Dynamic Coherence Research Articles

Dynamic θ Frequency Coordination within and between the Prefrontal Cortex-Hippocampus Circuit during Learning of a Spatial Avoidance Task.

θ-Scale coordination of prelimbic medial prefrontal cortex (mPFC) local field potentials (LFPs) and its influence via direct or indirect projections to the ventral hippocampus (vHC) and dorsal hippocampus (dHC) during spatial learning remains poorly understood. We hypothesized that θ frequency coordination dynamics within and between the mPFC, dHC, and vHC would be predetermined by the level of connectivity rather than reflecting differing circuit throughput relationships depending on cognitive demands. Moreover, we hypothesized that coherence levels would not change during learning of a complex spatial avoidance task. Adult male rats were bilaterally implanted with EEG electrodes and LFPs recorded in each structure. Contrary to predictions, θ coherence averaged across "Early" or "Late" training sessions in the mPFC-HC, mPFC-mPFC, and HC-HC increased as a function of task learning. Coherence levels were also highest between the indirectly connected mPFC-dHC circuit, particularly during early training. Although mPFC postacquisition coherence remained higher with dHC than vHC, dynamic mPFC coherence patterns with both hippocampal poles across avoidance epochs were similar. In the 3 s before avoidance, a regional temporal sequence of transitory coherence peaks emerged between the mPFC-mPFC, the mPFC-HC, and then dHC-dHC. During this sequence, coherence within θ bandwidth fluctuated between epochs at distinct subfrequencies, suggesting frequency-specific roles for the propagation of task-relevant processing. On a second timescale, coherence frequency within and between the mPFC and hippocampal septotemporal axis change as a function of avoidance learning and cognitive demand. The results support a role for θ coherence subbandwidths, and specifically an 8- to 9-Hz mPFC θ signal, for generating and processing qualitatively different types of information in the organization of spatial avoidance behavior in the mPFC-HC circuit.

Perpendicular magnetization anisotropy induced dynamical coherence reduction in stripe domain film

We investigated the magnetization dynamics of the 350 nm permalloy film with in plane domain (IPD), stripe domain (SD), and labyrinth domain (LD) patterns. Experimental and micromagnetic simulation results showed that the change in magnetic domain structure from IPD to LD was due to the increasing perpendicular magnetic anisotropy (PMA) of the film. The magnetization dynamics indicated that the resonant modes of the film strongly depended on the magnetic domain structure. IPD films presented a uniform precession mode. The film with well-regular SD exhibited clear acoustic and optical resonance modes, and the formation of LD suppressed both resonance modes. Finally, the dynamics of magnetization dependent on the domain structure in these films were discussed by using the phenomenological resonance models.

Optical coherence elastography for assessing the influence of intraocular pressure on elastic wave dispersion in the cornea

The cornea is a highly specialized organ that relies on its mechanical stiffness to maintain its aspheric geometry and refractive power, and corneal diseases such as keratoconus have been linked to abnormal tissue stiffness and biomechanics. Dynamic optical coherence elastography (OCE) is a clinically promising non-contact and non-destructive imaging technique that can provide measurements of corneal tissue stiffness directly in vivo. The method relies on the concepts of elastography where shear waves are generated and imaged within a tissue to obtain mechanical properties such as tissue stiffness. The accuracy of OCE-based measurements is ultimately dependent on the mathematical theories used to model wave behavior in the tissue of interest. In the cornea, elastic waves propagate as guided wave modes which are highly dispersive and can be mathematically complex to model. While recent groups have developed detailed theories for estimating corneal tissue properties from guided wave behavior, the effects of intraocular pressure (IOP)-induced prestress have not yet been considered. It is known that prestress alone can strongly influence wave behavior, in addition to the associated non-linear changes in tissue properties. This present study shows that failure to account for the effects of prestress may result in overestimations of the corneal shear moduli, particularly at high IOPs. We first examined the potential effects of IOP and IOP-induced prestress using a combination of approximate mathematical theories describing wave behavior in thin plates with observations made from data published in the OCE literature. Through wave dispersion analysis, we deduce that IOP introduces a tensile hoop stress and may also influence an elastic foundational effect that were observable in the low-frequency components of the dispersion curves. These effects were incorporated into recently developed models of wave behavior in nearly incompressible, transversely isotropic (NITI) materials. Fitting of the modified NITI model with ex vivo porcine corneal data demonstrated that incorporation of the effects of IOP resulted in reduced estimates of corneal shear moduli. We believe this demonstrates that overestimation of corneal stiffness occurs if IOP is not taken into consideration. Our work may be helpful in separating inherent corneal stiffness properties that are independent of IOP; changes in these properties and in IOP are distinct, clinically relevant issues that affect the cornea health.

