Influence Factors on Registration of Three-Dimensional Contrast-Enhanced Ultrasound Fusion Imaging in Evaluating the Ablative Margin - A Phantom Study

BACKGROUND: Registration of three-dimensional contrast-enhanced ultrasound fusion imaging (3DCEUS-FI) is timeconsuming to obtain high success rate. OBJECTIVE: To investigate the influence factors on registration success rate of 3DCEUS-FI. METHODS: Water tank phantoms were made to obtain mimicked pre- and post- radiofrequency ablation three-dimensional contrast-enhanced ultrasound (3DCEUS) and CT images. Orthogonal trials were designed according to factors including size, depth, enhancement level of mimicked tumor, diameter and number of mimicked adjacent vessels. Mimicked pre- and post-RFA 3DCEUS images of 72 trials were fused to assess ablative margin (AM) by two radiologists. With CT images as standard, 3DCEUS-FI accuracy was considered as the consistency of AM evaluation. The inter-observer agreement and the influence factors on registration success rates were analyzed. RESULTS: The intraclass correlation coefficient (ICC) for the consistency of AM evaluation between CT and 3DCEUS-FI in x-axis, y-axis or z-axis was 0.840 similar to 0.948 (P < 0.001). The ICC for inter-observer agreement was 0.840 similar to 0.948 (P < 0.001). The success rates of registration within mimicked vessels with diameter of 2mm were significantly lower than those with diameter of 3mm and 4 mm. CONCLUSIONS: The mimicked AM measured by 3DCEUS-FI had high accuracy and inter-observer agreement. Diameter of the mimicked adjacent vessels was significantly related to success rate of registration.