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TECHNICAL PAPERS: Fluids/Heat/Transport

# Feasibility of Extracting Velocity Distribution in Choriocapillaris in Human Eyes from ICG Dye Angiograms

[+] Author and Article Information
L. Zhu1

Department of Mechanical Engineering,  University of Maryland, Baltimore County, Baltimore, MD 21250zliang@umbc.edu

Y. Zheng, C. H. von Kerczek, L. D. Topoleski

Department of Mechanical Engineering,  University of Maryland, Baltimore County, Baltimore, MD 21250

R. W. Flower

Department of Ophthalmology,  University of Maryland at Baltimore, Baltimore, MD 21250 and  New York University, New York, NY

1

Corresponding author.

J Biomech Eng 128(2), 203-209 (Oct 20, 2005) (7 pages) doi:10.1115/1.2165692 History: Received August 02, 2004; Revised October 20, 2005

## Abstract

Indocyanine green (ICG) dye angiography has been used by ophthalmologists for routine examination of the choroidal vasculature in human eyes for more than $20years$. In this study, a new approach is developed to extract information from ICG dye angiograms about blood velocity distribution in the choriocapillaris and its feeding blood vessels. ICG dye fluorescence intensity rise and decay curves are constructed for each pixel location in each image of the choriocapillaris in an ICG angiogram. It is shown that at each instant of time the magnitude of the local instantaneous dye velocity in the choriocapillaris is proportional to both the slope of the ICG dye fluorescence intensity curve and the dye concentration. This approach leads to determination of the absolute value of blood velocity in the choriocapillaris, assuming an appropriate scaling, or conversion factor can be determined. It also enables comparison of velocities in different regions of the choriocapillaris, since the conversion factor is independent of the vessel location. The computer algorithm developed in this study can be used in clinical applications for diagnostic purposes and for assessment of the efficacy of laser therapy in human eyes.

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## Figures

Figure 1

Anatomic structure of the human eye and its retinal and choroidal vasculatures: (A) The eye in cross-section; (B) Magnified view of the retinal and choroidal vasculatures. Note that the retinal capillaries permeate the sensory retinal tissue, except for the foveal region, as shown in (C); (C) Anterior view of the retinal vasculature (corrosion cast), centered on the foveal region (yellow arrow) which is devoid of vessels and capillaries: (D) Anterior view of the sub-foveal choriocapillaris (corrosion cast). Note the retinal capillaries (blue arrow) at the edge of the fovea, visible in the upper left-hand corner; (E) Oblique sectional view of a corrosion cast of the choroidal vasculature showing the relationship of the choriocapillaris to the underlying choroidal arteries and veins that feed and drain it.

Figure 2

Two ICG dye angiogram images taken two seconds apart in a healthy subject. (a) ICG dye fills the choroidal arteries underlying the choriocapillaris, and in the macular region filling of the choriocapillaris appears as a faint superficial diffuse fluorescence. Note the clear image of individual choroidal arteries; (b) dye now fills the entire choriocapillaris and the choroidal veins and retinal arteries.

Figure 3

Schematic diagram of a dye bolus traveling along a straight blood vessel segment. The dye bolus may have an arbitrary concentration distribution in the axial direction, C(z). dp denotes the dimension of each image pixel, and Aarea represents the cross-sectional area of the volume contributing to the dye intensity in that pixel location.

Figure 4

Dye concentration C(z) and constructed dye intensity I(t) curves

Figure 5

ICG dye intensity curve at two axial locations along a blood vessel. Δz1‐2 is the axial distance between locations 1 and 2, and Δt0 is the time interval between the two peaks in the dye intensity curves.

Figure 6

Constructed ICG dye intensity curve at one spatial location. The left-hand y-axis denotes the ICG dye intensity I(t) or gray value at any time instant, and the right-hand y-axis represents the dimensionless dye intensity I(t)∕Imax.

Figure 7

Relationship between the measured velocity U∞ and the inverse of the fitted time constant 1∕τ in several retina vessels. The solid line is the least square residual fit, and its slope (m−1) is the value of the denominator in Eq. 3. The slope is used as the converting factor for the velocity of the choriocapillaris.

Figure 8

Velocity distribution in the underlying large choroidal arteries. Note that the velocity has not been calibrated and that the color bar denotes 1∕τ.

Figure 9

Two-dimensional mapping of the velocity distribution in the choriocapillaris. The color bar gives the relationship between the color and velocity (mm∕s).

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