Discovery, Properties & Production of X-rays Flashcards

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1
Q

Who discovered x-rays and when ?

A

The German scientist Wilhelm Conrad Roentgen on November 8, 1895

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2
Q

What tube was the first to be experimented with, and how did it work ?

A

The Crookes tube - William Conrad Roentgen discovered that there was a glow on a sheet of barium platinocyanide-coated paper far away from the tube. So he named the mysterious energy ray/ photon x-ray ‘x’ meaning unknown

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3
Q

What is the wave-particle duality ?

A

The concept by which light/x-ray can behave both as a wave and a particle (photon- particle of light).

Wave properties:

  • has oscillating electric and magnetic fields at right angles to each other (electromagnetic waves)
  • has an amplitude, wavelength and frequency as a wave - wavelength and frequency varies dependent on colour of light
  • can defract as a wave
  • have negative and positive interference

Particle properties:

  • can exhibit photoelectric effect (
    Blue light has high enough frequency to eject an electron off certain metals, whilst red light does not)
  • travel in straight lines
  • electrons behave same way but are charged whilst a photon is neutral
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4
Q

Why can x-rays be described as waves ?

A

They move in waves that have wavelength (f) and frequency (λ)

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5
Q

What is the symbol for speed of light ?

A

c = speed of light

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6
Q

What is the equation for speed of light ?

A

c = f λ

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7
Q

What is the definition of wavelength ?

A

The distance between 2 successive troughs or crests of a wave

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8
Q

What unit is wavelength measured in ?

A

Angstroms (Å) (1 Å = 10^ -10 m)

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9
Q

What amount of angstroms does x-rays used in radiography range between ?

A

0.1 to 1.0 Å

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10
Q

What is the definition of frequency?

A

The number of waves passing a given point per given unit of time (second)

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11
Q

What are the symbols for wavelength and frequency ?

A

Frequency : f
or the Greek letter v, pronounced ‘nu’

Wavelength : λ

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12
Q

What units is frequency measured in ?

A

Hertz (Hz) - (l/s)

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13
Q

What amount of Hertz does x-rays used in radiography range between ?

A

3x10^18 and 3x10^19 Hz

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14
Q

What describes the relationship between wavelength and frequency?

A

An inversely proportional relationship

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15
Q

What is the relationship between wavelength and frequency for higher energy-rays?

A

Decreased wavelength and increased frequency

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16
Q

What is the relationship between wavelength and frequency for lower energy-rays?

A

Increased wavelength and decreased frequency

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17
Q

What does the symbol E stand for?

A

E = Photon Energy (1.986 x 10 ^ -25)/ λ

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18
Q

What does the symbol h stand for?

A

Planks constant (6.62 x 10^ -34 Js)

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19
Q

What are three formulas for E ?

A

E = hv
E = hc/λ
E = (1.986 x 10^ - 34 Js)

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20
Q

What property of X-rays make it impossible for them to be felt, smelled or heard?

A

Invisibility

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21
Q

X-rays being electrically neutral make what impossible?

A

X-rays having neither a positive or negative charge make it impossible for them to be accelerated or made to change direction using a magnet or electrical field

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22
Q

Why do x-rays produce no resistance in being put into motion nor do they produce force?

A

Because they have no mass

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23
Q

What speed do x-rays travel at?

A

The speed of light in a vacuum ( 3 x 10^8 m/s) or (186,000 miles per second)

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24
Q

How do x-rays travel?

A

In a straight line

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25
Q

How can x-rays interact with matter?

A

They can be absorbed or scattered

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26
Q

What is a property of x-rays that involves lenses?

A

They cannot be optically focused - (no refraction nor focusing due to the effect of optical lenses)

27
Q

What are the four categories of ionizing radiation (electron interaction with matter) ?

A
  1. Bremsstrahlung (continuous X rays)
  2. Characteristic X-rays (discrete X-rays)
  3. Annihilation
  4. Gamma Emission
28
Q

How are Bremsstrahlung X-rays emitted?

A

They are emitted through electron-nuclear field interactions

29
Q

How are Characteristic X-rays emitted ?

A

They are emitted when orbital electrons transition from one allowed orbit to another vacancy in another allowed orbit

30
Q

How are x-rays produced from annihilation ?

A

The photon is produced when a positron and negatron interact

31
Q

How are x-rays produced by gamma emission?

A

A photon undergoes spontaneous emission by a radioactive nucleus, to regain stability

32
Q

What is the equation for hv?

A

hv = E1 - E2

33
Q

What does the probability or cross-section for each x-ray interaction depend on ?

