Motion Of Red Blood Cells Research Articles

Eulerian- lagrangian dense discrete phase model (DDPM) of stenotic LAD coronary arteries in comparison with single phase modeling

In computational fluid dynamic studies related to blood flow, investigating the behavior of blood particles is crucial, especially red blood cells as they constitute a significant proportion of blood particles. Additionally, studying red blood cell movements is necessary, especially in stenotic artery geometries. A new multiphase scheme was utilized to demonstrate the effect of red blood cells on hemodynamics in complex coronary arteries and investigate the consequence of their motion. To investigate the effect of red blood cell movement on flow, the dense discrete phase model (DDPM) was used. This simulation was performed in 3D coronary arteries with different degrees of stenosis, utilizing blood pressure as inlet and outlet boundary conditions while assuming the arterial wall to be rigid. The model prediction shows good agreement with experimental data. Velocity values were comparable in both single-phase and two-phase flow simulations, but the shear stress in two-phase modeling had higher values. In the two-phase DDPM modeling, the recirculation areas indicated a higher probability of atherosclerosis plaque re-formation in the pre-stenosis area compared to the stenosis and post-stenosis areas. The DDPM model was found to be more effective in obtaining shear stress values in the artery. Additionally, this model provides good results compared to the single-phase model in investigating the movement of particles along the artery as well as recirculation areas that lead to the deposition of particles.

Interferometric near-infrared spectroscopy (iNIRS) reveals that blood flow index depends on wavelength.

Blood flow index (BFI) is an optically accessible parameter, with unit distance-squared-over-time, that is widely used as a proxy for tissue perfusion. BFI is defined as the dynamic scattering probability (i.e. the ratio of dynamic to overall reduced scattering coefficients) times an effective Brownian diffusion coefficient that describes red blood cell (RBC) motion. Here, using a wavelength division multiplexed, time-of-flight- (TOF) - resolved iNIRS system, we obtain TOF-resolved field autocorrelations at 773 nm and 855 nm via the same source and collector. We measure the human forearm, comprising biological tissues with mixed static and dynamic scattering, as well as a purely dynamic scattering phantom. Our primary finding is that forearm BFI increases from 773 nm to 855 nm, though the magnitude of this increase varies across subjects (23% ± 19% for N = 3). However, BFI is wavelength-independent in the purely dynamic scattering phantom. From these data, we infer that the wavelength-dependence of BFI arises from the wavelength-dependence of the dynamic scattering probability. This inference is further supported by RBC scattering literature. Our secondary finding is that the higher-order cumulant terms of the mean squared displacement (MSD) of RBCs are significant, but decrease with wavelength. Thus, laser speckle and related modalities should exercise caution when interpreting field autocorrelations.

Mathematical modeling of the magnetic field generated by a network of parallel narrow capillaries

A three-dimensional mathematical model was constructed that simulates the movement of red blood cells (RBCs) through narrow capillaries. The charges located on RBC membrane generate a magnetic field (MF) in the surrounding space. The movement of erythrocytes along a capillary network built from parallel narrow capillaries is considered. The distribution of magnetic field strength (MFS) in planes parallel to the plane of the capillary network has been constructed. In the plane of a parallel capillary network, the dependence of the maximum and minimum values of MFS on the distance between the centers of the capillaries has been determined. It is shown that as the distance between the capillaries decreases, the magnitude of MFS in the plane parallel to the plane in which the capillaries lie increases, and the difference between the maximum and minimum values of MFS decreases.

Quantitative analyses of RBC movement in whole blood exposed to DC and ELF electric field.

