A real-time line-field optical coherence tomography (LF-OCT) system is demonstrated with image acquisition rates of up to 5000 B-frames or 2.5 million A-lines per second for 500 A-lines per B-frame. The system uses a high-speed low-cost camera to achieve continuous data transfer rates required for real-time imaging, allowing the evaluation of future applications in clinical or intraoperative environments. The light source is an 840 nm super-luminescent diode. Leveraging parallel computing with GPU and high speed CoaXPress data transfer interface, we were able to acquire, process, and display OCT data with low latency. The studied system uses anamorphic beam shaping in the detector arm, optimizing the field of view and sensitivity for imaging biological tissue at cellular resolution. The lateral and axial resolution measured in air were 1.7 µm and 6.3 µm, respectively. Experimental results demonstrate real-time inspection of the trabecular meshwork and Schlemm’s canal on ex vivo corneoscleral wedges and real-time imaging of endothelial cells of human subjects in vivo .

A line-field optical coherence tomography (LFOCT) application is implemented for real-time in vivo corneal and retinal imaging. In contrast to other described systems of LFOCT that use single-shot high-speed cameras, we describe the first results utilizing a camera with continuous high-speed data transfer and display. The system is based on a previously published design using a center wavelength of 840nm and a bandwidth of 50nm. The system's B-frame and en-face display speed reaches up to 5000 frames per second corresponding to 2,500,000 A-lines. A visible light camera is used to detect the interferometric signal to reduce costs and improve optomechanical integration. Balancing the sensitivity vs. acquisition speed allows continuous high data transfer and processing rates and simplifies the implementation as a bedside system. Higher frame rates are important for scan positioning on non-compliant subjects such as infants and children.

A real-time high-speed line-field optical coherence tomography (LFOCT) configuration at 5,000 B-frames or 2,500,000 A-lines per second for clinical applications is described. The development of the LFOCT technology has experienced increasing interest despite the challenge of achieving sufficient sensitivity and resolution due to crosstalk. Publications of research systems usually apply expensive infrared cameras to improve image quality. The costs, complexity, and lack of real-time data transfer of dedicated highspeed IR cameras make it challenging to employ LFOCT for a more comprehensive application range. We demonstrate using a comparatively low-cost, high-speed camera for real-time data transfer and image display in conjunction with a light source at a center wavelength of 840 nm and a bandwidth of 50 nm. Although the camera and available sample power limits the sensitivity (75 dB), we can demonstrate imaging on a human fingertip (in vivo) and the cornea of a rabbit eye. Further development of the system will focus on compensating for the camera's limited sensitivity and improving resolution to target clinical in vivo imaging such as ophthalmic applications.

Corneal disease is the fifth leading cause of global blindless. Optical coherence tomography (OCT) for anterior imaging is extensively used due to its non-invasive and high-resolution volumetric imaging characteristics. Optical coherence microscopy (OCM) is a technical variation of OCT that can image the cornea with cellular resolution. Here, we demonstrate a visible-light OCM as a low-cost and easily reproducible system to visualize various corneal cellular structures such as epithelial cells, endothelial cells, keratocytes, and collagen bundles within stromal lamellae. The visible-light OCM was also used to study pressure changes in anterior segment human donor eyes. The system achieved an axial resolution of 12 μm in tissue over a 1.2 mm imaging depth, and a lateral resolution of 1.6 µm over a field of view of up to 750 μm × 750 μm.

