Purpose: Comparison of various MR imaging techniques without and with the application of Gd-BOPTA for the follow-up of thermal tumor ablations by means of laser-induced therapy (LITT).
Materials and methods: Thermal tumor ablations were performed with LITT in 19 patients showing a local recurrence. The metastases were from colorectal carcinoma in 15 cases (78.9 %) and from cervix, bronchial, gastric and renal carcinoma respectively in one patient each. The size of the metastases before ablation was on average 38.5 mm (min = 25 mm, max = 58 mm). The MRI protocol consisted of T2 UTSE FS, T1 w GRE without and with Gd-BOPTA at an early (20 s post injection) and late stage (> 120 min post injection). Two independent radiologists evaluated image contrast of the local relapse and necrosis in comparison to the surrounding healthy liver parenchyma on a scale from - 10 to + 10. Liver parenchyma was in any sequence 0. Recurrences were confirmed with follow-up examinations in all patients. Statistical analysis was performed by means of Wilcoxon and Kendall's W-test.
Results: Both radiologists found absolute ratios for contrast differences between thermal necrosis and local recurrence, with an average of 10.95 for T2 w UTSE FS and of 6.58 for T1 w GRE without, and of 4.05 for T1 w GRE with Gd-BOPTA in the early and of 2.26 in the late stage. Superiority for UTSE FS was significant (p < 0.05). The statistical analysis showed a high agreement for both radiologists for all values (p < 0.001).
Conclusion: For early detection of local recurrences after thermal ablation T2 w UTSE FS is most suitable. For the detection of new foci, the use of liver specific contrast media is advisable.