Ultrasonic nonlinear imaging at fundamental frequencies

Abstract

Nonlinear tissue or contrast agent effects are detected by combining echoes from multiple, differently modulated transmit pulses below the second harmonic band. The received echoes may even overlap the fundamental transmit frequency band. The modulation may be amplitude modulation or phase or polarity modulation, and is preferably both amplitude and phase or modulation. The present invention affords the ability to utilize a majority of the transducer passband for both transmission and reception, and to transmit pulses which are less destructive to microbubble contrast agents.

What is claimed is:  
     
         1 . A method for nonlinear ultrasonic imaging comprising: 
 transmitting a first pulse exhibiting frequencies in a fundamental frequency band to a target exhibiting a nonlinear response;    transmitting a second pulse exhibiting frequencies in the fundamental frequency band to the target, the second pulse being differently modulated in at least one of amplitude, phase or polarity;    receiving echoes from the target in response to each pulse which include a frequency included in the fundamental frequency band;    combining the echoes received in response to the pulses to produce signals embodying a nonlinear effect of the target; and    using the nonlinear effect signals to produce an ultrasound image.    
     
     
         2 . The method of  claim 1 , wherein transmitting comprises transmitting pulses which are differently amplitude modulated.  
     
     
         3 . The method of  claim 1 , wherein transmitting comprises transmitting pulses which are differently modulated in phase or polarity.  
     
     
         4 . The method of  claim 1 , wherein transmitting comprises transmitting pulses which are differently modulated in amplitude and in phase or polarity.  
     
     
         5 . The method of  claim 2 , further comprising normalizing the received echoes to account for the amplitude modulation difference.  
     
     
         6 . The method of  claim 1 , wherein receiving comprises receiving echoes from the target in a band of frequencies which include a frequency which is within the fundamental frequency band and a frequency which is above the fundamental frequency band.  
     
     
         7 . The method of  claim 1 , wherein receiving comprises receiving echoes from the target in a band of frequencies which include a frequency which is within the fundamental frequency band and a frequency which is below the fundamental frequency band.  
     
     
         8 . The method of  claim 1 , wherein receiving comprises receiving echoes from the target in a band of frequencies which declines in frequency from a higher frequency band to a lower frequency band with increasing depth, wherein said band includes a frequency which is within the fundamental frequency band during at least a portion of a period of echo reception.  
     
     
         9 . The method of  claim 1 , wherein combining comprises canceling linear components of the received echoes and enhancing nonlinear components of the received echoes.  
     
     
         10 . The method of  claim 9 , wherein combining further comprises utilizing the modulation difference of the transmitted pulses to cancel linear components of the received echoes.  
     
     
         11 . The method of  claim 1 , wherein receiving comprises receiving echoes along at least two spatially distinct scanline directions in response to each act of transmitting.  
     
     
         12 . The method of  claim 2 , wherein transmitting a first pulse comprises transmitting a pulse of a given amplitude, and wherein transmitting a second pulse comprises transmitting a pulse of an amplitude which is less than the given amplitude.  
     
     
         13 . A method for nonlinear ultrasonic imaging comprising: 
 transmitting a plurality of pulses exhibiting frequencies in a fundamental frequency band to a target exhibiting a nonlinear response;    receiving echoes from the target in response to the transmitted pulses in frequency bands which overlap the fundamental frequency band;    identifying the nonlinear components of the received echoes; and    using the identified nonlinear signal components to produce an ultrasound image.    
     
     
         14 . The method of  claim 13 , wherein transmitting further comprises insonifying the target with differently modulated transmit pulses; and wherein identifying comprises combining echoes received in response to differently modulated transmit pulses.  
     
     
         15 . The method of  claim 13 , wherein transmitting comprises transmitting a plurality of pulses to a contrast agent; and wherein receiving comprises receiving echoes from the contrast agent.