Value of CT Volume Imaging for Optimal Placement of Radiofrequency Ablation Probes in Liver Lesions

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PURPOSE

To determine the value of multiplanar and volume-rendered modes of analysis versus axial imaging for the optimal placement of probes in spiral image computed tomography (CT)-guided radiofrequency (RF) ablation of liver lesions.

MATERIALS AND METHODS

Thirty-two malignant hepatic lesions in 21 patients with hepatocellular carcinoma (n = 10) or metastases (n = 11) were treated with percutaneous RF ablation. After axial CT-guided placement (biopsy mode) of the probe in the tumor, a contrast-enhanced spiral image set was obtained and data were viewed in contiguous axial sections and the multiplanar and volume-rendered modes. The position of the probe was characterized as “central,” “marginal,” or “outside,” corresponding with its position in the lesion. Outside positioning was corrected before ablation was performed and, in cases of “marginal” positioning, the probe was redirected after initial ablative therapy in the same session.

RESULTS

Multiplanar and volume-rendered analysis reclassified the needle position before 14 of 32 RF ablation procedures (44%; P = .0034, McNemar test). In 10 cases, probe positions considered “central” on biopsy-mode images were found to be “marginal” with multiplanar/volume-rendered analysis. In three cases, probe positions considered “marginal” on biopsy-mode images were found to be “outside” with multiplanar/volume-rendered analysis. In one lesion, multiplanar/volume-rendered analysis upgraded the probe position from “marginal” to “central.” Comparison of multiplanar and volume-rendered analysis revealed no difference in probe positioning. The time requirements to obtain additional data were 159 seconds ± 49 for multiplanar analysis and 434 seconds ± 78 for volume-rendered analysis.

CONCLUSION

A contrast-enhanced spiral CT image data set with multiplanar reformations to verify an optimal probe location after axial CT-guided needle placement should be obtained before RF ablation of liver lesions.

Section snippets

MATERIALS AND METHODS

The data of 21 patients who had hepatocellular carcinoma (n = 10), colorectal metastases (n = 9), or metastases of carcinoid tumor (n = 2) were included in this study. The mean age of all patients was 59 years (range, 46 –71 y) and there were 16 men and five women. Thirty-two hepatic lesions (mean size, 3.2 cm; range, 1.9 – 4.8 cm) were treated. Twelve patients presented with one lesion, seven patients with two lesions, and two patients with three lesions. Fourteen patients underwent one

Accuracy of Probe Placement

MPR reformations and VR reconstructions resulted in a reclassification of the needle position in 14 of 32 RF ablation procedures (44%; P = .0034). In 10 cases, probe positions considered “central” on biopsy-mode images were found to be “marginal” with MPR and VR analysis. In these cases, the probe was repositioned after initial RF ablation (Fig 2). In three procedures, probe positions considered “marginal” on biopsy-mode images were found to be “outside” with MPR and VR analysis (Fig 3). In

DISCUSSION

The success of RF ablation is in large part dependent on the correct positioning of the ablation probe (4, 5). Recognition of this relationship emphasizes the need for accurate guidance of the probe into the lesion. This study demonstrates the usefulness of collecting a limited contrast-enhanced CT spiral image data set to verify the probe position. In 13 of 32 procedures (41%), the location of the probe was downstaged based on an analysis of the spiral data set in the MPR mode, which resulted

CONCLUSION

The acquisition of a focused contrast-enhanced spiral CT data set with multiplanar reformations to verify an optimal probe location after conventional axial guidance of the probe is recommended before RF ablation of liver lesions.

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None of the authors has identified a conflict of interest.

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