Solid hydrogel coupling for ultrasound imaging and therapy

Abstract

The present invention employs hydrogels as acoustic couplings for clinical applications of ultrasound imaging and therapy, but is particularly applicable to high intensity focused ultrasound (HIFU) based therapy. While other materials can be used, it has been determined that polyacrylamide is sufficiently robust and transmissive to withstand the high temperatures encountered in HIFU therapy. One embodiment of a hydrogel coupling is configured in shape and size (length) to ensure that a focal region of an ultrasound transducer is disposed proximate the target area when the distal tip of the transducer is in contact with tissue. These couplings can be shaped to correspond to the beam focus characteristics of specific transducers. Water can be applied to hydrate the tip of the hydrogel coupling during use, and medication absorbed into the hydrogel material can be applied to the tissue in contact with the distal surface of the hydrogel.

1 . A method for using a dimensionally stable hydrogel mass to acoustically couple an ultrasound transducer with at least one of a target and a physical boundary associated with the target, wherein the ultrasound transducer is configured to apply high intensity focused ultrasound (HIFU) to a target, the method comprising the steps of: 
 (a) selecting an input power level and a duration to be used to energize the ultrasound transducer;    (b) providing a dimensionally stable hydrogel mass capable of maintaining its structural integrity when coupled to the ultrasound transducer used at the input power level and for the duration selected;    (c) coupling a proximal surface of the dimensionally stable hydrogel mass to an outer surface of the ultrasound transducer;    (d) coupling an outer extent of a distal surface of the dimensionally stable hydrogel mass to at least one of the target and a physical boundary separating the target from the distal surface of the dimensionally stable hydrogel mass; and    (e) energizing the ultrasound transducer according at the input power level and for the duration selected.    
   
   
       2 . The method of  claim 1 , further comprising the step of hydrating the distal surface of the dimensionally stable hydrogel mass, to prevent damage to the distal surface of the dimensionally stable hydrogel mass caused by the HIFU.  
   
   
       3 . The method of  claim 1 , further comprising the step of delivering a medicinal agent to at least one of the target and the physical boundary, after coupling the outer extent of the distal surface of the dimensionally stable hydrogel mass to at least one of the target and the physical boundary.  
   
   
       4 . The method of  claim 1 , wherein the step of providing a dimensionally stable hydrogel mass comprises the step of selecting a dimensionally stable hydrogel mass having a shape and size so that a length between the proximal surface and the outer extent of the distal surface of the dimensionally stable hydrogel mass ensures that a focal region of the ultrasound transducer is disposed proximate to the target.  
   
   
       5 . The method of  claim 1 , wherein the step of providing a dimensionally stable hydrogel mass comprises the step of selecting a dimensionally stable hydrogel mass having a melting point sufficiently high, and an acoustical absorbance sufficiently low to enable the dimensionally stable hydrogel mass to maintain its structural integrity when coupled with the ultrasound transducer, when: 
 (a) the outer extent of the distal surface of the dimensionally stable hydrogel mass is disposed proximate to a focal region of the ultrasound transducer;    (b) the ultrasound transducer is energized for a period ranging from about 1 second to about 100 seconds; and    (c) an intensity of an acoustical beam generated by the ultrasound transducer ranges from about 100 W/cm 2  to about 10,000 W/cm 2 .    
   
   
       6 . The method of  claim 1 , wherein the step of coupling the proximal surface of the dimensionally stable hydrogel mass to the outer surface of the ultrasound transducer comprises the step of using a retaining housing to removably couple the dimensionally stable hydrogel mass to the ultrasound transducer, the retaining housing substantially encompassing the dimensionally stable hydrogel mass, except for the proximal surface and the outer extent of the distal surface of the dimensionally stable hydrogel mass.  
   
   
       7 . The method of  claim 6 , wherein the step of coupling the proximal surface of the dimensionally stable hydrogel mass to the outer surface of the ultrasound transducer comprises the step of removably coupling the dimensionally stable hydrogel mass to the ultrasound transducer.  
   
   
       8 . The method of  claim 7 , further comprising the step of removing the dimensionally stable hydrogel mass after each use, to enable a replacement dimensionally stable hydrogel mass to be coupled to the ultrasound transducer.  
   
