Ultrasonic Dynamic Focusing Using an Analog FIFO and Asynchronous Sampling

A dynamic focusing method which employs an analog FIFO (AFIFO) for signal sampling and storage is proposed. The delay control on the ultrasound pulse echo at each array element for focusing delay compensation is achieved by the nonuniform sampling process, as suggested previously in a full digital beamforming system called Pipe-lined Sampled-Delay Focusing (PSDF). In the new focusing method, an analog sampling device, AFIFO, is used to sample and store values of the pulse echo as it arrives from each imaging point at each array element. Due to the first-in first-out operation of each AFIFO, all the samples for each imaging point along the axis of the beam are arranged at the same output position required on each channel and will be output simultaneously by a uniform output clock. Except for the nonuniform sampling control, all processing in the new dynamic beamforming method is carried out exactly the same as in conventional analog imaging systems. The advantages of the new system are that the sampling rate and hardware complexity for dynamic focusing can be greatly reduced by employing nonuniform sampling and analog signal processing. The performance and validity of the new method are verified experimentally.