Mesenchymal stromal cells (MSCs) are adult stem cells that have been widely investigated for their potential to regenerate damaged and diseased tissues. Multiple pre-clinical studies and clinical trials have demonstrated a therapeutic response following treatment with MSCs for various pathologies, including cardiovascular, neurological and orthopaedic diseases. The ability to functionally track cells following administration in vivo is pivotal to further elucidating the mechanism of action and safety profile of these cells. Effective monitoring of MSCs and MSC-derived microvesicles requires an imaging modality capable of providing both quantitative and qualitative readouts. Nanosensitive optical coherence tomography (nsOCT) is a recently developed technique that detects nanoscale structural changes within samples. In this study, we demonstrate for the first time, the capability of nsOCT to image MSC pellets following labelling with different concentrations of dual plasmonic gold nanostars. We show that the mean spatial period of MSC pellets increases following the labelling with increasing concentrations of nanostars. Additionally, with the help of extra time points and a more comprehensive analysis, we further improved the understanding of the MSC pellet chondrogenesis model. Despite the limited penetration depth (similar to conventional OCT), the nsOCT is highly sensitive in detecting structural alterations at the nanoscale, which may provide crucial functional information about cell therapies and their modes of action.

Digitally balanced detection (DBD) has been studied in Fourier domain optical coherence tomography systems to improve sensitivity. We report a technical advancement in a multiple reference optical coherence tomography (MR-OCT) system with the implementation of the DBD technique. We used a free-space, polarization-based balanced detection configuration, which is scalable and suitable for miniaturization. The efficiency of common-mode noise rejection is limited in free-space systems due to the non-uniform illumination of the sensors. We show that recording the signals separately and balancing them in the digital domain improves common mode rejection and signal quality. The application of the DBD scheme for MR-OCT achieves an average sensitivity improvement of 5 ± 0.5 dB over its analogue balanced detection counterpart. We also show that DBD improves the contrast on images of Scotch tapes and mouse eyes.

Optical Coherence Tomography (OCT) is a rapidly growing imaging modality in biomedical optics. OCT can perform high-resolution, cross-sectional imaging of the microstructure of biological tissues by measuring the coherent spectrum from the backscattered light. OCT systems with broad spectral bandwidths are often constructed using free-space optics to avoid dispersion by fibre optic components. This paper presents a fibre-based OCT system at a centre wavelength of 1300 nm with an axial resolution of 3.8 µm in air, surpassing any previously reported values to the best of our knowledge. Despite the challenges in transporting a broadband spectrum using fibre-optics, the system investigation was motivated by the ever-increasing demand for commercialization of high-resolution OCT systems and simplification of construction. We also evaluate and demonstrate the direct measurement method for axial resolution using an air wedge. Imaging of biomedical and other samples is demonstrated using a high numerical aperture sample lens and compared with images from a commercial OCT system. We discuss the effect of the improved structural visibility by achieving image voxels closer to an isometric shape with a high NA sample lens.

We demonstrate the capability of nsOCT technique to discern MSC pellets labelled with different concentrations of nanostars. Useful to track stem cell differentiation and interpret the mechanism by which stem cells deliver their therapeutic effect.

Corneal imaging is important for the diagnostic and therapeutic evaluation of many eye diseases. Optical coherence tomography (OCT) is extensively used in ocular imaging due to its non-invasive and high-resolution volumetric imaging characteristics. Optical coherence microscopy (OCM) is a technical variation of OCT that can image the cornea with cellular resolution. Here, we demonstrate a blue-light OCM as a low-cost and easily reproducible system to visualize corneal cellular structures such as epithelial cells, endothelial cells, keratocytes, and collagen bundles within stromal lamellae. Our blue-light OCM system achieved an axial resolution of 12 µm in tissue over a 1.2 mm imaging depth, and a lateral resolution of 1.6 µm over a field of view of 750 µm × 750 µm.

Although time-domain optical coherence tomography (TD-OCT) systems are straightforward to realize, the imaging speed, sensitivity, and imaging depth limit their range of applications. Multiple reference optical coherence tomography (MR-OCT) based on TD-OCT increases imaging range by about tenfold while providing sensitivity to image highly scattering biological samples. The multiple path-delays and free-space construction make MR-OCT also interesting for hybrid and compact systems, filling the gap between fibre-based and wafer-level integrated optical systems. We describe an optical configuration using a balanced detection scheme and the resulting signal properties due to the required use of polarizing optical components. We numerically simulate the signal properties using Jones calculus and compare the results with measurements. We discuss the origin of signal degradation due to birefringence of the sample in OCT and show that the quarter-wave plate in the sample arm of the Michelson interferometer can be adjusted to optimize the signal returning from a birefringent sample thereby improving the visibility of structures of interest. The theory discussed will be useful to understand and minimize signal degradation due to birefringence in Time-Domain and Fourier-Domain OCT systems.

