Functional Optical Coherence Tomography Research Articles

Functional Optical Coherence Tomography of Rat Cortical Neurovascular Activation during Monopulse Electrical Stimulation with the Microelectrode Array

This paper presents a study to evoke rat cortical functional activities, including hemodynamic and neural tissue signal changes, by monopulse electrical stimulation with a microelectrode array using functional optical coherence tomography (fOCT). Based on the principal component analysis and fuzzy clustering method (PCA-FCM), the hemodynamic response of different size blood vessels in rat cortex are analyzed, showing that the hemodynamic response of the superficial large blood vessels is more concentrated. In the regions of neural tissue where blood vessels are removed, positive significant pixels (the intensity of the pixel for five consecutive frames is greater than the average value plus triple standard deviation) and negative significant pixels (the intensity of the pixel for five consecutive frames is less than the average value minus triple standard deviation) exist, and the averaged intensity signal responds rapidly with an onset time of ~20.8 ms. Furthermore, the hemodynamic response was delayed by ~3.5 s from the neural tissue response. fOCT can provide a label-free, large-scale and depth-resolved map of cortical neurovascular activation, which is a promising technology to monitor cortical small-scale neurovascular activities.

Non-Invasive Tools in Perioperative Stroke Risk Assessment for Asymptomatic Carotid Artery Stenosis with a Focus on the Circle of Willis.

This review aims to explore advancements in perioperative ischemic stroke risk estimation for asymptomatic patients with significant carotid artery stenosis, focusing on Circle of Willis (CoW) morphology based on the CTA or MR diagnostic imaging in the current preoperative diagnostic algorithm. Functional transcranial Doppler (fTCD), near-infrared spectroscopy (NIRS), and optical coherence tomography angiography (OCTA) are discussed in the context of evaluating cerebrovascular reserve capacity and collateral vascular systems, particularly the CoW. These non-invasive diagnostic tools provide additional valuable insights into the cerebral perfusion status. They support biomedical modeling as the gold standard for the prediction of the potential impact of carotid artery stenosis on the hemodynamic changes of cerebral perfusion. Intraoperative risk assessment strategies, including selective shunting, are explored with a focus on CoW variations and their implications for perioperative ischemic stroke and cognitive function decline. By synthesizing these insights, this review underscores the potential of non-invasive diagnostic methods to support clinical decision making and improve asymptomatic patient outcomes by reducing the risk of perioperative ischemic neurological events and preventing further cognitive decline.

Intrinsic signal optoretinography of dark adaptation abnormality due to rod photoreceptor degeneration.

This research aims to investigate the potential of using intrinsic optical signal (IOS) optoretinography (ORG) to objectively detect dark adaptation (DA) abnormalities related to rod photoreceptor degeneration. Functional optical coherence tomography (OCT) was employed in both wild-type (WT) and retinal degeneration 10 (rd10) mice to conduct this assessment. Dynamic OCT measurements captured the changes in retinal thickness and reflectance from light-to-dark transition. Comparative analysis revealed significant IOS alterations within the outer retina. Specifically, a reduction in thickness from external limiting membrane (ELM) peak to retinal pigment epithelium (RPE) peak was observed (WT: 1.13 ± 0.69µm, 30min DA; rd10: 2.64 ± 0.86µm, 30min DA), as well as a decrease in the intensity of the inner segment ellipsoid zone (EZ) in 30min DA compared to light adaptation (LA). The reduction of relative EZ intensity was notable in rd10 after 5min DA and in WT after 15min DA, with a distinguishable difference between rd10 and WT after 10min DA. Furthermore, our findings indicated a significant decrease in the relative intensity of the hypo-reflective band between EZ and RPE in rd10 retinas during DA, which primarily corresponds to the outer segment (OS) region. In conclusion, the observed DA-IOS abnormalities, including changes in ELM-RPE thickness, EZ, and OS intensity, hold promise as differentiators between WT and rd10 mice before noticeable morphological abnormalities occur. These findings suggest the potential of this non-invasive imaging technique for the early detection of dysfunction in retinal photoreceptors.

