Feasibility study for implementing low-field MRI with SPIO nanoparticles for endovascular interventions: An alternative to X-ray guided techniques

Nowadays the preferred treatment of patients with critical limb ischemia (CLI) is minimally invasive endovascular revascularization using fluoroscopic imaging techniques enhanced with iodine contrast. Low field magnetic resonance imaging (lf-MRI) using an open bore system has the potential to overcome the current disadvantages of fluoroscopic guided treatment of CLI patients, because it 1) is radiation-free, 2) offers positive contrast without adverse effects, and 3) provides maximum accessibility to the patient. The use of SPIO contrast agents at low magnetic field strengths to achieve positive contrast in arteries was investigated in static and dynamic circumstances. The purpose of this study was to investigate the workflow of an endovascular intervention guided by lf-MRI and which image quality could be reached.

The proposed surgical workflow when using lf-MRI was adapted based on a state of the art hybrid operating room and currently used fluoroscopic workflow. The following steps were conducted in this research using the open configuration ESAOTE G-scan Brio 0.25 T MRI system:

1. A clinically relevant range of SPIO [1] nanoparticles concentrations (0 mM – 4.096 mM) was scanned using T1-weighted 2D spin echo sequences. We found a positive contrast with a CNR higher than 5 in a range of 30 μM to 400 μM iron with a maximum CNR of 18 at 64 μM.

2. Experiments were performed on a phantom mimicking iliac and femoral mean blood flow using 3D balanced and spoiled gradient echo sequences. Comparing coronal images from the series with and without SPIO contrast material showed a 236% increase in signal intensity.

3. 3D reconstructions were created from subtraction images and maximum intensity projection images. Visual assessment of 3D MIP images shows an adequate spatial resolution quality to visualize structures with sub-millimeter reconstructed resolution.

The proposed workflow can work in practice, with an adequate spatial resolution of at least 1 mm using lf-MRI. However, temporal resolution should be increased to make this technique feasible for guiding endovascular interventions.