Magnetic resonance properties of GdSLs. (A) T1-weighted MR images of GdSLs and MR-bester® at different concentrations of Gd(III). The MR images of SL were taken together for comparison. (B) Relaxivities (r1, in units of mM−1 s−1) of GdSLs and MR-bester®. Relaxivity was obtained from the slope of the linear fit of the inverse of the measured T1 (longitudinal relaxation time) as a function of Gd(III) concentration. 1/T1 data of SL without Gd(III)-DOTA-DSPE were presented as negative controls.