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.

Identification of venular capillary remodelling: a possible link to the development of periodontitis?

PurposeThe present study measured changes in arteriolar and venular capillary flow and structure in the gingival tissues during the development of plaque-induced gingival inflammation by combining dynamic optical coherence tomography (OCT), laser perfusion, and capillaroscopic video imaging.MethodsGingival inflammation was induced in 21 healthy volunteers over a 3-week period. Gingival blood flow and capillary morphology were measured by dynamic OCT, laser perfusion imaging, and capillaroscopy, including a baseline assessment of capillary glycocalyx thickness. Venular capillary flow was estimated by analysis of the perfusion images and mean blood velocity/acceleration in the capillaroscopic images. Readings were recorded at baseline and weekly over the 3 weeks of plaque accumulation and 2 weeks after brushing was resumed.ResultsPerfusion imaging demonstrated a significant reduction of gingival blood flow after 1 and 2 weeks of plaque accumulation (P<0.05), but by 3 weeks of plaque accumulation there was a more mixed picture, with reduced flow in some participants and increased flow in others. Participants with reduced flux at 3 weeks also demonstrated venular-type flow as determined by perfusion images and evidence of the development of venular capillaries as assessed by the velocity/acceleration ratio in capillaroscopic images. After brushing resumed, these venular capillaries were broken down and replaced by arteriolar capillaries.ConclusionsAfter 3 weeks of plaque accumulation, there was wide variation in microvascular reactions between the participants. Reduced capillary flow was associated with the development of venular capillaries in some individuals. This is noteworthy, as an early increase in venous capillaries is a key vascular feature of cardiovascular disease, psoriasis, Sjögren syndrome, and rheumatoid arthritis—diseases with a significant association with the development of severe gingival inflammation, which leads to periodontitis. Future investigations of microvascular changes in gingival inflammation might benefit from accurate capillary flow velocity measurements to assess the development of venular capillaries.

Aberrant Dynamics of Regional Coherence Measured by Resting-State fMRI in Children With Benign Epilepsy With Centrotemporal Spikes (BECTS).

Objective: To explore the dynamic features of intrinsic brain activity measured by fMRI in children with benign epilepsy with centrotemporal spikes (BECTS) and examine whether these indexes were associated with behaviors.Methods: We recruited 26 children with BECTS (10.35 ± 2.91 years) and 26 sex-, and age-matched (11.35 ± 2.51 years) healthy controls (HC) and acquired resting-state functional magnetic resonance imaging (rs-fMRI) and behavioral data. Dynamic regional homogeneity (dReHo), including mean and coefficient of variation (CV) metrics derived from the rs-fMRI data, and were compared between the BECTS and the HC groups.Results: Significantly decreased mean dReHo in bilateral supramarginal gyrus, left middle temporal gyrus (MTG.L), left postcentral gyrus and superior occipital gyrus were found in children with BECTS. Meanwhile, increased CV of dReHo in MTG.L and right fusiform in children with BECTS was revealed compared with HC. Further analyses of functional connectivity revealed decreased global signal FC existed in similar regions, linked with linguistic, social cognition, and sensorimotor processes, in children with BECTS compared with HCs. Moreover, the association analyses showed that the CV of dReHo in MTG.L was positively associated with age and a negative correlation was found between mean dReHo of MTG.L and disease duration. Besides, the CV of dReHo in MTG.L was found positively associated with the intelligence quotient (IQ) language scores and full IQ scores in children with BECTS, and the CV of dReHo in the left inferior temporal gyrus and Rolandic operculum were positively correlated with IQ operation scores and full IQ scores.Conclusion: Aberrant dynamic regional coherence in sensorimotor, linguistic, and lateral temporal regions suggests dynamical interplay that underlying cognitive performance in children with BECTS, suggesting an intrinsic dynamic mechanism for BECTS.