Functional OCT angiography reveals early retinal neurovascular dysfunction in diabetes with capillary resolution.

Altered retinal neurovascular coupling may contribute to the development and progression of diabetic retinopathy (DR) but remains highly challenging to measure due to limited resolution and field of view of the existing functional hyperemia imaging. Here, we present a novel modality of functional OCT angiography (fOCTA) that allows a 3D imaging of retinal functional hyperemia across the entire vascular tree with single-capillary resolution. In fOCTA, functional hyperemia was evoked by a flicker light stimulation, recorded by a synchronized time-lapse OCTA (i.e., 4D), and extracted precisely from each capillary segment (space) and stimulation period (time) in the OCTA time series. The high-resolution fOCTA revealed that the retinal capillaries, particularly the intermediate capillary plexus, exhibited apparent hyperemic response in normal mice, and significant functional hyperemia loss (P < 0.001) at an early stage of DR with few overt signs of retinopathy and visible restoration after aminoguanidine treatment (P < 0.05). Retinal capillary functional hyperemia has strong potential to provide sensitive biomarkers of early DR, and retinal fOCTA would provide new insights into the pathophysiology, screening and treatment of early DR.

Towards targeted colorectal cancer biopsy based on tissue morphology assessment by compression optical coherence elastography.

Identifying the precise topography of cancer for targeted biopsy in colonoscopic examination is a challenge in current diagnostic practice. For the first time we demonstrate the use of compression optical coherence elastography (C-OCE) technology as a new functional OCT modality for differentiating between cancerous and non-cancerous tissues in colon and detecting their morphological features on the basis of measurement of tissue elastic properties. The method uses pre-determined stiffness values (Young's modulus) to distinguish between different morphological structures of normal (mucosa and submucosa), benign tumor (adenoma) and malignant tumor tissue (including cancer cells, gland-like structures, cribriform gland-like structures, stromal fibers, extracellular mucin). After analyzing in excess of fifty tissue samples, a threshold stiffness value of 520 kPa was suggested above which areas of colorectal cancer were detected invariably. A high Pearson correlation (r =0.98; p <0.05), and a negligible bias (0.22) by good agreement of the segmentation results of C-OCE and histological (reference standard) images was demonstrated, indicating the efficiency of C-OCE to identify the precise localization of colorectal cancer and the possibility to perform targeted biopsy. Furthermore, we demonstrated the ability of C-OCE to differentiate morphological subtypes of colorectal cancer - low-grade and high-grade colorectal adenocarcinomas, mucinous adenocarcinoma, and cribriform patterns. The obtained ex vivo results highlight prospects of C-OCE for high-level colon malignancy detection. The future endoscopic use of C-OCE will allow targeted biopsy sampling and simultaneous rapid analysis of the heterogeneous morphology of colon tumors.

Optical coherence tomography for dynamic investigation of mammalian reproductive processes.

The biological events associated with mammalian reproductive processes are highly dynamic and tightly regulated by molecular, genetic, and biomechanical factors. Implementation of live imaging in reproductive research is vital for the advancement of our understanding of normal reproductive physiology and for improving the management of reproductive disorders. Optical coherence tomography (OCT) is emerging as a promising tool for dynamic volumetric imaging of various reproductive processes in mice and other animal models. In this review, we summarize recent studies employing OCT-based approaches toward the investigation of reproductive processes in both, males and females. We describe how OCT can be applied to study structural features of the male reproductive system and sperm transport through the male reproductive tract. We review OCT applications for in vitro and dynamic in vivo imaging of the female reproductive system, staging and tracking of oocytes and embryos, and investigations of the oocyte/embryo transport through the oviduct. We describe how the functional OCT approach can be applied to the analysis of cilia dynamics within the male and female reproductive systems. We also discuss the areas of research, where OCT could find potential applications to progress our understanding of normal reproductive physiology and reproductive disorders.

Temporal mirror-symmetry in functional signals recorded from rat barrel cortex with optical coherence tomography.

