Since the discovery of x-rays,it has been used to detect diseases in humans.However,because some organs in the human body have very little difference in the absorption of X rays,the X rays can be difficult to detect in those tissues that overlap.So scientists in the United States and Britain began looking for something new to make up for the lack of X-ray technology to check for human lesions.

　　In 1963,American physicist mark found the body of different groups of X ray transmittance is different,in the study also found some related calculation formula,the formula for the application of CT later laid a theoretical foundation.

　　In 1967,Hounsfield,a British electronics engineer,began working on a new technology without knowing the results of his research.First,the pattern recognition was studied,and a simple scanning device,which can be used to strengthen the X-ray source,was then used to measure the human head.Later,he used the device to measure the whole body,and obtained the same effect.

　　In September 1971,hensfield teamed up with a neurologist to install the device,which he had designed and built at a hospital outside London,and began a head examination.On October 4,the hospital checked the first patient with it.In the case of a fully conscious patients with great lie on your back,the top of the X-ray tube in patients,turn round inspection area,to a counter at the bottom of the patients at the same time,make human body each part of X-ray absorption how much reflects on the counter,again after the processing of the electronic computer,make human body each part of the image from the screen display.The experiment was a great success.

　　The first CT was born in 1972 and was used only for brain scans.In April,hensfield first published the results at the British school of radiology,officially announcing the birth of CT.

　　In 1974,a full-body CT was made to examine the chest,abdomen,spine and limbs.

　　The first generation CT machine USES rotate/translate mode to scan and collect information.Due to the use of the pencil X ray beam and only 1~2 detectors,the data collected is small,the required time is long and the image quality is poor.

　　Scanning for the second generation of CT machine keep up with the generation doesn't change,just change the X wiring harness to the fan,detector increased to 30,enlarged the scan range,increased the collected data,improve image quality,but still can't avoid artifacts caused by patient physiological movement(an Artifact).

　　The third generation of the CT machine detector surged to 300~800,and the X-ray tube and the relative will be used for the rotary motion(rotate/rotate mode),and gather more data,scan time within the 5 s,greatly reduce artifacts,obviously improve the image quality.

　　The fourth generation of CT machine controller increased to 1000~2400,and the ring arrangement was fixed.Only the X-ray tube was revolving around the patient,namely rotate/stationary mode,the scanning speed was fast and the image quality was high.

　　Fifth generation CT machine will scan time reduced to 50 ms,solved the heart scan,is an electron gun produced by electron beam(electron beam)into a circular tungsten target,annular array detector to collect information.The 64-slice CT is available,with only 0.33s to obtain the image of the patient's 64 layers,with the spatial resolution less than 0.4mm,which improves the image quality,especially the imaging of the beating heart.