Methods and apparatuses for measuring tissue stiffness changes using ultrasound elasticity imaging

Abstract

A method of evaluating tissue stiffness of a target area includes positioning an ultrasound elasticity imaging apparatus adjacent a surface of an area of tissue where the target area is located and applying a dynamic range of force to the tissue. A plurality of ultrasound beams can be directed at the tissue and a plurality of ultrasound echoes can be acquired from the strained tissue in the target area to calculate an amount of developed strain within the target area.

We claim: 
     
         1 . A method of using an insert to normalize measurements of tissue obtained by an ultrasound transducer, the method comprising:
 coupling an insert to an external surface of the ultrasound transducer;   directing a plurality of ultrasound beams through the insert and into an area of tissue;   acquiring a plurality of ultrasound echoes from the tissue and the insert; and   normalizing a measurement of strain on the tissue based on speckle tracking data obtained from ultrasound echoes reflected by the insert.   
     
     
         2 . The method of  claim 1 , further comprising:
 applying a first amount of force to the area of tissue to provide a first amount of applied strain on the area of tissue; and   calculating the first amount of applied strain on the area of tissue using speckle tracking.   
     
     
         3 . The method of  claim 2 , further comprising:
 applying a second amount of force to the area of tissue to provide a second amount of applied strain on the area of tissue; and   calculating the second amount of applied strain on the area of tissue using speckle tracking.   
     
     
         4 . The method of  claim 3 , wherein force is substantially continuously increased from the application of the first force to the application of the second force, and a varying amount of applied strain on the area of tissue is substantially continuously calculated from the application of the first force to the application of the second force. 
     
     
         5 . The method of  claim 4 , further comprising:
 extracting a nonlinear parameter from the relationship between the developed strain and the applied strain to identify a stiffness characteristic of the area of tissue.   
     
     
         6 . The method of  claim 1 , wherein the Young's modulus of the insert is known. 
     
     
         7 . An insert for normalizing speckle tracking data comprising:
 an insert configured to be coupled to an external surface of an ultrasound transducer, wherein the insert has a known Young's modulus and is generally ultrasonically transparent.   
     
     
         8 . The insert of  claim 7 , wherein the insert has a thickness that is between about 5 mm and 30 mm. 
     
     
         9 . The insert of  claim 7 , wherein the insert has a thickness that is between about 10 mm and 16 mm. 
     
     
         10 . The insert of  claim 7 , wherein the insert is sufficiently flexible to deform when coupled to the ultrasound transducer and the insert is brought into contact with soft tissue of a patient. 
     
     
         11 . The insert of  claim 10 , wherein the insert is sufficiently sturdy to experience an applied strain of at least 20% without breaking. 
     
     
         12 . The insert of  claim 11 , wherein the insert is sufficiently sturdy to experience an applied strain of at least 30% without breaking.