Full range complex spectral domain optical coherence tomography without additional phase shifters.

To report the utility of multimodal imaging including color photography, fundus autofluorescence (FAF), and spectral domain optical coherence tomography in a case of primary vitreoretinal lymphoma. Color photographs, FAF, and the spectral domain optical coherence tomography images were performed at baseline and through 12 months of follow-up. At baseline and follow-up visits, spectral domain optical coherence tomography and FAF were more sensitive than color photography in showing the extent of disease. With treatment, spectral domain optical coherence tomography showed resolution of subretinal hyperreflective material while FAF imaging showed a reduction in hyperreflective dots, which were present at baseline. Spectral domain optical coherence tomography and FAF were more sensitive than color photographs in showing the disease extent and response to treatment. These imaging techniques may supplement other metrics used to monitor the patients with primary vitreoretinal lymphoma.

Improved extended depth of focus full field spectral domain Optical Coherence Tomography

To highlight the use of high-density spectral domain optical coherence tomography (SD-OCT) in the detection of tamoxifen retinopathy. An 82-year-old asymptomatic woman with a history of tamoxifen therapy for breast cancer was found to have bilateral refractile retinal deposits on fundus examination. Detection on SD-OCT was compared across imaging techniques. High-density SD-OCT demonstrated hyperreflective deposits in the inner retinal layers of each eye consistent with the diagnosis of tamoxifen retinopathy. The optimal SD-OCT scan technique depends on the ocular condition being imaged. High-density scan techniques require longer acquisition time but may enhance the detection of focal retinal pathology.

Purpose:To report the use of intraoperative spectral domain optical coherence tomography (SD-OCT) for detecting anatomical changes during macular surgery.Methods:In a consecutive case series, 32 eyes of 32 patients undergoing concurrent pars plana vitrectomy and intraoperative SD-OCT for macular hole (MH), epiretinal membrane (ERM) and vitreomacular traction (VMT) were enrolled. Intraoperative changes in retinal thickness and dimensions of the macular hole were measured in patients with ERM and VMT following surgical manipulation using a hand-held SD-OCT device (iVue, Optovue Inc., Fremont, CA, USA).Results:SD-OCT images of sixteen eyes with macular hole were subjected to quantitative and qualitative analysis. All MH dimensions remained stable during consecutive stages of surgery except for MH apex diameter, which showed a significant decrease after internal limiting membrane (ILM) peeling (P=0.025). Quantitative analysis of ten patients with ERM showed a significant decrease in retinal thickness after membrane removal (P=0.018) which did not remain significant until the end of the procedure (P=0.8). In three cases, subretinal fluid was formed after ILM peeling. Quantitative analysis of five patients with VMT showed a decrease in retinal thickness during consecutive steps of the surgery, although these changes were not significant. In two cases, subretinal fluid was formed after ILM peeling.Conclusion:Intraoperative SD-OCT is a useful imaging technique which provides vitreoretinal surgeons with rapid awareness of changes in macular anatomy during surgery and may therefore result in better anatomical and visual outcomes.

Detection of residual tumor during resection of glial brain tumors remains a challenge because of a low inherent contrast of adjacent edematous brain, the surrounding infiltration zone, and the solid tumor. Therefore, new technologies that may facilitate an intraoperative analysis of the tissue at the resection edge are of great interest to neurosurgeons. For ex vivo imaging of gliomas in a mouse model and human biopsy specimens of brain tumors and nervous system tissue we have used a time-domain Sirius 713 Tomograph with a central wavelength of 1,310 nm and a coherence length of 15 microm equipped with a mono mode fiber and a modified optical coherence tomography (OCT) adapter containing a lens system for imaging at a working distance of 2.5 cm. A spectral-domain tomograph using 840 nm and 930 nm superluminescence diodes (SLD) with a central wavelength of 900 nm was used as a second imaging modelity. Both time-domain and spectral-domain coherence tomography delineated normal brain, the infiltration zone and solid tumor in murine intracerebral gliomas. Histological evaluation of H&E sections parallel to the optical plain demonstrated that tumor areas of less than a millimeter could be detected and that not only solid tumor, but also brain invaded by a low-density single tumor cells produced an OCT signal different from normal brain. Spectral-domain OCT (SD-OCT) demonstrated a significantly more detailed microstructure of tumor and normal brain up to a tissue depth of 1.5-2.0 mm, whereas the interpretation of time-domain OCT (TD-OCT) was difficult at a tissue depth >1.0 mm. Because of rapid scanning times SD-OCT data could be acquired as 3D data maps, which allowed a multi-planar analysis of the tumor to brain interface. Similar to our findings in experimental gliomas, images of human nervous system tissue acquired using SD-OCT showed a characteristic signal of normal brain tissue and a detailed microstructure of tumor parenchyma. Spectral-domain OCT of experimental gliomas and human brain tumor specimens differentiates solid tumor, diffusely invaded brain tissue, and adjacent normal brain based on microstructure and B-scan signal characteristics. In conjunction with the rapid image acquisition rates of SD-OCT, this technology carries the potential of a novel intraoperative imaging tool for the detection of residual tumor and guidance of neurosurgical tumor resections.

