Background The advent of second generation agent-SonoVue and low mechanical index real-time contrastenhanced ultrasonography ( CEUS) imaging have been shown to improve the diagnostic performance ofultrasonography in hepatocellular carcinoma (HCC)·But no report has described the effect of high mechanicalindex (MI) post-CEUS·This study aimed to investigate the value of post-CEUS in displaying tissue structures ofHCC·Methods Seventy-six HCCs in 65 patients were included in the study·Each patient underwent three scans,high-MI (MI: 0·15 -1·6) pre-contrast ultrasound, low-MI (MI: 0·04 -0·08) CEUS with contrast agentSonoVue, and high-MI post-contrast ultrasound, which was performed within 3 minutes after CEUS·The size,boundary, echogenicity, internal echotexture and posterior acoustic enhancementof the HCCs in the conventionalscans before and after CEUS were evaluated·According to pathological evidence, diagnosis rates of pre-contrast,CEUS and post-contrast scans were determined and compared·The potential mechanism of post-contrastultrasound imaging was also discussed·Results Compared with pre-contrast, post-contrast ultrasound showed improvement in image quality in mostHCCs: twenty-six (34·2%) more lesions showed well defined margins and fourteen (18·4%) more nodulesshowed halo sign; twenty-three (30·3%) lesions demonstrated enlarged in sizes; changes in echogenicity wereseen in 30 lesions (39·5%); eighteen (23·7%) more lesions showed heterogenecity and 20 (26·3%) morelesions showed“mosaic”or“nodule-in-nodule”sign; twelve (15·8%) more lesions showed posterior acousticenhancement·Post-contrast ultrasound showed increased diagnostic accuracy of93·4% (71/76), compare with88·2% (67/76) of CEUS alone·Conclusions High-MI post-contrast ultrasound utilizes harmonic signals during the rupture of microbubbles,and significantly improves the display of echo-characteristics of HCCs in ultrasound images, which addsdiagnostic values for CEUS·Post-contrast ultrasound could play an important role in tissue characterization, andmay be included in CEUS protocols· Background The advent of second generation agent-SonoVue and low mechanical index real-time contrastenhanced ultrasonography (CEUS) imaging have been shown to improve the diagnostic performance ofultrasonography in hepatocellular carcinoma (HCC). But no report has described the effect of high mechanical index (MI ) post-CEUS · This study aimed to investigate the value of post-CEUS in displaying tissue structures of HCC · Methods Seventy-six HCCs in 65 patients were included in the study · Each patient underwent three scans, high-MI (MI: 0 · 15 -1 · 6) pre-contrast ultrasound, low-MI (MI: 0.04-0.08) CEUS with contrast agent SonoVue, and high-MI post-contrast ultrasound, which was performed within 3 minutes after CEUS · The size , boundary, echogenicity, internal echotexture and posterior acoustic enhancement of the HCCs in the conventionals before and after CEUS were evaluated · According to pathological evidence, diagnosis rates of pre-contrast, CEUS and post-contrast scans were determined and · The potential mechanism of post-contrastultrasound imaging was also discussed · Results-contrast ultrasound showed improvement in image quality in mostHCCs: twenty-six (34 · 2%) more lesions initially defined margins and fourteen (18.4%) more nodulesshowed halo sign; twenty-three (30.3%) lesions were enlarged in sizes; changes in echogenicity wereseen in 30 lesions (39.5%); eighteen heterogenecity and 20 (26 · 3%) morelesions showed “mosaic” or “nodule-in-nodule” sign; twelve (15.8%) more lesions showed posterior acoustic enhancement · Post-contrast ultrasound showed increased diagnostic accuracy of 93 · 4% ( 71/76), compare with 88.2% (67/76) of CEUS alone Conclusions High-MI post-contrast ultrasound utilized harmonic signals during the rupture of microbubbles, and significantly improves the display of echo-characteristics of HCCs in ultrasound images , which adds diagnostic value for CEUS · Post-contrast ultrasound could play an important role in tissue characterization, andmay be included in CEUS protocols ·