A processing work-flow for measuring erythrocytes velocity in extended vascular networks from wide field high-resolution optical imaging data

Quantification of Blood Flow Velocity in the Human Conjunctival Microvessels Using Deep Learning-Based Stabilization Algorithm

The quantification of blood flow velocity in the human conjunctiva is clinically essential for assessing microvascular hemodynamics. Since the conjunctival microvessel is imaged in several seconds, eye motion during image acquisition causes motion artifacts limiting the accuracy of image segmentation performance and measurement of the blood flow velocity. In this paper, we introduce a novel customized optical imaging system for human conjunctiva with deep learning-based segmentation and motion correction. The image segmentation process is performed by the Attention-UNet structure to achieve high-performance segmentation results in conjunctiva images with motion blur. Motion correction processes with two steps—registration and template matching—are used to correct for large displacements and fine movements. The image displacement values decrease to 4–7 μm during registration (first step) and less than 1 μm during template matching (second step). With the corrected images, the blood flow velocity is calculated for selected vessels considering temporal signal variances and vessel lengths. These methods for resolving motion artifacts contribute insights into studies quantifying the hemodynamics of the conjunctiva, as well as other tissues.

Conjunctival Vessels in Diabetes Using Functional Slit Lamp Biomicroscopy

PURPOSE

This study used functional slit lamp biomicroscopy (FSLB) to quantify conjunctival microvessel parameters in individuals with and without diabetes and examined whether these metrics could be used as surrogate markers of diabetes-related complications.

METHODS

A cross-sectional study of 98 controls (C), 13 individuals with diabetes without complications (D-C), and 21 with diabetes and related complications (D+C), which included retinopathy, nephropathy, neuropathy, and cardiovascular-, peripheral vascular-, and cerebrovascular diseases, was performed. Bulbar conjunctival metrics (venule diameter, length, axial velocity [Va], cross-sectional velocity [Vs], flow [Q], and branching complexity) were measured using FSLB (digital camera mounted on traditional slit lamp).

RESULTS

The mean age was 60 ± 11 years, and demographics were similar across the groups. Va and Vs significantly differed between groups. Va was 0.51 ± 0.17 mm/s, 0.62 ± 0.17 mm/s, and 0.45 ± 0.17 mm/s in the C, D-C, and D+C groups, respectively (P = 0.025). Similarly, Vs was 0.35 ± 01.12, 0.43 ± 0.13, and 0.32 ± 0.13 mm/s in the C, D-C, and D+C groups, respectively (P = 0.031). Black individuals had increased Va, Vs, and Q compared with White individuals (P < 0.05), but differences in velocities persisted after accounting for race. Among patients with diabetes, Va and Vs correlated with number of organ systems affected (Va: ρ = -0.42, P = 0.016; Vs: ρ = -0.41, P = 0.021). Va, Vs, and Q significantly (P ≤ 0.005) discriminated between diabetic patients with and without complications (area under the receiver operating curve for Va = 0.81, Vs = 0.79, Q = 0.81).

CONCLUSIONS

Bulbar conjunctival blood flow metrics measured by FSLB differed between controls, diabetic patients without complications, and diabetic patients with complications. FSLB is a quick, easily accessible, and noninvasive alternative that might estimate the burden of vascular complications in diabetes.

Conjunctival microvascular responses to anti-inflammatory treatment in patients with dry eye

PURPOSE

This study characterized conjunctival microvascular morphological and haemodynamic responses after anti-inflammatory treatment in dry eye (DE).

MATERIALS AND METHODS

Twenty-five patients with moderate DE (17 females and 8 males aged 48 ± 16 years) who underwent anti-inflammatory therapy (0.1% fluorometholone) and 25 healthy subjects (20 females and 5 males aged 48 ± 17 years) recruited as controls were enrolled. The conjunctival blood flow rate (BFR), blood flow velocity (BFV) and vessel diameter were measured by functional slit-lamp biomicroscopy (FSLB). DE symptoms and signs were assessed. All measurements were performed at baseline and at 30 and 60 days after commencement of treatment.

