Immediate changes in MRI signals after the MRI-guided microwave ablation of malignant liver tumors.

Objective: To observe the immediate changes in MRI signals after the MRI-guided microwave ablation of malignant liver tumors and to explore the pattern of immediate signal changes post-ablation.

Materials and methods: A retrospective analysis was conducted on 23 patients with 27 lesions who underwent MRI-guided liver microwave ablation at Baoshan people's Hospital from September 2022 to December 2023. The relationship between the changes in MRI signals and time post-ablation was studied. The first scan was performed immediately after ablation (designated as 0 min) and followed by scans at 3 min, 6 min, 10 min, 15 min, 20 min, and 30 min post-ablation. The signal characteristics that changed in each sequence after each scan were measured and recorded.

Results: After ablation, the mean maximum diameter of the high-signal range in 27 T1WI ablation foci varied over a short period of time (0 min: 22.00 mm; at 3 min: 26.58 mm; at 6 min: 26.94 mm; at 10 min: 27.06 mm; at 15 min: 27.12mm; at 20 min: 27.16 mm; and at 30 min: 27.16 mm). The change from 0-10 min was statistically significant (t = -10.326, P < 0.001), whereas the change from 10-30 min was not statistically significant (t = -1.536, P = 0.068). And, the signal intensity increased over time. The signal intensity of the primary lesion remained unchanged while the range decreased. There were minimal differences in the range and intensity changes in the T2-weighted imaging (T2WI) sequence. In diffusion-weighted imaging (DWI), the lesions showed high-signal intensity pre-ablation, but in post-ablation, it exhibited a high-signal surrounding the ablation zone with iso-intense or mixed signals, and the apparent diffusion coefficient (ADC) value increased.

Conclusion: The high-signal range observed in the T1WI sequence at the 10th min scan after the ablation completely reflected the true extent of the ablated foci, whereas the low-signal range in the T2WI sequence was stable and unchanged.