickness of the applied foundation because light reflected from the surface and diffusively reflected from the inside of the tissue increases as the surface becomes flat applying the foundation. We confirmed experimentally the potential of the spectroscopic FF-OCT microscopy in investigating both qualitatively and quantitatively the effectiveness of facial foundation.

Imaging of Mohs Micrographic Surgery Sections Using Full-Field Optical Coherence Tomography: A Pilot Study

Full-field optical coherence tomography (FF-OCT) is a new noninvasive imaging technique that can see down to the cellular level without tissue preparation or contrast agents. To use FF-OCT to image Mohs micrographic surgery specimens and verify the ability of a dermatopathologist to identify or exclude malignancy. Two Mohs surgeons supplied 18 Mohs sections from 11 patients. Each section was scanned using the FF-OCT, and a dermatopathologist blinded to the diagnosis examined the images for malignancy. The FF-OCT images were then compared with the intraoperative hematoxylin and eosin (H&E)-stained frozen sections for concordance. All 9 FF-OCT images interpreted as negative for malignancy were in agreement with the H&E frozen sections. Six of the remaining FF-OCT images were correctly interpreted as positive for malignancy, and three were deferred because malignancy could not be confirmed or excluded. Malignancy in Mohs sections can correctly be identified or excluded using FF-OCT. Although not ready for clinical use in its current state, FF-OCT has the potential to be incorporated into the Mohs workflow in the future.

Rapid evaluation of fresh ex vivo kidney tissue with full field optical coherence tomography

Background Full-field optical coherence tomography (FFOCT) is a real-time imaging technique that rapidly generates images reminiscent of histology without any tissue processing, warranting its exploration for evaluation of ex vivo kidney tissue. Methods Fresh tissue sections from tumor and adjacent nonneoplastic kidney (n = 30 nephrectomy specimens) were imaged with a commercial FFOCT device (Light-CTTM, LLTech SAS, Paris, France) equipped with a 10× objective. Sections were submitted for routine histopathological diagnosis. Results Glomeruli, tubules, interstitium and blood vessels were identified in non-neoplastic tissue. In tumor sections, the normal architecture was completely replaced by either sheets of cells/ trabeculae or papillary structures. The former pattern was seen in clear cell/chromophobe RCC and the later in papillary RCC (confirmed on H&E). Although the cellular details were not very prominent at this magnification we could identify unique cytoplasmic signatures in kidney tumors, e.g., hyper-intense punctate signal in cytoplasm of clear cell RCC. In papillary RCC histiocytes, i.e, large cells with abundant hyperintense cytoplasm were seen. Conclusion The ability of FFOCT to differentiate non-neoplastic from neoplastic tissue and identify some tumors types makes it a valuable tool for rapid evaluation of ex vivo kidney tissue, e.g., for intra-operative margin assessment and kidney biopsy.

Non-Destructive Evaluation of Polymer Coating Structures on Pharmaceutical Pellets Using Full-Field Optical Coherence Tomography

Full-field optical coherence tomography (FF-OCT) using a conventional light-emitting diode and a complementary metal-oxide semiconductor camera has been developed for characterising coatings on small pellet samples. A set ofen-faceimages covering an area of 700 × 700 μm2was taken over a depth range of 166 μm. The three-dimensional structural information, such as the coating thickness and uniformity, was subsequently obtained by analysis of the recordeden-faceimages. Drug-loaded pharmaceutical sustained-release pellets with two coating layers and of a sub-millimetre diameter were studied to demonstrate the usefulness of the developed system. We have shown that both coatings can be clearly resolved and the thickness was determined to be 40 and 50 μm for the outer and inner coating layers, respectively. It was also found that the outer coating layer is relatively uniform, whereas the inner coating layer has many particle-like features. X-ray computed microtomography measurements carried out on the same pellet sample confirmed all these findings. The presented FF-OCT approach is inexpensive and has better spatial resolution compared with other non-destructive analysis techniques such as terahertz pulsed imaging, and is thus considered advantageous for the quantitative analysis of thin coatings on small pellet samples.