RESULTS

At baseline, the conjunctival BFR, BFV, and vessel diameter were higher in the DE group than in the control group (p < 0.05). The BFR, BFV and corneal fluorescein staining (CFS) scores decreased at 60 days after therapy compared to at baseline and 30 days (all p_corrected < 0.05); Ocular surface diseases index (OSDI), the hyperaemia index (HI) and vessel diameters only showed significant decreases at 30 days. Moreover, significant increases in the noninvasive tear film break-up time (NI-BUT) and Schirmer I test score (ST) were observed. The CFS score correlated positively with BFV (r = 0.46), BFR (r = 0.58) and vessel diameter (r = 0.47).

CONCLUSION

This study characterized conjunctival microvascular responses to anti-inflammatory treatment in DE patients. The results suggest that conjunctival BFV and BFR can be used as dynamic markers for treatment efficacy in DE.

A review of functional slit lamp biomicroscopy

Functional slit lamp biomicroscopy (FSLB) is a novel device which consists of a traditional slit-lamp and a digital camera. It can quantitatively assess vessel diameter, blood flow velocity, and blood flow rate and can create noninvasive microvascular perfusion maps (nMPMs). At present, FSLB is mainly used in contact lens (CL) and dry eye disease (DED) studies to advance our understanding of ocular surface microcirculation. FSLB-derived blood flow and vessel density measures are significantly altered in CL wearers and DED patients compared to normal people. These subtle changes in the ocular surface microcirculation may contribute to the monitoring of potential diseases of the body and provide a new way to diagnose dry eye disease. Therefore, this may also indicate that FSLB can be more widely applied in the study of other diseases to reveal the relationship between changes in ocular surface microcirculation and systemic diseases. The purpose of this paper is to summarize the functions of FSLB and the related studies especially in CL and DED.

Imaging single-cell blood flow in the smallest to largest vessels in the living retina

Tissue light scatter limits the visualization of the microvascular network deep inside the living mammal. The transparency of the mammalian eye provides a noninvasive view of the microvessels of the retina, a part of the central nervous system. Despite its clarity, imperfections in the optics of the eye blur microscopic retinal capillaries, and single blood cells flowing within. This limits early evaluation of microvascular diseases that originate in capillaries. To break this barrier, we use 15 kHz adaptive optics imaging to noninvasively measure single-cell blood flow, in one of the most widely used research animals: the C57BL/6J mouse. Measured flow ranged four orders of magnitude (0.0002-1.55 µL min^-1) across the full spectrum of retinal vessel diameters (3.2-45.8 µm), without requiring surgery or contrast dye. Here, we describe the ultrafast imaging, analysis pipeline and automated measurement of millions of blood cell speeds.

Measurement variability of the bulbar conjunctival microvasculature in healthy subjects using functional slit lamp biomicroscopy (FSLB)

The goal was to determine the variability of the quantitative measurement of the bulbar conjunctival microvascular morphology and hemodynamics by testing the repeatability and variation during office hours. Functional slit-lamp biomicroscopy (FSLB) was used to image the bulbar conjunctival microvasculature, including the vessel diameter, blood flow velocity/rate and fractal dimensions of the microvascular network. The temporal side of the bulbar conjunctiva in 20 healthy subjects was imaged. The subject was imaged at 9 AM to test the measurement repeatability by two independent graders. The intraclass correlation coefficient (ICC) and coefficient of repeatability (CoR) were calculated. These same subjects were then imaged every two hours from 9 AM to 5 PM to test the variation during office hours. Custom software was used to semi-automatically process all measurements. The CoR% and ICC values between two graders for measuring the vessel diameter were 4.87% and 0.989, respectively. For the axial blood flow velocity, the CoR% and ICC were 11.49% and 0.997, respectively. From 9 AM to 5 PM, there were no significant variations in the vessel diameter and hemodynamics (P>0.05), whereas the fractal dimensions of the non-invasive microvascular perfusion maps (nMPMs) were significantly increased at 3 PM and 5 PM compared with the baseline obtained at 9 AM (P<0.05). FSLB appears to be capable of measuring vessel diameter, blood flow velocity and fractal dimension of the microvascular network in the bulbar conjunctiva. Slight variations over office hours were observed in the microvascular network, while the blood flow velocity remained stable.