For the study of biological effects of direct current (DC) and extremely low frequency (ELF) electric fields, we have quantitatively analyzed red blood cell (RBC) movement in whole blood. Considering the inhomogeneous distribution of electric fields in vivo, five different electric field distributions were generated under a microscope. For theoretical analyses, we assumed electrophoresis and dielectrophoresis as basic motive forces and obtained the spatial distribution of blood cell velocity. The RBC velocity was measured using video image analysis. The spatial dependence of the velocity showed good agreement with that predicted by theoretical analysis. This result suggests the validity of the theoretical model based on electrophoresis and dielectrophoresis for the study of ELF electric field exposure to inhomogeneous animal and human bodies. Next, using the same measurement system, we attempted to find the electric field strength at which these effects occur. The threshold values were found to be 0.40and 1.6 kV/m, respectively, for DC and AC electric field exposures. Furthermore, we investigated the reproducibility of the field effects in more realistic conditions of human exposure. The RBCs in microchannels were exposed to the electric field generated in capacitive coupling using electrodes separated by an air gap. Even in the new condition, similar effects were observed, which also verified the validity of the analysis described above. These results will provide useful information for the safety assessment of field exposure and for the future biomedical applications of electric fields to manipulate RBCs in vivo.

Unraveling the motion and deformation characteristics of red blood cells in a deterministic lateral displacement device

Deterministic Lateral Displacement (DLD) device has gained widespread recognition and trusted for filtering blood cells. However, there remains a crucial need to explore the complex interplay between deformable cells and flow within the DLD device to improve its design. This paper presents an approach utilizing a mesoscopic cell-level numerical model based on dissipative particle dynamics to effectively capture this complex phenomenon. To establish the model’s credibility, a series of numerical simulations were conducted and the numerical results were validated with nominal experimental data from the literature. These include single cell stretching experiment, comparisons of the morphological characteristics of cells in DLD, and comparison the specific row-shift fraction of DLD required to initiate the zigzag mode. Additionally, we investigate the effect of cell rigidity, which serves as an indicator of cell health, on average flow velocity, trajectory, and asphericity. Moreover, we extend the existing theory of predicting zigzag mode for solid spherical particles to encompass the behavior of red blood cells. To achieve this, we introduce a new concept of effective diameter and demonstrate its applicability in providing highly accurate predictions across a wide range of conditions.

Evaluation of the Superficial Collecting Lymph Vessels’ Vasa Vasorum in Lymphoedematous Limbs Using Video Capillaroscopy

The pre-collecting and collecting lymph vessels have smooth muscle cells, and sufficient perfusion is vital to maintain their function. Although the vasa vasorum of the collecting lymph vessels (VVCL) have been histologically investigated, little is known about their physiology. This study aimed to investigate the relationship between morphology and blood flow of the VVCL in lymphoedematous limbs. Medical records of lower extremity lymphoedema patients who underwent video capillaroscopy observation during supermicrosurgical lymphaticovenous anastomosis (LVA) surgery were reviewed. The collecting lymph vessels, dissected for LVA, were examined under video capillaroscopy (GOKO Bscan-ZD, GOKO Imaging Devices Co., Japan) with a magnification of 175x and 620x. Blood flow velocity of the VVCL was calculated by measuring the red blood cell movement using software (GOKO-VIP ver. 1.0.0.4, GOKO Imaging Devices Co., Japan). Based on the video capillaroscopy findings, the VVCL were grouped according to their morphology; the VVCL morphology types and blood flow velocity were then compared according to lymphosclerosis severity grade. Sixty-seven lymph vessels in 20 lower extremity lymphoedema patients were evaluated, including s0 in 19 (28.4%), s1 in 34 (50.7%), s2 in 10 (14.9%), and s3 in four (6.0%) lymph vessels. The VVCLs were grouped into four types: type 1 (n = 4), type 2 (n = 37), type 3 (n = 19), and type 4 (n = 7). Blood flow velocity of the VVCL ranged 0 - 189.3 μm/sec (average 26.40 μm/sec). There were statistically significant differences in VVCL morphology (p < .001) and blood flow velocity (p < .001) according to lymphosclerotic severity. Vasa vasorum of the collecting lymph vessels could be grouped into four types with different characteristics. Morphological and physiological changes of the VVCL were related to sclerotic changes of the collecting lymph vessels.

