Focal nodular hyperplasia (FNH) in liver is the second common benign hepatic tumor. It usually shows hypervascular mass on imaging studies and it is not easy to differentiate with other hypervascular malignant tumor. For diagnosis of FNH, contrast-enhanced ultrasonography (US) has been used to detect 'spoke-wheel sign', which can be typically seen in FNH. However, temporal window of vascular phase using contrast-enhanced US (CEUS) is very short (about 10 sec) and coordination of patient`s respiration during US exam is absolutely needed. Thus, the investigators will use Superb-Microvascular imaging (SMI, Toshiba, Japan) for detection of 'spoke-wheel sign' in patients with proven FNH, which enable to detect slow micro vascular flow without using CEUS.