# Application of Image Fusion in Diagnosis and Treatment of Liver Cancer
## 1 Introduction  
Medical imaging equipment has developed rapidly in the last decade, with widespread usage in clinical diagnosis and treatment. Two main imaging modes are employed that utilize different principles and equipment. The first is the anatomical imaging mode that mainly provides anatomical information with high resolution. The X-ray-based method, computed tomography (CT), which falls into the category of anatomical imaging, is the first technique developed for the noninvasive acquisition of images within the human body. CT is particularly effective for imaging tissues with large differences in density. At present, whole-body scans can be performed with the latest generation of CT systems, including multi-slice detectors that allow precise visualization, even for very small vessels. Magnetic resonance imaging (MRI) uses radio waves and magnets to generate body tissue images. Compared to CT, MRI uses nonionizing electromagnetic radiation, and appears devoid of exposure-related hazards. The technique employs radiofrequency (RF) radiation in the presence of carefully controlled magnetic fields to produce high-quality, cross-sectional images of the body in any plane. Using MRI, high spatial resolution can be effectively used to identify soft tissue within the human body [1, 2]. The functional imaging mode mainly provides functional metabolic information. One such method is single photon emission computed tomography (SPECT). SPECT imaging instruments provide three-dimensional (tomographic) images of the distribution of radioactive tracer molecules introduced into the body which is generated from multiple 2D images of the body at different angles [3]. Another widely used method in this mode is positron emission tomography (PET). PET is a nuclear medicine functional imaging technique used to observe metabolic processes in tissue of organs, as an aid to disease diagnosis [4]. The main difference between SPECT and PET is the decay mechanism of the radiotracers used: while SPECT measures photons of Gamma decay from a tracer nuclide, the PET scan uses 0.511-kevannihilation photons that are created when positrons, which are emitted from radiotracers, come to rest and meet with free electrons in organs. At a relatively low resolution, both SPECT and PET can be applied to reflect functional and metabolic information. Ultrasonography (US), which also falls into this category, is a technique for detecting the scattering and reflection of sound at an ultra-frequency level that allows the effective imaging of muscle, soft tissue, blood vessel and bone surfaces. US equipment is easy to use, and produces real-time images. However, the depth penetration of US is limited by several factors, such as the medium through which the ultrasound travels. All these available image techniques have different strengths and weaknesses. Therefore, an optimal combination of these methods can allow a simultaneous expression of information from various aspects of the human body within a single image. Such an image can accurately reflect internal structure and function, in turn providing physiological and pathological information. These image-gathering and analysis procedures compose the medical image fusion process. The current review presents a chronicle of available studies on the application of image fusion in malignant tumor diagnosis, with particular focus on liver cancer. Various methods exist for a comprehensive liver cancer treatment, including surgical resection, radiofrequency ablation, tumor embolization, etc. In clinical practice, an individualized treatment plan is established, relying on patient information such as the localization of lesions, and is highly dependent upon imaging technology.