Functional optical coherence tomography (fOCT) detects activity-dependent light scattering changes in micro-structures of neural tissue, drawing attention as in vivo volumetric functional imaging technique at a sub-columnar level. There are 2 plausible origins for the light scattering changes: (i) hemodynamic responses such as changes in blood volume and in density of blood cells and (ii) reorientation of dipoles in cellular membrane. However, it has not been clarified which is the major contributor to fOCT signals. Furthermore, previous studies showed both increase and decrease of reflectivity as fOCT signals, making interpretation more difficult. We proposed combination of fOCT with Fourier imaging and adaptive statistics to the rat barrel cortex. Active voxels revealed barrels elongating throughout layers with mini-columns in superficial layers consistent with physiological studies, suggesting that active voxels revealed by fOCT reflect spatial patterns of activated neurons. These voxels included voxels with negative changes in reflectivity and those with positive changes in reflectivity. However, they were temporally mirror-symmetric, suggesting that they share common sources. It is hard to explain that hemodynamic responses elicit positive signals in some voxels and negative signals in the other. On the other hand, considering membrane dipoles, polarities of OCT signals can be positive and negative depending on orientations of scattering particles relative to the incident light. Therefore, the present study suggests that fOCT signals are induced by the reorientation of membrane dipoles.

Functional optical coherence tomography at altitude: retinal microvascular perfusion and retinal thickness at 3,800 meters.

Cerebral hypoxia is a serious consequence of several cardiorespiratory illnesses. Measuring the retinal microvasculature at high altitude provides a surrogate for cerebral microvasculature, offering potential insight into cerebral hypoxia in critical illness. In addition, although sex-specific differences in cardiovascular diseases are strongly supported, few have focused on differences in ocular blood flow. We evaluated the retinal microvasculature in males (n = 11) and females (n = 7) using functional optical coherence tomography at baseline (1,130 m) (day 0), following rapid ascent (day 2), and prolonged exposure (day 9) to high altitude (3,800 m). Retinal vascular perfusion density (rVPD; an index of total blood supply), retinal thickness (RT; reflecting vascular and neural tissue volume), and arterial blood were acquired. As a group, rVPD increased on day 2 versus day 0 (P < 0.001) and was inversely related to [Formula: see text] (R2=0.45; P = 0.006). By day 9, rVPD recovered to baseline but was significantly lower in males than in females (P = 0.007). RT was not different on day 2 versus day 0 (P > 0.99) but was reduced by day 9 relative to day 0 and day 2 (P < 0.001). RT changes relative to day 0 were inversely related to changes in [Formula: see text] on day 2 (R2=0.6; P = 0.001) and day 9 (R2=0.4; P = 0.02). RT did not differ between sexes. These data suggest differential time course and regulation of the retina during rapid ascent and prolonged exposure to high altitude and are the first to demonstrate sex-specific differences in rVPD at high altitude. The ability to assess intact microvasculature contiguous with the brain has widespread research and clinical applications.NEW & NOTEWORTHY Measuring the retinal microvasculature at high altitude provides a surrogate for cerebral microvasculature, offering potential insight into consequence of cerebral hypoxia in critical illness. This study demonstrates dynamic regulation of the retina during rapid ascent and prolonged exposure to high altitude and is the first to demonstrate sex-specific differences in retinal microvasculature at high altitude. The ability to dynamically assess intact microvasculature contiguous with the brain has widespread research and clinical applications.

Outcomes from the Retrospective Multicenter Cross-Sectional Study on Lamellar Macular Hole Surgery.

