Frequency synthesizer apparatus and method in ultrasonic imaging

Abstract

A frequency program synthesizing apparatus and method is disclosed for controlling delay circuitry in ultrasonic imaging systems. The ultrasonic system includes a multi-element ultrasonic transducer for propagating ultrasonic energy into a subject, display apparatus for producing visual information about the subject from the ultrasonic energy, and imaging electronics for processing image information representing electrical signals from the transducer and employs the processed signals to cause the display to generate a visual image of internal subject structure. The imaging electronics includes delay circuitry which required programs of precisely controlled stepped clocking frequencies, and have frequency program synthesizers for producing the clocking signals. The delay circuitry is employed to delay certain of the electrical signals from the transducer with respect to others so that the transducer's sensitivity to echoes is continuously focused in a moving region whose distance from the transducer varies with time to follow receding ultrasonic wavefronts propagated by the transducer. Each frequency program synthesizer includes an adjustable frequency source for producing the clocking signals and a multi-channel memory having a plurality of address channels each allocated for digitally storing a signal representing the frequency corresponding to one of said frequency program steps and circuitry for applying the stored signals in a sequence to cause the adjustable frequency generator to produce the frequency program. Each program synthesizer also includes updating circuitry for adjusting the values of the stored digital frequency representations to compensate for undesirable differences between the frequency of the generated program and a set of predetermined program frequency steps.