Question

What is the primary purpose of placing a filter in the primary beam of a diagnostic X-ray unit?

a)              Increasing the number of photons emitted by the X-ray tube

b)              Decreasing the number of high energy photons that reach the patient

c)              Increasing the number of low energy photons that reach the patient

d)              Decreasing the number of low energy photons that reach the patient

e)              Increasing the number of electrons flowing through the x-ray tube

Answer 1

answer is (d) Decreasing the number of low energy photons that reach the patient.

Filtration shall be placed in the primary beam to reduce the quantity of soft X-rays (low energy x-rays) to the patient.

So, Low energy x-rays (less than 30 keV) contribute little to the resultant image as they are heavily absorbed by the

patient's soft tissues (particularly the skin). Additionally, this absorption adds to the risk of stochastic (e.g. cancer) or

non stochastic radiation effects (e.g. tissue reactions) in the patient. Thus, it is favorable to remove these low

energy X-rays from the incident beam.