From supersonic shear wave imaging to full-field optical coherence shear wave elastography

Elasticity maps of tissue have proved to be particularly useful in providing complementary contrast to ultrasonic imaging, e.g., for cancer diagnosis at the millimeter scale. Optical coherence tomography (OCT) offers an endogenous contrast based on singly backscattered optical waves. Adding complementary contrast to OCT images by recording elasticity maps could also be valuable in improving OCT-based diagnosis at the microscopic scale. Static elastography has been successfully coupled with full-field OCT (FF-OCT) in order to realize both micrometer-scale sectioning and elasticity maps. Nevertheless, static elastography presents a number of drawbacks, mainly when stiffness quantification is required. Here, we describe the combination of two methods: transient elastography, based on speed measurements of shear waves induced by ultrasonic radiation forces, and FF-OCT, an en face OCT approach using an incoherent light source. The use of an ultrafast ultrasonic scanner and an ultrafast camera working at 10,000 to 30,000 images/s made it possible to follow shear wave propagation with both modalities. As expected, FF-OCT is found to be much more sensitive than ultrafast ultrasound to tiny shear vibrations (a few nanometers and micrometers, respectively). Stiffness assessed in gel phantoms and an ex vivo rat brain by FF-OCT is found to be in good agreement with ultrasound shear wave elastography.

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.

Refractive index measurements of multiple layers using numerical refocusing in FF-OCT

We propose and demonstrate the novel method of refractive index (RI) measurement for each layer of multilayered samples, which is based on numerical refocusing in full field optical coherence tomography (FF-OCT). The en-face FF-OCT image on an inner layer boundary of a multilayered sample is unintentionally blurred or defocused due to the RI of the sample itself, but can be numerically refocused. The refocusing is performed by numerically shifting the image sensor plane of the system, in general. However, by calculating the corresponding sample shift and then compared it with the actual sample shifting distance, we could extract the average RI of the layer between any two layer boundaries within the multilayered sample. In addition, the thickness of that particular layer could be derived at the same time. For the idea proof, several samples were prepared by stacking, for each sample, two transparent plates with a gap in between. While changing the material of the plate and filling the gap with oil, the RIs of the plate and the oil were measured. For oils of various RIs, from 1.2977 to 1.3857, the measured RIs were well matched with the reported ones within 0.205%. Moreover, even with a stack of various and multiple plates in front of the same oil layer, the oil RI and the physical thickness of the oil layer were extracted with average errors of only 0.065% and 0.990%, respectively.

Single-camera polarization-sensitive full-field optical coherence tomography with polarization switch

We present a single-channel detection-based polarization-sensitive full-field optical coherence tomography (PS-FF-OCT) for simultaneous acquisition of high-resolution OCT and linear retardance images. A linearly polarized sub-10-fs laser was used as a broadband light source for the OCT system. A bi-stable polarization switching device, composed of a ferroelectric liquid crystal cell and an analyzer, was employed to get the horizontal and the vertical polarization components of a full-field interference signal. The time-switched two perpendicular interference signals were sequentially recorded by a single charge-coupled device camera, then processed to extract en-face functional images of a biological sample. The rat tail tendon was imaged ex vivo to confirm the imaging feasibility of the proposed system, which showed axial and transverse resolutions of 2 and 1.3 μm, respectively.

3D static elastography at the micrometer scale using Full Field OCT

Full-Field OCT (FF-OCT) is able to image biological tissues in 3D with micrometer resolution. In this study we add elastographic contrast to the FF-OCT modality. By combining FF-OCT with elastography, we create a virtual palpation map at the micrometer scale. We present here a proof of concept on multi-layer phantoms and preliminary results on ex vivo biological samples such as porcine cornea, human breast tissues and rat heart. The 3D digital volume correlation that is used in connection with the 3D stack of images allows to access to the full 3D strain tensor and to reveal stiffness anisotropy.

