Using of the ultrasound frequency dependent attenuation and Nakagami distribution for cataract evaluation

Cataract is a clouding or opacity of the normally transparent crystalline lens of the eye. The cataract formation is associated with the increase of both inner fiber compaction and protein aggregation, which can be characterized by ultrasound backscattering. In this study, the tissue scatterers changing with cataract formation was investigated, and their influence in the frequency dependent attenuation such as in the Nakagami distribution was analyzed. For this purpose, cataracts were induced in twenty porcine lenses. A 25 MHz focused transducer was used to estimate the ultrasound attenuation considering the spectral ratio between echo signals from a reflector with and without lenses inserted. A power-law frequency dependence model was used to study the frequency dependent attenuation. The analyzed signals showed high backscattering and also a variation of the Nakagami parameter with cataract formation, indicating a scatter size increase. This conclusion could be important to assess the cataract hardness and to provide the correct information about its type and severity.