X-Ray Attenuation

Question 1

what is x-ray attenuation?

Answer 1

the reduction of the intensity of an x-ray beam as it traverses matter

Question 2

what does the transmitted intensity of an x-ray photon depend on?

Answer 2

the transmitted intensity of an x-ray photon depends on the thickness and type of material

Question 3

how much of the primary beam reaches the image receptor?

Answer 3

only about 3% of the primary photon reaches the receptor

Question 4

3 fates of x-ray photons?

Answer 4

absorbed, transmitted and scattered

Question 5

what energy of the photon is most commonly absorbed by the patient?

Answer 5

the lower energy photons are most likely to be absorbed by the patient

Question 6

what is used to absorb the lower energy photons normally absorbed by the patient?

Answer 6

a filter

Question 7

what is the linear attenuation coefficient (μ)?

Answer 7

this is the fractional change in x-ray intensity per unit thickness of the attenuating material

Question 8

name the factors affecting x-ray attenuation?

Answer 8

beam energy
intensity (no. of photons)
density of material
atomic number (Z) of the material
thickness of the material

Question 9

is attenuation linear or exponential?

Answer 9

attenuation follows an exponential rule

Question 10

what is used to measure the penetrating power of an x-ray beam?

Answer 10

the half value layer (HVL) 𝜇 = 0.693/ HVL is an NB equation for MCQ

Question 11

What is the HVL

Answer 11

The HVL is defined as the thickness of a standard material (usually aluminum) that reduces the beam intensity by a half.

Question 12

why measure the HVL?

Answer 12

To get an estimate of the quality of the x-ray beam

Question 13

diagnostic x-rays are polyenergetic, what fraction of the peak energy is the mean?

Answer 13

the mean energy is 1/2 to 1/3 of the peak energy

Question 14

what is beam hardening?

Answer 14

beam hardening is where the low energy photons are attenuated more rapidly than the high energy photons and so the effective energy of the beam increases

Question 15

where is the filter placed?

Answer 15

between the housing and collimator

Question 16

what filters the x-ray beam?

Answer 16

the inherent filtration within the tube and its housing, the patient, and added filtration between the housing and the collimator

Question 17

what is the basis behind added filtration and radiation protection?

Answer 17

added filtration removes the low energy photons which contribute to patient dose but not to the image

Question 18

what are K edge energy filters used in

Answer 18

mammography

Question 19

what do k edge filters do?

Answer 19

k edge filters remove the high and low energy photons and are relatively transparent to photons with energies just below the k edge energy for the filter material, which in mammography is Molybdenum (Mo). basically, K edge filters knock out energies that are below or above the binding energy of the K shell electron