The Microvascular Health Status Predicts Radio-Induced Acute Toxicities in Breast, Prostate and Head and Neck Cancer Patients

investigate the role of healthy/unhealthy microcirculation in predicting acute toxicity (tox) after breast (BC), prostate (PC) and Head & Neck (HNC) cancer RT. We enrolled BC patients (pts) treated with hypofractionated-RT after conservative surgery (42.4 Gy + 10 Gy boost to tumor bed), PC pts receiving radical-RT (65 Gy / 25 fractions), HNC pts treated with conventional RT (54-70 Gy @ 1.8-2 Gy/fr) or moderately hypofractionation (56.1-69.96 Gy @ 1.7-2.12 Gy/fr). We assessed baseline sublingual-microvasculature (MV) health status before RT using a sidestream dark-field camera coupled to the GlycoCheck™ software. The system records videos showing the live movement of red blood cells (RBCs) in the microvessels. It computes 5 functional parameters: (a) perfused boundary region (PBR) estimating the penetration of RBCs into the permeable part of the endothelial glycocalyx (higher PBR values result from damaged glycocalyx, indicating impaired microcirculation); (b) density of capillaries (1/mm2); (c) blood flow in the recorded area (103 μm3/s/mm2); (d) recruitment capacity (quantifying the ability to recruit additional capillaries); (e) a global MV_HealthScore (MVHS), higher values indicate healthier MV. MVHS is computed by weighting information from the previous parameters. The computation of MVHS needs a prolonged video acquisition not reached by less compliant patients. Endpoint for this analysis was acute tox. We selected a clinically relevant tox endpoint for each cancer site: grade≥2 erythema (G2+E) for BC, any grade≥3 tox (G3Tox) for HNC and persistent grade≥1 tox simultaneously present in gastrointestinal and genitourinary domains (G1+GIGU) for PC. We used logistic regression to assess MV functional parameters' association with toxicity. We evaluated 63 BC, 38 PC, 39 HNC pts. 77 (55%) had an evaluation for MVHS. 23/63 BC pts presented with G2+E, 12/38 PC pts with G1+GIGU, 12/39 HNC pts with G3Tox. Average MVHS was 3.6, 3.2, 2.7 in BC, HNC and PC, respectively (P>0.15). The MVHS associated with tox: healthy MV protects from tox (continuous, OR = 0.66 for 1 point increase, p = 0.01, AUC 0.69). Categorizing pts as low MVHS (<2.5), average MVHS (2.5-6.5) and high MVHA (>6.5), the observed toxicity rates in the 3 classes were 50%, 26%, 0% (p = 0.02). Also, a 3-variate model including the separated functional parameters predicted tox (AUC 0.67) on the 144 pts: higher PBR is a risk (OR = 7.6), higher capillary density protects (Logarithm, OR 0.002), higher blood flow is a risk (Logarithm, OR = 14.2). These data suggest an interaction of compromised MV with repair mechanisms. The MVHS model predicts acute toxicity in BC/PC/HN pts proving (i) a quantitative relationship between MV state and radio-susceptibility and (ii) in an organ-agnostic way. The systemic functional information derived by the sublingual microscope could boost the personalization of predictive models and tailor them to the single-patient functional status. Funded by AIRC IG 21479.

Optical Flow-Based Full-Field Quantitative Blood-Flow Velocimetry Using Temporal Direction Filtering and Peak Interpolation.

The quantitative measurement of the microvascular blood-flow velocity is critical to the early diagnosis of microvascular dysfunction, yet there are several challenges with the current quantitative flow velocity imaging techniques for the microvasculature. Optical flow analysis allows for the quantitative imaging of the blood-flow velocity with a high spatial resolution, using the variation in pixel brightness between consecutive frames to trace the motion of red blood cells. However, the traditional optical flow algorithm usually suffers from strong noise from the background tissue, and a significant underestimation of the blood-flow speed in blood vessels, due to the errors in detecting the feature points in optical images. Here, we propose a temporal direction filtering and peak interpolation optical flow method (TPIOF) to suppress the background noise, and improve the accuracy of the blood-flow velocity estimation. In vitro phantom experiments and in vivo animal experiments were performed to validate the improvements in our new method.

