I. History of CT: The photographic technique was a major innovation in diagnostic radiology in the early 1970s, which used a completely different method from ordinary X-ray photography to show tomographic images of various tissues and organs inside the body. Since its application in clinical practice, its development has undergone the following technical innovations: slip-ring CT in 1985; spiral CT in 1989; submillimeter scanning, double-spiral CT in 1991; real-time scanning technology in 1993; sub-second (0.75s) technology in 1995; and multilevel CT in September 1998. the scanning speed and imaging speed of CT have been significantly improved, making CT In 1999, multilevel CT became widely available worldwide. It is a new generation of CT machine. Second, the principle and technical characteristics of multi-level CT: Multi-slice CT scanner (abbreviated as MSCT), refers to the imaging system that can simultaneously obtain up to four levels of image projection data during a single scan rotation. Multi-slice CT scanner consists of the following systems: 1. scanning frame 2. a modified multilevel detector that allows a data acquisition system (DAS) capable of simultaneous data acquisition in four levels 3. a high-speed image reconstruction system capable of processing huge data volumes 4. A multi-level CT reconstruction technology system. Third, the advantages of multi-level CT currently shown the advantages of multi-level CT equipment, can be summarized as more, faster, better and save. The following are briefly described: 1. Longer scanning coverage (more): Since the detector has more than four data acquisition channels, the coverage is four times that of single-layer CT using the same layer thickness and the same scanning time, which is equivalent to the same pitch. Currently, multi-layer CT can scan the entire trunk from the upper thoracic opening to the pubic symphysis in 30 seconds with a thin layer of 2.5 mm up to 600 mm. 2. Shorter (faster) scanning time: Single-layer CT has shortened the examination time to nearly one-tenth of the original due to the elimination of the scanning interval. Multi-layer CT, while maintaining the original layer thickness and covering the same length as the original, equivalent to the same pitch, the scanning time is only a quarter of that of single-layer spiral CT, which can provide a fast scan of less than 0.5s, making the scanning time further shortened. This brings greater benefits to enhanced scans and post-enhanced staging scans, saving about 20% in contrast. At the same time, it expands the application of CT to a wider range of fields, such as the cardiovascular system. 3. Thinner scanning layer thickness (good): multi-layer CT has at least four data acquisition channels and shorter scanning time, which enables multi-layer CT to finish scanning with thinner layer thickness, greatly improving the spatial resolution in the Z-axis direction and obtaining various reorganization, reconstruction and three-dimensional imaging with significantly higher resolution in image post-processing work, broadening the application scope of CT and enriching the examination function of CT . 4.Reducing the loss (saving) of X-ray bulb: multi-level CT bulb emits the same amount of X-rays and can obtain more than four layers of images, which makes the utilization rate of X-rays increase to more than four times of single-level CT scan. Fourth, the clinical application of multilevel CT: Multilevel CT scanner was successfully developed in September 1998 and demonstrated during the meeting of the Radiological Society of North America in November of the same year, and its superiority has been widely recognized in the past three years. Its fast scanning speed, short imaging time and high spatial resolution make the application of CT, especially in the display of dynamic organs, more extensive and clinically effective. In addition, the application of multilevel CT makes CT-guided needle biopsy techniques faster and more accurate. Combined with real-time imaging technology (up to 12 images per second), multilevel CT fluoroscopy can clearly show the location of the puncture needle at multiple levels in a short period of time, improving the puncture success rate and positivity rate. The advent of multilevel CT not only improves CT technology, but also broadens the scope of CT applications and increases the value of CT use.