Wide-field imaging in behaving mice as a tool to study cognitive function

Cognitive functions are mediated through coordinated and dynamic neuronal responses that involve many different areas across the brain. Therefore, it is of high interest to simultaneously record neuronal activity from as many brain areas as possible while the subject performs a cognitive behavioral task. One of the emerging tools to achieve a mesoscopic field of view is wide-field imaging of cortex-wide dynamics in mice. Wide-field imaging is cost-effective, user-friendly, and enables obtaining cortex-wide signals from mice performing complex and demanding cognitive tasks. Importantly, wide-field imaging offers an unbiased cortex-wide observation that sheds light on overlooked cortical regions and highlights parallel processing circuits. Recent wide-field imaging studies have shown that multi-area cortex-wide patterns, rather than just a single area, are involved in encoding cognitive functions. The optical properties of wide-field imaging enable imaging of different brain signals, such as layer-specific, inhibitory subtypes, or neuromodulation signals. Here, I review the main advantages of wide-field imaging in mice, review the recent literature, and discuss future directions of the field. It is expected that wide-field imaging in behaving mice will continue to gain popularity and aid in understanding the mesoscale dynamics underlying cognitive function.

History information emerges in the cortex during learning

We learn from our experience but the underlying neuronal mechanisms incorporating past information to facilitate learning is relatively unknown. Specifically, which cortical areas encode history-related information and how is this information modulated across learning? To study the relationship between history and learning, we continuously imaged cortex-wide calcium dynamics as mice learn to use their whiskers to discriminate between two different textures. We mainly focused on comparing the same trial type with different trial history, that is, a different preceding trial. We found trial history information in barrel cortex (BC) during stimulus presentation. Importantly, trial history in BC emerged only as the mouse learned the task. Next, we also found learning-dependent trial history information in rostrolateral (RL) association cortex that emerges before stimulus presentation, preceding activity in BC. Trial history was also encoded in other cortical areas and was not related to differences in body movements. Interestingly, a binary classifier could discriminate trial history at the single trial level just as well as current information both in BC and RL. These findings suggest that past experience emerges in the cortex around the time of learning, starting from higher-order association area RL and propagating down (i.e., top-down projection) to lower-order BC where it can be integrated with incoming sensory information. This integration between the past and present may facilitate learning.

Follow-up of retinoblastoma using RetCam fluorescein angiography and correlation with clinical findings

PURPOSE

To report RetCam fluorescein angiographic (FA) changes and correlation with clinical findings in the follow-up of retinoblastoma (RB) after frontline intravenous chemotherapy and other treatments.

METHODS

Patients having RB who underwent post-treatment RetCam fundus photography and FA under general anesthesia between February 2020 and February 2022 were retrospectively analyzed.

RESULTS

78 eyes of 70 patients with RB were included. In 55 (70.5%) eyes with type 1, 2 or 3 regression patterns, the main tumor started to show hyperfluorescence in arterial phase in 24 eyes (43.6%), in early venous phase in 24 (43.6%) eyes, and in late venous phase in 7 (12.7%) eyes. Of thirty-six (46.2%) eyes with chorioretinal scars developing after focal treatments (cryotherapy and transpupillary thermotherapy), window defects and visible choroidal vessels were found in all eyes, scleral staining in 10 (27.8%), and gliosis on scar tissue in 8 (22.2%). Vitreous seeds showed hyperfluorescence if they were calcified (6 eyes, 7.7%) and hypofluorescence if non-calcified (11 eyes, 14.1%). Retrohyaloid seeds (11 eyes, 14.1%) were hypo/isofluorescent while subretinal seeds (6 eyes, 7.7%) were hyperfluorescent. Leakage from peripheral retinal vessels was detected in 14 (17.9%) eyes and non-perfusion in 6 (7.7%) eyes.

CONCLUSION

RetCam wide-angle FA is useful to evaluate the tumor and associated vascular and retinal changes after treatment in RB. Regressed tumors demonstrate later fluorescein uptake in venous phases. Fluorescein angiographic changes in chorioretinal scars include window defects, visibility of choroidal vessels, scleral staining, and leakage from vessels. Retinal vascular leakage and peripheral non-perfusion can be seen in eyes with regressed stable tumors.

