Investigation of SPIO T1-signature: Positive Contrast using Ultrashort TE Imaging

Purpose: Superparamagnetic iron oxide (SPIO) nanoparticles are efficient contrast agents for molecular and cellular MR imaging [1]. They are usually considered to be negative contrast agents, since their magnetic moment causes signal dephasing which results in signal voids on T2* weighted images. However SPIO agents also have intrinsic T1 shortening properties [2] that can induce signal enhancement using appropriate pulse sequences, although these are usually counterbalanced by the T2* effect at high iron concentrations. Several methodological studies have been done to investigate the balance between those two opposed effects using classical MR pulse sequences [3, 4]. In addition positive contrast methods have been proposed to track SPIO nanoparticles [5, 6]. Those methods rely on susceptibility related effects produced in vicinity of the iron core. Here we propose to investigate the positive contrast due to the T1 shortening using Utrashort TE (UTE) MR pulse sequences [7]. In addition to usual T2* contrast one could benefit from the T1 signature of SPIO agents to improve specificity as well as localization while avoiding misclassification of signal drop out. Potential applications are imaging of inflammation and tumor metastases.