Long-lasting aqueous dispersions or suspensions of pressure-resistant gas-filled microvesicles and methods for the preparation thereof

Abstract

One can impart outstanding resistance against collapse under pressure to gas-filled microvesicle used as contrast agents in ultrasonic echography by using as fillers gases whose solubility in water, expressed in liter of gas by liter of water under standard conditions, divided by the square root of the molecular weight does not exceed 0.003.

1 .- 18 . Canceled.  
     
     
         19 . A method for making dry precursors for gas filled microbubbles for ultrasonic imaging comprising the steps of: 
 dissolving a mixture of hydrogenated soya lecithin and dicetyl-phosphate in a chloroform solution;    evaporating said solution to yield a dried mixture;    adding an aqueous liquid to the dried mixture to form a suspension;    extruding said suspension to form a liposome suspension;    diluting said liposome suspension with a lactose solution to form a diluted suspension;    freezing said diluted suspension to form a frozen suspension; and    freeze-drying said frozen suspension in a vessel to form dried powder, said vessel filled with a gas selected from the group consisting of CF 4 , CBrF 3 , CF 4  and CHClF 2 .