PurposeTo analyze the functional and anatomical parameters of lamellar macular hole (LMH) surgery with internal limiting membrane peeling and determine which surgical technique provides the best visual outcome.MethodsThis is a retrospective multicenter cross-sectional study on patients who underwent pars plana vitrectomy (PPV) for LMH with or without combined phaco-vitrectomy, as well as gas-, air- or BSS-tamponade. Pre- and postoperative examination included best corrected visual acuity (BCVA) measurements for functional comparison and optical coherence tomography (OCT) scans to determine the contributing anatomical parameters.ResultsA total of 66 consecutive patients were included (age: 71.79 ± 8.52 years), of which 47 (71.2%) were diagnosed as tractional type LMH, and 19 patients (28.8%) as degenerative type. An epiretinal membrane (ERM) was present in 63 of the patients (95.5%), LMH-associated epiretinal proliferation (LHEP) was present in 19 patients (28.8%), and 16 patients (24.2%) had concomitant ERM and LHEP. In the group of tractional LMH, the mean central foveal thickness (CFT) was 81.1% thicker (P < 0.05) than in the degenerative group. Thirty-one patients (47.0%) underwent a combined phaco-vitrectomy procedure, while the rest underwent 23G, 25G or 27G PPV. Seventeen of the 66 patients received gas-tamponade (25.7%)-either SF6 or C3F8, 26 received air-tamponade (39.4%), while the remaining 23 patients received balanced salt solution (BSS)-tamponade (34.9%) during vitrectomy. The total BCVA showed significant improvement postoperatively (p < 0.001) and accordingly in the following groups: tractional LMH type (p < 0.001), degenerative type (p < 0.001), simple PPV (p < 0.001), phaco-vitrectomy (p < 0.001), BSS injection (p < 0.01), gas-tamponade (p < 0.05). None of the patients included in the study developed a full thickness macular hole postoperatively.ConclusionPPV provided a high success rate and functional improvement for treating LMH for both tractional and degenerative types, as well as combined phaco-vitrectomy treatment when cataract was present.

Dynamic volumetric imaging and cilia beat mapping in the mouse male reproductive tract with optical coherence tomography.

Spermatozoa transport within the male reproductive tract is a highly dynamic and biologically important reproductive event. However, due to the lack of live volumetric imaging technologies and quantitative measurements, there is little information on the dynamic aspect and regulation of this process. Here, we presented ex vivo dynamic volumetric imaging of the mouse testis, efferent duct, epididymis, and vas deferens at a micro-scale spatial resolution with optical coherence tomography (OCT). Micro computed tomography imaging is presented as a reference for the proposed OCT imaging. Application of functional OCT analysis allowed for 3D mapping of the cilia beat frequency in the efferent duct, which volumetrically visualized the spatial distribution of the ciliated cells and corresponding ciliary activities. Potentially these analyses could be expanded to in vivo settings through intravital approach. In summary, this study demonstrated that OCT has a great potential to investigate the microstructure and dynamics, such as cilia beating, muscle contractions, and sperm transport, within the male reproductive tract.

Functional Optical Coherence Tomography for Intrinsic Signal Optoretinography: Recent Developments and Deployment Challenges.

Intrinsic optical signal (IOS) imaging of the retina, also termed as optoretinogram or optoretinography (ORG), promises a non-invasive method for the objective assessment of retinal function. By providing the unparalleled capability to differentiate individual retinal layers, functional optical coherence tomography (OCT) has been actively investigated for intrinsic signal ORG measurements. However, clinical deployment of functional OCT for quantitative ORG is still challenging due to the lack of a standardized imaging protocol and the complication of IOS sources and mechanisms. This article aims to summarize recent developments of functional OCT for ORG measurement, OCT intensity- and phase-based IOS processing. Technical challenges and perspectives of quantitative IOS analysis and ORG interpretations are discussed.

Subretinal fluid disturbs the retinal venous blood flow in central serous chorioretinopathy

The significance of subretinal fluid in the retinal blood flow is unclear. Here, we evaluated the association between subretinal fluid (SRF) and retinal blood flow in eyes with central serous chorioretinopathy (CSC) using a retinal functional imager (RFI) and optical coherence tomography angiography (OCTA). In this retrospective case–control study involving 26 eyes from 18 CSC patients and 25 eyes from 21 age- and sex-matched controls, we found that the CSC group showed significant differences from the control group in terms of the retinal venule blood flow velocity (3.60 ± 0.43 vs 3.96 ± 0.56 mm/s; p = 0.030), retinal venule blood flow rate (8.75 ± 2.67 vs 12.51 ± 7.12 nl/s; p = 0.040), and the diameter of retinal venules (118.26 ± 14.25 vs 126.92 ± 35.31 μm; p = 0.045). Linear regression analysis showed that SRF thickness accounted for a 36.9% reduction in venous BFR (p = 0.013). The difference in the O2 saturation between retinal arteries and veins was greater in the CSC group. There was no correlation between SRF thickness and capillary densities in OCTA. Our findings suggest that disturbance in venous return and the associated altered oxygen may be significant changes in the retinal blood flow dynamics in eyes with SRF.

