ORIGINAL ARTICLE PURPOSE We aimed to detect possible differences in microwave ablation (MWA) volumes after different fluid preinjections using magnetic resonance imaging (MRI).
MATERIALS AND METHODSMWA volumes were created in 50 cuboid ex vivo bovine liver specimens (five series: control [no injection], 10 mL water, 10 mL 0.9% NaCl, 10 mL 6% NaCl, and 10 mL 12% NaCl preinjections; n=10 for each series). The operating frequency (915 megahertz), ablation time (7 min), and energy supply (45 watts) were constant. Following MWA, two MR sequences were acquired, and MR volumetry was performed for each sequence.
RESULTSFor both sequences, fluid preinjection did not lead to significant differences in MWA ablation volumes compared to the respective control group (sequence 1: mean MWA volumes ranged from 7.0±1.2 mm [water] to 7.8±1.3 mm [12% NaCl] vs. 7.3±2.1 mm in the control group; sequence 2: mean MWA volumes ranged from 4.9±1.4 mm [12% NaCl] to 5.5±1.9 mm [0.9% NaCl] vs. 4.7±1.6 mm in the control group). The ablation volumes visualized with the two sequences differed significantly in general (P < 0.001) and between the respective groups (control, P ≤ 0.001; water, P < 0.001; 0.9% NaCl, P < 0.001; 6% NaCl, P ≤ 0.001; 12% NaCl, P < 0.001). The volumes determined with sequence 1 were closer to the expected ablation volume of 8 mL compared to those determined with sequence 2. CONCLUSION For the fluid qualities and concentrations assessed, there is no evidence that fluid preinjection results in larger coagulation volumes after MWA. Because ablation volumes determined by MRI vary with the sequence used, interventionalists should gain experience in how to interpret postinterventional imaging findings (with the MR scanner, sequences, and parameters used) to accurately estimate the outcome of the interventions they perform.T hermal ablation techniques are increasingly used in the treatment of various primary and metastatic tumors at different sites, including the liver (1), kidneys (2), and lungs (3). Local ablation is most commonly performed using thermal ablation techniques such as radiofrequency ablation (RFA). Other techniques include laser-induced thermotherapy, cryoablation, high-intensity focused ultrasonography, and microwave ablation (MWA). Local ablation treatment is particularly appealing in combination with image guidance such as ultrasonography, computed tomography, and magnetic resonance imaging (MRI) to allow a minimally invasive approach to therapy (4-8).Several studies have demonstrated that combining RFA with preinjection of a fluid such as saline (different authors tested a range of concentrations) (9-14) or with diluted hydrochloric acid (15) can yield larger ablation volumes than RFA alone. In addition, both lowfield and high-field MRI can be used to monitor the effectiveness of RFA within NaCl-pretreated tissues, and the findings correlate well with pathologic results (9).Since the advent of MWA, several studies have introduced, tested, and compared this system (16)(17)(18)(19)(20)(21)(22), and the legitim...
