The Value of Magnetic Resonance Imaging in Assessing Immediate Efficacy After Microwave Ablation of Lung Malignancies

Abstract

Purpose: To investigate the imaging performance and parametric analysis of magnetic resonance imaging (MRI) immediately after microwave ablation (MWA) of lung malignancies.

Materials and methods: We retrospectively analyzed the MRI performance immediately after MWA of 34 cases of lung malignancies. The ablation zone parameters of lung malignancies were measured, including the long diameter (L), short diameter (S), and safety margin of the ablation zone on plain computed tomography (CT), T1-weighted imaging (T1WI), and T2-weighted imaging (T2WI) after MWA. The study calculated the tumor volume (V 0 ), the ablation zone volume (V 1 ), and the ratio of V 0 to V 1 (V%). Statistical differences between the parameters were analyzed.

Results: The ablation area of the lesion exhibited central low signal and peripheral high signal on T2WI, central high signal and peripheral equal or high signal on T1WI, and circumferential enhancement in the periphery. The safety margin measured on T2WI was greater than that measured on plain CT and T1WI. On plain CT, the L, S, and V 1 were smaller in the effective treatment group than in the ineffective treatment group ( P <0.05). On T1WI, the V% and safety margin were greater in the effective treatment group than in the ineffective treatment group ( P =0.009 and P =0.016, respectively).

Conclusions: MRI may be a new, valuable method to assess immediate efficacy after MWA for lung malignancies using the ablation zone parameters V% on T1WI and safety margin on T2WI.

FIGURE 1

Flow diagram of patient enrolment patients in the study. MWA indicates microwave ablation.

FIGURE 2

Small circles represent tumors and large circles represent ablation areas. (A) The solid line represents the safety margin. (B) The long solid line represents the longest diameter (L) and the short dotted line represents the shortest diameter (S).

FIGURE 3

(A-E) Ineffective MWA treatment case: Pulmonary metastases from colorectal cancer in the lower lobe of the right lung (A), immediate MWA plain CT scan (B) showed incomplete annular GGO margin in the ablation (solid black line), T1WI (C) showed high signal in the center of the ablation area (solid white line) and slightly high signal at the edge (dotted white line). T2WI (D) showed a slightly increased signal in the center of the ablation (solid white line), an incomplete annular high signal at the edge (dotted white line), and a small high signal area outside the ablation area (solid red line). CT (E) 12 months later showed a recurrence at the upper edge of the lesion (solid black line). (F-J) Effective MWA treatment case: Liver cancer lung metastasis in the left inferior lobe (F), immediate MWA CT plain scan (G) showed a complete annular GGO margin in the ablation (solid black line), and T1WI (H) showed high signal in the ablation center (solid white line) and margin (dashed white line). T2WI (I) showed a slightly increased signal in the ablation center (solid white line) and a complete annular high signal at the margin (dashed white line). CT (J) 12 months later showed that the lesion had evolved into a shadow (solid black line). GGO indicates ground-glass opacity; MWA, ; microwave ablation; T1WI, T1-weighted imaging; T2WI, T2-weighted imaging.

FIGURE 4

The parameters of L, S, and safety margin on plain CT, T1WI, and T2WI. (A) L. (B) S. (C) Safety margin. L indicates long diameter; S, short diameter; T1WI, T1-weighted imaging; T2WI, T2-weighted imaging.

FIGURE 5

Correlation analysis between energy and ablation zone volume (V₁) in different sequences. (A) CT. (B) T1WI. (C) T2WI.