Intrinsic signal optoretinography of dark adaptation kinetics

Delayed dark adaptation due to impaired rod photoreceptor homeostasis has been reported as the earliest symptom of eye diseases such as age-related macular degeneration, diabetic retinopathy, and retinitis pigmentosa. Objective measurement of dark adaptation can facilitate early diagnosis to enable prompt intervention to prevent vision loss. However, there is a lack of noninvasive methods capable of spatiotemporal monitoring of photoreceptor changes during dark adaptation. Here we demonstrate functional optical coherence tomography (OCT) for in vivo intrinsic signal optoretinography (ORG) of dark adaptation kinetics in the C57BL/6J mouse retina. Functional OCT revealed a shortening of the outer retina, a rearrangement of the cone and rod photoreceptor interdigitation zone, and a reduction in intrinsic signal amplitude at the photoreceptor inner segment ellipsoid (ISe). A strong positive correlation between the outer retinal shortening and ISe intensity reduction was also confirmed. Functional OCT of dark adaptation kinetics promises an objective method for rapid ORG assessment of physiological integrity of retinal photoreceptors.

B-scan-sectioned dynamic micro-optical coherence tomography for bulk-motion suppression

In this Letter, we present B-scan-sectioned dynamic micro-optical coherence tomography (BD-MOCT) for high-quality sub-cellular dynamic contrast imaging. Dynamic micro-optical coherence tomography (D-MOCT) is a functional optical coherence tomography (OCT) technique performed on high-resolution (micron level) OCT systems; hundreds of consecutive B-scans need to be acquired for dynamic signal extraction, which requires relatively long data acquisition time. Bulk motions occurring during data acquisition (even at the micron level) may degrade the quality of the obtained dynamic contrast images. In BD-MOCT, each full B-scan is divided into several sub-B-scans, and each sub-B-scan repeats multiple times before the sample beam moves to the next sub-B-scan. After all of the sub-B-scans for a full B-scan are completely acquired, we stitch all of the sub-B-scans into the same number of full B-scans. In this way, the time interval between two consecutive stitched B-scans could be reduced multiple times for bulk-motion suppression. The performed scanning protocol modulates the scanning sequences of fast scanning and repeat scanning for improving the dynamic contrast image quality, while the total data acquisition time remains almost the same.

Optical coherence tomography features and correlation of functional and structural parameters in patients of idiopathic intracranial hypertension.

Purpose:To determine the correlation between functional parameters and optical coherence tomography (OCT) features in patients of idiopathic intracranial hypertension (IIH).Methods:A prospective observational study in early and established cases of papilledema in IIH presenting from December 2017 to February 2019. Functional parameters (visual acuity, contrast sensitivity, mean deviation, VER, and MfERG) and structural parameters (RNFL, GCL-IPL, and optic disc height) were measured at baseline and every 6 weeks for 6 months.Results:At baseline, average RNFL had a moderate negative correlation with mean deviation (r = −0.45; P = 0.0007) and a positive correlation with logMAR visual acuity (r = 0.18; P = 0.17). On the contrary, baseline GCL and logMAR visual acuity had a negative correlation (r = −0.4, P = 0.02). Optic disc height (ODH) had a negative correlation with visual field mean deviation (r = −0.046; P = 0.0005). At 6 months, ODH and GCL-IPL complex had a statistically significant correlation with functional parameters. However, RNFL values did not show any significant correlation with any of the functional parameters. Baseline GCL-IPL and optic disc height values had a moderate and significant correlation with final functional parameters. However, RNFL did not show any correlation with final functional parameters. Correlation between GCL-IPL thickness at 6 weeks and final functional parameters were stronger than that with baseline GCL valuesConclusion:In the setting of severe papilledema, RNFL can misguide the prognosis. GCL-IPL can be a valuable tool for an objective evaluation of the integrity of the optic nerve in IIH and ODH may be used as an alternative or in combination with GCL-IPL in these cases.

