The present invention relates to a method of preparation of ultrasound contrast agent precursors comprising phospholipid-stabilised perfluorobutane microbubbles. The method is amenable to commercial scale manufacture, and provides more consistent vial-to-vial yields and size distribution of said microbubbles. Also provided are methods of preparing kits and ultrasound contrast agents using the method of the invention.本發明係關於一種製備包含磷脂穩定化全氟丁烷微泡之超音波對比劑前驅物之方法。該方法經得起商業規模製造之考驗,且提供該等微泡之更一致瓶間產量及粒度分佈。亦提供使用本發明方法製備套組及超音波對比劑之方法。