Characterization of scatterers concentration in cataractous lens using Nakagami distribution by ultrasounds

Cataract affects more than 20 million people in the world. Its formation is associated with the increase of protein aggregation in the eye lens. In the early stages the protein aggregates act as light scatterers and in the advanced stages these aggregates increase in size preventing the light propagation through the eye. This work aims to analyze the protein aggregates and its spatial distribution, for different stages of cataract formation. Cataract was induced in porcine lenses by immersion in an ethanol:2-propanol:formalin solution. Slices of 50 μm in thickness were obtained from the nucleus and the cortex, to locally analyze the frequency dependent attenuation and the Nakagami m parameter. The slices were stained and imaged with an inverted microscope. With cataract formation a significant increase was found for the ultrasound velocity (p>0.001), the frequency dependent attenuation (p<;0.001), the backscattering signals intensity - B-Scan images and the Nakagami m parameter (p<;0.001). The increase of the Nakagami m parameter in the cortex was in agreement with the increasing of the protein aggregates observed in the slices in this region, for different stages of cataract formation. The same was not observed for the nucleus, due to the higher compaction of the fibers in the nucleus in the advanced stages of the cataract, leading to weak backscattering signals. The results suggest that the interpretation of backscattering signals by the Nakagami distribution, when combined with the knowledge of the physical scatter properties are challenging for obtaining a distribution map of cataract hardness by a noninvasive method.