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Research Papers

Temperature Distribution During ICG-Dye-Enhanced Laser Photocoagulation of Feeder Vessels in Treatment of AMD-Related Choroidal Neovascularization

[+] Author and Article Information
Liang Zhu1

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

Rupak K. Banerjee

Departments of Mechanical Engineering, and Departments of Biomedical Engineering, University of Cincinnati, Cincinnati, OH 45221

Maher Salloum, Albert Bachmann

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

Robert W. Flower

Departments of Ophthalmology, New York University, New York, NY; Departments of Ophthalmology, University of Maryland at Baltimore, Baltimore, MD 21201

1

Corresponding author.

J Biomech Eng 130(3), 031010 (Apr 29, 2008) (10 pages) doi:10.1115/1.2898832 History: Received September 28, 2006; Revised June 29, 2007; Published April 29, 2008

Laser photocoagulation of the feeder vessels of age-related macula degeneration-related choroidal neovascularization (CNV) membranes is a compelling treatment modality, one important reason being that the treatment site is removed from the fovea in cases of sub- or juxtafoveal CNV. To enhance the energy absorption in a target feeder vessel, an indocyanine green dye bolus is injected intravenously, and the 805nm wavelength diode laser beam is applied when the dye bolus transits the feeder vessel; this tends to reduce concomitant damage to adjacent tissue. A 3D theoretical simulation, using the Pennes bioheat equation, was performed to study the temperature distribution in the choroidal feeder vessel and its vicinity during laser photocoagulation. The results indicate that temperature elevation in the target feeder vessel increases by 20% in dye-enhanced photocoagulation, compared to just photocoagulation alone. The dye bolus not only increases the laser energy absorption in the feeder vessel but also shifts the epicenter of maximum temperature away from the sensitive sensory retina and retinal pigment epithelial layers and toward the feeder vessel. Two dominant factors in temperature elevation of the feeder vessel are location of the feeder vessel and blood flow velocity through it. Feeder vessel temperature elevation becomes smaller as distance between it and the choriocapillaris layer increases. The cooling effect of blood flow through the feeder vessel can reduce the temperature elevation by up to 21% of the maximum that could be produced. Calculations were also performed to examine the effect of the size of the laser spot. To achieve the same temperature elevation in the feeder vessel when the laser spot diameter is doubled, the laser power level has to be increased by only 60%. In addition, our results have suggested that more studies are needed to measure the constants in the Arrhenius integral for assessing thermal damage in various tissues.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 8

Temperature profiles and temperature rises along the laser path at different time instants: (a) without dye; (b) with dye

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Figure 9

Effect of the location of the feeder vessel on the temperature profile along the laser path

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Figure 10

Effects of the diameter of the laser spot and the laser power on the temperature profiles along the laser path

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Figure 1

Anatomy of the eye and vasculature of the choroid in the macular region

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Figure 2

Three-dimensional geometrical representation of the eye in the heat transfer model and its coordinate system

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Figure 3

Contour plot of the temperature distribution in the vicinity of the feeder vessel at the end of the heating duration (t=1s): (a) without dye; (b) with dye; (c) enlarged temperature contours in the vicinity of the feeder vessel

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Figure 4

Temperature rises in RPE, choriocapillaries, and choroidal feeder vessel during the heating

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Figure 5

Lateral temperature distributions from the center of the choroidal feeder vessel in the y direction as a function of the blood flow velocity in the vessel. The red circle represents the feeder vessel and the pink area refers to the region covered by the laser spot. The FWHM is denoted by the double arrows.

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Figure 6

Lateral temperature distributions in the axial direction of the feeder vessel. Note the change in the FWHM under different blood flow velocities.

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Figure 7

Temperature elevations at the center of the choroidal feeder vessel as a function of the blood flow velocity when t=1s

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