Dynamic Fluorangiography

In order to assess blood circulation in the human retina, fluorescein angiography is currently used. A dynamic sequence of retinal angiograms is acquired by a scanning laser ophthalmoscope (SLO) after the injection of a fluorescein dye. One current clinical procedure requires the measurement of the transit time of the dye between two user-selected locations on a retinal vessel.
At present, ophthalmologists estimate these times in a qualitative manner and with a difficult and time-consuming manual procedure, which involves the visual examination of many image frames to identify those of interest. We studied a computerized system, based on image processing and analysis techniques, to automatically and accurately measure the transit time of fluo-rescein dye between the user-selected retinal loca-tions.




From left to right: Dye starts to appear - Arterial filling - Venous and choroidal filling




On the left: Raw data - pixel gray-level intensity varying with time. Sampling time is 25ms. On the right: Filling model fitted to data.

 


The filling model is fitted to each time series obtained from pixels within a vein.

Different filling dynamics are evident within a vein: grey represents early filling areas whereas white represents a late venous filling.

The bottom panel shows data and the model for the late filling pixels of the vessel.











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