Question

There is natural conflicct in radilogy between providing high subject contrast for image formation and kepping enterance radiation eposure low.
Describe from fundamental physical principles why this is the case.

Answer 1

High subject contrast is required to get good information from an x-ray image. To get good contrast the intensity of x-ray radiation has to be significantly high like what we get in a normal photograph. When we take photograph of any object, the intensity of light received from the object must be good enough, the photographic chemical on the film will react with light and produces contrast on the film. With x-ray radiation too the principle is same.

But radiation is damaging to the body tissue. it can cause health issues in near future or long run depending on the amount of exposure to the x-rays. It deposit radiation energy in the body tissue which is called radiation dose. In the interest of the patient health, it is necessary to keep radiation exposure to the minimum possible. Thus there is always a conflict between subject contrast and the radiation exposure.