Convolutional neural network classifies visual stimuli from cortical response recorded with wide-field imaging in mice

ObjectiveThe optic nerve is a good location for a visual neuroprosthesis. It can be targeted when a subject cannot receive a retinal prosthesis and it is less invasive than a cortical implant. The effectiveness of an electrical neuroprosthesis depends on the combination of the stimulation parameters which must be optimized, and an optimization strategy might be performing closed-loop stimulation using the evoked cortical response as feedback. However, it is necessary to identify target cortical activation patterns and to associate the cortical activity with the visual stimuli present in the visual field of the subjects. Visual stimuli decoding should be performed on large areas of the visual cortex, and with a method as translational as possible to shift the study to human subjects in the future. The aim of this work is to develop an algorithm that meets these requirements and can be leveraged to automatically associate a cortical activation pattern with the visual stimulus that generated it.ApproachThree mice were presented with 10 different visual stimuli, and their primary visual cortex response was recorded using wide-field calcium imaging. Our decoding algorithm relies on a convolutional neural network (CNN), trained to classify the visual stimuli from the correspondent wide-field images. Several experiments were performed to identify the best training strategy and investigate the possibility of generalization.Main resultsThe best classification accuracy was 75.38%±4.77%, obtained pre-training the CNN on the MNIST digits dataset and fine-tuning it on our dataset. Generalization was possible pre-training the CNN to classify Mouse 1 dataset and fine-tuning it on Mouse 2 and Mouse 3, with accuracies of 64.14%±10.81% and 51.53%±6.48% respectively.SignificanceThe combination of wide-field calcium imaging and CNNs can be used to classify the cortical responses to simple visual stimuli and might be a viable alternative to existing decoding methodologies. It also allows us to consider the cortical activation as reliable feedback in future optic nerve stimulation experiments.

Open-source statistical and data processing tools for wide-field optical imaging data in mice

Significance

Wide-field optical imaging (WOI) can produce concurrent hemodynamic and cell-specific calcium recordings across the entire cerebral cortex in animal models. There have been multiple studies using WOI to image mouse models with various environmental or genetic manipulations to understand various diseases. Despite the utility of pursuing mouse WOI alongside human functional magnetic resonance imaging (fMRI), and the multitude of analysis toolboxes in the fMRI literature, there is not an available open-source, user-friendly data processing and statistical analysis toolbox for WOI data.

Aim

To assemble a MATLAB toolbox for processing WOI data, as described and adapted to combine techniques from multiple WOI groups and fMRI.

Approach

We outline our MATLAB toolbox on GitHub with multiple data analysis packages and translate a commonly used statistical approach from the fMRI literature to the WOI data. To illustrate the utility of our MATLAB toolbox, we demonstrate the ability of the processing and analysis framework to detect a well-established deficit in a mouse model of stroke and plot activation areas during an electrical paw stimulus experiment.

Results

Our processing toolbox and statistical methods isolate a somatosensory-based deficit 3 days following photothrombotic stroke and cleanly localize sensory stimulus activations.

Conclusions

The toolbox presented here details an open-source, user-friendly compilation of WOI processing tools with statistical methods to apply to any biological question investigated with WOI techniques.

Comparison of different methods of retinal imaging for the screening of diabetic retinopathy: a systematic review

BACKGROUND

Screening for diabetic retinopathy (DR) is recommended to detect sight-threatening complications prior to visual loss. Early Treatment Diabetic Retinopathy Study (ETDRS) seven standard field (7SF) retinal imaging has traditionally been regarded the gold standard for DR classification, but other methods are often preferred clinically. The purpose of this systematic review was to determine whether 7SF is the most optimal screening method for DR grading, or if similar results can be achieved by other methods using a smaller field of view (<7SF) or ultra-wide field (UWF) imaging.

METHODS

Based on Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines, two independent reviewers initially identified 7167 publications in PubMed, Cochrane and Embase databases. Of these, 16 publications were included based on predefined inclusion criteria.

RESULTS

7SF was used as reference standard in 12 studies (compared with < 7SF in five studies and UWF in seven studies), and four studies compared other reference standards. Compared to 7SF, studies using < 7SF and UWF images both reported of similar agreement. A lower rate of ungradable images was reported for mydriatic and non-mydriatic UWF as compared to non-mydriatic < 7SF modalities.

CONCLUSION

Retinal imaging of <7SF and UWF both provide acceptable performance compared to 7SF. Given the time-consuming nature of the latter, these methods could be reasonable options in DR screening, even though a high number of ungradable images in non-mydriatic < 7SF may pose a clinical challenge.

