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Vascular Guide Wire Navigation with a Magnetic Guidance System: Experimental Results in a Phantom¹

¹ From the Institute of Diagnostic and Interventional Radiology, University Hospital Frankfurt, Johann Wolfgang Goethe-University, Theodor-Stern-Kai 7, D-60590 Frankfurt am Main, Germany (M.S., N.A., T.J.V.); Siemens Medical Solutions, Forchheim, Germany (R.K., M.K.); and Stereotaxis, St Louis, Mo (J.F.). Received April 9, 2003; revision requested June 25; final revision received November 18; accepted January 2, 2004. Address correspondence to M.S. (e-mail: m.schiemann@vff.uni-frankfurt.de).

View larger version (49K): [in a new window]   Figure 1. Diagram of the magnet system. This system contains two 0.1-T permanent magnets (1) located on opposite sides of the patient table (2). Each magnet and its respective positioner (3) are contained in a fiberglass cover (4), which is sized to allow movement of the magnets within the stationary cover during navigation. The magnets may be retracted via semicircular tracks permanently installed in the floor.

View larger version (110K): [in a new window]   Figure 2. Photograph of the magnetic navigation system. Experimental setup with silicone liver phantom (1) and engaged magnet positioners. The tableside magnet controller (2) enables the movement of the magnet positioners. The vector tablet (3) and pen (4) are used to enter the desired orientation for the tip of the magnetic guide wire displayed on the interface screens.

View larger version (82K): [in a new window]   Figure 3. Diagram of the magnet articulation axes. The magnet (1) articulates along three articulation axes by mechanical positioning mechanisms rotating (2) about the z axis, tilting about an axis located behind the magnet (3), and moving toward or away from the navigation volume along the z axis (4). The combination of rotating, translating, and tilting provides a magnetic field of a given strength in any direction at any location within the navigation volume.

View larger version (50K): [in a new window]   Figure 4. Diagram of guide wire tip configuration. A gold tube is welded to the distal paddle of the wire core, forming the distal tip and marker. A spacer collar is located between the platinum coil and the gold tube. Within the gold tube, a single 2-mm-long neodynium iron boron magnet is encased or potted. The distal tip is rounded to minimize trauma to the surrounding tissue during navigation.

View larger version (26K): [in a new window]   Figure 5. Diagram of magnetic guide wire deflection. The force (F) exerted on the tip of a guide wire equipped with a small permanent magnet inside a magnetic field (B) depends on the magnitude of the external magnetic field, sin () of the angle between the external field and the axis of the permanent magnet, magnetization (M) of the magnet, length (L) of the magnet, and cross-sectional area of the magnet (not shown).

View larger version (114K): [in a new window]   Figure 6. Radiograph of glass phantom shows an example navigation procedure, with the starting point (0) and seven target turns (1-7). In this image, the microcatheter is located at turn 6, and the magnetic guide wire has just been pushed past turn 7. Navigation with the conventional guide wire system was not successful beyond turn 5 (not shown).

View larger version (96K): [in a new window]   Figure 7. Surface-shaded display of the liver phantom. Volume rendering of rotational angiography is shown. Turns for wires are marked (1-8). The fluoroscopic image shows the tip of the magnetic guide wire inserted past turn 5.

View larger version (23K): [in a new window]   Figure 8. Box plots show that procedure and fluoroscopy times averaged more than 42 turns each. Center lines denote the median, the bounds of the boxes represent first and third quartiles, and the ends of the lines indicate maximum and minimum observed values. c = conventional navigation, m = magnetic navigation. The procedure time to reach a target did not differ significantly between methods, although fluoroscopy time was lower with the magnetic guidance system (P < .01).

View larger version (24K): [in a new window]   Figure 9. Box plots show fluoroscopy times averaged over 10 procedures each. Center lines denote the median, the bounds of the boxes represent first and third quartiles, and the ends of the lines indicate maximum and minimum observed values. c = conventional navigation (c1-c8), m = magnetic navigation (m1-m8). The differences between c and m were highly significant (P < .001).

View larger version (24K): [in a new window]   Figure 10. Box plots show procedure times averaged over 10 procedures each. Center lines denote the median, the bounds of the boxes represent first and third quartiles, and the ends of the lines indicate maximum and minimum observed values. c = conventional navigation (c1-c8), m = magnetic navigation (m1-m8). The differences between c and m were highly significant (P < .001).