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B. Torok, R. Eberhard, P. Bischoff, G. Szekely; The Filling Characteristics of Indocyanine Green and Fluorescein Dyes Measured by Simultaneous Digital ICG and Fluorescein Angiography . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4050.
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Purpose: Measurement of the filling pattern of indocyanine green (ICG) and fluorescein dyes during clinical angiography. Methods: The angiography was done with a mixture of 5 ml 20% sodium fluorescein and 25 mg ICG injected into the cubital vein. Simultaneous ICG and Fluorescein (SIF) angiography images of a two-channel scanning laser Ophthalmoscope were digitized on-line and written to disk with a rate of 25 images/s as a non-compressed video file with a personal computer. The filling of the two dyes was calculated automatically as the average intensity measured in multiple regions of interests (ROI) in the macula. Unavoidable head and the eye movements during clinical angiographies lead to horizontal and vertical shifts in the acquired images. Since subsequent measurements must be performed on exactly the same region of the fundus, the ROIs had to be individually positioned on all images of the sequence. An automatic method based on the 2-dimensional template matching has been developed for positioning the ROIs. Filling time difference (FD) of the two dyes was calculated at 25% and 100% relative intensity levels in the ROIs (FDROI) and in the retinal arteries near the optic disk (FDartery). Angiograms of 21 good cooperating subjects were analyzed. Results: In 86 % of the cases fluorescein filling was faster than ICG in the macular ROIs. Fluorescein appeared always prior ICG in the retinal arteries. To eliminate the effect of the extraocular filling difference (FDartery), intraocular filling difference of the two dyes in the macula (FDmacula) was calculated with the formula FDmacula = FDROI - FDartery. The results of this calculation showed that ICG filling occurred prior fluorescein in all examined subjects. Conclusions: Our findings suggest that the transit times of the two dyes measured from the cubital vein to the central retinal artery are different. When calculating the intraocular FD of the two dyes with cubital injection of the dyes, FDartery has to be considered. With the calculation of FDROI - FDartery the effect of an intracarotidal injection can be simulated. Our results with the corrected FDs of the two dyes in the macula are correlating well with experimental data of Flower where the filling of the two dyes was evaluated after intracarotidal injection of a mixture of ICG and fluorescein in monkeys. When interpreting the results of clinical SIF-angiographies with the Rodenstock SLO, it has to be taken into consideration that the two dyes do not enter the eye simultaneously.
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