Full‐field optical coherence tomography of human donor and diseased corneas

AbstractPurpose To evaluate the performance of a full‐field optical coherence tomography (FF‐OCT) system in the study of human donor and diseased corneas and assess its suitability for use in eye banksMethods Our study was carried out using a full‐field OCT system from LLTech ®, developed for non‐invasive imaging of tissue structures in depth. Images were acquired on human donor corneas (in normal and oedematous conditions) and surgical specimens of diseased corneas (Fuchs dystrophy, keratoconus, stromal scar after keratitis)Results The Full‐field OCT device from LLTech® enabled three dimensional images to be obtained with ultrahigh resolution (1 micron in all directions) comparable to traditional histological sections. This allowed a precise visualisation of the cells and the different structures (epithelium, Bowman’s membrane, stroma, Descemet’s membrane and endothelium) in normal corneas , but also in diseased corneas (even in the presence of an oedema), with specific lesions in each condition.Conclusion Optical and specular microscopy, with a detailed view of the corneal endothelium and a cell density determination, remain the « gold standard » in the study of human cornea grafts. However, full‐field OCT, thanks to a more complete anatomical stydy of the cornea, could be helpful in the evaluation and the selection of human cornea grafts which quality plays a major role in the outlook of the corneal transplant

Full-field OCT: a non-invasive tool for diagnosis and tissue selection

Full-field OCT: a non-invasive tool for diagnosis and tissue selection

Full-field optical coherence tomography using immersion Mirau interference microscope

In this study, an immersion Mirau interference microscope was developed for full-field optical coherence tomography (FFOCT). Both the reference and measuring arms of the Mirau interferometer were filled with water to prevent the problems associated with imaging a sample in air with conventional FFOCT systems. The almost-common path interferometer makes the tomographic system less sensitive to environmental disturbances. En face OCT images at various depths were obtained with phase-shifting interferometry and Hariharan algorithm. This immersion interferometric method improves depth and quality in three-dimensional OCT imaging of scattering tissue.

Tomographie par cohérence optique plein champ des biopsies de la prostate : un pas vers le diagnostic pré-histologique ?

To evaluate the value of full field optical coherence tomography (FFOCT) for cancer detection on prostate biopsies Eight consecutive patients who underwent prostate biopsies for an elevated PSA or suspicious DRE findings were included in the study. For each patient, one to three biopsy cores were imaged with FFOCT immediately after sampling. Images obtained were analyzed by a pathologist blinded to the pathological results, and classified into three categories: non-cancerous tissue, suspicion of malignancy and prostate carcinoma. A pathological correlation analysis was further performed. Sixteen biopsy cores were analyzed. The median FFOCT procedure time was of 4 (3-5) minutes. No artifact was noted in subsequent pathological analysis. Six cores were involved with cancer and eight cores showed no evidence of cancer. On two cores, diagnosis was uncertain, and immuno-histochemical analysis confirmed cancer involvement in one of them. The agreement rate between standard histological analysis and FFOCT evaluation was of 81% (13/16). The three cases of disagreement were due to one false positive and two false negatives of FFOCT analysis. FFOCT of prostate biopsy cores seemed to be feasible and to allow concordant results with those of pathological analysis in the majority of the cases.

Noninvasive three-dimensional live imaging methodology for the spindles at meiosis and mitosis

The spindle plays a crucial role in normal chromosome alignment and segregation during meiosis and mitosis. Studying spindles in living cells noninvasively is of great value in assisted reproduction technology (ART). Here, we present a novel spindle imaging methodology, full-field optical coherence tomography (FF-OCT). Without any dye labeling and fixation, we demonstrate the first successful application of FF-OCT to noninvasive three-dimensional (3-D) live imaging of the meiotic spindles within the mouse living oocytes at metaphase II as well as the mitotic spindles in the living zygotes at metaphase and telophase. By post-processing of the 3-D dataset obtained with FF-OCT, the important morphological and spatial parameters of the spindles, such as short and long axes, spatial localization, and the angle of meiotic spindle deviation from the first polar body in the oocyte were precisely measured with the spatial resolution of 0.7 μm. Our results reveal the potential of FF-OCT as an imaging tool capable of noninvasive 3-D live morphological analysis for spindles, which might be useful to ART related procedures and many other spindle related studies.

Subaperture correlation based digital adaptive optics for full field optical coherence tomography

This paper proposes a sub-aperture correlation based numerical phase correction method for interferometric full field imaging systems provided the complex object field information can be extracted. This method corrects for the wavefront aberration at the pupil/ Fourier transform plane without the need of any adaptive optics, spatial light modulators (SLM) and additional cameras. We show that this method does not require the knowledge of any system parameters. In the simulation study, we consider a full field swept source OCT (FF SSOCT) system to show the working principle of the algorithm. Experimental results are presented for a technical and biological sample to demonstrate the proof of the principle.