(a) In vivo blood elimination kinetics of NPs and CNPs at a dose of 5 mg kg−1 body weight (n=3 for each group). The results were expressed as the mean±s.d. (b) Gd distribution in tissues of SKOV3 ovarian cancer mice 24 h post injection of Gd-DTPA, Gd-NP and Gd-CNPs, measured by inductively coupled plasma mass spectrometry (ICP-MS, Agilent Techologies, 7500ce). Three mice were used in each experiment. Mice received Gd-DTPA, Gd-NP and Gd-CNP at the dose of Gd 20 mg kg−1. After 24 h, mice were killed. Tumour and major organs were collected and weighted. Tissue samples were treated with 200 μl of nitric acid under 60 °C for 2 h till most tissues were digested. Fat was digested by adding another 200 μl of 50% H2O2 for 2–4 h and total volume was adjusted to 1 ml. Equal amounts of clear samples were used for ICP-MS analysis to detect Gd concentration. Results were normalized to original tissue weight and present as mg Gd per gram tissue (n=3 for each group). The results were expressed as the mean±s.d.