Two decades ago, in the beginning of 2002, we decided to organize a graduate school in the field of biophotonics and biomedical optics. The purpose of the International Graduate Summer School Biophotonics is to provide education at the highest international level for postgraduate students and early career stage researchers. The school always experienced higher interest than the number of students we can accommodate, illustrating the needs it continues to fill in the field. Apart from learning from renowned lecturers and scientists, the international atmosphere in having about 80 biophotonics scientists from across the world for a week in a confined space, on the beautiful Island of Ven, makes networking opportunities phenomenally good. The school certainly has the potential to create lifelong friendships, and to help advance the field by exchange of ideas. We collaborate with the Journal of Biomedical Optics on publishing a special section (Selected Topics in Biophotonics) containing invited review papers from lecturers at the school and contributed papers from students at the school, respectively. They have been compiled into open access online teaching material.
Sample handling is an important consideration when aiming for replicating in vivo conditions ex vivo for the sake of validating imaging protocols and identifying biomarkers of disease. We tested five different handling methods: snap frozen in isopentane, directly frozen at -80°C, slowly frozen in a cryobox with and without cryopreservation media, and formalin fixed. The samples were imaged using optical coherence tomography (OCT) for qualitative and quantitative validation based on morphological features and optical properties. All handling methods were compared to fresh tissue samples using OCT-derived optical properties and morphological features. The results indicate a significant difference in the optical attenuation coefficient as well as morphological differences between the five different methods and support the hypothesis that proper sample handling is crucial for obtaining translatable results.
Optical coherence tomography (OCT) is a powerful label-free approach for volumetric morphological imaging, especially within biomedicine. However, the penetration depth of OCT is limited. We postulate that in OCT, multiple scattering can enhance image contrast at depth. We demonstrate this using spatially offset OCT (SO-OCT), an original collection geometry that leads to a preferential collection of multiply scattered light. SO-OCT images have improved contrast at depth, especially in highly scattering tissues. We show that by merging images from several offsets, we can generate a composite image with reduced speckle and improved contrast over a large depth range. Finally, we investigate opportunities for using SO-OCT to improve segmentation of tissues, an important step in image interpretation. Our results show the high potential of SO-OCT as a new tool in biomedical imaging and diagnosis.
Parametric imaging of attenuation using optical coherence tomography (OCT) is a powerful tool for assessing changes in tissue morphology associated with disease. Several models are available for extracting the optical properties of tissue from OCT images. However, the accuracy of these models and their dependence on the tissue optical properties has yet to be established. Here, we investigate the accuracy of several OCT models and assess their suitability for extracting optical properties. We establish that the single scattering models produce more precise results (lower variance), but the EHF model is more accurate. Furthermore, the accuracy of the single scattering model degrades as the scattering coefficient and thickness of the tissue increase. We intend that the results of this study will aid in the development of standardized protocols for extracting optical properties from OCT images.
Quantitative assessment of retinal microvasculature in optical coherence tomography angiography (OCTA) images is important for studying, diagnosing, monitoring, and guiding the treatment of ocular and systemic diseases. However, the OCTA user community lacks harmonized image analysis tools that provide reliable and consistent microvascular metrics from diverse datasets. We present a retinal version of the OCTA vascular analyzer (OCTAVA) that addresses the challenges of robust and reproducible analysis of retinal OCTA images. We validate OCTAVA using images collected by four commercial OCTA instruments demonstrating robust performance across datasets from different instruments acquired at different sites. We show that OCTAVA characterizes retinal microvascular metrics accurately and reduces their variation between studies. By making OCTAVA publicly available, we aim to expand standardized research and improve the reproducibility of quantitative analysis of retinal microvascular imaging.
Optical coherence tomography angiography (OCTA) has growing application for microvascular assessment in dermatology. Various instruments, imaging protocols, processing methods, and metrics have been used to describe the microvasculature, so comparing different study outcomes is currently not generally feasible. We present a user-friendly, open-source toolbox, OCTAVA, to help remedy this shortcoming. We present three use cases for assessing software accuracy and repeatability, and we investigate how OCTAVA can support wider adoption of OCTA as a clinical tool. Wide adoption of this software will help drive the development of reliable microvascular biomarkers for early detection and treatment guidance of diseases.