Separation of Cells From Plasma by Means of Ultrasonics

This paper presents an analysis of use of ultrasonic standing wave in cell separation from bodily fluids based on the example of erythrocyte separation from plasma. It describes movement of red blood cells in plasma under the influence of the acoustic field (whose forces result from interaction of red blood cells with plasma as the vibrating medium) and under the influence of resistance forces in Stokes’ and Oseen’s approximation. The general properties of solutions of the motion equation are given. The solutions for the parameters of the ultrasonic wave and blood cells which are interesting in terms of practical applications in medical diagnostics are discussed. Time constants of the cell transportation to the regions of stable equilibrium in the field of ultrasonic standing wave are estimated. The formulas which determine the time needed to obtain the assumed concentration increase in plasma in nodes and/or anti-nodes of the standing wave are derived.

Influence of the vessel wall geometry on the wall-induced migration of red blood cells.

The geometry of the blood vessel wall plays a regulatory role on the motion of red blood cells (RBCs). The overall topography of the vessel wall depends on many features, among which the endothelial lining of the endothelial surface layer (ESL) is an important one. The endothelial lining of vessel walls presents a large surface area for exchanging materials between blood and tissues. The ESL plays a critical role in regulating vascular permeability, hindering leukocyte adhesion as well as inhibiting coagulation during inflammation. Changes in the ESL structure are believed to cause vascular hyperpermeability and entrap immune cells during sepsis, which could significantly alter the vessel wall geometry and disturb interactions between RBCs and the vessel wall, including the wall-induced migration of RBCs and the thickening of a cell-free layer. To investigate the influence of the vessel wall geometry particularly changed by the ESL under various pathological conditions, such as sepsis, on the motion of RBCs, we developed two models to represent the ESL using the immersed boundary method in two dimensions. In particular, we used simulations to study how the lift force and drag force on a RBC near the vessel wall vary with different wall thickness, spatial variation, and permeability associated with changes in the vessel wall geometry. We find that the spatial variation of the wall has a significant effect on the wall-induced migration of the RBC for a high permeability, and that the wall-induced migration is significantly inhibited as the vessel diameter is increased.

Study of red blood cells and particles in stenosed microvessels using coupled discrete and continuous forcing immersed boundary methods

A computational study of the blood flow in a stenosed microvessel is presented using coupled discrete ghost-cell and continuous-forcing immersed boundary methods. This study focuses on studying platelet behaviors near the stenosis with deformable red blood cells (RBCs). The influence of varying hematocrit, area blockage, stenosis shape, and driving force on flow characteristics, RBCs, and particle behaviors is considered. Distinct flow characteristics are observed in stenosed microvessels in the presence of RBCs. The motion of RBCs is the major cause of time-dependent oscillations in flow rates, while the contribution of particles to the fluctuations is negligible. However, this effect decreases when the stenosis is elongated in the axial direction. Interestingly, as the hematocrit level increases, downstream particles move closer to the vessel wall due to the enhanced shear-induced lift force resulting from the interaction among RBCs and particles. Furthermore, it is observed that geometrical changes in the stenosis have a more significant impact on the axial profile of particle concentration compared to changes in hematocrit or driving force. An asymmetric stenosis leads to asymmetric profiles in the flow velocity and the distribution of cells and particles due to the geometric focusing effect of the stenosis. There is no significant change in flow rates until a blockage of 0%–50%, but a sudden increase in the root mean square of flow rates occurs at an 80% blockage. This study contributes to our understanding of the rheological behaviors of RBCs and rigid particles in a stenosed microvessel under various hemodynamic conditions.

Autocorrelation analysis-based OCT velocimetry for axial blood flow velocity imaging of the cerebral capillary network.

