What is the essential difference between CT and X-ray? Can CT replace X-ray?

In fact, the essence of ct and X-ray is the same. Both use the penetrating effect of X-ray to image the internal structure of human body, but the difference is the different scanning angles.

Let's briefly introduce the penetrating principle of X-ray.

X-ray was discovered accidentally by a physicist named Qin Lun in the experiment of 1895. The wavelength of this light is higher than visible light and lower than gamma ray, which makes it enough to penetrate anything. But for different substances, the X-ray penetration rate is different, so we can apply this property to observe the internal shape of the object through the image formed after X-ray irradiation. This feature has been applied to medicine, creating a professional medical field: medical imaging.

If we pay attention to the doctor's X-ray checklist, we will find that the doctor will indicate the positive and lateral film or chest plain film on the checklist. What does this mean?

Because X-rays will penetrate our whole human body, and the human body is three-dimensional, the image formed after penetrating the human body is like reducing a three-dimensional person into a two-dimensional picture, and all the information at this angle is compressed. Generally, it is required to take a positive lateral radiograph of the limbs and a plain radiograph of the chest and abdomen, which is our normal positive X-ray.

But there is a problem with this approach. For example, if we find a tumor in the abdominal cavity, we can only know its position on the plane, but we don't know its depth position, that is, the position of Z axis in three-dimensional coordinates. In order to solve this problem, people invented CT.

How does CT work? Imagine that you are a cucumber. The X-ray emitted by CT will scan your body from head to toe to generate a cross-sectional image, just like a knife cutting a cucumber into pieces, and each piece is a cross-sectional view of your body. Through CT images, we can judge the exact position of a tumor or other things in the three-dimensional human body more accurately.

CT and X-ray machine, different situations have their own advantages and disadvantages. For example, orthopedics depends on the images of fractures, and CT is not needed, so all the cross sections of bones are taken, so it is impossible to judge the fracture. However, things like tumors are usually further examined and located after X-rays find abnormalities. That's when CT appeared. Therefore, the two have different uses and cannot replace each other.