Enhanced medical diagnosis for dOCTors: a perspective of optical coherence tomography.

.Significance: After three decades, more than 75,000 publications, tens of companies being involved in its commercialization, and a global market perspective of about USD 1.5 billion in 2023, optical coherence tomography (OCT) has become one of the fastest successfully translated imaging techniques with substantial clinical and economic impacts and acceptance.Aim: Our perspective focuses on disruptive forward-looking innovations and key technologies to further boost OCT performance and therefore enable significantly enhanced medical diagnosis.Approach: A comprehensive review of state-of-the-art accomplishments in OCT has been performed.Results: The most disruptive future OCT innovations include imaging resolution and speed (single-beam raster scanning versus parallelization) improvement, new implementations for dual modality or even multimodality systems, and using endogenous or exogenous contrast in these hybrid OCT systems targeting molecular and metabolic imaging. Aside from OCT angiography, no other functional or contrast enhancing OCT extension has accomplished comparable clinical and commercial impacts. Some more recently developed extensions, e.g., optical coherence elastography, dynamic contrast OCT, optoretinography, and artificial intelligence enhanced OCT are also considered with high potential for the future. In addition, OCT miniaturization for portable, compact, handheld, and/or cost-effective capsule-based OCT applications, home-OCT, and self-OCT systems based on micro-optic assemblies or photonic integrated circuits will revolutionize new applications and availability in the near future. Finally, clinical translation of OCT including medical device regulatory challenges will continue to be absolutely essential.Conclusions: With its exquisite non-invasive, micrometer resolution depth sectioning capability, OCT has especially revolutionized ophthalmic diagnosis and hence is the fastest adopted imaging technology in the history of ophthalmology. Nonetheless, OCT has not been completely exploited and has substantial growth potential—in academics as well as in industry. This applies not only to the ophthalmic application field, but also especially to the original motivation of OCT to enable optical biopsy, i.e., the in situ imaging of tissue microstructure with a resolution approaching that of histology but without the need for tissue excision.

External Limiting Membrane Disruption Predicts Long-Term Outcome in Strict Treat-And-Extend Regimen in Neovascular Age-Related Macular Degeneration.

The use of anti-vascular-endothelial growth factor agents for neovascular age-related macular degeneration (nAMD) in different treatment schemes is widely common in clinical practice. However, there is currently limited data on the long-term outcomes of a strict treat-and-extend regimen (TER) and imaging biomarkers to predict both functional outcome and the potential for a TER exit due to success. In this retrospective study we followed treatment-naïve subjects with nAMD starting treatment with either ranibizumab or aflibercept in a TER without loading dose but with predefined exit criteria for up to 8 years. We evaluated both the functional outcome and several spectral-domain optical coherence tomography parameters in a follow-up mode using a standardized protocol. Within the 211 eyes followed for a mean of 60.3 ± 20.9 months, follow-up adherence was high with major part of discontinuations of TER being due to success. Mean best-corrected visual acuity (BCVA) increased from initially 63.9 ± 15.5 ETDRS letters to 70.0 ± 14.7 after 1 year (+6.1 letters, p < 0.001) and to 68.5 ± 18.1 (+4.6 letters, p = 0.028) at 5 years. A worse BCVA (p = 0.001) and a better external limiting membrane (ELM) disruption score at baseline predicted (p = 0.019) BCVA gain at 5 years. The probability of reaching the exit criteria was significantly associated with a better ELM disruption score (p = 0.044) and the absence of a central pigment epithelial detachment (PED) (p = 0.05) at baseline. Significant visual gains were sustained in a long-term TER in a real-world setting. Integrity of ELM at baseline predicted BCVA gain at 5 years and the potential for TER exit due to success.

