Real-time vascular interventional magnetic resonance imaging

Electromagnetic tracking for registration and navigation in endovascular aneurysm repair: a phantom study

OBJECTIVE

To assess the feasibility of using an electromagnetic tracking for both registration and navigation in endovascular aneurysm repair.

MATERIALS AND METHODS

A registration process was implemented to align computed tomography (CT) data and electromagnetic tracking data. Two abdominal aortic aneurysm (AAA) phantoms were used, a rigid plastic AAA model (phantom A) and a soft silicon AAA model (phantom B). A pre-procedural CT volume was acquired for each phantom. Intra-operative simulation was performed by placing each phantom in the magnetic field of the tracking device. Using a modified electromagnetic catheter, a set of three-dimensional positions was acquired in the phantom's aortic lumen. Pre-procedural CT images and intra-procedural tracked positions were registered. Four reference points were used to calculate the registration accuracy of phantom A. Three surgeons simulated catheterisation of the left renal artery with phantom B using only image-guided procedure software.

RESULTS

The mean registration error was 1.3 mm (range 0.88-1.89). The median time for left renal catheterisation was 22 s (range 15-59).

CONCLUSION

Registration of CT data and electromagnetic tracking data is feasible using catheter positions in the aorto-iliac structure as landmark. This navigation system could reduce X-ray exposure time and the use of contrast medium injections.

Feasibility of stent-graft placement with real-time MR fluoroscopy in a nonrigid aortic phantom

PURPOSE

To evaluate the feasibility of using real-time magnetic resonance (MR) fluoroscopic guidance to place a stent-graft mounted on a guide wire in a nonrigid aortic phantom.

MATERIALS AND METHODS

Real-time fast low-angle shot and true fast imaging with steady-state precession MR imaging sequences were used for device tracking. A modified fiber-optic guide wire and catheter embedded with titanium oxide in predefined positions were used for navigation in a homemade silicone thoracic aortic phantom.

RESULTS

Susceptibility artifacts caused by the modified guide wire and catheters mounted in the descending thoracic aorta of the phantom were found to enable adequate determination of the guide wire position in relation to the surrounding anatomy and to cause no image distortion. Real-time MR imaging enabled visualization of both the vessel lumen and the delivery system with the mounted stent-graft, providing an image quality sufficient for successful localization of the lesion and deployment of the stent-graft.

CONCLUSIONS

The results of this study prove the possibility of passive guidance in MR imaging-guided stent placement in vitro. The modified guide wire can be used with interventional commercial catheters and recent implant devices with selective tracking in the surrounding anatomy.

New aspects of technical testing of intravascular stents

Maximum magnetic resonance artifacts from stents are often determined by the presence of ferromagnetic compounds in the delivery system. We propose a mathematic model describing artifacts caused by nitinol stents. A method for evaluation of critical radial rigidity of the stents was developed.