Real-time Monitoring of Radiofrequency Ablation and Postablation Assessment: Accuracy of Contrast-enhanced US in Experimental Rat Liver Model

Abstract

Purpose:To examine the accuracy of the unenhanced zone at contrast material-enhanced ultrasonography (US) in predicting coagulative necrosis during and 21 days after radiofrequency (RF) ablation by using radiologic-pathologic comparison. Materials and methods:Animal studies were approved by the Institutional Animal Care and Use Committee. The livers of 28 rats underwent US-guided RF ablation. In four animals, contrast-enhanced US was performed during ablation and 2 hours and 2, 7, 14, and 21 days after ablation. The unenhanced zone area on US images was measured. DiI-labeled microbubbles were administered during ablation at 2, 4, and 6 minutes or at 2 hours and 2, 7, 14, and 21 days after ablation in the remaining 24 animals (n = 3 at each time point). One minute later, the animal was euthanized, and the ablated liver was harvested. Tissue samples were imaged to quantify total fluorescence, and NADH staining was performed on the same slice. Hematoxylin-eosin staining was also performed. The findings on fluorescence images, NADH-stained images, and hematoxylin-eosin-stained images were compared. The areas of DiI bubble-negative zones, NADH-negative zones, and lightly NADH-staining zones were measured. Data were analyzed by using one-way analysis of variance. Results:The area of the unenhanced zone on contrast-enhanced US images increased during RF ablation and reached a maximum within 2 days after ablation. At histopathologic examination, a transition zone manifested adjacent to the coagulation zone until 2 days after ablation. The DiI-bubble negative zone on fluorescence images and the damaged zone (transition zone plus coagulation zone) on NADH-stained images increased rapidly within 2 hours after ablation, then slowly reached the maximum on day 2. The ratios of the mean areas of these two zones at hour 2 to those at day 2 were 94.6% and 95.6%, respectively. High uniformity between the damaged zone on NADH-stained images and the DiI bubble-negative zone on fluorescence images was noted at all time points. Conclusion:The temporary transition zone in NADH staining is partially damaged and should transition to nonviability 2 days after ablation. These results demonstrate that contrast-enhanced US can help delineate the maximum area of cell damage (to within 5% of the maximum) as early as 2 hours after ablation. Contrast-enhanced US may be a simple and accurate tool for monitoring the effects of RF ablation and quantifying the size of thermal damage after treatment.q RSNA, 2013

Chronological changes of radiofrequency ablation zone in rabbit liver: an in vivo correlation between gross pathology and histopathology

“…This result is consistent with a previous study in which a damaged zone eventually transitioned to non-viability within 2 days after RF ablation. 12 The study reported that lightly stained peripheral zone on NADH staining increased rapidly within 2 h after ablation. 12 However, we did not notice a rapid increase in the lightly NADH-stained peripheral zone up to 2 h after RF ablation.…”

“…12 The study reported that lightly stained peripheral zone on NADH staining increased rapidly within 2 h after ablation. 12 However, we did not notice a rapid increase in the lightly NADH-stained peripheral zone up to 2 h after RF ablation. The reason for this discrepancy is not clear and further study on this issue is needed.…”

“…Hence, they could not evaluate early changes in the ablation zone. Wu et al 12 also assessed changes in ablation zones during RF ablation and at 2 h and 2, 7, 14 and 21 days after RF ablation using radiological-pathological comparisons. The study reported that a lightly stained peripheral zone on NADH staining correlated with a peripheral zone that had dilated sinusoids with packed erythrocytes, which corresponds well with our results.…”

“…The efficiency of new ablation technologies is usually evaluated by comparing gross pathology using a conventional method and a new method. [2][3][4][5] Although many studies have investigated histopathological evaluation and radiological-pathological correlations of hepatic RF ablation zones, [6][7][8][9][10][11][12] no definition of the ablation zone on gross pathology has been established. 13 The exact boundary of the ablation zone in gross pathology is still controversial; some studies only include the central, white ablation zone, whereas others also include the peripheral red zone.…”

2D shear-wave ultrasound elastography (SWE) evaluation of ablation zone following radiofrequency ablation of liver lesions: is it more accurate?

“…Contrast-enhanced imaging studies such as contrast-enhanced MRI (CEMRI), contrastenhanced CT (CECT) and contrast-enhanced ultrasound (CEUS) have been widely used to evaluate the treatment response. [4][5][6][7][8] The disappearance of arterial enhancement in the treated tumour region and an adequate safety margin on contrast-enhanced imaging studies indicate a successful treatment. 5,6 However, in general, the patients have to wait 1 month or more until the peritumoral hyperaemia reaction around the ablation zone disappears when these contrastenhanced imaging studies are applied, and the immediate contrast-enhanced imaging studies after RFA have been regarded as insufficient.…”