Decoding of cortex-wide brain activity from local recordings of neural potentials

Objective. Electrical recordings of neural activity from brain surface have been widely employed in basic neuroscience research and clinical practice for investigations of neural circuit functions, brain-computer interfaces, and treatments for neurological disorders. Traditionally, these surface potentials have been believed to mainly reflect local neural activity. It is not known how informative the locally recorded surface potentials are for the neural activities across multiple cortical regions.Approach. To investigate that, we perform simultaneous local electrical recording and wide-field calcium imaging in awake head-fixed mice. Using a recurrent neural network model, we try to decode the calcium fluorescence activity of multiple cortical regions from local electrical recordings.Main results. The mean activity of different cortical regions could be decoded from locally recorded surface potentials. Also, each frequency band of surface potentials differentially encodes activities from multiple cortical regions so that including all the frequency bands in the decoding model gives the highest decoding performance. Despite the close spacing between recording channels, surface potentials from different channels provide complementary information about the large-scale cortical activity and the decoding performance continues to improve as more channels are included. Finally, we demonstrate the successful decoding of whole dorsal cortex activity at pixel-level using locally recorded surface potentials.Significance. These results show that the locally recorded surface potentials indeed contain rich information of the large-scale neural activities, which could be further demixed to recover the neural activity across individual cortical regions. In the future, our cross-modality inference approach could be adapted to virtually reconstruct cortex-wide brain activity, greatly expanding the spatial reach of surface electrical recordings without increasing invasiveness. Furthermore, it could be used to facilitate imaging neural activity across the whole cortex in freely moving animals, without requirement of head-fixed microscopy configurations.

Functional Architecture of Motion Direction in the Mouse Superior Colliculus

Motion vision is important in guiding animal behavior. Both the retina and the visual cortex process object motion in largely unbiased fashion: all directions are represented at all locations in the visual field. We investigate motion processing in the superior colliculus of the awake mouse by optically recording neural responses across both hemispheres. Within the retinotopic map, one finds large regions of ∼500 μm size where neurons prefer the same direction of motion. This preference is maintained in depth to ∼350 μm. The scale of these patches, ∼30 degrees of visual angle, is much coarser than the animal's visual resolution (∼2 degrees). A global map of motion direction shows approximate symmetry between the left and right hemispheres and a net bias for upward-nasal motion in the upper visual field.

Comparative Evaluation of Genetically Encoded Voltage Indicators

Imaging voltage using fluorescent-based sensors could be an ideal technique to probe neural circuits with high spatiotemporal resolution. However, due to insufficient signal-to-noise ratio (SNR), imaging membrane potential in mammalian preparations is still challenging. In recent years, many genetically encoded voltage indicators (GEVIs) have been developed. To compare them and guide decisions on which GEVI to use, we have characterized side by side the performance of eight GEVIs that represent different families of molecular constructs. We tested GEVIs in vitro with 1-photon imaging and in vivo with 1-photon wide-field imaging and 2-photon imaging. We find that QuasAr2 exhibited the best performance in vitro, whereas only ArcLight-MT could be used to reliably detect electrical activity in vivo with 2-photon excitation. No single GEVI was ideal for every experiment. These results provide a guide for choosing optimal GEVIs for specific applications.

The Shifting Sands of Cortical Divisions

In this issue of Neuron, a new study by Minderer et al. (2019) examines the activity of thousands of cortical neurons during a navigation task and reveals that features of the task encoded by neurons vary smoothly across cortex rather than falling into functionally discrete cortical regions.

Comparison between transgenic and AAV-PHP.eB-mediated expression of GCaMP6s using in vivo wide-field functional imaging of brain activity

We employ transcranial wide-field single-photon imaging to compare genetically encoded calcium sensors under transgenic or viral vector expression strategies. Awake, head-fixed animals and brief visual flash stimuli are used to assess function. The use of awake transcranial imaging may reduce confounds attributed to cranial window implantation or anesthesia states. We report differences in wide-field epifluorescence brightness and peak Δ F / F 0 response to visual stimulation between expression strategies. Other metrics for indicator performance include fluctuation analysis (standard deviation) and regional correlation maps made from spontaneous activity. We suggest that multiple measures, such as stimulus-evoked signal-to-noise ratio, brightness, and averaged visual Δ F / F 0 response, may be necessary to characterize indicator sensitivity and methods of expression. Furthermore, we show that strategies using blood brain barrier-permeable viruses, such as PHP.eB, yield comparable expression and function as those derived from transgenic mice. We suggest that testing of new genetically engineered activity sensors could employ a single-photon, wide-field imaging pipeline involving visual stimulation in awake mice that have been intravenously injected with PHP.eB.

