Release pattern of DOX from GdSLs and SL. (A) The release of DOX from the liposomes after irradiation of 20-kHz ultrasound at various intensities and (B) the release of DOX from the liposomes after incubation at 37°C or 50°C. Molar ratio of Gd(III)-DOTA-DSPE, CHOL, and DSPE-mPEG2000 for GdSL1 was 31:15:4. Molar ratios of Gd(III)-DOTA-DSPE, CHOL, DSPE-mPEG2000, and DSPE for GdSL2 and GdSL3 were 20:15:4:11 and 10:15:4:21, respectively. Molar ratio of CHOL, DSPE-mPEG2000, and DSPE for SL was 15:4:31. All samples were treated for 1 min. Mean and S.D. are shown (n = 3) (asterisk, two asterisks, and three asterisks denote p < 0.05, Student's t test).