title: Experimental application of thermosensitive paramagnetic liposomes for monitoring magnetic resonance imaging guided thermal ablation.
abstract: The use of a liposomal paramagnetic agent with a T(1)-relaxivity that increases markedly at temperatures above the phase transition temperature (T(m)) of the liposomal membrane was evaluated during magnetic resonance imaging (MRI) guided hyperthermia ablation. A neodymium-yttrium aluminum garnet (Nd-YAG) laser unit and a radiofrequency ablation system were used for tissue ablation in eight rabbit livers in vivo. One ablation was made in each animal prior to administration of the liposomal agent. Liposomes with a T(m) of 57 degrees C containing gadodiamide (GdDTPA-BMA) were injected iv, and two additional ablations were performed. T(1)-weighted scans were performed in heated tissue, after tissue temperature had normalized, and 15-20 min after normalization of tissue temperature. Increase in signal intensity (DeltaSI) for ablations prior to injection of the agent was 13.0% (SD = 5.7) for the laser group and 9.1% (SD = 7.9) for the radiofrequency group. Signal intensity after administration of the agent unrelated to heating was not statistically significant (DeltaSI = 1.4%, P = 0.35). For ablations made after injection of the agent, a significant increase was found in the laser (DeltaSI = 34.5%, SD = 11.9) and radiofrequency group (DeltaSI = 21.6%, SD = 22.7). The persistent signal enhancement found in areas exposed to a temperature above the threshold temperature above T(m) allows thermal monitoring of MRI guided thermal ablation.
authors.affiliation: The Interventional Centre, Rikshospitalet University Hospital, 0027 Oslo, Norway. lars.frich@labmed.uio.no
authors.forename: Lars
authors.initials: L
authors.lastname: Frich
authors.forename: Atle
authors.initials: A
authors.lastname: Bjørnerud
authors.forename: Sigrid
authors.initials: S
authors.lastname: Fossheim
authors.forename: Terje
authors.initials: T
authors.lastname: Tillung
authors.forename: Ivar
authors.initials: I
authors.lastname: Gladhaug
mesh_terms: D000818:Animals; D017115:Catheter Ablation / Q000295:instrumentation; D003287:Contrast Media / Q000008:administration & dosage; D005240:Feasibility Studies; D019786:Gadolinium DTPA / Q000008:administration & dosage; D006979:Hyperthermia, Induced / Q000295:instrumentation*; D007091:Image Processing, Computer-Assisted; D008081:Liposomes / Q000008:administration & dosage*; D008099:Liver / Q000528:radiation effects*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011817:Rabbits
chemical_list: D003287:Contrast Media; D008081:Liposomes; D019786:Gadolinium DTPA