Co-movement of Banking Stress Across Emerging and Developed Economies: A Dynamic Factor Model and Wavelet Coherence Approach

This study develops a robust banking stability indicator for emerging and advanced economies and examines the linkage of banking stress across economies. We contribute by including interbank borrowings and banking sector volatility to measure contagious risk besides the traditional variables. Second, we use aggregate banking sector data for five countries (China, India, Japan, the UK and the USA) from 1998 to 2015 and employ dynamic factor model to develop the index. Results show higher stress levels in the UK and China, and all economies witness increased stress during the 2007–2009 crises, but the recovery phase varies. Finally, we use wavelet coherence analysis and find evidence of stress transmission from emerging economies to other emerging and advanced economies.

Nailfold Microvascular Imaging by Dynamic Optical Coherence Tomography in Systemic Sclerosis: A Case-Controlled Pilot Study

In systemic sclerosis, outcome measures of skin microvasculopathy are needed for both clinical trials and practice. The aim of this study was to determine whether dynamic-optical coherence tomography (D-OCT) is able to provide information on microvasculopathy compared with the current gold standard, nailfold videocapillaroscopy (NVC), in patients with systemic sclerosis. This case-controlled study included (i) 40 patients with systemic sclerosis, classified by NVC pattern in four age- and sex-matched groups (normal/nonspecific, early, active, late); (ii) a fifth group of 10 age- and sex-matched healthy controls. All participants underwent NVC and D-OCT. D-OCT images were compared with the corresponding NVC images. Reliability was assessed. D-OCT images visualized the corresponding NVC patterns. D-OCT microvascular flow density was different across the five NVC pattern groups (P= 0.0114) with a significant trend test (P= 0.0006). Microvascular flow density correlated with the NVC semiquantitative score (r=-0.7, P < 0.0001), number of abnormal shapes/mm (r= ‒0.3, P= 0.0264), and number of capillaries/mm (r= 0.6, P < 0.0001). Reliability was excellent (intraclass correlation coefficient > 0.9). In conclusion, in patients with systemic sclerosis, D-OCT provided qualitative and quantitative information on nailfold microvasculopathy, showing a correlation between microvascular flow density and NVC scores. The development of D-OCT as a standardized imaging technique could provide a quantitative outcome measure in clinical trials and practice.

Quantitative evaluation of the dynamic activity of HeLa cells in different viability states using dynamic full-field optical coherence microscopy

Dynamic full-field optical coherence microscopy (DFFOCM) was used to characterize the intracellular dynamic activities and cytoskeleton of HeLa cells in different viability states. HeLa cell samples were continuously monitored for 24 hours and compared with histological examination to confirm the cell viability states. The averaged mean frequency and magnitude observed in healthy cells were 4.79±0.5 Hz and 2.44±1.06, respectively. In dead cells, the averaged mean frequency was shifted to 8.57±0.71 Hz, whereas the magnitude was significantly decreased to 0.53±0.25. This cell dynamic activity analysis using DFFOCM is expected to replace conventional time-consuming and biopsies-required histological or biochemical methods.

Effects of early-life seizures on coordination of hippocampal-prefrontal networks: influence of sex and dynamic brain states

The development and maturation of neurological circuits associated with learning and memory can be negatively impacted by early life seizures (ELS). While this has been a long-established concept, the pathophysiological mechanism underpinning ELS induced cognitive deficits is not as well understood. Further, the influences of crucial variables such as sex on cognitive outcomes following ELS have not been explored. We hypothesized that when compared to their control (CTL) counterparts, ELS rats would display impairments in spatial cognition as the result of impaired dynamic coordination between the hippocampus and medial prefrontal cortex (mPFC). To test this, flurothyl seizures were induced in both male and female rats at postnatal day (P) 15. We then assessed spatial cognition of the animals as adults using an active avoidance task. After initial testing, the animals were implanted with microwire tetrodes in the mPFC and CA1 of the hippocampus so that single cells and local field potentials could be recorded and analyzed during subsequent active avoidance testing and during sleep. We found that ELS male animals exhibited impairments in the active avoidance task learning while ELS female animals were unaffected. Control female rats had an increased mPFC-hippocampus coherence compared to control males across all bandwidths during active avoidance. ELS males that did not learn the task during training showed significantly lower coherences in all bandwidths than all other groups. ELS male non-learners also showed decreased dynamic coherence and cell modulation specifically in the 8–9 Hz range. Additionally, recordings taking during sleep showed that ELS male non-learners had less coherence and phase locking compared to all other groups. In male animals, ELS decreased hippocampus-mPFC coherence during active cognition and slow wave sleep while female rats showed no differences in these measures. The ELS animals that exhibited the lowest dynamic coherence were also the animals that performed the worst while learning the active avoidance task. Taken in concert, these results show that there may be a gender dependent influence on the effect of critical period seizures on spatial cognition. Furthermore, incoherent theta signal coordination between the mPFC and hippocampus presents a mechanism for adverse cognitive outcomes following ELS.

