METHOD AND APPARATUS FOR DISTRIBUTED FOCUS CONTROL WITH SLOPE TRACKING

To overcome the disadvantages of the prior art, the present invention provides a method and apparatus for distributed focus control with slope tracking. The invention operates in the context of an ultrasonic imaging system having an array of transducers. Each transducer converts received energy into an echo signal. A beamformer of the invention dynamically focuses the received energy. The beamformer includes delay computation circuitry for computing a delay function for the echo signal at a predetermined focal range. The delay of the echo signal with respect to range has a slope. Tracking circuitry varies the delay function to track the slope, thereby determining the delay function for a next focal range. The beamformer further comprises delay circuitry for compensating for the delay function of the echo signal. The delay function is an estimated relative delay with respect to a reference delay of an echo signal from a reference transducer. Alternatively, the delay function is a compensating delay adapted to be applied to the echo signal of the transducer for which the delay function is being computed. In another embodiment, the beamformer includes decision circuitry for selecting an update value from a set of update values. Delay computation circuitry updates a delay function of the echo signal for a predetermined focal range by the selected update value to thereby provide a delay function for a next focal range. Tracking circuitry varies the plurality of update values as a function of range. In yet another embodiment, decision circuitry selects an update value from a set of update values, where the set includes a first update value and the first update value modified by a change value. The first update value can be nonzero. Delay computation circuitry updates a delay function of the echo signal for a predetermined focal range by the selected update value to thereby provide a delay function for a next focal range.