In general, cancers bring about a four-step change which causes a disease. Genetic, biochemical and physiological changes tend to happen and until these stages, cancer patients usually have no subjective symptoms. An anatomical change generally incurs subjective symptoms, but at this time, most of the patients already have lost chances of treatment. In case of diseases like cancers for which the causes and treatments haven't been designated, the shape and size of tumors are important factors in judging further developments of the diseases. It also is very important to visually confirm if the cancer has spread to other organs. When the patients go through an endoscopy for their stomach or intestines, they feel pain due to cameras and cables being inserted in their body. The solution is to conduct endoscopy on patients while they are sleeping. Like this, it is not easy to look into the human body. Currently, doctors use three methods to monitor the interior of the human body without using their hands. They are ultrasonography, X-ray tests and nuclear magnetic resonance. In consequence medical devices, such as CT, MRI, Ultra Sonic, SPECT and PEt/CT, have been developed. Notable things among these are PET and PET/CT. As shown at the following chart, PET and PET/CT reduce cancers at an early stage by showing images of biochemical changes in the human body which happen earlier than physiological or anatomical changes.
Positron Emission Tomography or PET was developed at Uppsala in Sweden in the 1970s. Its basic technology is nuclear coincidence for nuclear measurement which is widely used for nuclear physics experiments. Researchers put a radiation source in the middle and study characteristics of the materials by comparing the time of the radiation's reaching using two detectors at the same time.
PET is to produce an array of several ringshaped detectors using this and to show the position of the radiation after measuring the quantity of radiation administered into the body.
Scientists took notice 16 _ March 2007 KOREA IT TIMES KOREA IT TIMES March 2007 _ 17 of the differences of amount of absorbed dextrose between cancer tissues and normal tissues by recognizing that the energy source of the human body is dextrose. Dextrose goes through a chemical replacement with F-18, a radioisotope, and makes injections using FDG, or Fluoride Dioxide Glucose. If the injections are administered into the human body, they show data of images and figures about differences between the amount of radiation emitted from the cancer tissues and that of radiation emitted from normal tissues, providing information for the spread of cancers, as well as the their early progress. The F-18 used at this time is not harmful to the human body because its half-life is very short - an hour and 50 minutes - and the amount of radiation for diagnosis is very small. In addition, the F-18 can be produced using cyclotron and the related principles and technological methods will be described later.
