MR imaging of hydrogel filament embolic devices loaded with superparamagnetic iron oxide or gadolinium

Introduction We evaluated hydrogel filaments loaded with barium sulphate and either gadolinium or superparamagnetic iron oxide (SPIO) in an effort to develop an embolic material that is visible with fluoroscopic and magnetic resonance imaging. Methods Hydrogel filaments were prepared with gadolinium and iron concentrations ranging from 1,500 to 7,500 and 500 to 2,500 ppm, respectively. The filaments were encased in agar and imaged using an MR scanner. Embolisation of eight aneurysms (seven bifurcation, one sidewall) in seven rabbits was performed using hydrogel filaments loaded with gadolinium ( n = 4) or SPIO ( n = 4). Angiographic evaluations occurred immediately post-treatment and at 13 weeks. Magnetic resonance angiography (MRA) evaluations occurred immediately post-treatment or 13 weeks post-treatment. Results Based on the in vitro results, we selected 4,500 and 2,000 ppm for gadolinium and iron loadings, respectively, for the in vivo experiments. Loading the filaments with gadolinium or SPIO did not affect the angiographic results, as embolic masses were readily evident with some distinguishing of individual filaments. In MRA, the hydrogel filaments loaded with SPIO were hypointense, and the hydrogel filaments loaded with Gd were hyperintense. The hyperintensity of the Gd-loaded filaments confounded the ability to distinguish between flow and the embolic devices. The hypointensity of the hydrogel filaments loaded with SPIO provided sufficient contrast between the embolic devices and the blood flow to allow of aneurysm occlusion evaluation using MRA. Conclusion Based on these results, we are focusing on loading hydrogel filaments with SPIO in an effort to provide adequate visualisation for use in MR-guided interventions.