Some doctors recommend CT and some recommend MRI for the same part of the patient’s body, leaving the patient perplexed and confused. The indications for CT and MRI are different due to the different imaging principles. (CT) examination is, in the end, an X-ray examination, which can scan all organs of the body, and the scanning speed is fast, with a few seconds or a dozen seconds for a certain organ or the whole body. However, like ordinary X-ray examinations, excessive CT examinations can be significantly harmful to the human body in terms of the amount of radiation, especially in children, and should not be done frequently. (MRI) Magnetic resonance, which uses magnetic fields and radio pulses for imaging, is a safer test that is suitable for any population, including children and pregnant women. However, the use of MRI used to be limited in some ways, mainly because of the slow scan speed. Now that it has changed to a fully digital MRI device, the scan time is getting faster and faster, which benefits patients a lot. It used to take about 50 minutes, or even longer, to do an abdominal exam, but now it takes about 10 minutes to solve the problem. Another example is a neurological scan of the brain, which now takes about 8 minutes, or even faster. In the past, some tiny lesions may not be seen clearly, and the internal structure of some tissues and organs or lesions or may be shown ambiguously on the image, but now it can be shown more clearly. Although the examination time of MRI is much faster than before, it is still slower than CT; in addition, MRI examination is noisy, although some noise reduction treatment has been carried out, it still takes some time to completely remove the noise, so during the examination, the doctor will give the patient earplugs to reduce the psychological impact of the noise on the patient. CT and MRI, in terms of examination functions, have overlap, but they are not substitutes for each other and should be chosen according to the patient’s specific situation. For soft tissue lesions and tumors, the resolution of MRI is higher than that of CT, so MRI has advantages for the nervous system (including brain and cremaster), abdominal organs (liver, pancreas, kidney), breast, joints in various parts of the body, and soft tissues of the whole body. For organs containing gas like the lungs and gastrointestines, or if you want to understand the condition of the coronary arteries, CT examinations are preferred. For cerebral hemorrhagic disease, CT examination should be done as soon as possible to clarify the diagnosis. Although MRI can also confirm the diagnosis for cerebral hemorrhagic lesions, the examination time is relatively long. If acute cerebral infarction is suspected, MRI should be done immediately. This is because within 12 hours of the onset of acute cerebral infarction, CT is difficult to detect the lesion, while MRI can identify the lesion site within about 30 minutes of onset. With the widespread use of CT and MRI in clinical practice and the continuous updating of equipment, they each show their own advantages in the examination and diagnosis of diseases. Patients have a general understanding of their examination principles, which is more or less beneficial for doctors to cooperate with the examination and treatment. A CT high risk is equivalent to 442 x-ray chest sweeps.