Method, apparatus and applications for combining transmit wave functions to obtain synthetic waveform in ultrasonic imaging system

A method of operating an ultrasound imaging system having an array of transducer elements, comprising the steps of:

• transmitting a first transmit ultrasound waveform having a first frequency spectrum which is centered at a first frequency by exciting selected transducer elements during a first time interval, said first transmit ultrasound waveform being focused at a first focal point in a focal zone;
• transmitting a second transmit ultrasound waveform having a second frequency spectrum which is centered at a second frequency by exciting selected transducer elements during a second time interval, said second transmit ultrasound waveform being focused at a second focal point in said focal zone, said first and second focal points being separated by a distance less than a depth of said focal zone, said second frequency being different than said first frequency, and said second time interval being immediately subsequent to said first time interval;
• forming a first complex signal pair of a first receive ultrasound waveform derived from the portion of said first transmit ultrasound waveform reflected back to selected receiving transducer elements by scatterers in said focal zone;
• forming a second complex signal pair of a second receive ultrasound waveform derived from the portion of said second transmit ultrasound waveform reflected back to selected receiving transducer elements by scatterers in said focal zone;
• filtering said first and second complex signal pairs;
• adding said filtered first and second complex signal pairs to form a third complex signal pair having components which are the sum of the respective components of said first and second complex signal pairs;
• forming the envelope of said third complex signal pair;
• and
• displaying an image vector which is a function of said envelope of said third complex signal pair.

A ultrasound imaging system comprising:

• an array of ultrasound transducer elements;
• means for transmitting a first transmit ultrasound waveform having a first frequency spectrum which is centered at a first frequency by exciting selected transducer elements during a first time interval, said first transmit ultrasound waveform being focused at a focal point;
• means for transmitting a second transmit ultrasound waveform having a second frequency spectrum which is centered at a second frequency by exciting selected transducer elements during a second time interval, said second transmit ultrasound waveform being focused at said focal point, said second frequency being different than said first frequency, and said second time interval being immediately subsequent to said first time interval;
• beamforming means for generating first and second complex signal pairs of first and second receive ultrasound waveforms respectively derived from the respective portions of said first and second transmit ultrasound waveforms reflected back to selected receiving transducer elements by scatterers in a focal zone encompassing said focal point;
• means for filtering said first and second complex signal pairs;
• means for adding said filtered first and second complex signal pairs to form a third complex signal pair having components which are the sum of the respective components of said first and second complex signal pairs;
• an envelope detector for forming the envelope of said third complex signal pair;
• and
• means for displaying an image vector which is a function of said envelope of said third complex signal pair.