Contrast-enhanced intraoperative ultrasound (CE-IOUS) during surgery for colorectal liver metastases (CLM) is entered in clinical practice. However, its impact seems to decrease with the improvement of preoperative imaging. Therefore, if CE-IOUS should be selectively or routinely applied remains unclear: a profile of patients who may benefit of CE-IOUS application has to be disclosed. The aim of this study is to define reliable criteria for a selective use of CE-IOUS during surgery for CLM. IOUS is performed using 3-6 MHz convex probe, and a 7.5-10 MHz micro convex probe. Staging is completed by CE-IOUS using the standard 3-6 MHz convex probe and the dedicated 1.88-3.76 MHz harmonic frequency probe. In all patients, 2.4 mL of sulphur-hexafluoride microbubbles (SonoVue®, Bracco, Milan, Italy) are injected through a peripheral vein by the anesthesiologist. Ultrasound guidance is used to drive the dissection plane as previously described. Reference standards are histology and imaging at 6 months after surgery. Univariate and multivariate analyses are performed. Statistical significance is set at P=0.05.