[Application of high frequency color Doppler ultrasound combined with wide-field imaging in the preoperative navigation of anterolateral thigh perforator flap surgery]

Objective

To investigate the application of high frequency color Doppler ultrasound (HFCDU) combined with wide-field imaging in the preoperative navigation of anterolateral thigh perforator flap graft.

Methods

Between January 2017 and March 2018, 28 patients with skin and soft tissue defects were treated, including 22 males and 6 females, with an average age of 33.5 years (range, 17-66 years). The causes of injury included 2 cases of scald scar, 7 cases of heavy object crushing injury, 12 cases of traffic accident injury, 4 cases of fall injury, 2 cases of machine injury, and 1 case of infection ulcer. Injury sites included 6 cases of hand and wrist, 12 cases of lower leg, 10 cases of foot. After debridement, the wound area ranged from 6.0 cm×3.5 cm to 24.0 cm×9.0 cm, and all patients were treated with free circumflex femoral artery perforator flap graft. Combo of HFCDU and wide-field imaging navigation were done preoperatively to detect the origin, quantity, course, surface location, hemodynamic characteristics, and the relationship with body area of perforator branch of lateral circumflex femoral artery. According to the perforator information displayed by wide-field imaging of source artery, the dominant perforator was determined to be a pedicle for designed flap. The flap size ranged from 7.0 cm×4.5 cm to 26.0 cm×7.0 cm. The flap donor area was sutured directly.

Results

The dominant perforator was successfully detected by HFCDU combined with wide-field imaging in 28 patients before operation. The existence of the perforator was confirmed during operation, and the location was accurate. The course characteristics of the perforate were consistent with the results of wide-field imaging. The grafted flaps survived completely among 27 patients after operation. Necrosis at the edge of the flap was observed in 1 patient, which healed after dressing change. All patients were followed up 3-12 months, with an average of 9 months. All the flaps have good blood supply, good elasticity and shape. The donor areas healed perfectly.

Conclusion

Using HFCDU and wide-field imaging navigation for designing of anterolateral thigh perforator flaps can clearly show the characteristics of perforators, hemodynamic information, and the relationship with body area, so that the surgeons can understand the perforators more accurately and intuitively, and improve the success and efficiency of flap graft surgery.

Automatic Cell Segmentation by Adaptive Thresholding (ACSAT) for Large-Scale Calcium Imaging Datasets

Advances in calcium imaging have made it possible to record from an increasingly larger number of neurons simultaneously. Neuroscientists can now routinely image hundreds to thousands of individual neurons. An emerging technical challenge that parallels the advancement in imaging a large number of individual neurons is the processing of correspondingly large datasets. One important step is the identification of individual neurons. Traditional methods rely mainly on manual or semimanual inspection, which cannot be scaled for processing large datasets. To address this challenge, we focused on developing an automated segmentation method, which we refer to as automated cell segmentation by adaptive thresholding (ACSAT). ACSAT works with a time-collapsed image and includes an iterative procedure that automatically calculates global and local threshold values during successive iterations based on the distribution of image pixel intensities. Thus, the algorithm is capable of handling variations in morphological details and in fluorescence intensities in different calcium imaging datasets. In this paper, we demonstrate the utility of ACSAT by testing it on 500 simulated datasets, two wide-field hippocampus datasets, a wide-field striatum dataset, a wide-field cell culture dataset, and a two-photon hippocampus dataset. For the simulated datasets with truth, ACSAT achieved >80% recall and precision when the signal-to-noise ratio was no less than ∼24 dB.

Behavioral Strategy Determines Frontal or Posterior Location of Short-Term Memory in Neocortex

The location of short-term memory in mammalian neocortex remains elusive. Here we show that distinct neocortical areas maintain short-term memory depending on behavioral strategy. Using wide-field and single-cell calcium imaging, we measured layer 2/3 neuronal activity in mice performing a whisker-based texture discrimination task with delayed response. Mice either deployed an active strategy-engaging their body toward the approaching texture-or passively awaited the touch. Independent of strategy, whisker-related posterior areas encoded choice early after touch. During the delay, in contrast, persistent cortical activity was located medio-frontally in active trials but in a lateral posterior area in passive trials. Perturbing these areas impaired performance for the associated strategy and also provoked strategy switches. Frontally maintained information related to future action, whereas activity in the posterior cortex reflected past stimulus identity. Thus, depending on behavioral strategy, cortical activity is routed differentially to hold information either frontally or posteriorly before converging to similar action.