   
       9 . The method of  claim 7 , wherein further comprising the step of removing and disposing of the dimensionally stable hydrogel mass after using the dimensionally stable hydrogel mass in conjunction with the target, and repeating steps (a)-(e) of claim  68  to apply ultrasound to a different target.  
   
   
       10 . A method for making a dimensionally stable hydrogel mass to acoustically couple an ultrasound transducer configured to apply a high intensity focused ultrasound (HIFU) to a target, wherein the dimensionally stable hydrogel mass includes a proximal surface configured to removably couple with the ultrasound transducer and a distal surface having an outer extent configured to couple with at least one of a target and a physical boundary separating the target from the ultrasound transducer, the method comprising the steps of: 
 (a) mixing appropriate quantities of at least one monomer capable of forming a dimensionally stable hydrogel mass and a quantity of water sufficient to hydrate the at least one monomer that will be polymerized, to form a mixture;    (b) introducing the mixture into a mold;    (c) enabling the mixture in the mold to polymerize, forming the dimensionally stable hydrogel mass; and    (d) removing the dimensionally stable hydrogel mass from the mold.    
   
   
       11 . The method of  claim 10 , wherein: 
 (a) the step of mixing comprises the step of adding an agent for inducing polymerization of each monomer in the mixture; and    (b) the step of enabling the mixture in the mold to polymerize comprises waiting a period of time sufficient for the polymerization induced by each agent to reach completion.    
   
   
       12 . The method of  claim 10 , wherein the step of enabling the mixture in the mold to polymerize includes the step of irradiating the mixture in the mold with light having a wavelength selected to induce polymerization of the mixture.  
   
   
       13 . The method of  claim 10 , wherein the step of mixing comprises the step of including at least one monomer selected to produce a dimensionally stable hydrogel mass having a melting point sufficiently high, and an acoustical absorbance sufficiently low to enable the dimensionally stable hydrogel mass to maintain its structural integrity, when: 
 (a) the outer extent of the distal surface of the dimensionally stable hydrogel mass is disposed proximate to a focal region of the ultrasound transducer;    (b) the ultrasound transducer is energized for a period ranging from about 1 second to about 100 seconds; and    (c) an intensity of an acoustical beam generated by the ultrasound transducer ranges from about 100 W/cm 2  to about 10,000 W/cm 2 .    
   
   
       14 . The method of  claim 10 , further comprising the step of adding a medicinal agent to the mixture before the mixture is introduced into the mold, such that the dimensionally stable hydrogel mass produced includes a medicinal agent.  
   
   
       15 . The method of  claim 10 , further comprising the step of adding a medicinal agent to the dimensionally stable hydrogel mass after it has polymerized.  
   
   
       16 . The method of  claim 10 , wherein the mold comprises a volume corresponding to a size and a shape desired for the dimensionally stable hydrogel mass, and the step of introducing the mixture into the mold comprises the step of introducing the mixture into a volume corresponding to the size and shape desired for the dimensionally stable hydrogel mass.  
   
   
       17 . The method of  claim 10 , wherein the mold comprises a reservoir in fluid communication with a volume corresponding to a size and shape desired for the dimensionally stable hydrogel mass, and the step of introducing the mixture into the mold comprises the step of introducing the mixture into the reservoir, such that the volume is filled with the mixture flowing from the reservoir, leaving at least a portion of the mixture in the reservoir.  
   
   
       18 . The method of  claim 17 , further comprising the step of inhibiting the polymerization of the mixture in the reservoir while the mixture in the volume is polymerizing, to enable additional mixture from the reservoir to flow into the volume, accommodating shrinkage of the mixture in the volume, as the mixture in the volume polymerizes.  
   
   
       19 . The method of  claim 18 , wherein the step of inhibiting the polymerization of the mixture in the reservoir comprises the step of stirring the mixture in the reservoir.  
   
   
       20 . The method of  claim 17 , wherein the reservoir is disposed above the volume and is coupled to the volume through a fluid channel.  
   
   
       21 . The method of  claim 17 , further comprising the step of removing any undesired portion of the dimensionally stable hydrogel mass after the step of removing the dimensionally stable hydrogel mass from the mold.