For MRI visualization of its MR safe guidewires MaRVis employs passive-negative MR markers. Iron microparticles centrically localized in the guidewire have been well optimized so that nicely balanced artifacts are generated longitudinal and perpendicular to B0 which normally are quite different between the two directions (due to magneto-physical reasons) and therefore less appropriate.
Due to continuous doping of the MaRVis Guidewires with MR markers a continuous „line“ image is generated. This simplifies adaptation to the new imaging modality for physicians as they are used to this type of visual representation from X-ray imaging. In order to precisely and reliably identify the location of the guidewire tip an additional ball-shaped MR tip marker with a slightly larger artifact diameter than the continuous artifact has been added. Thereby the physician can simply ensure that the tip is present in the actually displayed image slice.
High quality MR images of MaRVis Guidewires have been achieved on MR scanners of all three major manufacturers (GE, Philips, Siemens) using standard real-time interventional MR sequences (FGRE, bSSFP/bTFE, TrueFISP) without major alterations of standard MR sequences. Fast sequences with up to 7 images/second have been successfully tested on 1.5T and 3T MR scanners. The dimensions of the susceptibility artifacts generated by MaRVis Guidewires are close to the actual diameters of the devices themselves.
Testing in vessel phantom flow models (in water) did not result in significant differences to MRI visualization in a steady-state model (without flow).
Fig. 2-1: Philips 1.5T MR scanner, bTFE
(cooperation with Dr. Mirja Neizel-Wittke, University Hospital Düsseldorf, Germany)
Fig. 2-2: Siemens 1.5T MR scanner, TrueFISP
(testing with Prof. Mark E. Ladd, University Hospital Essen, Germany)
An extensive testing series using a vessel phantom for real-time MRI-guided stent implantation into the visceral, aortal, iliac and peripheral vasculature has been performed by the group of Prof. Arno Bücker, Prof. Günther K. Schneider and Dr. Alexander Maßmann (Saarland University Medical Center, Homburg/Saar, Germany). Visualization, handling and stability of the guidewires were rated good for all three guidewires. Accurate positioning of the delivery catheter and stent deployment was successful in all vessel regions.
Fig. 2-3: 0.014” micro MaRVis Guidewire with Cobra 4F catheter
Fig. 2-4: 0.035” standard MaRVis Guidewire with Optimed sinus-SuperFlex-Visual 5F stent
Fig. 2-5: 0.035” stiff MaRVis Guidewire
Fig. 2-6: 0.035” stiff MaRVis Guidewire
The conclusion was that in vitro MRI-guided simulation of typical basic interventional vascular maneuvers including stent implantation with the MaRVis Guidewires was successful and promising for further in vivo testing.