Aim: To evaluate the choroidal thickness in patients with different refractive status measured by spectral-domain optical coherence tomography. Material and methods: This cross-sectional observational study consisted of 60 subjects, who visited the out-patient department of Ophthalmology, Chattrapati Shivaji Subharti Hospital, Meerut, India and were randomly selected over a period of 1 year. Subjects were classified into three groups based on refractive error: those with a +1 diopter or greater refractive power were assigned to the hyperopia group; those with a diopter lower than +1 and greater than –1 were assigned to the emmetropia group; and those with a –1 diopter or lower diopter were assigned to the myopia group. All patients underwent a clinical history taking and a complete ophthalmic examination. OCT scanning was performed using Optovue RTvue 100 which utilises spectral domain (SD)-OCT. The choroid was visualized by enhanced depth imaging (EDI) technique. Choroidal scans were obtained for all the eyes using enhanced depth imaging (EDI) using spectral-domain optical coherence tomography (SD-OCT). Data was recorded in excel sheet and subjected to statistical analysis. Results: Compared to emmetropic participants, myopic subjects had significantly thinner choroid in all the regions. Choroid of hyperopic subjects was significantly thicker than that of emmetropic subjects in most regions. Linear correlation testing revealed a close correlation between refractive error and choroidal thickness in all of the regions. Conclusion: High myopes have significantly thinner choroids than the emmetropic controls at all the retinal points studied, with the thinnest choroid at 1.5 mm nasal to the fovea.

PurposeMacular telangiectasia (MacTel) type 2 is observed in patients in their 5th–8th decades of life. The clinical and imaging findings in younger patients is unknown in larger cohorts. The study purpose is to report prevalence, baseline clinical and spectral domain optical coherence tomography (SDOCT) findings in young MacTel patients below 40 years.MethodsThis hospital-based, multicentre, retrospective, cross-sectional study included patients between 2011 and 2023. Retinal photographs from multiple imaging techniques were evaluated to diagnose and stage type 2 MacTel and describe their SDOCT findings. Imaging characteristics were correlated with clinical stages and visual acuity.ResultsAmong all MacTel patients seen in hospital, prevalence of young MacTel cases less than age 40 was 1.77% (32/1806; 62 eyes). Youngest participant was 34 years, while mean age was 38.44 ± 1.795 years. Sixteen patients (50%) were diabetics. Perifoveal greying (n = 56, 90%) and perifoveal hyperreflective middle retinal layers (n = 47, 76%) were the most prevalent clinical and SDOCT imaging finding respectively. Less than 10% (n = 6) eyes had proliferative disease. Presence of retinal pigment clumps (RPC) (7% vs. 67%; p = 0.002) coincided with proliferative MacTel. Poor vision was associated with presence of outer retinal layer SDOCT findings like outward bending of inner retinal layers (p = 0.047), RPC (p = 0.007), subfoveal neurosensory detachment (p = 0.048) and subretinal neovascular membrane (p = 0.001).ConclusionType 2 MacTel before age 40 is rare, common in women and diabetics, and affects vision in advanced stage. Disease symmetry, comparison with older cases, and longitudinal SDOCT changes in such patients require further study.

