Motion-compensated real-time MR thermometry augmented by tracking coils.
OBJECTIVE
To develop and evaluate a real-time proton resonant frequency (PRF) based MR thermometry method with a novel motion compensation technique, using linear phase model and active tracking coils.


METHODS
A 6F catheter with multiple tracking coils and radiofrequency (RF) ablation tip was built for ex vivo experiments using excised bovine liver on a 1.5 Tesla scanner. A real-time MR acquisition scheme with interleaved active catheter tracking and multislice imaging was implemented. To evaluate the proposed method, in-plane periodic linear motion and through-plane irregular motion were induced by the rocker capability of the scanner and hand, respectively. Real-time temperature maps of the tissue undergoing a 2-min RF ablation cycle were obtained and used to compare the performance of the proposed method with that of the multi-baseline method.


RESULTS
The temporal window achieved per acquisition of one slice and catheter tracking is ∼380 ms. The standard deviations of tracking errors are less than 1 mm for both irregular and periodic motions in x-y plane. The measurements at the heated and unheated regions demonstrate that the proposed thermometry method perform equally well for both in-plane and through-plane motion while maintaining a similar accuracy (σ = 1.10 versus 1.04°C) compared with the conventional multi-baseline method.


CONCLUSIONS
The new MR thermometry method using catheter-based tracking coils and linear phase model for motion compensation and phase correction is promising and may offer reliable MR thermometry for real-time MRI-guided thermal therapies.
Medical Physics, University of Wisconsin - Madison, Wisconsin, USA.
Peng
P
Wang
Orhan
O
Unal
D000818:Animals; D017115:Catheter Ablation; D002417:Cattle; D008099:Liver; D053783:Magnetic Resonance Imaging, Interventional / Q000379:methods*; D009038:Motion; D013696:Temperature; D013817:Thermography / Q000379:methods*
MR thermometry; RF ablation; catheter tracking; interventional MRI