Ultrasonic contrast agent detection and imaging by low frequency manipulation of high frequency scattering properties

Abstract

A method for improved detection and imaging of ultrasound contrast agents using dual-band transmitted pulses, is described. The method is based on transmitting a pulse consisting of two frequency bands, a low frequency band which purpose is to manipulate the high frequency scattering properties of the contrast agent, and a high frequency band from which the image reconstruction is based. In addition, a general form of pulse subtraction is used to significantly suppress the received tissue signal.

We claim:  
     
         1 . A method for detection and imaging of ultrasound contrast agent in a region of soft tissue, where, 
 at least one ultrasound pulse containing frequency components in separated low and high frequency bands, is transmitted toward said region,    the time signals of said low and high frequency components are overlapping in time, so that said transmitted low frequency components are used to manipulate the acoustic scattering properties of the contrast agent for the incident frequency components in said high frequency band,    where the scattered signal from said transmitted high frequency components is used for ultrasound image reconstruction of said region.    
     
     
         2 . A method for detection and imaging of ultrasound contrast agent according to  claim 1 , where to reduce the low frequency components in the received signal before image reconstruction, the received signal is filtered in range to attenuate the low frequency components.  
     
     
         3 . A method for detection and imaging of ultrasound contrast agent according to  claim 1 , where, 
 at least two ultrasound pulses are transmitted consecutively toward said region with substantially same focus and direction of the ultrasound beam,    the phase of said low frequency components in said pulses is changed for each transmitted pulse,    the received signal from the consecutive pulses are for each depth combined to suppress tissue signal components.    
     
     
         4 . A method for detection and imaging of ultrasound contrast agent according to  claim 3 , where, 
 the ultrasound beam direction is scanned in steps, and for each radial image line a group of pulses is transmitted, each pulse with differences in the phase and/or amplitude of said low frequency components,    the back-scattered signal is sampled as a function of depth for each pulse and the samples for each depth are combined linearly along the pulse number coordinate,    the linear combination for each depth being selected so that the received high frequency components from the tissue are heavily suppressed, while the received high frequency components from the contrast agent are not significantly suppressed by the linear combination,    so that the output of the linear combination is used to form the image of the contrast agent for each depth along said radial image line.    
     
     
         5 . A method for imaging and detection of ultrasound contrast agent according to  claim 1 , where, 
 multiple ultrasound pulses are transmitted consecutively while the ultrasound beam direction is swept continuously over the region to be imaged,    the phase and/or amplitude of said low frequency components of the transmitted pulses being changed for each transmitted pulse,    the received signal being sampled in depth along the beam direction, and the samples used as input to high-pass filters operating along the pulse number coordinate for each depth,    the output of the high-pass filters for each depth being sampled at defined radial image lines to be used for construction of the contrast agent image as a function of depth along said radial image lines.    
     
     
         6 . A method for imaging and detection of ultrasound contrast agent according to  claim 3 , where the received signals from the consecutive pulses are digitally interpolated and temporally adjusted relative to each other before combination to adequately suppress the high frequency tissue components.  
     
     
         7 . A method for imaging and detection of ultrasound contrast agent according to  claim 3 , where in said transmitted pulses the amplitude of said high frequency bands may be separately adjusted.  
     
     
         8 . A method for imaging and detection of ultrasound contrast agent according to  claim 3 , where in said transmitted pulses the amplitude of said low frequency bands may be separately adjusted.  
     
     
         9 . A method for imaging and detection of ultrasound contrast agent according to  claim 1 , where the resulting contrast agent image is shown as an overlay on the resulting tissue image with a different intensity, color, or pattern.  
     
     
         10 . A method for imaging and detection of ultrasound contrast agent according to  claim 6 , where the temporal adjustment is done so that a part of the received high frequency tissue signal remains after the combination and is shown as a weak tissue image overlayed by the contrast agent image.  
     
     
         11 . A method for imaging and detection of ultrasound contrast agent according to  claim 5 , where the received signals from the consecutive pulses are digitally interpolated and temporally adjusted relative to each other before combination to adequately suppress the high frequency tissue components.  
     
     
         12 . A method for imaging and detection of ultrasound contrast agent according to  claim 5 , where in said transmitted pulses the amplitude of said high frequency bands may be separately adjusted.  
     
     
         13 . A method for imaging and detection of ultrasound contrast agent according to  claim 5 , where in said transmitted pulses the amplitude of said low frequency bands may be separately adjusted.