The increased usage of the phase shifting transformers in various fields within power systems has introduced new challenges in performing on-site maintenance testing. These special transformers were used as converter transformers, rectifier transformers, harmonic mitigating transformers, zigzag transformers and quadrature boosters with unconventional vector groups, having an additional phase shift such as +/-7.50, +/-150 combined with normal `Delta and Star' configurations. The challenges now faced by the increased use of these transformers are testing them for accuracy on the voltage ratio and phase shift at site during commissioning and maintenance. Different test methods were performed / studied and were compared. A prototype of a three-phase converter transformer with variable ratio taps and vector groups was constructed and tested. The prototype transformer is constructed to have variable parameters for test trials on different vector groups and ratios. The three phase converter transformer prototype will have options to regulate the output voltage on varying input voltage using the tap changer and also can vary the phase shift by varying the vector group combinations. On-site testing of ratio and phase shift will be done on different types of traction rectifier transformers. The approach for factory testing and onsite testing of the special transformers will be different. The effect on the phase shift values when the ratio taps are changed will be the focus and the results compared. The study on the importance of phase shift on these special transformers is presented. The test results of different test methods using modern portable test equipment and conventional classical methods were compared and presented. The results of the ratio testing and the phase shift measurement variation during vector group variation and tap change were presented. (6 pages)

Transmission optical coherence tomography (tOCT) is gaining interest for imaging biological samples; however, so far, quantitative phase information has not been directly obtained. This study introduces SOPHAST-OCT, an approach for integrated 2D phase recovery in Off-Axis Full-Field Swept-Source tOCT. It uses phase-shifting to leverage OCT’s inherent phase changes between recorded interferograms. SOPHAST-OCT demonstrates promising phase agreement with the simulated ground truth phase. This approach represents a first step toward quantitative imaging in tOCT. Full Text: PDF References Y. Park, C. Depeursinge, G. Popescu, "Quantitative phase imaging in biomedicine", Nature Photon 12, 578 (2018). CrossRef K. Alm, H. Cirenajwis, L. Gisselsson, A.G. Wingren, B. Janicke, A. Mölder, et al., in Holography, Research and Technologies (IntechOpen, 2011). CrossRef W. Drexler, J. Fujimoto, editors , Optical Coherence Tomography: Technology and Applications, 2nd ed. (Springer Cham, 2015). CrossRef W. Krauze, P. Ossowski, M. Nowakowski, M. Szkulmowski, M. Kujawińska, "Enhanced QPI functionality by combining OCT and ODT methods", Quantitative Phase Imaging VII, 11653, 19 (2021). CrossRef B.C. Wilson, S.L. Jacques, "Optical reflectance and transmittance of tissues: principles and applications", IEEE J. Quantum Electron. 26, 2186 (1990). CrossRef J. van der Horst, A.K. Trull, J. Kalkman, "Deep-tissue label-free quantitative optical tomography", Optica 7, 1682 (2020). CrossRef P. Hosseini, Y. Sung, Y. Choi, N. Lue, Z. Yaqoob, P. So, "Scanning color optical tomography (SCOT)", Opt. Expr. 23, 19752 (2015). CrossRef P. de Groot, "Phase Shifting Interferometry" in Optical Measurement of Surface Topography, edited by R. Leach (Springer, Berlin, Heidelberg, 2011). CrossRef M. Wojtkowski, A. Kowalczyk, R. Leitgeb, A.F. Fercher, "Full range complex spectral optical coherence tomography technique in eye imaging", Opt. Lett. 27, 1415 (2002). CrossRef Q. Zhang, S. Zhong, J. Lin, W. Chen, M. Luo, J. Zhong, Y. Yu, Z. Peng, S. Cheng, "Full-range Fourier-domain optical coherence tomography based on Mach–Zehnder interferometer", Opt. Lasers Engin. 124, 105794 (2020). CrossRef R. Juarez-Salazar, C. Robledo-Sanchez, F. Guerrero-Sanchez, A. Rangel-Huerta, "Generalized phase-shifting algorithm for inhomogeneous phase shift and spatio-temporal fringe visibility variation", Opt. Express 22, 4738 (2014). CrossRef R. Juarez-Salazar, C. Robledo-Sánchez, C. Meneses-Fabian, F. Guerrero-Sánchez, L. M. Arévalo Aguilar, "Generalized phase-shifting interferometry by parameter estimation with the least squares method", Opt. Lasers Engin. 51, 626 (2013). CrossRef M.A. Herráez, D.R. Burton, M.J. Lalor, M.A. Gdeisat, "Fast two-dimensional phase-unwrapping algorithm based on sorting by reliability following a noncontinuous path", Appl. Opt. 41, 7437 (2002). CrossRef Z. Wang, A.C. Bovik, "A universal image quality index", IEEE Signal Proc. Lett. 9, 81 (2002). CrossRef

