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Received May 3, 2018; Accepted Jun 4, 2018
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1. Introduction
It can be challenging to ablate small hepatocellular carcinomas (HCCs) under B-mode ultrasonography (US) guidance as small HCCs sometimes have poor sonographic conspicuity [1]. Fusion imaging (FI) of B-mode US and pre-acquired computed tomography (CT)/magnetic resonance imaging (MRI) has emerged as a useful guidance modality for percutaneous radiofrequency ablation (RFA) of small HCCs [2–5]. FI increases the confidence of a subtle lesion by colocalizing it to pre-acquired CT/MRI. However, when a tumor is completely isoechoic compared to surrounding normal liver, FI can only estimate the location of what is in essence a “virtual target,” and incomplete ablation can occur even after FI-guided RFA [6]. This shortcoming is due to the inherent registration error that occurs when applying rigid registration to a deformable organ during motion.
Contrast-enhanced US (CEUS) using Sonazoid (gaseous perflubutane, GE Healthcare, New York City, NY) has emerged as a promising technique for localizing small HCCs and guiding percutaneous RFA [7, 8]. HCCs can be localized with high confidence using the post-vascular phase unique to Sonazoid [9].
CEUS is now often combined with FI for percutaneous RFA of challenging small HCCs [10, 11]. This combination has been shown to enhance the feasibility of percutaneous RFA for HCCs inconspicuous on FI alone [11, 12] and also better assess the ablation zone [13]. However, most of these studies had retrospective designs. They included heterogeneous mixtures of liver tumors and only evaluated the value of CEUS-added FI for localizing liver tumors without sufficient follow-up data [11, 12, 14, 15]. To our knowledge, there are no solid data regarding how many tumors initially inconspicuous on FI become conspicuous after adding CEUS, thus enabling direct targeting for RFA.
Therefore, the primary endpoint of this trial was to assess the value of adding CEUS to FI for improving lesion conspicuity and the technical feasibility of percutaneous RFA of HCCs (1–2 cm) inconspicuous on FI alone. The secondary endpoint was to assess the therapeutic outcomes of RFA under CEUS-added FI guidance for HCCs inconspicuous on FI alone.
2. Materials and...