title: Tracking of an interventional catheter with a ferromagnetic tip using dual-echo projections.
abstract: Interventional devices with ferromagnetic components can be manipulated remotely using forces induced by the MRI gradients. To deflect the tip of an endovascular catheter, large ferromagnetic spheres of 2 mm diameter are required to exert sufficiently high magnetic forces; however, tracking of these devices is difficult due to the large image artifacts. In this study, a new dual-echo technique is proposed to improve the stability of localizing and tracking medical devices with ferromagnetic components. MR tracking methods with selective off-resonant excitation and phase compensation with a rephasing gradient can detect ferromagnetic spheres up to a diameter of 1 mm only. In this work, a dual-echo technique is used with two rephasing gradients to stabilize the off-set localization. With rephasing being applied in orthogonal directions, an SNR of 5 was achieved in the signal projections. Compared to a single-echo acquisition the dual-echo method reduces the position error in a phantom from 8 mm to 1.6 mm. In an in vivo study a tracking precision of 4 mm was measured without steering gradients at an image update rate of 2 images per second. Steering experiments were successfully performed with a prototype catheter with ferromagnetic sphere in an aorta phantom and in the vena cava of a pig.
authors.affiliation: Department of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
authors.forename: Ke
authors.initials: K
authors.lastname: Zhang
authors.forename: Florian
authors.initials: F
authors.lastname: Maier
authors.forename: Axel Joachim
authors.initials: AJ
authors.lastname: Krafft
authors.forename: Reiner
authors.initials: R
authors.lastname: Umathum
authors.forename: Wolfhard
authors.initials: W
authors.lastname: Semmler
authors.forename: Michael
authors.initials: M
authors.lastname: Bock
mesh_terms: D000465:Algorithms; D000818:Animals; D016477:Artifacts; D057785:Catheters; D005260:Female; D005583:Fourier Analysis; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008280:Magnetics; D059346:Magnets; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D013552:Swine
keywords: Dual-echo projection; Ferromagnetic sphere; Interventional catheter; Interventional magnetic-resonance imaging; Passive tracking; Real-time tracking