When you go to the hospital, you will inevitably have a variety of tests. Many people are confused about the various types of “films”, which tests are suitable for which diseases? Will there be any radiation when you have a test “film”? How many times a year can we do the examination? The presence of radiation depends on what “film” is taken, but normal examinations do not have to worry about harm to the body. What kinds of examinations do we usually talk about? Usually the “film” test done in the hospital includes ultrasound, X-ray, CT and MRI. Which of these tests are more accurate in diagnosing which diseases? No one test is better than another, and the various tests complement each other. In general, ultrasound is preferred for special organs such as the thyroid, breast, gallbladder, stones, uterus, and ovaries because they are more easily accessible and can be observed dynamically. MRI is more sensitive and specific for the nervous system (brain, cremaster), abdomen (liver, gallbladder, pancreas and spleen), limb joints (meniscus, ligaments, muscle lesions, microfractures, bone tumors), cremaster (intervertebral discs), breast, gynecological tumors, head and neck soft tissues, etc. In contrast, MRI is not effective in the lungs due to the lack of water (hydrogen protons), so CT is recommended as an option. x-rays are suitable for bones and other parts of the body, and gastrointestinal imaging (barium meal) can also be performed. Is there radiation for these tests? MRI and ultrasound do not have ionizing radiation, and both tests can be done repeatedly with no harm to the body. MRI for fetal malformations has been carried out in many hospitals in Japan and abroad, and it is said that many mothers have had that test. And X-ray machines and CT machines have no radiation when they are not doing the test. The doses used in routine diagnostic X-ray examinations (including X-rays and CT) are very small and limited to safe doses, and the chances of causing cancer are even negligible. With the advancement of technology, most hospitals now use digital imaging, and the radiation dose is greatly reduced compared to the previous X-ray and CT examinations, so there is no need to refuse the examination because of this concern. Since MRI is highly accurate, can you give me a full-body examination? No. MRI cannot do a whole-body examination, but can only do one organ at a time. MRI uses a different device, a coil, for each part of the body. This coil is similar to a lamp at home, there are chandeliers, table lamps, floor lamps, etc. Different lamps are used for different situations, not one lamp can solve all problems. What medical history is not suitable for these examinations? For X-ray and CT examinations, pregnant women and women who are preparing to get pregnant recently should do as little as possible, and children need to be strictly protected from critical areas during the examination. Generally speaking, the magnetic field of MRI can produce thermal effects, displacement, distortion and interference with images on metal products. Therefore, patients with heart/vascular stents, pacemakers and orthopedic surgery implants in their bodies are advised to consult with the doctor who placed the stent or performed the implant surgery to understand the material condition of the stent or implant before choosing whether the examination can be done. In addition, young children are prone to crying and cannot be imaged, and mostly require sedation. It is best to choose a specialized pediatric hospital for MRI examinations.