With the advent of stem cell therapy for spinal cord injuries, stroke, burns, macular degeneration, heart diseases, diabetes, rheumatoid arthritis and osteoarthritis; the need to track the survival, migration pathways, spatial destination and differentiation of transplanted stem cells in a clinical setting has gained increased relevance. Indeed, getting regulatory approval to use these therapies in the clinic depends on biodistribution studies. Although optoacoustic imaging (OAI) or photoacoustic imaging can detect functional information of cell activities in real-time, the selection and application of suitable contrast agents is essential to achieve optimal sensitivity and contrast for sensing at clinically relevant depths and can even provide information about molecular activity. This review explores OAI methodologies in conjunction with the specific application of exogenous contrast agents in comparison to other imaging modalities and describes the properties of exogenous contrast agents for quantitative and qualitative monitoring of stem cells. Specific characteristics such as biocompatibility, the absorption coefficient, and surface functionalization are compared and how the labelling efficiency translates to both short and long-term visualization of mesenchymal stem cells is explored. An overview of novel properties of recently developed optoacoustic contrast agents and their capability to detect disease and recovery progression in clinical settings is provided which includes newly developed exogenous contrast agents to monitor stem cells in real-time for multimodal sensing.

Optical coherence tomography (OCT) is a rapidly evolving technology with a broad range of applications, including biomedical imaging and diagnosis. Conventional intensity-based OCT provides depth-resolved imaging with a typical resolution and sensitivity to structural alterations of about 5–10 microns. It would be desirable for functional biological imaging to detect smaller features in tissues due to the nature of pathological processes. In this article, we perform the analysis of the spatial frequency content of the OCT signal based on scattering theory. We demonstrate that the OCT signal, even at limited spectral bandwidth, contains information about high spatial frequencies present in the object which relates to the small, sub-wavelength size structures. Experimental single frame imaging of phantoms with well-known sub-micron internal structures confirms the theory. Examples of visualization of the nanoscale structural changes within mesenchymal stem cells (MSC), which are invisible using conventional OCT, are also shown. Presented results provide a theoretical and experimental basis for the extraction of high spatial frequency information to substantially improve the sensitivity of OCT to structural alterations at clinically relevant depths.

Corneal cross-linking (CXL) has grown from an interesting concept to a practical clinical treatment for corneal ectatic disease globally in the past three decades. In both understanding the principle of how CXL proceeds and monitoring the clinical procedure, detection of structural changes during cornea CXL plays a significant role. This paper demonstrates a novel over-sampling nano-sensitive optical coherence tomography (osnsOCT) method, which is potential to detect nanoscale structural changes in various tissues, to simultaneously measure the structural variations during the corneal CXL treatment.

In biomedical optics, Optical Coherence Tomography (OCT) is an emerging optical imaging modality during the last three decades. OCT can perform high resolution, cross-section imaging of the internal microstructure in biological tissues by measuring echoes of backscattered light. We have developed a broadband, high-resolution spectral domain OCT system whose central wavelength is 1300 nm with bandwidth ~400 nm. Theoretical axial resolution of the system is ~3.71 μm and experimentally we get ~5 μm in air. Furthermore, we will apply this system for nano-sensitive detection and visualization in varieties of biological tissues.

Multiple reference optical coherence tomography (MR-OCT) is a time-domain interferometric imaging platform which promises to be realized as a low cost, compact imaging technology. The optical configuration of MR-OCT makes use of multiple reflections between a partial mirror and the axially scanning reference mirror to enhance the axial imaging depth compared to the otherwise shallow scanning range of the voice coil or piezo actuator. Since each reflection on the partial mirror causes an optical path delay, the focusing of each higher order of reflection is changing. That means the beam diameter, beam collimation and therefore the interference visibility are changing as well. This investigation focuses on how the spacing between the partial mirror and the scanning mirror affects the system’s sensitivity and SNR values. The potential to improve the sensitivity of higher orders of reflections related to deeper regions in a sample will be studied.