Vascular characteristics of port wine birthmarks as measured by dynamic optical coherence tomography

Port wine birthmarks (PWBs) are congenital capillary malformations. Vessel characteristics, such as diameter and depth, may impact presentation and outcomes. They can be imaged using dynamic optical coherence tomography, a high-resolution, noninvasive imaging method. We conducted a cross-sectional observational study to measure invivo vascular characteristics as a function of PWB color. Patients undergoing treatment for PWB were recruited from 3 sites. PWBs were classified by color. Dynamic optical coherence tomography images with calculations were obtained. One hundred eight patients were enrolled. Mean age correlated with PWB color, with birthmarks being lighter in younger patients and darker in older patients (P<.01). Mean superficial plexus depth was significantly shallower in purple PWBs than in pink PWBs. Color was not associated with significant differences in mean superficial vessel density or diameter. Among pink PWBs, each 10-year increase in age was associated with a 10.6-μm increase in superficial plexus depth. Among purple PWBs, each 10-year increase in age was associated with a 16.2-μm reduction in superficial plexus depth. In lesions without prior treatment, vessel density was 12.7% lower in purple PWBs than in pink PWBs. Superficial vessels of purple PWBs were significantly closer to the epidermis than those of pink PWBs, which might impact optimal laser parameters.

Correlation of choriocapillaris hemodynamic data from dynamic indocyanine green and optical coherence tomography angiography

To investigate the correlation between posterior pole choroidal blood flow evaluated with digital subtraction indocyanine green angiography and enface optical coherence tomography angiography (OCTA). Imaging in animal study. The anatomy of 2 cynomogulus monkeys was studied. Each monkey was given a 0.75 mg/kg injection of indocyanine green in the saphenous vein. The dynamic angiographic filling sequence was recorded at 15 frames per second using the Heidelberg Spectralis. After image registration, sequential frame subtraction was used to image the dye front moving through the choroid. The OCTA was obtained by frame averaging nine separate choriocapillaris slab flow images obtained from the Zeiss Plex Elite 9000. Posterior pole choriocapillaris filling pattern in relation to the choriocapillaris anatomy as imaged by OCTA. In the posterior pole, the choriocapillaris fills in the pattern of discrete units with variable sizes and shapes. The cycle of dye filling begins in the peripapillary area and progresses toward the periphery in a wavelike manner. This filling pattern repeats in a cyclical manner, consistent with the cardiac cycle. OCTA shows a uniform mesh of vessels. While OCTA shows a uniform meshwork appearance of the choriocapillaris, the dynamic dye angiography suggests an irregular configuration of functional units partitioned by pressure gradients as opposed to structural boundaries. Disturbance of local perfusion pressure within choroidal vasculature may result in abnormal flow patterns, which could be evaluated in the clinic using commercially available equipment.

Non-invasive Clinical Measurement of Ocular Rigidity and Comparison to Biomechanical and Morphological Parameters in Glaucomatous and Healthy Subjects.

Purpose: To assess ocular rigidity using dynamic optical coherence tomography (OCT) videos in glaucomatous and healthy subjects, and to evaluate how ocular rigidity correlates with biomechanical and morphological characteristics of the human eye.Methods: Ocular rigidity was calculated using Friedenwald's empirical equation which estimates the change in intraocular pressure (IOP) produced by volumetric changes of the eye due to choroidal pulsations with each heartbeat. High-speed OCT video was utilized to non-invasively measure changes in choroidal volume through time-series analysis. A control-case study design was based on 23 healthy controls and 6 glaucoma cases. Multiple diagnostic modalities were performed during the same visit including Spectralis OCT for nerve head video, Pascal Dynamic Contour Tonometry for IOP and ocular pulse amplitude (OPA) measurement, Corvis ST for measuring dynamic biomechanical response, and Pentacam for morphological characterization.Results: Combining glaucoma and healthy cohorts (n = 29), there were negative correlations between ocular rigidity and axial length (Pearson R = −0.53, p = 0.003), and between ocular rigidity and anterior chamber volume (R = −0.64, p = 0.0002). There was a stronger positive correlation of ocular rigidity and scleral stiffness (i.e., stiffness parameter at the highest concavity [SP-HC]) (R = 0.62, p = 0.0005) compared to ocular rigidity and corneal stiffness (i.e., stiffness parameter at the first applanation [SP-A1]) (R = 0.41, p = 0.033). In addition, there was a positive correlation between ocular rigidity and the static pressure-volume ratio (P/V ratio) (R = 0.72, p < 0.0001).Conclusions: Ocular rigidity was non-invasively assessed using OCT video and OPA in a clinic setting. The significant correlation of ocular rigidity with biomechanical parameters, SP-HC and P/V ratio, demonstrated the validity of the ocular rigidity measurement. Ocular rigidity is driven to a greater extent by scleral stiffness than corneal stiffness. These in vivo methods offer an important approach to investigate the role of ocular biomechanics in glaucoma.

