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Magnetic Resonance Blood Volume Measurement with MS 325 in Experimental Choroidal Melanoma

1Krause M., 2Xiong J., 3Kwong K. K., 2Gragoudas E. S., 2Young L. H. Y.,
1Universität des Saarlandes, Universitäts-Augenklinik Homburg (Homburg/Saar)
2Harvard Medical School , Massachusetts Eye and Ear Infirmary, Department of Ophthalmology (Boston)
3Harvard Medical School , Massachusetts General Hospital, Nuclear Magnetic Resonance (MGH-NMR) Center (Charlestown)

Purpose: Functional magnetic resonance imaging (MRI) is a non-invasive method, which offers quantitative imaging of blood volume at a high resolution. This method was applied for untreated and hypothermia-treated choroidal melanoma. MS 325 was used as new intravascular albumin bound gadolinium-based contrast agent.
Methods: Pigmented choroidal melanomas were established in female albino rabbits. Seven untreated eyes and 7 eyes treated with a Neodymium: Yttrium-Lanthanum-Fluoride (Nd: YLF-) laser at 1047 nm were imaged with MRI. T1 weighted axial images were obtained by using 3D-spoiled gradient echo pulse sequences. First, a series of images was acquired without contrast agent. MS 325 was then administered intravenously and images were collected within 12 min after the injection. Signal intensities were determined for melanoma, ciliary body, choroid, and iris, and relative signal intensities in relation to vitreous were calculated for these tissues.
Results: In untreated tumors, the relative signal intensity was higher after injection of MS 325 (5.61+0.70) than without MS 325 (2.90+0.33; p=0.018). Conversely, the relative signal intensity of treated tumors was not significantly different before and after MS 325 (6.19+1.59 and 6.13+1.64). Vascular occlusion was found in histopathological sections of treated tumors. A significant increase of the relative signal intensity after MS 325 was detected in the other treated and untreated tissues.
Conclusions: MRI measurement of blood volume with MS 325 was adapted for experimental choroidal melanoma. A reduced change of relative signal intensity can be explained by compromised blood volume as a result of vascular occlusion after hypothermic treatment. Further studies are required to determine whether this technique allows investigation of tumor viability after treatment.