Ultra-Widefield Imaging for Pediatric Retinal Disease

This article explores the development of retinal imaging, with particular emphasis on ultra-widefield imaging and the key concept of field of view. Two ultra-widefield imaging platforms are examined in detail-Optomap and Spectralis-noncontact imaging systems that include protocols for performing angiography in infants. Applications of ultra-widefield imaging are illustrated using case studies, including diagnosis, monitoring, and screening.

Development of a modular fluorescence overlay tissue imaging system for wide-field intraoperative surgical guidance

Fluorescence imaging is a well-established optical modality that has been used to localize and track fluorophores in vivo and has demonstrated great potential for surgical guidance. Despite the variety of fluorophores currently being researched, many existing intraoperative fluorescence imaging systems are specifically designed for a limited number of applications. We present a modular wide-field fluorescence overlay tissue imaging system for intraoperative surgical guidance that is comprised of commercially available standardized components. Its modular layout allows for the accommodation of a broad range of fluorophores, fields of view (FOV), and spatial resolutions while maintaining an integrated portable design for intraoperative use. Measurements are automatic and feature a real-time projection overlay technique that intuitively displays fluorescence maps directly onto a [Formula: see text] FOV from a working distance of 35 cm. At a 20-ms exposure time, [Formula: see text] samples of indocyanine green could be measured with high signal-to-noise ratio and was later tested in an in vivo mouse model before finally being demonstrated for intraoperative autofluorescence imaging of human soft tissue sarcoma margins. The system's modular design and ability to enable naked-eye visualization of wide-field fluorescence allow for the flexibility to adapt to numerous clinical applications and can potentially extend the adoption of fluorescence imaging for intraoperative use.

Correcting for motion artifact in handheld laser speckle images

Laser speckle imaging (LSI) is a wide-field optical technique that enables superficial blood flow quantification. LSI is normally performed in a mounted configuration to decrease the likelihood of motion artifact. However, mounted LSI systems are cumbersome and difficult to transport quickly in a clinical setting for which portability is essential in providing bedside patient care. To address this issue, we created a handheld LSI device using scientific grade components. To account for motion artifact of the LSI device used in a handheld setup, we incorporated a fiducial marker (FM) into our imaging protocol and determined the difference between highest and lowest speckle contrast values for the FM within each data set (Kbest and Kworst). The difference between Kbest and Kworst in mounted and handheld setups was 8% and 52%, respectively, thereby reinforcing the need for motion artifact quantification. When using a threshold FM speckle contrast value (KFM) to identify a subset of images with an acceptable level of motion artifact, mounted and handheld LSI measurements of speckle contrast of a flow region (KFLOW) in in vitro flow phantom experiments differed by 8%. Without the use of the FM, mounted and handheld KFLOW values differed by 20%. To further validate our handheld LSI device, we compared mounted and handheld data from an in vivo porcine burn model of superficial and full thickness burns. The speckle contrast within the burn region (KBURN) of the mounted and handheld LSI data differed by <4  %   when accounting for motion artifact using the FM, which is less than the speckle contrast difference between superficial and full thickness burns. Collectively, our results suggest the potential of handheld LSI with an FM as a suitable alternative to mounted LSI, especially in challenging clinical settings with space limitations such as the intensive care unit.

Variable Familial Exudative Vitreoretinopathy in a family harbouring variants in both FZD4 and TSPAN12

PURPOSE

To report a family affected by familial exudative vitreoretinopathy (FEVR) in which more severe disease phenotypes segregated with digenic rather than monogenic variants in FEVR-related genes.

METHODS

Phenotype was documented with high-resolution imaging of retinal structure and wide-field fundus photography. Next-generation sequencing (NGS) of known genes involved in FEVR was performed.