Quantifying dynamical coherence with coherence measures

Quantum coherence, like entanglement, is a fundamental resource in quantum information. In recent years, remarkable progress has been made in formulating resource theory of coherence from a broader perspective. The notions of block-coherence and POVM-based coherence have been established. Certain challenges, however, remain to be addressed. It is difficult to define incoherent operations directly, without requiring incoherent states, which proves a major obstacle in establishing the resource theory of dynamical coherence. In this paper, we overcome this limitation by introducing an alternate definition of incoherent operations induced via coherence measures and quantify dynamical coherence based on this definition. Finally, we apply our proposed definition to quantify POVM-based dynamical coherence.

Optical coherence tomography quantifying photo aging: skin microvasculature depth, epidermal thickness and UV exposure.

Photo aging predominantly occurs in the face, neck and hands due to UVA and UVB irradiation. It is associated with skin cancer and histological studies indicate thinning of the epidermis and elastosis occurs. Dynamic Optical coherence tomography (D-OCT) is a non-invasive imaging tool able to visualize the epidermis and upper dermis and its blood vessels as well as to evaluate epidermal thickness (ET) and blood flow. To investigate ET and blood vessel depth using D-OCT in human subjects correlated to UV exposure. We evaluated data from 249 healthy adults, that had D-OCT-scans conducted at four different regions (forehead, neck, arm and hand) and correlated ET and blood vessel depth with occupational UV exposure (total standard erythema dose, Total SED), season and demographic data. Regional differences in ET and blood vessel depth were found (p values < 0.001). Multiple linear regressions showed a seasonal effect on both ET (- 0.113 to - 0.288µm/day, p values < 0.001) and blood vessel depth (0.168-0.347µm/day, p values < 0.001-0.007) during August-December. Significant age-related decrease of ET was seen in forehead, arm and hand (0.207-0.328µm/year, p values = 0.002-0.18) and blood vessel depth in forehead (0.064-0.553µm/year, p values = 0.01-0.61). Males had thicker epidermis (3.92-10.93µm, p values = 0.002-0.15). Changing seasons are a major predictor of both ET and blood vessel depth, showing strongest effect in non-exposed areas, suggesting a systemic effect, possibly due to seasonal vitamin D fluctuation. Sex, age and occupational UV exposure affect ET. This study demonstrated the feasibility of D-OCT to evaluate epidermal thickness and blood vessel depth.

Elasticity Changes in the Crystalline Lens during Oxidative Damage and the Antioxidant Effect of Alpha-Lipoic Acid Measured by Optical Coherence Elastography

Age-related cataracts are one of the most prevalent causes of visual impairment around the world. Understanding the mechanisms of cataract development and progression is essential to enable early clinical diagnosis and treatment to preserve visual acuity. Reductive chemicals are potential medicines effective on cataract treatment. In this work, we investigated the cataract-induced oxidative damage in the crystalline lens and a kind of reductant, α-lipoic acid (ALA), ability to reduce the damage. We created oxidative environment to investigate the relationship between the progression of oxidative cataract and lenticular biomechanical properties measured by dynamic optical coherence elastography in porcine crystalline lenses ex vivo. The efficacy of ALA to minimize the stiffening of the lens was also quantified. The results showed a significant increase in Young’s modulus of the lens due to the formation of the oxidative cataract. We found a statistically significant difference between Young’s modulus of the lenses stored in phosphate-buffered saline and ALA solution after incubation in H2O2 solution for 3 h (43.0 ± 9.0 kPa versus 20.7 ± 3.5 kPa, respectively). These results show that the lens stiffness increases during oxidative cataract formation, and ALA has the potential to reverse stiffening of the lens caused by oxidative damage.

