LAUSR

C ultrasound imaging can characterize perfusion of the kidney transplant microcirculation. More recently, perfluorobutane has been advocated as a fluorocarbon that can be emulsified with consistent microsphere diameter of <10 micrometers capable of circulating through the peritubular capillaries of the kidney. We have recently shown that perfluorobutane microspheres can assist with diagnosis and monitoring of antirejection therapy using a murine model of organ transplantation. Perfluorobutane as a low-boiling point fluorocarbon (−2C) compared with physiologic or high boiling point fluorocarbons can be packaged efficiently in diacylphosphatidylcholine lipid microspheres using the technique of microbubble condensation. Low boiling point perfluorocarbons offer intravascular stability that can be disrupted with less transmitted energy than physiologic or high boiling point fluorocarbons. For the first time, we performed contrast-enhanced ultrasound imaging utilizing perfluorobutane-filled phospholipid microspheres (Sonazoid) correlating human kidney transplant microperfusion with kidney biopsy results (Figure 1). Full methods are described in Supplemental Materials and Methods (SDC 1, http://links.lww.com/TP/B769). In the future, similar low-boiling point fluorocarbons may be utilized for both diagnostic and targeted drug delivery with less risk of tissue injury because of lower mechanical index required for microsphere dissolution.