Real-life experiences with Brolucizumab in recalcitrant neovascular age-related macular degeneration

Pivotal clinical trials have proven brolucizumab to be apotent intravitreal anti-vascular endothelial growth factor (VEGF) drug in patients with neovascular age-related macular degeneration (nAMD). Therefore, it seems to be apromising drug also in patients with recalcitrant nAMD. This article presents the results of patients who were switched to brolucizumab due to persistent fluid under previous anti-VEGF treatment. In this study 21 eyes were retrospectively analyzed in which treatment was switched to brolucizumab due to persistent intraretinal (IRF), subretinal (SRF) and/or sub-retinal pigment epithelium (sub-RPE fluid) fluid despite long-term anti-VEGF treatment. Functional and spectral domain optical coherence tomography (SD-OCT) data were investigated at diagnosis of nAMD(I), at switch to brolucizumab(II), 4 weeks after upload of brolucizumab(III) and at first reactivation of macular neovascularization (MNV,IV). There were no significant changes in fluid distribution between(I) and(II). After upload of brolucizumab(III) asignificant reduction of central subfield retinal thickness (CSRT, p = 0.0001), SRF (p = 0.004) and sub-RPE fluid (p = 0.04), but no visual acuity improvement (p = 0.56) were observed. Intravitreal brolucizumab treatment can achieve significant reductions particularly of SRF and sub-RPE in patients refractory to previous anti-VEGF treatment. Future studies should further investigate the effects of brolucizumab in patients with recalcitrant nAMD.

Dissecting the microvascular contributions to diffuse correlation spectroscopy measurements of cerebral hemodynamics using optical coherence tomography angiography.

.Significance: Diffuse correlation spectroscopy (DCS) is an emerging noninvasive, diffuse optical modality that purportedly enables direct measurements of microvasculature blood flow. Functional optical coherence tomography angiography (OCT-A) can resolve blood flow in vessels as fine as capillaries and thus has the capability to validate key attributes of the DCS signal.Aim: To characterize activity in cortical vasculature within the spatial volume that is probed by DCS and to identify populations of blood vessels that are most representative of the DCS signals.Approach: We performed simultaneous measurements of somatosensory-evoked cerebral blood flow in mice in vivo using both DCS and OCT-A.Results: We resolved sensory-evoked blood flow in the somatosensory cortex with both modalities. Vessels with diameters smaller than featured higher peak flow rates during the initial poststimulus positive increase in flow, whereas larger vessels exhibited considerably larger magnitude of the subsequent undershoot. The simultaneously recorded DCS waveforms correlated most highly with flow in the smallest vessels, yet featured a more prominent undershoot.Conclusions: Our direct, multiscale, multimodal cross-validation measurements of functional blood flow support the assertion that the DCS signal preferentially represents flow in microvasculature. The significantly greater undershoot in DCS, however, suggests a more spatially complex relationship to flow in cortical vasculature during functional activation.

Polymerically modified superparamagnetic iron oxide nanoparticles as a multi-model molecular probe for functionalized optical coherence tomography

We demonstrate the synthesis, characterization, and potential application of polymerically modified superparamagnetic nanoparticles over bare SPIONs, as a multi-model molecular probe for functionalized optical coherence tomography (fOCT). The synthesized magnetic nanoparticles (MNPs) also have the ability of photo thermionic excitation under near-infrared irradiation (980 nm). By having dual excitation properties, the SPIONs are used as exogenous contrast agents for magnetomotive optical coherence tomography (MMOCT) as well as photothermal optical coherence tomography (PTOCT). We developed a functionalized OCT system and signal processing algorithms for MMOCT and PTOCT. Further, non-invasive in-vivo imaging was performed on swiss-albino mice to demonstrate the potential application of polymerically modified SPIONs. A diffusion dynamics study and contrast-to-noise ratio (CNR) study of the dispersed synthesized SPIONs inside skin tissue of mice as a function of time and depth is also reported. We found that PEG-SPIONs are excellent candidate for molecular contrast agent of functional OCT.