The accurate measurement of blood flow velocity in the capillary network is challenging due to the small size of the vessels and the slow flow of red blood cells (RBCs) within the vessel. Here, we introduce an autocorrelation analysis-based optical coherence tomography (OCT) method that takes less acquisition time to measure the axial blood flow velocity in the capillary network. The axial blood flow velocity was obtained from the phase change in the decorrelation period of the first-order field autocorrelation function (g1) of the OCT field data, which was acquired with M-mode acquisition (repeated A-scans). The rotation center of g1 in the complex plane was first re-centralized to the origin, then the phase change due to the movement of RBCs was extracted in the g1 decorrelation period which is usually 0.2-0.5 ms. In phantom experiments, the results suggest that the proposed method could accurately measure the axial speed with a wide range of 0.5-15 mm/s. We further tested the method on living animals. Compared with the phase-resolved Doppler optical coherence tomography (pr-DOCT), the proposed method can obtain robust axial velocity measurements with more than five times shorter acquisition time.

AI-based analysis of 3D position and orientation of red blood cells using a digital in-line holographic microscopy.

The morphological and mechanical characteristics of red blood cells (RBCs) largely vary depending on the occurrence of hematologic disorders. Variations in the rheological properties of RBCs affect the dynamic motions of RBCs, especially their rotational behavior. However, conventional techniques for measuring the orientation of biconcave-shaped RBCs still have some technical limitations, including complicated optical setups, complex post data processing, and low throughput. In this study, we propose a novel image-based technique for measuring 3D position and orientation of normal RBCs using digital in-line holographic microscopy (DIHM) and artificial intelligence (AI). Formaldehyde-fixed RBCs are immobilized in coagulated polydimethylsiloxane (PDMS). Holographic images of RBCs positioned at various out-of-plane angles are acquired by precisely manipulating the PDMS-trapped RBC sample attached to a 4-axis optical stage. With the aid of deep learning algorithms for data augmentation and regression analysis, the out-of-plane angle of RBCs is directly predicted from the captured holographic images. The 3D position and in-plane angle of RBCs are acquired by employing numerical reconstruction and ellipse detection methods. Combining these digital image processing techniques, the 3D positional and orientational information of each RBC recorded in a single holographic image is measured within 23.5 and 3.07s, respectively. The proposed AI-based DIHM technique that can extract the 3D position, orientation, and morphology of individual RBCs would be utilized to analyze the dynamic translational and rotational motions of abnormal RBCs with hematologic disorders in shear flows through further research.

RESEARCH NEW GENERATION ULTRASOUND TECHNOLOGIES IN BLOOD FLOW MONITORING

Currently, ultrasound machines are widely used in hospitals for the first diagnosis of various pathologies. There is also an ultrasound Doppler method to determine and monitor blood flow. Through this method, it is possible to get information about the general condition of the veins and whether there are any problems during the examination of the veins in the clinic. But, it does not have the ability to continuously monitor the condition of the veins. Continuous monitoring of blood flow rate will facilitate the work of doctors during post-operative monitoring or diagnosis of the patient's condition. At the same time, traditional ultrasound transducers may not be comfortable for post-operative examinations. In this article, a number of difficulties encountered during examinations conducted using a conventional ultrasound machine were investigated. At the same time, as a solution to these difficulties, one of the newest technologies of the modern era, the new generation ultrasound machine “USM patch”, its main features and advantages were discussed. This device, based on the working principle of the Doppler effect, is suitable for continuous monitoring of the absolute speed of blood flow in the arteries of the deep layers. It is lightweight, small in size, and has the potential to increase the accuracy and quality of the examination. Keywords: Blood Flow Sensor, movement of red blood cells, Doppler effect, ultrasound machine, Doppler ultrasound patch, biodegradable sensor, automatic

Tissue Oxygenation Around Capillaries: Effects of Hematocrit and Arteriole Oxygen Condition.

