title: Bottom-up study of the MRI positive contrast created by the Off-Resonance Saturation sequence.
abstract: Superparamagnetic iron oxide nanoparticles (SPM particles) are used in MRI to highlight regions such as tumors through negative contrast. Unfortunately, sources as air bubbles or tissues interfaces also lead to negative contrast, which complicates the image interpretation. New MRI sequences creating positive contrast in the particle surrounding, such as the Off-Resonance Saturation sequence (ORS), have thus been developed. However, a theoretical study of the ORS sequence is still lacking, which hampers the optimization of this sequence. For this reason, this work provides a self-consistent analytical expression able to predict the dependence of the contrast on the sequence parameters and the SPM particles properties. This expression was validated by numerical simulations and experiments on agarose gel phantoms on a 11.7 T scanner system. It provides a fundamental understanding of the mechanisms leading to positive contrast, which could allow the improvement of the sequence for future in vivo applications. The influence of the SPM particle relaxivities, the SPM particle concentration, the echo time and the saturation pulse parameters on the contrast were investigated. The best contrast was achieved with SPM particles possessing the smallest transverse relaxivity, an optimal particle concentration and for low echo times.
authors: Biomedical Physics Department, Université de Mons, Place du Parc 20, 7000 Mons, Belgium.
authors: S
authors: S
authors: Delangre
authors: Biomedical Physics Department, Université de Mons, Place du Parc 20, 7000 Mons, Belgium.
authors: Q L
authors: QL
authors: Vuong
authors: Biomedical Physics Department, Université de Mons, Place du Parc 20, 7000 Mons, Belgium.
authors: D
authors: D
authors: Henrard
authors: Biomedical Magnetic Resonance Research Group, Louvain Drug Research Institute, Université Catholique de Louvain, Brussels, Belgium.
authors: C
authors: C
authors: Po
authors: Biomedical Magnetic Resonance Research Group, Louvain Drug Research Institute, Université Catholique de Louvain, Brussels, Belgium.
authors: B
authors: B
authors: Gallez
authors: Biomedical Physics Department, Université de Mons, Place du Parc 20, 7000 Mons, Belgium. Electronic address: yves.gossuin@umons.ac.be.
authors: Y
authors: Y
authors: Gossuin
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D017352:Echo-Planar Imaging / Q000379:methods*; D005290:Ferric Compounds / Q000737:chemistry*; D052203:Ferrosoferric Oxide; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D053768:Metal Nanoparticles / Q000737:chemistry*; D019047:Phantoms, Imaging; D012685:Sepharose
chemical_list: D005290:Ferric Compounds; C000499:ferric oxide; D012685:Sepharose; D052203:Ferrosoferric Oxide
keywords: Contrast agents; Iron oxide nanoparticles; Magnetic resonance imaging; Off-resonance imaging; Positive contrast imaging; Superparamagnetic nanoparticles