Trace of Electrodes on Follow-up Liver Ultrasonography After Percutaneous Ultrasound-Guided Radiofrequency Ablation: "Tram-Track Sign"

ABSTRACT

PURPOSE: The purpose of this study is to report on the trace of the electrode used for a radiofrequency ablation (RFA) for a hepatic tumor on US images and to determine its frequency, factors affecting it, and its usefulness. MATERIALS AND METHODS: Twenty three patients had 44 RFA zones in the liver. Two parallel echogenic lines in the RFA zone were regarded as the trace of electrode and classified into four groups according to length. Parametric variables, including diameter of the tumor, location of the RFA zone, type of RFA electrode, length of the exposed tip, and the interval between the RFA procedure and follow-up US examination, were correlated with grades. RESULTS: Mean diameter of tumors was 2 cm and 28 of 44 RFA zones were located in the right hepatic lobe. Forty single and four cluster electrodes were used. Exposed tips measured 2 cm (n = 8), 2.5 cm (n = 4), and 3 cm (n = 32) in length. Two parallel echogenic lines more than 1 cm in length were detected in 23 of 44 RFA zones (52%). The grade of the trace showed negative correlation with the interval (p = 0.014). CONCLUSION: According to the results of our study, the frequency of traces of the electrodes (two parallel echogenic lines more than 1 cm in length, named the "tram-track sign") was 52%, and these fade over time. This sign could be useful as a landmark for accurate targeting in cases of local tumor progression.