Spin-Lock MR Enhances the Detection Sensitivity of Superparamagnetic Iron Oxide Particles

To evaluate spin-lock MR for detecting superparamagnetic iron oxides and compare the detection sensitivity of quantitative T1? with T2 imaging.In vitro experiments were performed to investigate the influence of iron oxide particle size and composition on T1? . These comprise T1? and T2 measurements (B0 = 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). T1? dispersion was measured for a range of spin-lock amplitudes (?B1 = 6.5-91 kHz). Under relevant in vivo conditions (B0 = 9.4T; ?B1 = 100-1500 Hz), T1? and T2 mapping of the liver was performed in seven mice pre- and 24 h postinjection of Sinerem.Addition of iron oxide nanoparticles decreased T1? as well as the native T1? dispersion of agar, leading to increased contrast at high spin-lock amplitudes. Changes of T1? were highly linear with iron concentration and much larger than T2 changes. MPIO did not show this effect. In vivo, a decrease of T1? was observed with no clear influence on T1? dispersion.By suppression of T1? dispersion, iron oxide nanoparticles cause enhanced T1? contrast compared to T2 . 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.? 2014