Sonazoid-enhanced Ultrasound for the Detection of Colorectal Liver Metastases Less Than 2 cm

Preoperative chemotherapy is often used for patients with colorectal cancer liver metastasis (CLM). Many small CLMs (\<=2cm) may disappear after chemotherapy, while most of these are still alive. Ultrasonography (US) is a common imaging modality for the intraoperative detection tumor. Sonazoid is new echo-contrast agent, which is more stable and sensitive for detecting of small tumor. Investigators initially this prospective study to compare the detection performance before and after using sonazoid.