Ultrasound contrast agents and process for the preparation thereof

Abstract

Injectable aqueous suspension of microbubbles filled with a biocompatible gas and a method of preparation thereof. At least 10% of the total volume of gas contained in the microbubbles is contained in microbububbles with a diameter of 1.5 μm or less. The microbubbles can be obtained by preparing an emulsion comprising an aqueous medium, a phospholipid and a water immiscible organic solvent. The emulsion is then freeze-dried and then reconstituted in an aqueous suspension of gas-filled microbubbles.

1 . An injectable aqueous suspension of microbubbles filled with a biocompatible gas and comprising a stabilizing layer predominantly comprising a phospholipid, wherein at least 10% of the total volume of gas contained in the microbubbles is contained in microbubbles with a diameter of 1.5 μm or less.  
     
     
         2 . The aqueous suspension according to  claim 1  wherein at least 25% of the total volume of gas contained in the microbubbles is contained in microbubbles with a diameter of 1.5 μm.  
     
     
         3 . The aqueous suspension according to  claim 1  wherein at least 50% of the total volume of gas contained in the microbubbles is contained in microbubbles with a diameter of 1.5 μm  
     
     
         4 . The injectable suspension according to  claim 1  wherein at least 70% of the total volume of gas contained in the microbubbles is contained in microbubbles with a diameter of 1.5 μm  
     
     
         5 . The aqueous suspension according to  claim 1  wherein said microbubbles have a D V50 /D N  ratio of about 2.00 or lower.  
     
     
         6 . The aqueous suspension according to  claim 1  wherein said microbubbles have a D V50 /D N  ratio of about 1.80 or lower.  
     
     
         7 . The aqueous suspension according to any one of the preceding claims obtainable by a method which comprises the steps of: 
 a) preparing an aqueous-organic emulsion comprising i) an aqueous medium including water, ii) an organic solvent substantially immiscible with water, iii) an emulsifying composition of amphiphilic materials comprising more than 50% by weight of a phospholipid and iv) a lyoprotecting agent;    b) lyophilizing said emulsified mixture, to obtain a lyophilized matrix comprising said phospholipid;    c) contacting said lyophilized matrix with a biocompatible gas; and reconstituting said lyophilized matrix by dissolving it in a physiologically acceptable aqueous carrier liquid.    
     
     
         8 . A method for diagnostic imaging comprising administering to a subject a contrast-enhancing amount of an aqueous suspension of any one of  claims 1  to  6  and imaging at least a part of said subject.  
     
     
         9 . A method for diagnostic imaging comprising administering to a subject a contrast-enhancing amount of an aqueous suspension of any one of  claims 1  to  6  and imaging at least a part of said subject wherein said imaging comprises insonating said subject by means of an ultrasound device generating an ultrasound wave with a predetermined transmit frequency, from which a corresponding resonance size of microbubbles is determined, and administering a contrast agent comprising gas-filled microbubbles having a narrow size distribution and a mean size close to half the resonance size.  
     
     
         10 . A method for preparing a lyophilized matrix which, upon contact with an aqueous carrier liquid and a gas, is reconstitutable into a suspension of gas-filled microbubbles stabilized predominantly by a phospholipid, said method comprising the steps of: 
 a) preparing an aqueous-organic emulsion comprising i) an aqueous medium including water, ii) an organic solvent substantially immiscible with water comprising, dispersed therein, an emulsifying composition of amphiphilic materials comprising more than 50% by weight of a phospholipid and iv) a lyoprotecting agent;    b) lyophilizing said emulsified mixture, to obtain a lyophilized matrix comprising said phospholipid.    
     
     
         11 . The method according to  claim 10  wherein the lyoprotecting agent is dissolved in the aqueous carrier.  
     
     
         12 . The method according to  claim 10  wherein the lyoprotecting agent is polyethylenglycol.  
     
     
         13 . A method for preparing an injectable contrast agent comprising a liquid aqueous suspension of gas-filled microbubbles stabilized predominantly by a phospholipid, which comprises the steps of: 
 preparing a lyophilized matrix according to the method of any one of the preceding  claims 10  to  12 ;    contacting said lyophilized matrix with a biocompatible gas; and    reconstituting said lyophilized matrix by dissolving it into a physiologically acceptable aqueous carrier liquid, to obtain a suspension of gas-filled microbubbles stabilized predominantly by said phospholipid.