Quantitative assessment of ablation zone accuracy in 3D stack-of-spirals proton resonance frequency shift thermometry during clinical hepatic microwave ablation

Introduction

Real-time temperature feedback is critical for hepatic tumor ablation. Volumetric MR PRFS thermometry, including 3D stack-of-spirals sequences, shows promise; however, clinical validation for microwave ablation (MWA) is lacking. This study evaluated feasibility, spatial accuracy and susceptibility-related artifacts during hepatic MWA.

Methods

In 24 consecutively treated patients, 48 ablations targeting 34 hepatic lesions were included. After excluding 12 patients with overlapping ablations and one with severe artifacts, a retrospective analysis was conducted in 11 patients with 15 lesions. Thermometry-derived ablation zones were compared with post-ablative contrast-enhanced segmented ground truth. Spatial accuracy was quantified by Dice score (DS), sensitivity and mean surface distance (MSD) for full volumes and central five slices (1.25 cm) orthogonal to B0. Volumetric agreement was assessed by Pearson correlation. Voxel-wise temperature stability in unheated liver, needle orientation relative to B0 and capsule distance were correlated with ablation precision metrics.

Results

Unheated tissue temperature SD was 1.69 ± 0.51 °C. Mean full-volume accuracy was DS 0.64 ± 0.07, sensitivity 0.71 ± 0.11, MSD 3.91 mm ± 1.32 mm; mid-slice metrics yielded DS 0.75 ± 0.06, sensitivity 0.88 ± 0.08, MSD 4.33 mm ± 1.50 mm (all p < 0.001). DS correlated negatively with temperature SD (r = -0.61) and positively with capsule distance (r = .75); MSD showed inverse patterns. Needle orientation bore no significant correlation. Thermometry and ground truth volumes correlated strongly (r = 0.87).

Conclusion

Clinical 3D stack-of-spirals PRFS thermometry enables feasible volumetric and spatial estimation during hepatic MWA, though residual deviations remain. Central slices approach clinically relevant precision despite susceptibility effects. Targeted correction strategies and faster reconstruction may enable reliable real-time thermometry for guiding and validating thermal therapies in the abdomen.