Catheter Visualization and Guidance with MR

---

Overview:
In order to perform endovascular procedures, the interventional practitioner must be able to clearly visualize the precise location and orientation of the catheter tip, in real time, and with reference to the tissue background. We are investigating two strategies for visualizing catheters with MR: 'passive tracking' and 'active tracking'. Both require rapid acquisition with 'real-time' image reconstruction and display. For the passive approach, catheters may be labeled with materials that will show up in appropriately weighted MR imaging sequences. For the active approach, a coil carrying a small electric current will be incorporated in the catheter, and this will transmit a signal to the MR detector coil.

In addition to visualizing the catheter, however, interventional practitioners must be able to direct the catheter tip into an assortment of challenging vessel geometries. Conventional approaches to this problem have involved development of catheter materials, tip geometries and the 'hands-on' exact skill of the interventional practitioner. Interventional MR, however, affords a special opportunity for remote orienting of the catheter by exploiting the ambient strong magnetic field. Current research at UCSF is also seeking to exploit this opportunity and to develop a device for remotely controlling the orientation of the catheter tip.

Findings:

Steering catheter tips A prototype device consisting of a minute electrical coil wound around the tip of a catheter has been developed (Figure 1). When an electric current is passed through the coil, a magnetic moment (and small magnetic field) is generated. In the presence of a strong external magnetic field, this magnetic moment (and thus the coil, and catheter tip) experiences a turning force, or 'torque', tending to align the magnetic moment with the external field of the MR scanner. Depending on the strength and polarity of the applied current, the coil will tend to align, or anti-align, with the magnetic field to a greater or lesser degree. This is demonstrated in Figure 2, where an assortment of different currents are applied to the coil and images are taken to depict the deflection of the catheter tip. These results were achieved with a single coil winding. With 3-axis coils, under independent control, the tip can then be deflceted arbitrarily in 3D space, under remote control.

Figure 1: Prototype coil windings Figure 2: Coil deflections with applied current

---

Return to Research Main Page

---

Last update February 27, 2001