DE20019484U1 - MR-compatible guide wire or catheter - Google Patents

Description

Prof. Dr. med. Dipl.-Ing. Thomas Schmitz-Rode Kupferstrasse 5, 52070 Aachen

Priv.-Doz. Dr. med Arno Bücker Leopoldstrasse 9, 52349 Düren

Joachim-Georg Pfeffer Feldstrasse 8, 52070 Aachen

Prof. Dr. med. Rolf W. Günther Brüsseler Ring 73c, 52074 Aachen

UTILITY MODEL REGISTRATION

MR compatible guidewire or catheter

Minimally invasive procedures in the human body require guidewires and catheters. These are available in a variety of shapes, sizes, configurations and mechanical properties for fluoroscopy-guided procedures.

These catheters and guide wires cannot be used for magnetic resonance imaging (MRI)-guided procedures because they usually contain metal. This creates artifacts that make image assessment difficult or impossible. They also pose the risk of inductive heating in the magnetic field and thus pose a potential risk to the patient.

Three essential requirements for the instrumentation must be met in order to be suitable for MRI:

1. It must not contain any elongated metal parts, such as metal mesh for catheter reinforcement or wire cores for guide wires.

· · a

2. It should be possible to image the entire length of the instrument in the MRI image acquisition so that the position of the instrument in relation to the organ(s) becomes clear.

3. Since the spatial resolution of real-time MRI does not currently allow a direct visualization of catheters and guide wires, clearly visible effects along the instrumentation must be created in the MRI image.

4. Such effects should be large enough to ensure that the instruments are clearly visible in the MRI image, but small enough to ensure that important neighboring structures are not obscured.

The strong magnetic field of an MRI scanner means that the absence of ferromagnetism is a prerequisite for the use of instruments within this device. This rules out, for example, many standard catheters, which can be attracted and deflected by the strong magnetic field. Materials made solely from plastics meet the requirement of the absence of ferromagnetism. The small size of the instruments used, such as guide wires or catheters, poses a particular problem in the context of magnetic resonance imaging and particularly in the context of fast imaging. The faster the data is recorded in the MRI, the lower the spatial resolution. If you want to display an object as small as a catheter, which appears dark due to the relative lack of hydrogen protons, in the MRI, correspondingly high-resolution and therefore slow images are required. Furthermore, it is very difficult to image such a small object with the normally produced layer thicknesses of around 10 mm in such a way that it lies within the recorded layer and is not invisible due to partial volume effects. One solution to this problem is to use markings that lead to a local signal cancellation in the MRI image and thus make the instrument easier to find and display. In principle, materials that have a susceptibility (magnetizability) different from water are suitable for this. In order to determine the dependence of these

To avoid deviations from the orientation of an instrument in relation to the main magnetic field, these markings must be applied locally '. Rare earths, which are also used as MRI contrast agents, have been used in high concentrations for this purpose. They have been applied locally both as markers ² ' ³ ' ⁴ and as catheter fillings ³ in order to achieve better visibility of instruments in MRI. A major disadvantage of the substances used to date for local marking is the relatively large mass required to achieve a sufficient marking effect in MRI. This is reflected, for example, in the fact that much more complicated techniques have been developed which conduct current through a wire along the instrument ⁶ ' ⁷ ' ⁸ or which mount microcoils on catheters ⁹ '^{10>u> 12} ' ¹³ , although the safety problems associated with these, such as heating due to the radiofrequency field, have not yet been resolved in any way ¹⁴ . Such heating occurs when electrical conductors, such as metals, are exposed to radio frequency fields over a longer distance in the MR tomograph. If resonance occurs, the radiated radio energies are summed up via a standing wave, with the possible effect of significant heating of the conductor ' ⁴ .

The invention described here is based on the object of realizing an MRI-compatible guide wire or catheter which does not have any long, connected metal parts and is therefore not subject to the risk of inductive heating, but on the other hand can be displayed over its entire length longitudinally and transversely to the main magnetization in suitable MRI sequences without the body structures in the vicinity of the instrument being made unrecognizable by artifacts.

To specifically solve this problem, a tubular non-ferromagnetic base body doped at regular intervals with minimal amounts of ferromagnetic particles is used with the properties specified in the characterizing part of the claim.

1. The amount of particles is so small that no problems with magnetic attraction occur.

A segment of the guide wire according to the invention is shown in Fig. 1. Similarly, a segment of the catheter according to the invention is shown in Fig. 2.

The guide wire is formed from a cylindrical hollow tube ® made of non-ferromagnetic material (preferably plastic) which contains a cylindrical carrier (D), also made of non-ferromagnetic material (preferably plastic). Carrier ® is marked at regular intervals with clusters of ferromagnetic particles ® . Carrier (D is embedded in the hollow tube ® by a filling compound ©.

