Adaptive gain control and contrast improvement for medical diagnostic ultrasound B-mode imaging system using charge-coupled devices

A B-mode ultrasound imaging system operates by transmitting a high-frequency sound pulse and measuring the strength and time of flight of the reflected signal. The ultrasound signal may be attenuated as much as 60 dB in its round trip to a target and must be normalized so that contrast is not lost in the far field. Manual controls for adjusting receiver gain versus depth are common in many clinical uses but are impractical in most surgical applications. The goal of this project was to design a circuit to automatically adjust the gain. A two-dimensional low-pass filter is used to approximate the returned signal´s local average value which is a measure of the total attenuation, scattering, and beam spreading experienced by the ultrasound energy. The attenuation is compensated by dividing the returned signal by its average value to remove the attenuation