RESULTS

Three affected individuals within a family with FEVR presented with variable disease severity. All three affected family members harboured mutation c.349T>C (p.Cys117Arg) in FZD4. In addition, the youngest family member, a 9-year-old boy, who presented with bilateral tractional retinal detachment, and his mother, who presented with retinal pigmentary alterations and bilateral dragging of the macula and atrophy, both harboured the variant c.565T>C (p.Cys189Arg) in TSPAN12. Both suffered from bilateral severe visual loss. On the other hand, the older sister who presented with mild visual loss, temporal avascularity in the right eye and dragging of the blood vessels over the disc and macula in the left eye did not harbour the variant p.Cys189Arg in TSPAN12.

CONCLUSION

These data suggest variants in more than one FEVR-related gene can underlie variable expressivity for FEVR phenotypes in a single family. Further studies of phenotype-genotype correlation, including next-generation sequencing, in larger cohorts of patients with FEVR are needed to investigate whether changes in more than one gene coding for proteins in the Norrin-β-catenin pathway are a recurrent cause for variable expressivity in the disease.

Ready, Steady, Go! Imaging Cortical Activity during Movement Planning and Execution

In this issue of Neuron, Chen et al. (2017) examine premotor activity representing motor planning, Allen et al. (2017) observe the global representation of goal-directed movement on the cortical network, and Makino et al. (2017) track changes in such dynamics throughout learning.

Automated algorithm for actinic cheilitis diagnosis by wide-field fluorescence imaging

Actinic cheilitis (AC) is a disease caused by prolonged and cumulative sun exposure that mostly affects the lower lip, which can progress to a lip squamous cell carcinoma. Routine diagnosis relies on clinician experience and training. We investigated the diagnostic efficacy of wide-field fluorescence imaging coupled to an automated algorithm for AC recognition. Fluorescence images were acquired from 57 patients with confirmed AC and 46 normal volunteers. Three different algorithms were employed: two based on the emission characteristics of local heterogeneity, entropy and intensity range, and one based on the number of objects after K-mean clustering. A classification model was obtained using a fivefold cross correlation algorithm. Sensitivity and specificity rates were 86% and 89.1%, respectively.

Characterizing optical properties and spatial heterogeneity of human ovarian tissue using spatial frequency domain imaging

A spatial frequency domain imaging (SFDI) system was developed for characterizing ex vivo human ovarian tissue using wide-field absorption and scattering properties and their spatial heterogeneities. Based on the observed differences between absorption and scattering images of different ovarian tissue groups, six parameters were quantitatively extracted. These are the mean absorption and scattering, spatial heterogeneities of both absorption and scattering maps measured by a standard deviation, and a fitting error of a Gaussian model fitted to normalized mean Radon transform of the absorption and scattering maps. A logistic regression model was used for classification of malignant and normal ovarian tissues. A sensitivity of 95%, specificity of 100%, and area under the curve of 0.98 were obtained using six parameters extracted from the SFDI images. The preliminary results demonstrate the diagnostic potential of the SFDI method for quantitative characterization of wide-field optical properties and the spatial distribution heterogeneity of human ovarian tissue. SFDI could be an extremely robust and valuable tool for evaluation of the ovary and detection of neoplastic changes of ovarian cancer.

Wide-field optical coherence tomography angiography using extended field imaging technique to evaluate the nonperfusion area in retinal vein occlusion

Purpose

Optical coherence tomography angiography (OCTA) is a newly developed technology which allows us to reconstruct the three-dimensional chorioretinal vasculature without dye injection. OCTA is a noninvasive, rapid, and reproducible method to assess retinal ischemia. However, one of its limitations is the size of scanning area. A novel yet simple technique to expand the scan length on optical coherence tomography has been reported as an extended field imaging (EFI) technique. It involves imaging the posterior pole through trial frames fitted with a +20 diopter lens. We applied this technique to OCTA to evaluate retinal vein occlusion.

Materials and methods

Ten eyes of nine patients with retinal vein occlusion were studied. The average age was 69.0 years (range: 49–93 years). We obtained OCTA images by using RTVue XR Avanti OCT with AngioVue^®. The images of OCTA with scan size of 8×8 mm were obtained with and without EFI, and then they were compared.

Results

OCTA with EFI technique was performed successfully in all eyes. The nonperfusion area was well defined in superficial capillary plexus layer. The images with EFI were able to capture the larger area of the fundus by an average of 188.5% than those without EFI. The posterior pole inside the vascular arcade was well covered with this technique. The area of the fundus imaged by OCTA with EFI technique was even larger than that of fluorescein angiography using Heidelberg Retina Angiograph 2, which captured a 30° field.

