Comparison of susceptibility artefacts of different RF-electrodes at 0.2 Tinfluence of alloy, sequence design and k-space acquisition methods.

Purpose: interventional MRI procedure monitoring requires small but accurat e susceptibility artifacts of the instruments used, In this investigation, susceptibility artifacts of different RE-electrode designs were compared us ing a variety of pulse sequences and k-space acquisition methods. Methods: 4 different 18-gauge RF-electrodes (with three single electrodes made of st ainless steel, copper, inconal, and a triple-clustered electrode configurat ion made of inconal) were placed in a 0.2T MR-scanner perpendicular to the main magnetic field. Pulse sequences used included: TSE T-2, FISP, true-FIS P, PSIF, and a temperature sensitive ES-GRE sequence. In addition to the 2D Cartesian k-space trajectory with Fourier transformation (2DFT), projectio n reconstruction (PR) was used with the FISP, true-FISP and PSIF sequences. Results: The best tip accuracy was achieved with the combination of incona l electrodes and TSE it. The usefulness of the tested sequences was found t o be: TSE T-2 > PSIF > FISP/true-FISP > ES-GRE. In general 2DFT provided be tter or equal tip accuracy than PR. The apparent shaft width was smaller us ing the copper electrode compared to the inconal electrode. However, the "m atch shaped" tip artifact of the copper probe led to a higher error in tip accuracy. Conclusions: TSE-T-2 sequences and Cartesian 2DFT acquisitions sh ould be used for accurate tip positioning at 0.2T. Further, artifact size o f the electrode shaft prevents the use of inconal for temperature sensitive sequences. Copper electrodes can be used for these purposes, although copp er is not considered to be biocompatible at present.