On a plane, the brain is irradiated by X-ray rotation. Because different brain tissues have different absorption capacities for X-rays, images of brain cross sections can be constructed. By superimposing the brain scanning images of each layer, we can construct a three-dimensional image of the brain.
CT technology belongs to structural imaging technology, which can only be used to observe the static structure of the brain, but not the dynamic function of the brain. Although the resolution of CT image is not high, it is enough to visualize the main structure of the brain, so it can be used to observe brain tumors.
MRI and CT are the same. The general principle of nuclear magnetic resonance imaging is that when an object is placed in a magnetic field and irradiated with appropriate electromagnetic waves, the rotational arrangement direction of hydrogen atoms (or other atoms, such as oxygen atoms) can be changed to make it resonate, and then we can analyze the electromagnetic waves released in this process.
Because the proportion of water in brain tissues is different, that is, the number of hydrogen-containing nuclei is different, so the intensity of nuclear magnetic resonance signals varies among different tissues. Using this difference as a feature quantity, various tissues can be separated. Similar to CT, MRI can also be used to detect brain structures and observe tumors in tissues.
There is no absolute difference between CT and MRI. In some cases, they can complement each other to make up for their respective shortcomings.