In vitro artefact assessment of a new MR-compatible microwave antenna and a standard MR-compatible radiofrequency ablation electrode for tumour ablation.

Hoffmann, Rüdiger; Rempp, Hansjörg; Eibofner, Frank; Keßler, David-Emanuel; Blumenstock, Gunnar; Weiß, Jakob; Pereira, Philippe L; Nikolaou, Konstantin; Clasen, Stephan

OBJECTIVE To evaluate and compare artefact configuration and diameters in a magnetic resonance (MR)-compatible prototype microwave (MW) applicator and a standard MR-compatible radiofrequency (RF) applicator for MR-guided tumour ablation. METHODS Both applicators were tested in a phantom study at 1.5T with three sequences: T1-weighted three-dimensional volume interpolated breath-hold examination (VIBE), T1-weighted fast low angle shot (FLASH), T2-weighted turbo spin echo (TSE). Applicator orientation to main magnetic field (B0) and slice orientation were varied. Needle tip location error (TLE) was assessed, and artefact diameters were calculated. Influence of imaging parameters on artefacts was assessed with analysis of variance (ANOVA) and post hoc testing. RESULTS MW applicator: the shaft artefact diameter measured 2.3 +/- 0.8 mm. Tip artefact diameter and length measured 2.2 ± 0.8 mm and 2.4 ± 1.3 mm, respectively. A prominent oval artefact (diameter: 16.5 +/- 1.8 mm, length: 19.1 +/- 2.5 mm) appeared close to the tip. TLE: - .3 +/- 0.6 mm. RF applicator: shaft and tip diameter measured 8.9 +/- 4.7 mm and 9.0 +/- .0 mm, respectively. TLE: -0.1 +/- 0.8 mm. Minimal artefacts were measured with RF applicator orientation parallel to B0 (P < 0.0001), whereas no such influence was found for MW applicator. For both applicators, significantly large artefacts were measured with T1 FLASH (P = 0.03). CONCLUSION The MW applicator's artefact is satisfactory and seems useable for MR-guided ablation procedures. KEY POINTS MW applicator's artefact appearance is independent of angulation to main magnetic field. MW applicator's prominent distal artefact may increase visibility under MR-guidance. RF and MW applicator's artefacts are precise concerning tip depiction. Largest artefact diameters are measured with T1-weighted fast low angle shot sequence.