Oxygen transfer in the microvasculature is a complex phenomenon that involves multiple physical and chemical processes and multiple media. Hematocrit, the volume fraction of red blood cells (RBCs) in blood, has direct influences on the blood flow as well as the oxygen supply in the microcirculation. On the one hand, a higher hematocrit means that more RBCs present in capillaries, and thus, more oxygen is available at the source end. On the other hand, the flow resistance increases with hematocrit, and therefore, the RBC motion becomes slower, which in turn reduces the influx of oxygen-rich RBCs entering capillaries. Such double roles of hematocrit have not been investigated adequately. Moreover, the oxygen-hemoglobin dissociation rate depends on the oxygen tension and hemoglobin saturation of the cytoplasm inside RBCs, and the dissociation kinetics exhibits a nonlinear fashion at different oxygen tensions. To understand how these factors and mechanisms interplay in the oxygen transport process, computational modeling and simulations are favorite since we have a good control of the system parameters and also we can access to the detailed information during the transport process. In this study, we conduct numerical simulations for the blood flow and RBC deformation along a capillary and the oxygen transfer from RBCs to the surrounding tissue. Different values for the hematocrit, arteriole oxygen tension, tissue metabolism rate and hemoglobin concentration and affinity are considered, and the simulated spatial and temporal variations of oxygen concentration are analyzed in conjunction with the nonlinear oxygen-hemoglobin reaction kinetics. Our results show that there are two competing mechanisms for the tissue oxygenation response to a hematocrit increases: the favorite effect of the higher RBC density and the negative effect of the slower RBC motion. Moreover, in the low oxygen situations with RBC oxygen tension less than 50mmHg at capillary inlet, the reduced RBC velocity effect dominates, resulting in a decrease in tissue oxygenation at higher hematocrit. On the opposite, for RBC oxygen tension higher than 50mmHg when entering the capillary, a higher hematocrit is beneficial to the tissue oxygenation. More interestingly, the pivoting arteriole oxygen tension at which the two competing mechanisms switch dominance on tissue oxygenation becomes lower for higher oxygen-hemoglobin affinity and lower hemoglobin concentration. This observation has also been analyzed based on the oxygen supply from RBCs and the oxygen-hemoglobin reaction kinetics. The results and discussions presented in this article could be helpful for a better understanding of oxygen transport in microcirculation.

High-speed measurement of retinal arterial blood flow in the living human eye with adaptive optics ophthalmoscopy.

We present a technique to measure the rapid blood velocity in large retinal vessels with high spatiotemporal resolution. Red blood cell motion traces in the vessels were non-invasively imaged using an adaptive optics near-confocal scanning ophthalmoscope at a frame rate of 200 fps. We developed software to measure blood velocity automatically. We demonstrated the ability to measure the spatiotemporal profiles of the pulsatile blood flow with a maximum velocity of 95-156 mm/s in retinal arterioles with a diameter >100 µm. High-speed and high-resolution imaging increased the dynamic range, enhanced sensitivity, and improved the accuracy when studying retinal hemodynamics.

Multi-level optical angiography for photodynamic therapy.

Blood flow imaging is widely applied in photodynamic therapy (PDT) to provide vascular morphological and statistical parameters. This approach relies on the intensity of time-domain signal differences between blood vessels and background tissues; therefore, it often ignores differences within the vasculature and cannot accommodate abundant structural information. This study proposes a multi-level optical angiography (MOA) method for PDT. It can enhance capillaries and image vessels at different levels by measuring the signal frequency shift associated with red blood cell motion. The experimental results regarding the PDT-induced chorioallantoic membrane model showed that the proposed method could not only perform multi-level angiography but also provide more accurate quantitative information regarding various vascular parameters. This MOA method has potential applications in PDT studies.

Real-time, multi-spectral motion artefact correction and compensation for laser speckle contrast imaging

Laser speckle contrast imaging (LSCI) is so sensitive to motion that it can measure the movement of red blood cells. However, this extreme sensitivity to motion is also its pitfall as the clinical translation of LSCI is slowed down due to the inability to deal with motion artefacts. In this paper we study the effectiveness of a real-time, multi-spectral motion artefact correction and compensation by subduing an in vitro flow phantom and ex vivo porcine kidney to computer-controlled motion artefacts. On the in vitro flow phantom, the optical flow showed a good correlation with the total movement. This model results in a better signal-to-noise ratios for multiple imaging distances and the overestimation of perfusion was reduced. In the ex vivo kidney model, the perfusion overestimation was also reduced and we were still able to distinguish between ischemia and non-ischemia in the stabilized data whereas this was not possible in the non-stabilized data. This leads to a notably better perfusion estimation that could open the door to a multitude of new clinical applications for LSCI.