Light is everywhere. Light, optics, and photonics impact almost every aspect of our lives, from seeing, and entertainment to medicine, communications, energy, agriculture, art, and culture. Light: A Spectrum of Opportunity offers a fascinating introduction to this important part of STEM. The book starts with short sentences and beautiful pictures, demonstrating the presence of light in our lives. It then moves to more complex descriptions, which make it valuable as a longstanding companion for everyone.
A free card game is included with the book and can be downloaded from this link: https://spie.org/samples/Pressbook_Supplemental/CB03_sup.zip
Jesse Explores Vision and Vision Impairment is an exciting picture book introducing the fascinating topic of vision and why some people cannot see well. The book offers a narrative introduction to the topic by a little boy called Jesse, is full of beautiful pictures, and includes fun, hands-on activities. Thus, it is a perfect read for a young reader to learn about the beauty of vision and raise awareness about vision impairment and its challenges.
Type 2 Diabetes Mellitus (T2DM) is increasing in prevalence and its complications are potentially fatal. Recent studies suggest that long-term complications of T2DM include alterations of the bone, evident by a high coexistence rate of diabetes mellitus with both osteoporosis and different fracture types. Current measurements of fracture risk are based on Bone Mineral Density (BMD) measured via Dual-energy X-ray Absorptiometry (DXA); however, this method does not measure bone quality and often underestimates fracture risk in T2DM. Optical Coherence Tomography (OCT) holds the promise of early detection of diabetic bone microarchitectural alteration and serves as a possible non-ionizing alternative to DXA. The aim of this study is to evaluate the viability of using OCT-derived attenuation coefficients as a method for differentiating between healthy and diabetic bones in a diagnostic process. A TALLYHO/JngJ mouse model of diabetes was used and compared to a healthy control SWR/J; the differences in bone structure and quality of the TALLYHO/JngJ model compared with SWR/J is well documented in the literature. OCT cross-sectional images of four ex-vivo mouse femurs, two healthy and two T2DM, were used to calculate attenuation coefficients. Coefficients were calculated for the anterior side and the posterior side of the femurs. The posterior side was used as a control for the anterior side of the same femur sample. The attenuation-based comparison between healthy and diabetic bones shows that it is possible to differentiate between healthy and diabetic bones (p = 0.002). No significant difference in attenuation between the anterior and posterior side (p = 0.543, T2DM and p =0.055, healthy) was found. These preliminary results indicate that OCT-derived attenuation coefficients have the potential to differentiate between healthy and diabetic bones in a mouse model of T2DM.
Optical Coherence Tomography (OCT) is a powerful label-free approach for volumetric morphological imaging with numerous applications, especially within biomedicine. The penetration depth of OCT reaches well beyond conventional microscopy; however, signal reduction with depth leads to a rapid degradation of the signal below the noise level. The important pursuit of imaging at depth has been largely approached by extinguishing multiple scattering. This has been valid for many microscopies; however, here, we postulate that in OCT, multiple scattering can enhance image contrast at depth. We demonstrate this using an original geometry that completely decouples the incident and collection light fields by introducing a spatial offset between them. This approach leads to a preferential collection of multiply scattered light with depth, compensating for signal attenuation and enhancing the image contrast at depth. A wave optics model and unified theoretical framework supports our experimentally demonstrated improvement in contrast. The effective signal attenuation can be reduced by over 24 dB. Our approach reveals mesoscale features in images of ex vivo mouse bone. Considering most approaches to date have aimed to minimize multiple scattering, our results suggest that the problem of OCT imaging at depth should be distinguished from optical microscopy at depth. This facile and widely applicable geometry enables a power capacity to dynamically tune for contrast at depth.
