# Application of Image Fusion in Diagnosis and Treatment of Liver Cancer
## 5 Clinical Applications of Image Fusion in Liver Cancer Diagnosis and Treatment
### Ultrasonography/MRI, Ultrasonography/CT and Ultrasonography/PET-CT
#### Utility of CEUS/PET-CT in Transarterial Chemoembolization Treatment of Liver Cancer  
Transarterial Chemoembolization (TACE) has been employed for the treatment of liver tumors since the 1980s. With increasing information on the mechanisms underlying liver cancer progression, clinicians are gradually realizing that surgical resection is inadequate to treat cases with a background of liver cirrhosis and the biological characteristics of polycentric or multiple liver cancer, which are responsible for the high recurrence of liver cancer after surgery [174]. In addition, pathologists have confirmed that once the size of the hepatocellular carcinoma exceeds 5 cm, the incidence of tumor lesions invading the portal and hepatic vein branches to form vascular thrombus vessels is greatly increased, which is the basis of intrahepatic dissemination and distant hematogenous metastasis. TACE therapy for liver cancer has been gradually applied for clinical treatment with minimal trauma and significant efficacy. However, clinicians are yet to establish the type of liver tumor suitable for TACE therapy, the optimal means to evaluate the efficacy of TACE therapy and the specific indicators that should be evaluated before intervention. According to clinical practice, before interventional embolization for liver cancer, the scope of lesions and the number of sub-lesions should be determined, considering the clinical difficulty of the TACE-mediated control of the intrahepatic dissemination of tumors. Methods of application of existing imaging technologies to evaluate the residual tumor range after TACE, the specific times of new rounds of TACE treatment, and outcomes of tumor necrosis after treatment, are of clinical significance. TACE treatment is based on vascular embolization, and its effect depends on efficient blood flow into the tumor. Although enhanced CT or MRI is currently accepted as the gold standard for the imaging diagnosis of liver cancer, information provided by enhanced CT or MRI is mostly static, which is unable to help clear tissue perfusion of the tumor-bearing liver segment. Detailed images of the blood vessels furnishing liver cancer could not be clearly defined in previous analyses, and it was therefore impossible to assess whether the route of TACE into the tumor-bearing liver segment was effective, and the level of tumor necrosis after TACE. CEUS can be used to display micro-perfusion in liver tissues in real time, but its success is highly dependent on the experience of the operator, with interference from various objective factors. First, reactive congestion of liver tissue around the lesion in the early stages after interventional embolization is reported to affect measurement of the range of residual tumor lesions [163]. Second, contrast-enhanced images of the focal arterial stage were not evident when TACE was applied to intrahepatic cholangiocarcinoma with blood supply deficiency, and the detection rate of residual lesions was low. Additionally, contrast enhancement and regression were rapid in the arterial phase of tumor lesions with a rich blood supply, presenting the imaging characteristics of \"fast in and fast out\" [162]. CEUS may overlook residual lesions in different section scans. CEUS/PET-CT fusion imaging technology integrates the advantages of CEUS and PET-CT or enhanced PET-CT to display iodine-oil deposition, the even distribution of the embolization agent and the area of tumor necrosis in liver cancer. Therefore, the technique allows not only accurate estimation of the scope of the tumor lesion necrosis area after TACE, but also the recognition of blood flow signals in the necrotic area and a timely detection of residual lesions, which is of significant value in improving the efficacy of TACE, reducing recurrence, and ultimately improving the survival rate and the quality of life of patients. Due to the speed requirement of real-time CUES and CT/MRI fusion, arithmetic combination is usually used in the above clinical applications.