Ultrasonic diagnostic imaging of response frequency differing from transmit frequency

A method for producing an ultrasonic image from the harmonic response of tissue in the interior of the body comprising the steps of:

• transmitting ultrasonic energy from the elements of an array transducer into the body at a fundamental frequency in wave components emanating over a plurality of elements in the near field and which wave components become focused to develop harmonic frequency components at a greater death;
• receiving ultrasonic echo signals by said array transducer which have been returned by said tissue at a harmonic of said fundamental frequency;
• forming coherent echo signals from said received ultrasonic echo signals;
• passing tissue harmonic signals to the substantial exclusion of fundamental frequency signals;
• and
• processing said tissue harmonic signals from which fundamental frequency signals have been substantially excluded to produce ultrasonic image display signals;
• and
• displaying said ultrasonic image display signals,
• whereby multipath clutter in said tissue harmonic ultrasonic image is substantially reduced.

An ultrasonic diagnostic imaging system for imaging the harmonic response of tissue inside a body which exhibits depth dependent attenuation of ultrasonic energy, comprising:

• a transmit controller operable to cause the elements of an array transducer to transmit wave components, the energy of which is distributed over the array in the near field and becomes focused to develop harmonic frequency components at a focal depth;
• a transducer array responsive to said transmit controller for transmitting ultrasonic energy into the body at a fundamental frequency which is equal to or less than 5 MHz and which is responsive to said transmitted ultrasonic energy for receiving ultrasonic echo signals from tissue at a harmonic of said fundamental frequency which is equal to or less than 10 MHz;
• means for digitizing said received ultrasonic echo signals,
• a digital beamformer for forming coherent echo signals from said digitized ultrasonic echo signals;
• a filter which passes, tissue harmonic echo signals to the substantial exclusion of fundamental frequency signals;
• and
• an image processor, responsive to said tissue harmonic echo signals from which fundamental frequency signals have been substantially excluded, for producing an ultrasonic image from said tissue harmonic echo signals,
• whereby the multipath clutter of said image of tissue harmonic echo signals is substantially reduced.