Non-Gaussian beams can provide extended depth of focus (DOF) at constant and potentially uncompromised transverse resolution, as well as a degree of self-reconstruction after beam shadowing, which may be present in tissue imaging. Hence such beams are being developed for imaging systems throughout many disciplines, including endoscopic imaging, where they hold great potential. General possibilities include up to more than 20-fold extension of DOF, tunable working distance, imaging around obstacles and integrated all-fiber designs.
In all-fiber based optical imaging systems; however, these advantages are limited by system design considerations. Trade-offs between miniaturization, extended DOF, SNR, and fiber availability arise, and estimating the effects of design modifications can be difficult and time consuming.
We model zero-order quasi-Bessel illumination and detection for a range of common probe and sample materials based on an analytic solution of the Fresnel diffraction integral and compare the results to Gaussian beams. We show that these beams, on scales that match optical fiber dimensions, generally have an upper limit for the spot size above which their distinct advantages over Gaussian beams fade. Similarly, we show the existence of a lower limit of practical performance of quasi-Bessel beams, where the imaging SNR penalty compared to a Gaussian beam becomes significant. Additionally to general theoretic considerations we discuss designs, modeling and characterization of all-fiber imaging probes.
This work provides an accessible overview for researchers to estimate what potential benefit non-Gaussian beams can introduce into their optical imaging system.
Optical coherence tomography (OCT) is a non-invasive imaging technique that measures reflectance from within biological tissues. Current higher-NA optical coherence microscopy (OCM) technologies with near cellular resolution have limitations on volumetric imaging capabilities due to the trade-offs between resolution vs. depth-of-field and sensitivity to aberrations. Such trade-offs can be addressed using computational adaptive optics (CAO), which corrects aberration computationally for all depths based on the complex optical field measured by OCT. However, due to the large size of datasets plus the computational complexity of CAO and OCT algorithms, it is a challenge to achieve high-resolution 3D-OCM reconstructions at speeds suitable for clinical and research OCM imaging. In recent years, real-time OCT reconstruction incorporating both dispersion and defocus correction has been achieved through parallel computing on graphics processing units (GPUs). We add to these methods by implementing depth-dependent aberration correction for volumetric OCM using plane-by-plane phase deconvolution. Following both defocus and aberration correction, our reconstruction algorithm achieved depth-independent transverse resolution of 2.8 um, equal to the diffraction-limited focal plane resolution. We have translated the CAO algorithm to a CUDA code implementation and tested the speed of the software in real-time using two GPUs - NVIDIA Quadro K600 and Geforce TITAN Z. For a data volume containing 4096×256×256 voxels, our system’s processing speed can keep up with the 60 kHz acquisition rate of the line-scan camera, and takes 1.09 seconds to simultaneously update the CAO correction for 3 en face planes at user-selectable depths.
We report the fabrication and characterization of lithographically-fabricated arrays of micron-scale collimating channels, arranged like spokes around a single source position, for use in 3D, or confocal x-ray uorescence microscopy. A nearly energy-independent depth resolution of 1.7±0.1μm has been achieved from 4.5-10 keV, degrading to 3⊥0.5μm at 1.7 keV. This represents an order-of-magnitude improvement over prior results obtained using state-of-the-art, commercial polycapillaries as the collection optic. Due to their limited solid angle, the total collection efficiency of these optics is approximately 10× less than that obtained with polycapillaries. Three designs have been tested, with 1, 2, and 5-μm-wide channels ranging from 30-50 μm in depth and 2 mm in length. In addition to characterizing the devices in confocal geometry, the transmission behavior of individual channels was characterized using a small, highly collimated incident beam. These measurements reveal that, despite taking no particular steps to create smooth channel walls, they exhibit close to 100% reectivity up to the critical angle for total external reflection. Most of this reflected power is spread into a diffuse angular region around the specular reflection condition. These results significantly impact future designs of such collimating channels, since transmission through the channels via side-wall reflection limits their collimating power, and hence device resolution. Ray-tracing simulations, designed specifically for modeling the behavior of channel arrays, successfully account for the transmission behavior of the optics, and provide a useful tool for future optic design.
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