Lanthanide‐based susceptibility contrast agents: Assessment of the magnetic properties

Abstract

The T2* contrast efficacy of paramagnetic contrast agents is dependent on their magnetic properties. Vibrating sample magnetometry (VSM) and the Live Chan NMR method have been used to evaluate the influence of ligand structure on the bulk magnetic susceptibility (BMS) of low-molecular weight (LMW) lanthanide chelates. VSM was also used for the BMS assessment of LMW lanthanide chelates covalently attached to cross-linked starch particles. The ligand structure had no influence on the BMS of the gadolinium (Gd) and dysprosium (Dy) chelates. The mean BMS value of the Dy-chelates was 1.8 fold higher than that of the Gd-chelates. The holmium (Ho) DTPA-BMA chelate had a similar BMS to that of Dy-DTPA-BMA while the lowest BMS was found for europium (Eu(III)) DTPA-BMA. The covalent attachment of Gd-DTPA and Dy-DTPA to a cross-linked starch particle had no impact on their intrinsic magnetic properties. The BMS data were in good accordance with those obtained for non-particulate bound LMW Dy- and Gd-chelates. The magnetic susceptibility of the Gd-DTPA labeled particles was described by the Curie law, indicative of no magnetic interactions between Gd-DTPA molecules. The magnetic susceptibility 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, not be affected by such magnetic interactions at physiological temperatures.

Microspheres with Ultrahigh Holmium Content for Radioablation of Malignancies

“…The paramagnetic nature of holmium locally induces a magnetic field inhomogeneity, leading to an enhanced MRI signal decay in gradient echo images (13). The resulting r 2 * relaxivity of the HoAcAc microspheres with a holmium load of 45% (w/w), is 264± 5.7 s −1 mg −1 ml, which is substantially higher than the r 2 * value for the HoPLLA microspheres with a holmium load of 17% (w/w) (92±3.2 s −1 mg −1 ml) (26).…”

“…The lack of (quantitative) imaging options for 90 Y (9) has lead to the development of holmium-166 loaded poly(L-lactic acid) ( 166 HoPLLA) microspheres, since 166 Ho emits gamma rays and beta particles that can be used for nuclear imaging and therapy, respectively (10)(11)(12). Moreover, holmium is highly paramagnetic and has a high linear attenuation coefficient allowing for visualization by magnetic resonance imaging (MRI) and X-ray computed tomography (CT), respectively (13,14).…”

Frequency-shift based detection of BMS contrast agents using SSFP: potential for MRA

“…If the cylinder axis is parallel to B 0 (h = 0), there is no frequency shift. Elements of the lanthanide series exhibit different magnetic properties [26][27][28]32,33]. Gadolinium is both an efficient dipolar relaxation enhancer and a susceptibility agent.…”

Investigation of lanthanide-based starch particles as a model system for liver contrast agents

“…The magnetic properties of particles with 2.7% metal content have previously been determined by variabletemperature vibrating sample magnetometry (11). The magnetic susceptibilities of the Dy-DTPA-SP and Gd-DTPA-SP at 22°C were 4.9 and 2.4·10 -2 cm 3 mol -1 , respectively.…”

“…The metal content of the particles was determined by inductively coupled plasma atomic emission spectrophotometry (ICP-AES) (11). For the Dy-DTPA-SP, the Dy content varied from 2.7% to 12.7% (w/w), and the Gd content of the Gd-DTPA-SP ranged from 2.7% to 9.3%.…”