Vobi One: a data processing software package for functional optical imaging

Optical imaging is the only technique that allows to record the activity of a neuronal population at the mesoscopic scale. A large region of the cortex (10-20 mm diameter) is directly imaged with a CCD camera while the animal performs a behavioral task, producing spatio-temporal data with an unprecedented combination of spatial and temporal resolutions (respectively, tens of micrometers and milliseconds). However, researchers who have developed and used this technique have relied on heterogeneous software and methods to analyze their data. In this paper, we introduce Vobi One, a software package entirely dedicated to the processing of functional optical imaging data. It has been designed to facilitate the processing of data and the comparison of different analysis methods. Moreover, it should help bring good analysis practices to the community because it relies on a database and a standard format for data handling and it provides tools that allow producing reproducible research. Vobi One is an extension of the BrainVISA software platform, entirely written with the Python programming language, open source and freely available for download at https://trac.int.univ-amu.fr/vobi_one.

Functional slit lamp biomicroscopy for imaging bulbar conjunctival microvasculature in contact lens wearers

PURPOSE

To develop, test and validate functional slit lamp biomicroscopy (FSLB) for generating non-invasive bulbar conjunctival microvascular perfusion maps (nMPMs) and assessing morphometry and hemodynamics.

METHODS

FSLB was adapted from a traditional slit-lamp microscope by attaching a digital camera to image the bulbar conjunctiva to create nMPMs and measure venular blood flow hemodynamics. High definition images with a large field of view were obtained on the temporal bulbar conjunctiva for creating nMPMs. A high imaging rate of 60 frames per second and an ~210× high magnification were achieved using the camera inherited high speed setting and Movie Crop Function, for imaging hemodynamics. Custom software was developed to segment bulbar conjunctival nMPMs for further fractal analysis and quantitatively measure blood vessel diameter, blood flow velocity and flow rate. Six human subjects were imaged before and after 6h of wearing contact lenses. Monofractal and multifractal analyses were performed to quantify fractality of the nMPMs.

RESULTS

The mean bulbar conjunctival vessel diameter was 18.8 ± 2.7 μm at baseline and increased to 19.6 ± 2.4 μm after 6h of lens wear (P=0.020). The blood flow velocity was increased from 0.60 ± 0.12 mm/s to 0.88 ± 0.21 mm/s (P=0.001). The blood flow rate was also increased from 129.8 ± 59.9 pl/s to 207.2 ± 81.3 pl/s (P=0.001). Bulbar conjunctival nMPMs showed the intricate details of the bulbar conjunctival microvascular network. At baseline, fractal dimension was 1.63 ± 0.05 and 1.71 ± 0.03 analyzed by monofractal and multifractal analyses, respectively. Significant increases in fractal dimensions were found after 6h of lens wear (P<0.05).

CONCLUSIONS

Microvascular network's fractality, morphometry and hemodynamics of the human bulbar conjunctiva can be measured easily and reliably using FSLB. The alternations of the fractal dimensions, morphometry and hemodynamics during contact lens wear may indicate ocular microvascular responses to contact lens wear.

Improved blood velocity measurements with a hybrid image filtering and iterative Radon transform algorithm

Neural activity leads to hemodynamic changes which can be detected by functional magnetic resonance imaging (fMRI). The determination of blood flow changes in individual vessels is an important aspect of understanding these hemodynamic signals. Blood flow can be calculated from the measurements of vessel diameter and blood velocity. When using line-scan imaging, the movement of blood in the vessel leads to streaks in space-time images, where streak angle is a function of the blood velocity. A variety of methods have been proposed to determine blood velocity from such space-time image sequences. Of these, the Radon transform is relatively easy to implement and has fast data processing. However, the precision of the velocity measurements is dependent on the number of Radon transforms performed, which creates a trade-off between the processing speed and measurement precision. In addition, factors like image contrast, imaging depth, image acquisition speed, and movement artifacts especially in large mammals, can potentially lead to data acquisition that results in erroneous velocity measurements. Here we show that pre-processing the data with a Sobel filter and iterative application of Radon transforms address these issues and provide more accurate blood velocity measurements. Improved signal quality of the image as a result of Sobel filtering increases the accuracy and the iterative Radon transform offers both increased precision and an order of magnitude faster implementation of velocity measurements. This algorithm does not use a priori knowledge of angle information and therefore is sensitive to sudden changes in blood flow. It can be applied on any set of space-time images with red blood cell (RBC) streaks, commonly acquired through line-scan imaging or reconstructed from full-frame, time-lapse images of the vasculature.