Conclusion

Our results suggested that OCTA with EFI technique is very useful to evaluate the retinal ischemia in retinal vein occlusion.

Spatio-temporal visualization of light transport in complex photonic structures

Spatio-temporal imaging of light propagation is very important in photonics because it provides the most direct tool available to study the interaction between light and its host environment. Sub-ps time resolution is needed to investigate the fine and complex structural features that characterize disordered and heterogeneous structures, which are responsible for a rich array of transport physics that have not yet been fully explored. A newly developed wide-field imaging system enables us to present a spatio-temporal study on light transport in various disordered media, revealing properties that could not be properly assessed using standard techniques. By extending our investigation to an almost transparent membrane, a configuration that has been difficult to characterize until now, we unveil the peculiar physics exhibited by such thin scattering systems with transport features that go beyond mainstream diffusion modeling, despite the occurrence of multiple scattering.

Pixel super-resolution using wavelength scanning

Undersampling and pixelation affect a number of imaging systems, limiting the resolution of the acquired images, which becomes particularly significant for wide-field microscopy applications. Various super-resolution techniques have been implemented to mitigate this resolution loss by utilizing sub-pixel displacements in the imaging system, achieved, for example, by shifting the illumination source, the sensor array and/or the sample, followed by digital synthesis of a smaller effective pixel by merging these sub-pixel-shifted low-resolution images. Herein, we introduce a new pixel super-resolution method that is based on wavelength scanning and demonstrate that as an alternative to physical shifting/displacements, wavelength diversity can be used to boost the resolution of a wide-field imaging system and significantly increase its space-bandwidth product. We confirmed the effectiveness of this new technique by improving the resolution of lens-free as well as lens-based microscopy systems and developed an iterative algorithm to generate high-resolution reconstructions of a specimen using undersampled diffraction patterns recorded at a few wavelengths covering a narrow spectrum (10-30 nm). When combined with a synthetic-aperture-based diffraction imaging technique, this wavelength-scanning super-resolution approach can achieve a half-pitch resolution of 250 nm, corresponding to a numerical aperture of ~1.0, across a large field of view (>20 mm²). We also demonstrated the effectiveness of this approach by imaging various biological samples, including blood and Papanicolaou smears. Compared with displacement-based super-resolution techniques, wavelength scanning brings uniform resolution improvement in all directions across a sensor array and requires significantly fewer measurements. This technique would broadly benefit wide-field imaging applications that demand larger space-bandwidth products.

Multifrequency synthesis and extraction using square wave projection patterns for quantitative tissue imaging

We present a method for spatial frequency domain data acquisition utilizing a multifrequency synthesis and extraction (MSE) method and binary square wave projection patterns. By illuminating a sample with square wave patterns, multiple spatial frequency components are simultaneously attenuated and can be extracted to determine optical property and depth information. Additionally, binary patterns are projected faster than sinusoids typically used in spatial frequency domain imaging (SFDI), allowing for short (millisecond or less) camera exposure times, and data acquisition speeds an order of magnitude or more greater than conventional SFDI. In cases where sensitivity to superficial layers or scattering is important, the fundamental component from higher frequency square wave patterns can be used. When probing deeper layers, the fundamental and harmonic components from lower frequency square wave patterns can be used. We compared optical property and depth penetration results extracted using square waves to those obtained using sinusoidal patterns on an in vivo human forearm and absorbing tube phantom, respectively. Absorption and reduced scattering coefficient values agree with conventional SFDI to within 1% using both high frequency (fundamental) and low frequency (fundamental and harmonic) spatial frequencies. Depth penetration reflectance values also agree to within 1% of conventional SFDI.

Advanced demodulation technique for the extraction of tissue optical properties and structural orientation contrast in the spatial frequency domain

We have developed a method for extracting spatial frequency information content from biological tissue, which is used to calculate tissue optical properties and determine tissue structural orientation. This demodulation method employs a two-dimensional Hilbert transform using a spiral phase function in Fourier space. The approach presented here allows for the determination of tissue optical properties using a single frame of data for each modulation frequency, increasing imaging speed by two to threefold versus conventional, three-phase spatial frequency domain imaging (SFDI). This new single-phase Hilbert transform approach recovers optical property and scattering orientation index values within 1% and 10% of three-phase SFDI, respectively. These results suggest that, using the Hilbert demodulation technique, SFDI data acquisition speed can be increased significantly while preserving data quality, which will help us move forward toward the implementation of a real-time SFDI platform.

