Quantitative assessment of ablation zone accuracy in 3D stack-of-spirals proton resonance frequency shift thermometry
Dominik Horstmann1,2, Othmar Belker1,2, Daniel Düx1,2
1Department of Diagnostic and Interventional Radiology, Hannover Medical School, Hannover, Germany.
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.
