Assessment of the boundary of ablation zone in liver neoplasms using 2D shear-wave elastography

Abstract

Objective To explore the cut-off value of elasticity(Ecut-off) of the ablative tissue and the optimum scale for shear-wave elastography(SWE) to best delineate the liver ablations. Methods A total of 27 patients with hepatic tumor(27 nodules) were studied. 2D ultrasound and SWE images for every target focal liver lesion and SWE images for the right liver parenchyma were taken pre-operation.SWE images and contrast-enhanced ultrasound(CUES) images of the ablation in the same plane were taken at 2 h,1 d and 1 month post-ablation. The quality of SWE images was evaluated,Grade Ⅰ or Ⅱ were considered satisfied. The mena value of SWE(Emean) for both the target lesion and right liver parenchyma were measured. The non-enhanced area in the portal phase of CEUS image was considered as the ablation region. Young Modulus of corresponding region of the ablation area in SWE image were measured,which were boundary of the ablation zone and besides the boundary. ROC curve was made by minimum value of SWE(Emin) of the boundary and maximum value of SWE(Emax) of that besides the boundary to get the Ecut-off value of the ablative tissue. The Ecut-off was taken as the scale. The maturation region of SWE images and the non-enhanced regions of CEUS images were compared. An overlap above 80% was considered satisfied. Results Sixty percent (16 cases) of target lesions got Ⅰ Grade SWE images and forty percent (11 cases) got Grade Ⅱ.Emean for lesions was (66.0±47.0)kPa and that for right liver parenchyma was (10.7±5.4)kPa. The Ecut-off values for ablative tissues at 2 h,1 d and 1 m postablation were (48.25,47.10,47.80)kPa respectively.Maturation regions in SWE images with the scale of 50 kPa overlapped well with the corresponding non-enhanced areas of CEUS. Conclusions The Ecut-off values for ablative tissues are 47~50 kPa. SWE images with the scale of 50 kPa can well delineate the non-enhanced region of the corresponding CEUS images. Key words: Elastography; Contrast-enhanced ultrasound; Liver neoplasms; Radiofrequency ablation