Diffuse reflectance spectroscopy in Barrett's esophagus: developing a large field-of-view screening method discriminating dysplasia from metaplasia

We evaluated diffuse reflectance spectroscopy implemented as a small field-of-view technique for discrimination of dysplasia from metaplasia in Barrett's esophagus as an adjuvant to autofluorescence endoscopy. Using linear discriminant analysis on 2579 spectra measured in 54 patients identified an optimum a 4-wavelength classifier (at 485, 513, 598 and 629 nm). Sensitivity and specificity for a test data set were 0.67 and 0.85, respectively. Spectroscopic results show that this technique could be implemented in wide-field imaging mode to improve the accuracy of existing endoscopy techniques for finding early pre-malignant lesions in Barrett's esophagus. Results show that the discrimination occurs likely due to redistribution of blood content in the tissue sensed by the optical probing with the wavelength-dependent sampling depth.

Lookup-table method for imaging optical properties with structured illumination beyond the diffusion theory regime

Sinusoidally structured illumination is used in concert with a phantom-based lookup-table (LUT) to map wide-field optical properties in turbid media with reduced albedos as low as 0.44. A key advantage of the lookup-table approach is the ability to measure the absorption (mu(a)) and reduced scattering coefficients (mu(s) (')) over a much broader range of values than permitted by current diffusion theory methods. Through calibration with a single reflectance standard, the LUT can extract mu(s) (') from 0.8 to 2.4 mm(-1) with an average root-mean-square (rms) error of 7% and extract mu(a) from 0 to 1.0 mm(-1) with an average rms error of 6%. The LUT is based solely on measurements of two parameters, reflectance R and modulation M at an illumination period of 10 mm. A single set of three phase-shifted images is sufficient to measure both M and R, which are then used to generate maps of absorption and scattering by referencing the LUT. We establish empirically that each pair (M,R) maps uniquely to only one pair of (micro(s) ('),micro(a)) and report that the phase function (i.e., size) of the scatterers can influence the accuracy of optical property extraction.

Quantitation and mapping of tissue optical properties using modulated imaging

We describe the development of a rapid, noncontact imaging method, modulated imaging (MI), for quantitative, wide-field characterization of optical absorption and scattering properties of turbid media. MI utilizes principles of frequency-domain sampling and model-based analysis of the spatial modulation transfer function (s-MTF). We present and compare analytic diffusion and probabilistic Monte Carlo models of diffuse reflectance in the spatial frequency domain. Next, we perform MI measurements on tissue-simulating phantoms exhibiting a wide range of l values (0.5 mm to 3 mm) and (micro(s) (')micro(a)) ratios (8 to 500), reporting an overall accuracy of approximately 6% and 3% in absorption and reduced scattering parameters, respectively. Sampling of only two spatial frequencies, achieved with only three camera images, is found to be sufficient for accurate determination of the optical properties. We then perform MI measurements in an in vivo tissue system, demonstrating spatial mapping of the absorption and scattering optical contrast in a human forearm and dynamic measurements of a forearm during venous occlusion. Last, metrics of spatial resolution are assessed through both simulations and measurements of spatially heterogeneous phantoms.

Metal-based nanorods as molecule-specific contrast agents for reflectance imaging in 3D tissues

Anisotropic metal-based nanomaterials have been proposed as potential contrast agents due to their strong surface plasmon resonance. We evaluated the contrast properties of gold, silver, and gold-silver hybrid nanorods for molecular imaging applications in three-dimensional biological samples. We used diffuse reflectance spectroscopy to predict the contrast properties of different types of nanorods embedded in biological model systems of increasing complexity. The predicted contrast properties were then validated using wide-field and high-resolution imaging. Results demonstrated that silver nanorods yield images with higher positive-contrast than gold nanorods; however, it is more difficult to synthesize silver nanorods which are homogeneous in shape and size. Gold-silver hybrid nanorods combine the homogeneous synthesis of gold nanorods with the higher scattering properties of silver nanorods. The spectroscopic and imaging results demonstrated that the image contrast properties that can be achieved with anisotropic nanomaterials depend strongly on the material composition, mode of imaging, presence of targeting molecules, and the biological environment. We also found that gold, silver, and gold-silver hybrid nanorods are stable and biocompatible sources of positive and absorptive contrast for use in reflectance molecular imaging and are promising for future clinical translation.