Image-text discourse coherence relation discoveries on multi-image and multi-text documents

The occurrences of the image-text pairs are common in social media such as image captions, image annotations, and cooking instructions. However, the links between images and texts as well as the coherence relationship among them are always implicit. We developed a multi-modal approach by firstly establishing the links between image and text in an unsupervised way, then discovered their coherence relations through computational models of discourse to improve the consistency and quality of the images and their corresponding texts and also explore a dynamic and flexible image-text coherence relation.

Blood Vessel Density Measured Using Dynamic Optical Coherence Tomography is a Tool for Wound Healers.

Dynamic optical coherence tomography (D-OCT) is a relatively new technique that may be used to study the substructures in the retina, in the skin and its microcirculation. Furthermore, D-OCT is a validated method of imaging blood flow in skin microcirculation. The skin around venous and mixed arterio-venous ulcers was imaged and found to have tortuous vessels assumed to be angiogenic sprouts, and classified as dots, blobs, coils, clumps, lines, and curves. When these images were analyzed and measurements of vessel density were made, it was observed that the prevalence of coils and clumps in wound borders was significantly greater compared with those at wound centers. This reinforced the belief of inward growth of vessels from wound edge toward wound center which, in turn, reposed confidence in following the wound edge to study healing. D-OCT imaging permits the structure and the function of the microcirculation to be imaged, and vessel density measured. This offers a new vista of skin microcirculation and using it, to better understand angiogenesis in chronic wounds.

Electron-Vibration Entanglement of Resonating Dimers in Quantum Transport.

Electron transport in a single molecule resulting from the superposition of its vibronic states depends on the coupling strength with the metallic leads. However, dynamical coherence and Fermionic correlation in molecule-molecule and molecule-lead coupling necessitates a critical approach to treat the current and its noise level, especially in the presence of a variable external bias for temperature-dependent conduction. Primarily, this work is a generalization of the theoretical approach of the atomic dimers to incorporate the effect of vibrational modes in current and conductance characteristics. The variation of current and differential conductance due to the external bias reveals a vibrational Coulomb blockade structure corresponding to the functioning vibrational mode in the system. The numerical demonstration for a diverse class of molecules generically shows that electron-vibration interaction can quantitatively predict the nature of coherent electron transport and current noise. Secondly, an attempt has been made to illustrate the effect of magnitude of coherence-induced noise suppression of current as a signature of electron-vibration entanglement. Finally, temperature-dependent conductance of the molecular junction in dimer structure has been estimated along with the peak shifts due to the applied gate voltage.

Two-dimensional (2D) dynamic vibration optical coherence elastography (DV-OCE) for evaluating mechanical properties: a potential application in tissue engineering.

Mechanical properties in tissues are an important indicator because they are associated with disease states. One of the well-known excitation sources in optical coherence elastography (OCE) to determine mechanical properties is acoustic radiation force (ARF); however, a complicated focusing alignment cannot be avoided. Another excitation source is a piezoelectric (PZT) stack to obtain strain images via compression, which can affect the intrinsic mechanical properties of tissues in tissue engineering. In this study, we report a new technique called two-dimensional (2D) dynamic vibration OCE (DV-OCE) to evaluate 2D wave velocities without tedious focusing alignment procedures and is a non-contact method with respect to the samples. The three-dimensional (3D) Fourier transform was utilized to transfer the traveling waves (x, y, t) into 3D k-space (kx, ky, f). A spatial 2D wavenumber filter and multi-angle directional filter were employed to decompose the waves with omni-directional components into four individual traveling directions. The 2D local wave velocity algorithm was used to calculate a 2D wave velocity map. Six materials, two homogeneous phantoms with 10 mm thickness, two homogeneous phantoms with 2 mm thickness, one heterogeneous phantom with 2 mm diameter inclusion and an ex vivo porcine kidney, were examined in this study. In addition, the ARF-OCE was used to evaluate wave velocities for comparison. Numerical simulations were performed to validate the proposed 2D dynamic vibration OCE technique. We demonstrate that the experimental results were in a good agreement with the results from ARF-OCE (transient OCE) and numerical simulations. Our proposed 2D dynamic vibration OCE could potentially pave the way for mechanical evaluation in tissue engineering and for laboratory translation with easy-to-setup and contactless advantages.