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Clinical Imaging > Week 5- Interactions Of X-Rays > Flashcards

Week 5- Interactions Of X-Rays Flashcards

1
Q

How does EMR behave

A

Like streams or packets or energy called photons that have no mass or electric charge

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2
Q

How does EMR energy travel

A

Straight lines

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3
Q

What is E(photon energy) proportional to

A

Wave frequency (F)

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4
Q

How many fates are there for X-Ray photons when they pass through matter

A

1) penetration
2) absorption
3) scattered with energy loss
4) scattered without energy loss

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5
Q

Describe penetration

A

The photon penetrates the matter withoutinteracting with it

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6
Q

Describe absorption

A

The photon interacts with the matter and iscompletely absorbed by depositing ALL of its energy into thematter

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7
Q

Describe scattered

A

The photon interacts with the matter and isscattered (deflected) from its original direction, depositing eitherPART or [4] NONE of its energy into the matter

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8
Q

What is attenuation

A

the attempt to numerically describe the collectivefates of a large number of photons as they interact with

Represents deduction in beam intensity , reduction in energy content, reduction in number of photons

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9
Q

Name the 2 main components of attenuation

A

Scatter

Absorption

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10
Q

How many processes are involved in attenuation

A

5

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11
Q

List 1,2,3 attenuation processes

A

-elastic or unmodified scatter (no energy loss)

2) Compton or modified scatter (energy loss)

3) photoelectric absorption

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12
Q

Describe elastic scatter

A

occurs at very low X-Ray energies and involvesscattering (deflection) of photons without loss of energy.§

This type of scatter is of little practical relevance to diagnosticimaging; but is discussed for the sake of completenes

Energy of photon is less than energy gap. Doesn’t excite to shell so electron doesn’t absorb energy.

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13
Q

Does elastic scatter have energy loss

A

No

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14
Q

What is in elastic scatter

A

involvesscattering (deflection) of photons with an associated loss of photonenergy.§

main scattering process important from a diagnosticimaging perspective is Compton scatter

Energy loss

Energy from photon is transferred to atomic electron, raising to next shell. Electron falls back to original shell, emitting radiation

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15
Q

The greater the angle of scatter, the…

A

Greater the energy and range of the recoil electron

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16
Q

Does a side or forward scatter photon have more energy

A

Forward

Greater loss of energy of scattered photon

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17
Q

What does scattered radiation make up

A

50-90% of total number of photons emerging from patient

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18
Q

What is photoelectric absorption

A

an inelastic collision of a photonwith an orbiting electron in an atom of an absorbing material, withall the energy of the photon given up to the electron.

photon disappears (absorbed). There is recoil of theelectron, emission of characteristic radiation, and the productionof Auger electrons

Energy of photon is greater than energy gap and binding energy of inner shell electron. All energy is transferred to electron, allowing ionisation of atom. Electron vacancy is filled by an electron from another shell, EMITTIJNG RADIATIOMN

19
Q

How is they’re a signal difference (contrast) in soft tissue and bone

A

Due to different atomic numbers

Tissue- 7
Bone- 14

Magnitude is 8x greater

20
Q

Explain cascade effect

A

INCIDENT PHOTON ISCOMPLETELY ABSORBEDLEAVING A VACANCY INTHE K SHELl

2) VACANCY IS FILLED BY AN ELECTRON FROM HIGHER ENERGY LEVEL

3) RADIATION IS EMITTED AS HIGHER ENERGY ELECTRON DROPS TO LOWER LEBEL

21
Q

What is the Auger effect

A

the emission of an electronfrom an atom that accompanies the filling of an innerelectron shell vacancy

Inner shell electron is removed. Ionised and left in excited energy state. Relaxation to ground occurs rapidly. Vacancy filled by outer shell electron, releasing energy. If energy released is small it is absorbed immediately with ejection of very low energy AUGER ELECTRON

22
Q

What is the linear attenuation coefficient

A

is the fraction of photons removedfrom the beam per unit thickness of the attenuating material

23
Q

What is photon fluence

A

Photons per unit area

24
Q

What is energy fluence

A

Energy per unit area

25
Q

When dopes intesnity of the beam decrease

A

As thickness of absorbing material increases

Linear attention coefficient is affected by pressure or temperature

26
Q

What is linear attenuation coefficient affected by

A

Pressure and temperature

27
Q

As pressure increases and vol decreases what happens to density

A

Increases

28
Q

As temp increases and vol increases what happens to density

A

Decreases

29
Q

When is photoelectric coefficient high

A

When photon energy is greater than binding energy of electrons within a shell

The more tightly the electron is bound to the atom, and the nearerthe photon energy is to its binding energy

30
Q

When does probability of photoelectric absorption decrease

A

asphoton energy increases. It increases markedly as the atomicnumber [ Z ] increases

31
Q

When does scatter increase

A

When kv, thick body parts, field size increases

32
Q

Why is scatter a problem

A

It can cause foggy image

Affects radiology workers

33
Q

Does lead have high or low attenuation

A

HIGH

34
Q

Give symbol for tube voltage

A

KV

35
Q

What does tube voltage determine

A

thephoton energies within the beam.

The greater the tube voltage, the greater the range of photon energieswithin the beam, and the greater the penetrating power of the beam.

rise in penetration through all tissues – a decreasein attenuation differences – resulting in a lower contrast radiograph and alarger range of shades of grey

36
Q

What is increased if photon energy and kV Is reduced

A

Photoelectric absorption

Scatter photons reduced

37
Q

When is scatter generally lower

A

At lower kV values

38
Q

Name 2 factors which reduce amount of scatters

A

1] thin body tissue is easier for photons topenetrate; [2] the presence of bone [high Z] means thatmost interactions are photoelectric

39
Q

What does a higher tube voltage mean

A

Decrease in attenuation differences

Lower contrast

40
Q

When is a high kV technique good

A

produces a more uniformly dense image to betterdemonstrate lung markings. There is a reduction in dose, too

As decrease in attention differences so lower contrast

41
Q

what are anti-scatter grids

A

placed between the patient and the image receptor to reduce the scattered photons reaching the receptor produced by Compton scatter; thus, improving image quality. GRIDS are made of parallel strips of high attenuating material [ Lead ]with an interspace filled with low attenuating material

scatter increases withincreased tissue thickness andlarger field sizes; thus, GRIDS arerequired to improve image contrast.

42
Q

what is scatter air gap

A

an additional distance between a patient and an image detector. The gap decreases the likelihood for scattered x-ray radiation to reach the detector, as radiation is partially absorbed and scattered in the air.

43
Q

what is the amount of scattered radiatipn related to

A

tube voltage [controlledby kV], body part thickness [controlled using grids], and field size

Clinical Imaging (15 decks)

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