Numerical Study of Supra-Wavelength Axial Motion Compensation in Contact-Mode Optical Coherence Angiography Using Fourier-Shift Procedures

Label-free angiographic methods based on optical coherence tomography (OCT) visualize blood vessels utilizing detection of red blood cells motion against surrounding static tissue. However, in practice, the surrounding tissue is never still due to natural motions of living organisms (e.g., breathing or heart beating). To mitigate large scale motions of the tissue relatively to the OCT probe the tissue examination can be made in contact mode. In such a case, however, the OCT probe inevitably exerts some pressure onto the tissue, so that bulk motions lead to interframe deformations and depth-dependent tissue displacements which have to be numerically compensated prior to angiographic visualization. Usually, sufficiently small deformations primarily affect pixel phases in OCT images rather than pixel amplitudes, and, therefore, phase-only compensation of the masking motions may be fairly sufficient. However, in case of larger strains and supra-wavelength displacements, larger inter-scan phase variations of the order of several periods lead to the appearance of pronounced “decorrelation noise” in which variations in pixel amplitudes and phases are combined. This effect significantly degrades the quality of the final OCT-angiography images. In this paper, we present a new method allowing to a significant degree to compensate this phase-amplitude decorrelation caused by spatially-inhomogeneous supra-wavelengths displacements. This compensation is based on the Fourier-shift theorem which allows one to back-shift fragments of the deformed OCT-scans to their initial positions before deformation. At the same time variations of pixels due to the motion of blood particles within smaller-in-size vessel cross sections are retained. Although such backshifts do not compensate relative motions of sub-resolution particles, this procedure efficiently reduces decorrelation even for fairly big spatially-inhomogeneous displacements and leads to much lower signal variability outside blood vessels while preserving high variability inside. The proposed compensation method is compared to the earlier proposed phase-only compensation using simulated data. Pronouncedly lower strain-induced artefacts and much higher contrast between blood vessels and background are demonstrated.

Characteristics and Limitations of Video-capillaroscopy in Reconstructive Microsurgery for Different Histologic Components of Flaps.

Indocyanine green, ultrasonography, and handheld Doppler can be used to evaluate blood flow at the donor and recipient site during microvascular reconstruction. However, these methods do not provide direct visualization and assessment of real-time blood flow. Video-capillaroscopy has been shown to be useful in clinical practice to assess microcirculation in rheumatologic disorders. In this report we used video-capillaroscopy to assess different tissue components involved in microvascular surgery. Seven patients who underwent head and neck oncologic microvascular reconstruction between November 2021 and February 2022 were included in this study. Video-capillaroscopy (GOKO-BscanZD, GOKO Imaging Devices Co., Ltd., Japan) was used to evaluate the donor-site and recipient-site tissue components. Optimal red blood cell movement was graded with a score of four, while no flow was graded with a score of 0. Seven myocutaneous flaps and seven recipient sites were evaluated. For the donor-site, our analysis demonstrated a significantly higher video-capillaroscopy quality for skin (3.43), adipose tissue (3.7) and perforators (3.7) when compared with muscle (0.429), muscle fascia (0.857), and de-epithelialized skin (1) (P < 0.001). For the recipient-site, a significantly higher video-capillaroscopy quality for skin (2.7), adipose tissue (3.5), and the periosteum (2.1) was noted when compared with muscle (0) (P < 0.001). Video-capillaroscopy efficiency is limited in the muscular component and injured (de-epithelialized) skin surface areas of flaps. Herein, we provide evidence that assessment of flap perfusion with video-capillaroscopy can be reliably achieved in the skin, periosteum, perforators, and adipose tissue. Video-capillaroscopy is expected to be applied for intraoperative real-time blood flow evaluation.