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Journal of Biomedical Optics

Temperature mapping of laser-induced hyperthermia in an ocular phantom using magnetic resonance thermography
Author(s): Saher M. Maswadi; Stephen J. Dodd; Jia Hong Gao; Randolph D. Glickman
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Paper Abstract

Laser-induced heating in an ocular phantom is measured with magnetic resonance thermography (MRT) using temperature-dependent phase changes in proton resonance frequency. The ocular phantom contains a layer of melanosomes isolated from bovine retinal pigment epithelium. The phantom is heated by the 806-nm output of a continuous wave diode laser with an irradiance of 2.4 to 21.6 W/cm2 in a beam radius of 0.8 or 2.4 mm, depending on the experiment. MRT is performed with a 2T magnet, and a two-turn, 6-cm-diam, circular radio frequency coil. Two-dimensional temperature gradients are measured within the plane of the melanin layer, as well as normal to it, with a temperature resolution of 1°C or better. The temperature gradients extending within the melanin layer are broader than those orthogonal to the layer, consistent with the higher optical absorption and consequent heating in the melanin. The temperature gradients in the phantom measured by MRT closely approximate the predictions of a classical heat diffusion model. Three-dimensional temperature maps with a spatial resolution of 0.25 mm in all directions are also made. Although the temporal resolution is limited in the prototype system (22.9 s for a single image "slice"), improvements in future implementations are likely. These results indicate that MRT has sufficient spatial and temperature resolution to monitor target tissue temperature during transpupillary thermotherapy in the human eye.

Paper Details

Date Published: 1 July 2004
PDF: 8 pages
J. Biomed. Opt. 9(4) doi: 10.1117/1.1751399
Published in: Journal of Biomedical Optics Volume 9, Issue 4
Show Author Affiliations
Saher M. Maswadi, Univ. of Texas/San Antonio (United States)
Stephen J. Dodd, Univ. of Texas/San Antonio (United States)
Jia Hong Gao, Univ. of Texas/San Antonio (United States)
Randolph D. Glickman, Univ. of Texas/San Antonio (United States)

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