Spin‐lock MR enhances the detection sensitivity of superparamagnetic iron oxide particles

Purpose To evaluate spin‐lock MR for detecting superparamagnetic iron oxides and compare the detection sensitivity of quantitative T 1ρ with T 2 imaging. Methods In vitro experiments were performed to investigate the influence of iron oxide particle size and composition on T 1ρ . These comprise T 1ρ and T 2 measurements (B 0 = 1.41T) of agar (2%) with concentration ranges of three different iron oxide nanoparticles (IONs) (Sinerem, Resovist, and ION‐Micelle) and microparticles of iron oxide (MPIO). T 1ρ dispersion was measured for a range of spin‐lock amplitudes (γB 1 = 6.5–91 kHz). Under relevant in vivo conditions (B 0 = 9.4T; γB 1 = 100–1500 Hz), T 1ρ and T 2 mapping of the liver was performed in seven mice pre‐ and 24 h postinjection of Sinerem. Results Addition of iron oxide nanoparticles decreased T 1ρ as well as the native T 1ρ dispersion of agar, leading to increased contrast at high spin‐lock amplitudes. Changes of T 1ρ were highly linear with iron concentration and much larger than T 2 changes. MPIO did not show this effect. In vivo, a decrease of T 1ρ was observed with no clear influence on T 1ρ dispersion. Conclusion By suppression of T 1ρ dispersion, iron oxide nanoparticles cause enhanced T 1ρ contrast compared to T 2 . The underlying mechanism appears to be loss of lock. Spin‐lock MR is therefore a promising technique for sensitive detection of iron oxide contrast agents. Magn Reson Med 74:1740–1749, 2015. © 2014 Wiley Periodicals, Inc.