Low molecular weight lanthanide contrast agents: in vitro studies of mechanisms of action.

The MR contrast properties of a series of structurally dissimilar low molecular weight (LMW) gadolinium (Gd) and dysprosium (Dy) chelates have been investigated under controlled experimental conditions in various in vitro test systems. Relaxation analysis (water, pH = 5.8, 37 degrees C, .47 T) demonstrated the high dipolar relaxation efficacy of the tested Gd chelates. The T1 and T2 relaxivities of both metal chelate series decreased with decreasing hydration number, confirming the strong correlation between metal chelate structure and dipolar relaxivity. Susceptibility-induced T2 relaxation, commonly known as the susceptibility effect, is modulated primarily by the magnetic susceptibility and compartmentalization of the contrast agent. The influence of these parameters on the susceptibility effect of Dy diethylenetriamine penta-acetic acid bis-methylamide (DTPA-BMA) and GdDTPA-BMA was investigated in two-compartment in vitro models. In red blood cell suspensions (45% hematocrit, 37 degrees C, .47 T, 2 and 3 mM metal ion concentration), the T2 relaxation efficacy of DyDTPA-BMA was markedly improved due to susceptibility effects that were shown to depend on compartmentalization. As the relaxation ability of GdDTPA-BMA was modulated by the dipolar interactions, compartmentalization was not a prerequisite for its T2 relaxation efficacy. In a coaxial glass system with no intercompartmental water exchange, which eliminated the dipolar relaxation mechanism, DyDTPA-BMA was shown to be the most efficient susceptibility agent because of its higher magnetic susceptibility. The reported one- and two-compartment model studies have demonstrated the different mechanism of action of LMW Gd- and Dy-based contrast agents. Gd chelates are predominantly dipolar relaxation enhancers, whereas Dy chelates are efficient susceptibility agents only in compartmentalized systems.

NC100150-enhanced 3D-SPGR MR angiography of the common carotid artery in a pig vascular stenosis model. Quantification of stenosis and dose optimization.

PURPOSE: NC100150 is a new type of ultra-small iron oxide (USPIO) blood pool agent. The aim of this study was to compare NC100150-enhanced MR angiography (MRA) to time-of-flight (TOF) MRA, phase-contrast (PC) MRA, and digital subtraction angiography (DSA) in experimental stenoses in pigs, and furthermore to determine the optimal dose of the contrast agent. MATERIAL AND METHODS: An experimental stenosis of the right and left common carotid artery (CCA) was applied surgically in 6 Yorkshire pigs. DSA was performed as the gold standard, followed by 3D-TOF, 3D-PC, and NC100150-enhanced MRA. RESULTS: Eleven stenoses of the CCA were successfully applied. The degree of the stenosis, determined by NC100150-enhanced MRA, did not differ significantly from DSA, whereas TOF and PC MRA underestimated it. The image quality of the NC100150-enhanced MRA was superior to both TOF and PC MRA. The optimal dose of NC100150 was 5-6 mg Fe/kg, since higher doses did not further increase signal-to-noise ratio or contrast-to-noise ratio. There was a linear relationship between blood relaxation rate and contrast dose. CONCLUSION: NC100150-enhanced MRA has the potential for quantification of carotid stenoses and provides an alternative to DSA. The optimal dose of NC100150 was 5-6 mg Fe/kg.