LANTHANIDE-BASED SUSCEPTIBILITY CONTRAST AGENTS - ASSESSMENT OF THE MAGNETIC-PROPERTIES

The T-2 contrast efficacy of paramagnetic contrast agents is dependen t on their magnetic properties. Vibrating sample magnetometry (VSM) an d the Live Chan NMR method have been used to evaluate the influence of ligand structure on the bulk magnetic susceptibility (EMS) of low-mol ecular weight (LMW) lanthanide chelates, VSM was also used for the EMS assessment of LMW lanthanide chelates covalently attached to cross-li nked starch particles. The ligand structure had no influence on the EM S of the gadolinium (Gd) and dysprosium (Dy) chelates. The mean EMS va lue of the Dy-chelates was 1.8 fold higher than that of the Gd-chelate s. The holmium (He) DTPA-BMA chelate had a similar EMS to that of Dy-D TPA-BMA while the lowest EMS was found for europium (Eu(lll)) DTPA-BMA , The covalent attachment of Gd-DTPA and Dy-DTPA to a cross-linked sta rch particle had no impact on their intrinsic magnetic properties. The EMS data were in good accordance with those obtained for non-particul ate bound LMW Dy- and Gd-chelates. The magnetic susceptibility of the Gd-DTPA labeled particles was described by the Curie law, indicative o f no magnetic interactions between Gd-DTPA molecules. The magnetic sus ceptibility of the Dy-DTPA labeled particles followed the Curie-Weiss law with a Curie-Weiss temperature of about -2 K, indicating magnetic interactions. The magnetic susceptibility of Dy-DTPA will, however, no t be affected by such magnetic interactions at physiological temperatu res.