Ultrasound imaging with spectral compounding for speckle reduction

Abstract

Ultrasound imaging systems and methods with frequency (spectral) compounding for speckle reduction are disclosed. In one aspect, an ultrasound imaging system includes a transducer probe with interleaved transmit and receive arrays. The system may utilize ultrasound pulses having an optimized time-bandwidth product. In one aspect, a transducer probe with separate transmit and receive elements can enable transmission and reception of multiple ultrasound pulses, each centered at a different frequency, during the time of one A-scan. Thus, such a system can capture multiple independent speckle images without reducing overall B-mode framerate. In another aspect, the system may transmit a broadband pulse and may obtain separate speckle images by filtering the received echo using multiple spectral filters. The system may compound multiple images captured at different frequencies to provide speckle reduction. The ultrasound imaging system further includes a processor configured to generate an ultrasound image based on the echoes.

What is claimed is: 
     
         1 . A method of ultrasound imaging with frequency compounding for speckle reduction, the method comprising:
 transmitting, from a transducer array, N ultrasound pulses each having a different center frequency into a medium being imaged during a round trip time for a first pulse of the N ultrasound pulses, wherein the round trip time for the first pulse is time for the first pulse to propagate from a transducer array to the medium and to propagate from the medium to the transducer array, wherein N is a positive integer that is greater than one;   receiving, with the transducer array, echoes of the N ultrasound pulses from the medium;   generating a plurality of images from the received echoes, wherein each of the images is formed from an echo associated with a particular pulse of the N ultrasound pulses; and   frequency compounding, with a processing circuit, the images so as to generate a plurality of frequency-compounded ultrasound images.   
     
     
         2 . The method of  claim 1 , wherein the transmitting is performed with a first linear transducer array of the transducer array, and the receiving is performed with a second linear array of the transducer array. 
     
     
         3 . The method of  claim 2 , wherein the transmitting and the receiving are performed at least partly concurrently. 
     
     
         4 . The method of  claim 2 , wherein the first linear array is interleaved with the second linear array. 
     
     
         5 . The method of  claim 1 , wherein the N ultrasound pulses propagate along a line scan. 
     
     
         6 . The method of  claim 1 , wherein the transmitting of the N ultrasound pulses comprises chirping the N ultrasound pulses. 
     
     
         7 . The method of  claim 1 , wherein the generating comprises frequency filtering the received echoes and compensating for time delays of the N ultrasound pulses. 
     
     
         8 . The method of  claim 1 , further comprising generating a B-mode ultrasound image based on the frequency compounded images from a plurality of line scans and visually displaying the B-mode ultrasound image. 
     
     
         9 . The method of  claim 8 , wherein the B-mode ultrasound image has a frame rate of at least 10 Hertz. 
     
     
         10 . The method of  claim 1 , wherein the N ultrasound pulses comprise three consecutive pulses with increasing center frequencies. 
     
     
         11 . The method of  claim 1 , wherein the images formed from the echoes and the frequency-compounded ultrasound images have a transverse resolution at least partially defined by properties of the transducer array and have an axial resolution at least partially defined by pulse durations of the N ultrasound pulses and wherein transmitting, from the transducer array, the N ultrasound pulses comprises transmitting N ultrasound pulses with pulse durations short enough that the axial resolution is within 10% of the transverse resolution. 
     
     
         12 . An ultrasound system for generating frequency compounded ultrasound images with reduced speckle, the ultrasound system comprising:
 a first phased transducer array configured to transmit a plurality of ultrasound pulses having different respective center frequencies into a medium being imaged, wherein the first phased transducer array comprises a plurality of transmitting elements;   a second phased transducer array configured to receive ultrasound echoes associated with the ultrasound pulses from the medium, wherein the second phased transducer array comprises a plurality of receiving elements and wherein the transmitting elements of the first phased transducer array are interleaved with the receiving elements of the second phased transducer array; and   a processing circuit in communication with the second phased transducer array, the processing circuit configured to generate frequency compounded images based on the received echoes.   
     
     
         13 . The ultrasound system of  claim 12 , wherein the first phase transducer array is configured to transmit the ultrasound pulses during a round trip time for a first pulse of the ultrasound pulses. 
     
     
         14 . The ultrasound system of  claim 12 , wherein the ultrasound system is configured to perform a line scan. 
     
     
         15 . The ultrasound system of  claim 14 , wherein the ultrasound system is configured to perform a plurality of line scans and wherein the processing circuit is configured to generate a B-mode image based on frequency compounded images associated with the line scans. 
     
     
         16 . The ultrasound system of  claim 15 , further comprising a display configured to visually present the B-mode image. 
     
     
         17 . The ultrasound system of  claim 12 , wherein the transmitting elements of the first phased transducer array are configured to receive excitation signals having configurable phase delays so as to provide transmit focusing, and the processing circuit is configured to implement receive focusing. 
     
     
         18 . A method of ultrasound imaging with frequency compounding for speckle reduction, the method comprising:
 applying a drive signal to a transducer array so as to excite the transducer array and compensate for a frequency response of the transducer array;   transmitting a broadband ultrasound signal in a medium being imaged, wherein the applying causes the transmitted broadband ultrasound signal to have a flattened spectrum across a bandwidth of the transducer array;   receiving echoes of the broadband ultrasound signal from the medium;   frequency filtering, with a plurality of digital filters, the received echoes to produce a plurality of ultrasound images; and   generating a frequency-compounded ultrasound image by compounding the ultrasound images.   
     
     
         19 . The method of  claim 18 , further comprising:
 generating a plurality of additional frequency-compounded ultrasound images;   forming a B-mode scan from the additional frequency compounded ultrasound images and the frequency-compounded ultrasound image; and   outputting a representation of the B-mode scan.   
     
     
         20 . The method of  claim 18 , wherein the transmitting of the broadband ultrasound signal comprises transmitting the broadband ultrasound signal with a phased array that focuses the broadband ultrasound signal on at least one voxel within the medium being imaged.