Medical imaging transmit spectral control using aperture functions

Abstract

Methods and systems are provided for controlling the transmit spectrum in medical imaging. A combination of different delays and/or sign changes are used control the spectrum. The different delays and/or sign changes are applied across the transmit aperture. For example, a repeating pattern of three different delays in addition to focusing delays is provided, such as no additional delay, a quarter cycle advance and a quarter cycle delay. As another example, a repeating pattern is applied where one waveform has an additional delay and a sign change. The use of three or more different amounts of delay in addition to focusing delays and/or the use of delay and sign change may be used in simple unipolar or bipolar transmitters or in more complex transmitters. For example, delay is implemented with a phase shift. The combinations of delays, phase shifts and sign changes is selected to cause acoustic summation along the transmit beam with desired spectral content. By summing the waveforms in the acoustic domain, a more desired spectral content than available for any given transmit waveform is provided. For example, harmonic, second harmonic, odd harmonics, even harmonics or any other frequency bands may be suppressed.

1 - 10 . (canceled)  
   
   
       11 . A system for controlling a transmit spectrum in medical imaging, the system comprising: 
 an array of transducer elements;    a transmit beamformer connectable with the array and operable to relatively delay signals from at least three channels by focusing delays and additional relative delays such that each of the at least three channels is associated with a different amount of delay in addition to the focusing delays, the additional relative delay of signals being in a pattern across the array.    
   
   
       12 . The system of  claim 11  wherein the transmit beamformer comprises a bipolar transmitter.  
   
   
       13 . The system of  claim 11  wherein the transmit beamformer comprises a unipolar transmitter.  
   
   
       14 . The system of  claim 11  wherein the transmit beamformer is operable to apply an about one quarter period delay to about a first quarter of the elements, apply an about negative one quarter period delay to about a second quarter of the elements, the first quarter being different elements than the second quarter, and maintain about half the elements free of additional delays, the about half being different elements than the first and second quarters.  
   
   
       15 . The system of  claim 11  wherein the transmit beamformer is operable to inverse signals for at least one of the at least three channels.  
   
   
       16 . The system of claim  111  wherein the pattern of additional relative delays is a repeating pattern  
   
   
       17 - 23 . (canceled)  
   
   
       24 . A system for controlling a transmit spectrum in medical imaging, the system comprising: 
 an array of transducer elements;    a transmit beamformer connectable with the array and operable to relatively delay signals from at least two channels by focusing delays, an additional relative delay and a sign change, the additional relative delay of signals being in a pattern across the array.    
   
   
       25 . The system of  claim 24  wherein the transmit beamformer comprises one of: a bipolar transmitter and a unipolar transmitter.  
   
   
       26 . The system of  claim 24  wherein the transmit beamformer is operable to invert a first of the at least two waveforms and delay the first waveform relative to a second of the at least two waveforms by an about one half period delay.  
   
   
       27 . The system of  claim 24  wherein the transmit beamformer is operable to apply the repeating pattern over at least three channels, operable to maintain about half the elements of the array free of additional delays, operable to invert and delay by about one half a period of a center frequency for about a first quarter of the elements, the first quarter being different elements than the half, and operable to invert and advance by about one half a period of the center frequency for about a second quarter of the elements, the second quarter being different elements than the first quarter and the half.