Phase shifts from scattering are used to analyze and engineer acoustic radiation forces. With the aid of phase shifts, analytical results for acoustic radiation forces can be simplified into compact and physically meaningful expressions, which can be used to develop a simplified procedure for the engineering of the radiation force. The desired radiation force can be fulfilled by a specific set of phase shifts up to a certain order, and then the required phase shifts can be fulfilled by engineering object and beam parameters. As an example, the phase shift approach is used to engineer the inner-to-outer radius ratio and the outer radius of a spherical shell to show how to use the phase shift method for the design of acoustic radiation forces. The example here is a force that is desired to pull particles against the propagation of a Bessel beam. A small paraxial parameter to pull a spherical shell is satisfied by in-phase scattering of monopole, dipole, quadrupole, octupole, and beyond. The example presented here is relatively simple yet reveals the advantages of the phase shift approach. The phase shift method can provide a simplified route for the design of acoustic tweezers using either traveling beams or standing waves.

Hyporeflective Wedge-Shaped Band in Geographic Atrophy Secondary to Age-related Macular Degeneration: An Underreported Finding

Retinal imaging devices made dramatic progress in these several years. These new devices reveal various anatomical and functional changes in the fundus by high resolution images, which may develop and improve diagnosis, treatment, and surgical maneuver. The special issue on multimodal imaging of the fundus published one review article and five clinical research articles. The review article of Y. Mitamura et al. showed that the three lines in the outer retina detected by spectral-domain optical coherence tomography (SD-OCT) could serve as hallmarks for evaluation of photoreceptor condition in retinitis pigmentosa and recovery process after macular hole surgery. Of the five clinical research articles, N. F. Mokwa et al. compared sensitivity and specificity of imaging techniques of color fundus photography, fluorescein angiography, and SD-OCT for detecting age-related macular degeneration (AMD) and activity of choroidal neovascularization (CNV). F. Pichi et al. evaluated multimodal visualization of retinal genetic diseases by fundus autofluorescence, FA, indocyanine green (ICG) angiography, and SD-OCT to monitor progression of the diseases. O. A. Osmanbasoglu et al. analyzed diurnal variation of central choroidal thickness by enhanced depth imaging technique of SD-OCT in healthy emmetropic subjects. M. Sahin et al. reported hyperautofluorescence after cataract surgery, and J. M. Munoz et al. compared ranges of contrast values in autofluorescence imaging between 2 fundus cameras. All the six articles in this special issue underwent a rigorous peer-review process.

Under the “weak phase object” approximation, the component of the electron wave scattered by an object is phase shifted by π/2 with respect to the unscattered component. This phase shift has been confirmed for thin carbon films by many experiments dealing with image contrast and the contrast transfer theory. There is also an additional phase shift which is a function of the atomic number of the scattering atom. This shift is negligible for light atoms such as carbon, but becomes significant for heavy atoms as used for stains for biological specimens. The light elements are imaged as phase objects, while those atoms scattering with a larger phase shift may be imaged as amplitude objects. There is a great deal of interest in determining the complete object wave, i.e., both the phase and amplitude components of the electron wave leaving the object.

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.

A line-field, spectral domain optical coherence tomography (LF-SD-OCT) system was developed for in-vivo, noncontact, cellular resolution imaging of biological tissue. The LF-SD-OCT system utilizes a broadband laser with a spectrum centered at ~790 nm and spectral bandwidth of ~140 nm to achieve 1.8 μm axial and ~5 μm isotropic lateral resolution in biological tissue. A high speed 2D camera was used to achieve frame rate of 2.5k B-scans/s. The system's SNR was measured to be 92 dB at 100 μm away from the zero-delay line for 2.8 mW optical power incident on the imaged object, with 18 dB roll-off over a scanning range of 1 mm. The LF-SD-OCT system was used to image the cellular structure of cucumber and the cucumber seed where the high spatial resolution was sufficient to resolve cellular nuclei. Then the system was used to image in-vivo human skin (fingertip), where the spiral structures of the sweat glands, as well as a large number of capillaries were observed in the epidermal layer. Images of the healthy human cornea were also acquired from locations near the corneal apex and the periphery and showed the tissue cellular structure and vasculature. Currently, the corneal images were acquired ex-vivo, as we are waiting for ethics clearance to conduct in-vivo corneal imaging studies with the novel LF-SD-OCT system.