Real-Time FIR Filter Equalisation of Analog Front Ends for Soft-Tissue Quantitative Ultrasound

A typical ultrasound imaging system analogue front end (AFE) consists of a series of stages, including transmit/receive switch, amplifiers and analog-digital converter (ADC). Each stage will have an impact on the signal in the form of noise, but also in the form of distortion from a frequency-dependent gain profile. This gain response will be applied to any ultrasound echo signal received by the system. This paper highlights the presence of this distortion and proposes a method of identifying the distortion caused by the front end and performing compensation in realtime using per-channel finite-impulse-response (FIR) filters. The University of Leeds Ultrasound Array Research Platform (UARP) was used as a typical example system for which the AFE frequency response was analysed, though any system using integrated analogue front ends will exhibit similar behaviour. The proposed method was used to determine the necessary inverse response filter for the UARP system. With the filter inserted into the digital signal processing path and the resulting frequency response is measured to verify functionality. The presented results demonstrate how digital FIR filters can be used to effectively equalise the gain profile of the AFE in real-time using hardware Finite Impulse Response (FIR) filters within the UARP research system.