title: MR imaging of therapeutic magnetic microcarriers guided by magnetic resonance navigation for targeted liver chemoembolization.
abstract: OBJECTIVE
  Magnetic resonance navigation (MRN), achieved with an upgraded MRI scanner, aims to guide new therapeutic magnetic microcarriers (TMMC) from their release in the hepatic vascular network to liver tumor. In this technical note, in vitro and in vivo MRI properties of TMMC, loaded with iron-cobalt nanoparticles and doxorubicin, are reported by following three objectives: (1) to evaluate the lengthening of echo-time (TE) on nano/microparticle imaging; (2) to characterize by MRI TMMC distribution in the liver; and (3) to confirm the feasibility of monitoring particle distribution in real time.
  
  
  METHODS
  Phantom studies were conducted to analyze nano/microparticle signals on T 2*-weighted gradient-echo (GRE) MR images according to sample weight and TE. Twelve animal experiments were used to determine in vivo MRI parameters. TMMC tracking was evaluated by magnetic resonance imaging (MRI) in four rabbits, which underwent MRN in the hepatic artery, three without steering, two in real-time, and three as blank controls. TMMC distribution in the right and left liver lobes, determined by ex vivo MR image analysis, was compared to the one obtained by cobalt level analysis.
  
  
  RESULTS
  TMMC induced a hypointense signal that overran the physical size of the sample on MR images. This signal, due to the nanoparticles embedded into the microparticles, increased significantly with echo-time and sample amount (p < 0.05). In vivo, without steering, contrast-to-noise ratio (CNR) values for the right and left lobes were similar. With MRN, the CNR in the targeted lobe was different from that in the untargeted lobe (p = 0.003). Ex vivo, TMMC distribution, based on MRI signal loss volume measurement, was correlated with that quantified by Co level analysis (r = 0.92). TMMC accumulation was tracked in real time with an 8-s GRE sequence.
  
  
  CONCLUSIONS
  MRI signal loss induced by TMMC can serve to track particle accumulation and to assess MRN efficiency.
authors.affiliation: NanoRobotics Laboratory, Department of Computer and Software Engineering and Institute of Biomedical Engineering, Ecole Polytechnique de Montréal (EPM), C.P. 6079, Succursale Centre-ville, Montreal, QC, H3C 3A7, Canada, pierre.pouponneau@polymtl.ca.
authors.forename: Pierre
authors.initials: P
authors.lastname: Pouponneau
authors.forename: Gilles
authors.initials: G
authors.lastname: Soulez
authors.forename: Gilles
authors.initials: G
authors.lastname: Beaudoin
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Leroux
authors.forename: Sylvain
authors.initials: S
authors.lastname: Martel
mesh_terms: D000818:Animals; D016461:Chemoembolization, Therapeutic / Q000379:methods*; D003035:Cobalt; D004317:Doxorubicin / Q000008:administration & dosage* / Q000493:pharmacokinetics; D004337:Drug Carriers; D016503:Drug Delivery Systems; D005240:Feasibility Studies; D007501:Iron; D008099:Liver / Q000378:metabolism*; D008113:Liver Neoplasms / Q000188:drug therapy; D008279:Magnetic Resonance Imaging / Q000379:methods*; D053758:Nanoparticles / Q000008:administration & dosage*; D019047:Phantoms, Imaging; D011817:Rabbits
chemical_list: D004337:Drug Carriers; D003035:Cobalt; D004317:Doxorubicin; D007501:Iron