The characterization of an amplified piezoelectric actuator (APA) as a new axial scanning method for multiple-reference optical coherence tomography (MR-OCT) is described. MR-OCT is a compact optical imaging device based on a recirculating reference-arm-scanning optical delay using a partial mirror that can enhance the imaging depth range by more than 10 times the reference mirror's scanning amplitude. The scanning amplitude of the used APA was varied between 30 μm and 250 μm, depending on the scanning frequency of between 0.8 kHz and 1.2 kHz. A silver-coated miniature mirror was attached to the APA via ultraviolet-cured optical adhesive, and the light source was a super-luminescent diode with 1310 nm center wavelength and 56 nm bandwidth. The sensitivity was measured with and without the partial mirror in the reference delay line as a function of scan speed, frequency, and range, therefore providing results for MR-OCT and TD-OCT modes. It was found that the APA provides more than twice the mechanical scanning range compared to other opto-mechanic actuators, but results indicate degradation of signal-to-noise ratio and sensitivity at larger imaging depths. In conjunction with MR-OCT, the scan range of maximum 200 μm can be enhanced up to 1-1.5 mm by using a reduced amount of orders of reflections, which could be of interest to increase sensitivity in the future.

We present a detailed characterization of noise sources in multiple reference optical coherence tomography (MR-OCT) compared to time-domain OCT (TD-OCT). The noise characteristics were modeled based on the TD-OCT noise model and modified for MR-OCT and confirmed with measurements. The MR-OCT sensitivity characteristics are significantly affected by the reflection from the partial mirror, which also introduces a natural attenuation in the reference arm, partially matching the reflectivity intensity profile of human tissue. At optimal balance between sample and reference armand using balanced detection, the peak sensitivity was measured to be 95 dB, which is close to simple Fourier-domain systems. The results provide a better understanding of the application range for MR-OCT and higher order effects observed, suggesting a nontrivial noise model for MR-OCT.

Multiple reference optical coherence tomography (MR-OCT) is a recently developed, low-cost and compact time-domain OCT solution for primary care and consumer level applications. A combination of a voice coil actuator and a partial mirror (PM) extends the scan range for imaging depths of approximately 1 mm in biological samples. Our previous research on MR-OCT is based only on intensity information obtained from the depth-resolved interference signal. In this Letter, we extract the phase information from the MR-OCT signal and, hence, provide an additional contrast modality. The phase sensitivity of the system is measured to be approximately 0.2 and 1.5 rad for the first and twelfth orders of reflection when using a mirror as the sample. This Letter describes first results of phase-sensitive data measured on a phantom obtained with MR-OCT. Data from a chick embryo chorioallantoic membrane (CAM) is used to demonstrate the feasibility of MR-OCT for in vivo phase-sensitive imaging.

A technique based on multiple reference optical coherence tomography (MR-OCT) is proposed for simultaneous imaging at multiple depths. The technique has been validated by imaging a reference sample and a fingerprint in-vivo. The principle of scanning multiple selected layers is shown by imaging a partial fingerprint with 200×200×200 voxels of 3×3×0.5  mm size and obtaining an arbitrary amount of layers merely by digital processing. The spacing among the layers can be adjusted arbitrarily, and the SNR roll-off is shown for three different spacings. At a mirror scan frequency of 1 kHz and an A-line rate of 2 kHz, the acquisition time was 20 s for one volume. The results show the feasibility of the application of layer scanning MR-OCT that uses a partial mirror in the reference arm of the Michelson interferometer. The reduced scan range required for layer scanning allows even higher scan rates that are limited only by the voice coil design and the mass-spring system, e.g., mirror mass, spring constant, and damping.