Search

The purpose of this work was to obtain more quantitative knowledge about the yield of fluorescence from retinal vessels during indocyanine green angiography (ICG). The yield of fluorescence from blood was investigated for various shear rates, concentrations of ICG, and layer thicknesses. Measurements were performed in vitro on samples of human blood in a cone-plate shear chamber using frontal illumination as in scanning laser angiography. In blood and in plasma, the yield of fluorescence of ICG increased with concentration up to 0.05 and 0.1 mg/ml, respectively. At higher concentrations, the yield decreased for all layer thicknesses. For increasing layer thicknesses, both in plasma and in blood, the yield of ICG fluorescence increased nonlinearly for concentrations higher than 0.012 mg/ml. Saturation occurred for layers thicker than 200 microns in combination with ICG concentrations of 0.4 mg/ml and higher. Application of shear rates within the physiological range of the microcirculation (88/sec and 528/sec) increased the yield of fluorescence from the blood sample compared with stasis. The high transparency of blood for the excitation and emission light of ICG that was demonstrated will lead to superposition of fluorescence from superficial and deeper layers. This superposition precludes quantitative indocyanine angiography of ocular vessels.

The purpose of this work was to obtain more quantitative knowledge about the yield of fluorescence from retinal vessels during fluorescein angiography. The influence of shear rate, concentration of sodium fluorescein, hematocrit, and layer thickness on the yield of fluorescence from blood were investigated. Measurements were performed in vitro on samples of human blood in a cone-plate shear chamber using frontal illumination. Application of physiologically relevant levels of shear (> 88/sec) decreased the yield of fluorescence from the blood sample considerably as compared with stasis. The yield of fluorescence was proportionally related to the logarithm of the sodium fluorescein concentration in blood up to a sodium fluorescein concentration of 1.2 mg/ml. Above that concentration quenching occurred. An increase in layer thickness at a hematocrit of 45% resulted only in an increase of the yield of fluorescence up to a layer thickness of 25 microns. In conclusion, the sodium fluorescein concentration in blood is the only important factor that determines the yield of fluorescence from the larger retinal vessels in the successive phases of the fluorescein angiogram in a subject with a given hematocrit and hemoglobin concentration. The yield of fluorescence from retinal vessels (> 25 microns) is proportionally related to the logarithm of the sodium fluorescein concentration over a broad range of concentrations.

Several methods to measure red blood cell velocity in microvessels by electronic means are discussed. Signals are generated by the red blood cells present in the microscopic image of the microvessels. These signals can be converted to obtain an output signal proportional to the actual red blood cell velocity. The method of spatial filtering by interlacing gratings is discussed in terms of a filter with an input signal. Adaptation of optical factors that might improve the velocity measurement is obtained by a mathematical analysis. Different methods of correlation are presented. The temporal correlation (dual slit and video window) and spatial correlation methods are discussed in relation to factors influencing the quality of the correlogram, the peak of which is proportional to red blood cell velocity. The conversion of red blood cell velocity to volume flow is put in perspective.