The catheter consists of a hollow tube with a double lumen (D). This has a large lumen © as a working channel for receiving a guide wire and a small lumen ®, which contains the components ®, (D and ® analogous to the guide wire shown in Fig. 1.

' Bakker CJG, Hoogeven RM, Weber J, van Vaals JJ, Viergever MA, and Mali WPTM. Visualization of dedicated catheters using fast scanning techniques with potential for MR-guided interventions. Magn Reson Med 1996; 36:816-820.

² Bakker CJG, Hoogeven RM, Hurtak WF, van Vaals JJ, Viergever MA, and Mali WPTM. MR guided endovascular interventions: susceptibility-based catheter and near-real-time imaging techniques. Radiology 1997; 202:273-276.

³ Bakker CJ, Smits HF, Bos C, Weide van der R, Zuiderveld KJ, Vaals van JJ, Hurtak WF, Viergever MA, and Mali WP. MR-guided balloon angioplasty: In vitro demonstration of the potential of MRI for guiding, monitoring, and evaluating endovascular interventions. J Magn Reson Imaging 1998; 8:245-250.

⁴ Adam G, Glowinski A, Neuerburg J, Buecker A, Vaals van JJ, Hurtak W, and Guenther RW. Catheter visualization in MR tomography: first animal experimental experiences with field inhomogeneity catheters. Fortschr Röntgenstr 1997; 166:324-328.

⁵ Omary RA, Unal O, Koscielski DS, Frayne R, Korosec FR, Mistretta CA, Strother CM, Grist TM. Real-time MR imaging-guided passive catheter tracking with use of gadolinium-filled catheters. J Vase Interv Radiol 2000; 11:1079-85.

⁶ Adam G, Glowinski A, Neuerburg J, Bücker A, van Vaals JJ, and Günther RW. Visualization of MR-compatible catheters by electrically induced local field inhomogeneities: evaluation in vivo. J Magn Reson Imaging 1998; 8:209-213.

⁷ Glowinski A, Adam G, Buecker A, Neuerburg J, Vaals van JJ, and Guenther RW. Catheter visualization using locally induced, actively controlled field inhomogeneities. Magn Reson Med L997; 38:253-258.

^s Glowinski A, Kiirsch J, Adam G, Bücker A, Noll TG, and Günther RW. Device visualization for interventional MRI using local magnetic fields: Basic theory and its application to catheter visualization. IEEE Trans Med Imaging 1998; 17:786-793.

⁹ Ackerman JL, Offutt MC, Buxton RB, and Brady TJ. Rapid 3-D tracking of small RF coils. Proc SMRM 5th Annual Meeting, Montreal, Canada 1986; 1131.

¹⁰ Ladd ME, Erhart P, Debatin JF, Hofmann E, Boesiger P, Schulthess von GK, and McKinnon GC. Guidewire antennas for MR fluoroscopy. Magn Reson Med 1997; 37:891-897.

¹ ' Ladd ME, Zimmermann GG, Quick HH, Debatin JF, Boesiger P, von Schulthess GK, and McKinnon GC. Active MR visualization of a vascular guidewire in vivo. J Magn Reson Imaging 1998; 8:220-225.

¹² Wildermuth S, Debatin JF, Leung DA, Dumoulin CL, Darrow RD, Uhlschmid G, Hoffmann E, and von Schulthess GK. MR imaging guided intravascular procedures: initial demonstration in a pig model. Radiology 1997; 202:578-583.

¹³ Wildermuth S, Erhart P, Leung DA, Göhde S, Schoenenberger A, and Debatin JF. Active instrument guidance in interventional MR imaging: introduction to a new concept. Fortschr Röntgenstr 1998; 169:77-84.

¹⁴ Königs MK, Bartels LW, Smits HFM, Bakker CJG. Heating around intravascular guidewires by resonantine RF waves. JMRI 2000:12:79-85

Claims (4)

1. Tubular, non-ferromagnetic base body, characterized in that it is marked with clusters of ferromagnetic particles at regular intervals along its longitudinal axis, wherein the weight of an individual cluster of particles is in the microgram range and thus, due to the small amount, does not substantially influence the external shape, stability and torsion properties of the base body. 2. Device according to claim 1, characterized in that the particle clusters are produced by selective application of a mixture of iron powder and carrier material. 3. Device according to claim 1 and 2, characterized in that the particle clusters are accommodated in the inner lumen of a non-metallic hollow tube, wherein a non-metallic cylinder introduced into the inner lumen acts as a carrier of the particle clusters. 4. Device according to claims 1-3, characterized in that the hollow tube has a hydrophilic coating on its outer surface.