Ebook Clark''s essential physics in imaging for radiographers: Part 1

al of three atoms per molecule.
In clinical radiography, the materials we consider to have a high
water content are soft tissues and fat and it follows therefore, that
the largest amounts of Compton scatter will be encountered anywhere where there are significant amounts of these materials. As
radiographers, you should think about the X-ray examinations and
patient types where secondary radiation grids are needed – these
are probably areas with larger amounts of soft tissue present.
Don’t forget, you are likely to be able to remove large amounts
of soft tissue (including fatty tissues) from the image by using
displacement bands which will really reduce the amount of
scatter produced. This is an effective and much underused dose
reduction measure.

MCQs
1.
In diagnostic radiography, photoelectric absorption occurs
most in:
a.
Air
b.
Bone
c.
Tissue
d.
Fat.
2.
Attenuation of an X-ray beam within matter is not affected by:
a.
Compton scatter
b.
Photoelectric absorption

c.
Transmission of X-rays
d.
Atomic number and electron density.

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MCQs

3.
Mass attenuation increases with:
a.
Decreasing mass number
b.
Increasing temperature of the material
c.
Increasing beam energy
d.
Electron density.
4.
The linear attenuation coefficient:
a.
Defines the probability of absorption or scattering process
taking place
b.
Is higher for fat than soft tissue for the same photon energy
c.
Decreases attenuation per cm of the attenuating medium
d.

Defines the fractional reduction in X-rays per unit mass of
the attenuator.
5.
Which interaction process does not take place in the range of
intensities of a diagnostic beam?
a.
Compton scatter
b.
Photoelectric absorption
c.
Pair production
d.
Coherent scatter.
6.
The probability of photoelectric absorption occurring is greatest when:
a.
The energy of the incoming photon is equal to or just
above the ionisation energy of the atom with which it is
interacting.
b.
The energy of the incoming photon is much greater than the
ionisation energy of the atom with which it is interacting.
c.
The energy of the incoming photon is less than the ionisation energy of the atom with which it is interacting.
d.
The energy of the incoming photon is much less than the
ionisation energy of the atom with which it is interacting.
7.
As the photon energy of an X-ray beam increases:
a.

The incidence of Compton scattering increases.
b.
The incidence of photoelectric absorption increases.
c.
The incidence of Compton scattering and photoelectric
absorption both decrease.
d.
The incidence of Compton scattering increases and photoelectric absorption decreases.

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X-ray Interactions in Matter

8.
The mass attenuation coefficient is:
a.
Equal to the linear attenuation process multiplied by the density
b.
Equal to the linear attenuation process divided by the density
c.
Independent of atomic number
d.
Different for ice and water.
9.
The probability of a Compton interaction is:
a.
Proportional to electron density of the medium
b.
Inversely proportional to electron density

c.
Proportional to atomic number
d.
Proportional to the beam energy.
10.In the photoelectric absorption process:
a.
All energy of the photon is passed to the free electron.
b.
No ionisation of the atom takes place.
c.
The vacancy from the photoelectron is filled from an inner
shell electron.
d.
The vacancy from the photoelectron is filled by an electron
from an orbital (shell) further out in the atom.

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