How is the image generated on the X-ray plate?

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X-rays are generated inside a vacuum bulb where a cathode (associated with an incandescent filament that acts as a source of electrons) and an anode (associated with a focus where radiation is generated by the impact of the electrons emitted by the cathode) are aligned. The system is powered by a high voltage source and is located inside an insulating metal structure (usually lead) that has a diaphragm through which the generated X-ray beam exits. The mission of the diaphragm or collimator is to control the width of the X-ray beam produced, so that we use the greatest amount of radiation orthogonal to the object to be x-rayed and reduce non-orthogonal or scattered radiation.

The X-ray beam emerging from the collimator aperture propagates in a straight line in an isotropic manner (in all directions and with equal intensity):

Some of it is scattered into the environment (depending on the degree of collimation).
Another part, direct radiation, passes through the target object of the study (in our case, the area of ​​the patient's body being studied). From direct radiation:
Part of it is absorbed by the target object depending on the applied physical parameters (amperage and voltage). We are interested in keeping this radiation to a minimum, since, as we have said, X-rays are ionizing, which is why they produce alterations in matter, and can cause alterations at the DNA level.
Another part is reflected outside the object (the so-called Compton effect). To reduce the effect of this radiation, an anti-scattering grid is placed between the body (object) and the X-ray plate.
And another is capable of passing through it with the proper attenuation. This last part is the one that will be useful for the production of the image due to its capacity to more or less hide the radiographic film located behind the object.


The conventional X-ray plate is a base support covered with a gelatin containing silver halides. Since it is altered by visible light, it must always remain in the dark. For use, it is introduced into a chassis that has elements inside called reinforcement plates that produce a certain luminescence that helps to enhance the image created by the X-rays.

To get an X-ray:

The X-ray tube emits a beam of radiation (X-rays)
Radiation passes through the patient's body.
Different fabrics absorb it to different degrees depending on their characteristics.
The radiation that manages to pass through the tissues impresses the X-ray plate.
Silver crystals in the film emulsion absorb X-rays during exposure and store the energy, forming a pattern, an invisible image within the emulsion crystals on the exposed film. The taiwan phone data stored energy pattern cannot be observed and is known as a latent image.
To obtain the final image, development and fixation must be carried out .
The developed plate will show a greyscale image, which represents the different structures of the body. The silver halides on the plate turn black when they oxidise, that is, when they are exposed to radiation. The black part that we see on the X-ray will be the area that has received the radiation, due to the action of some reducing chemical substance that gives up its electrons to the silver halides during development. The white part is caused by the action of chemicals that act on the area of ​​the X-ray that has not been exposed to radiation in that area of ​​the X-ray.

In an X-ray, black indicates that the rays have not been attenuated (they pass through the tissue), which is called radiotransparent or radiolucent . On the other hand, white suggests that the density of the tissue does not allow the radiation to pass through, and the term that describes it is radiodense or radiopaque .

The effect of absorption, dispersion and penetration means that in the human body we can find 5 basic radiological densities , with which we can interpret an X-ray. These densities are identified as different shades, from black to white, in a gray scale and are: