Improving MR thermometry for microwave ablations: Quantitative assessment of target temperature and ablation duration

Objectives To investigate and optimize the quality of magnetic resonance imaging (MRI) thermometry during microwave ablations (MWAs). Materials & Methods Thirty-two MWAs were performed in 10 ex vivo bovine livers in a 1.5-tesla MRI system with real-time three-dimensional (3D) thermometry yielding temperature and thermal dose maps. The experiments were conducted twice using all combinations of four target temperatures (60; 80; 100; 120°C) and four ablation times (5:00; 7:30; 10:00; 15:00 min). Thermometry quality was rated on a 5‑point Likert scale. Ablation areas were compared with histopathology (hematoxylin and eosin, H&E; and nicotinamide adenine dinucleotide, NADH‑diaphorase) and correlated using Spearman coefficients. Likert scores were compared across temperatures using Kruskal-Wallis and Mann-Whitney U tests. All evaluations were performed independently by two readers. Results Lesion areas varied from 2.6 to 12.9 cm², increasing primarily with target temperature. Ablation areas from temperature and thermal dose maps correlated strongly with macroscopically visual necrosis ( p  < 0.01). Likert scores differed significantly across temperatures ( p  < 0.05). The highest image quality was achieved at 60°C for 7:30 min, showing comparable scores as at 80° for 15:00 min, but significantly differing from 100°C and 120°C. Conclusion Lower target temperatures were associated with improved MRI thermometry quality, providing more reliable visualization of ablation zones.