A

The energy of the photon and the atomic number of the attenuator

34
Q

What are the three ways photons (x-rays) interact with matter ?

A
  1. With a tightly bound electron
  2. With the field of the nucleus
  3. With a ‘free’ orbital election
35
Q

What is a tightly bound electron within the context of photon interaction ?

A

An orbital electron with a binding energy of the order of or larger than the photon energy

36
Q

What is a free electron within the context of photon interaction ?

A

An electron with a binding energy that is much smaller than the photon energy

37
Q

What are the two things that can happen during the process where a photon (x-ray) interacts with matter ?

A

It can either completely disappear or be scattered

38
Q

What are the 2 types of scattering a photon (x-ray) may undergo during interaction with matter?

A
  1. Coherent (Rayleigh)
  2. Incoherent (Compton effect)
39
Q

What are the processes in photon (x-ray) interaction with matter where a photon may completely disappear

A
  1. Photoelectric effect (photoeffect)
  2. Pair production
  3. Photodisintegration
  4. Triplet production
40
Q

How does a photon (x-ray) interact with matter in the photoelectric effect?

A

The photon (incident photon) interacts with a tightly bound orbital electron of an attenuator then disappears, while that orbital electron is ejected from the atom as a photoelectron with kinetic energy

41
Q

How does a photon (x-ray) interact with matter in Coherent (Rayleigh) scattering?

A

The incident photon interacts with a bound orbital electron (along with the combined action of the whole atom). The photon loses none of its energy (elastic event) and is scattered through a small angle

  • since no energy transfer from photon to charged particle - no role in energy transfer coefficient but contributes to attenuation coefficient
42
Q

How does a photon (x-ray) interact with matter in Incoherent scattering?

A

The incident photon interacts with a free and stationary orbital electron. This photon’s energy is much larger than the binding energy of the orbital electron. This photon loses part of its energy to the recoil electron (Compton electron) and is then scattered through a scattering angle

43
Q

How does a photon (x-ray) interact with matter in pair production ?

A

The incident photon disappears and an electron-positron pair with a combined kinetic energy are produced in the nuclear coulomb field. Mass is produced from this (energy threshold: 1.02 Mev) - 0.51 Mev each photon

44
Q

How does a photon (x-ray) interact with matter in triplet production ?

A

This is when pair production occurs in the field of an orbital electron. Three particles share the available energy (electron-positron pair and an electron). Pair production increase rapidly with photon energy above the threshold

45
Q

Vacancies are produced in atomic shells through the ejection of orbital electrons in which processes?

A

The photoelectric effect, the Compton effect and triplet production

  • electron interaction with orbital electron
46
Q

Which processes come before annihilation of the positron with a free and stationary electron, producing 2 annihilation quanta

A

Pair production and triplet production

47
Q

Describe the effect that increasing tube potential (kV) has on the x-ray spectrum

A

Increased:

  • quantity of x-ray photons
  • average energy
  • maximum energy
  • If kV is great enough characteristic energy is produced
48
Q

Describe the effect that increasing tube current (mA ) has on the x-ray spectrum

A
  • Increases quantity of X-ray photons
  • no change in energy - characteristic, minimum, maximum, average
49
Q

What is the effect of filtration on a X-ray spectrum

A

It produces fewer lower energy photons

  • increases average energy of photons (x-ray beam quality)
  • decreases total number of photons (reduces AUC - X-ray beam quantity)
  • if we increase density of filter it increases photoelectric effect which increases likelihood of X-rays to be attenuated.
    *If increased atomic number also more attenuation - Aluminum typical used - Atomic number 13
  • If we increase energy of X-rays attenuation decreases likelihood of photoelectric effect to occur (denominator of equation increases)

Inherent filtration - glass envelope, conducting oil, glass window (silicone mainly - atomic number 14, beryllium atomic number 4 or aluminum) , mirror in collimator of X-ray tube

Added filtration - 0.5 to 1.5 mm aluminum equivalent or beryllium or copper

Types of filters - added/compensation/equilibrium filters:

allows more equal distribution of exposure to detector

Wedge filter - attenuate more of beam over thinner part of patient’s body eg. Foot toe to heel

Bow tie filter - CT scanners - filter thicker at sides to attenuate X-rays more - as less tissue to go through at sides

Photoelectric effect Equation:
first symbol (likelihood of effect to occur), p = density, Z = atomic number, E = energy

Trough filter - X-rays attenuated more by thicker part towards thinner periphery of mediastinum (lungs) vs thicker center with sternum, heart and great vessels

50
Q

What are the effects of having a more uniform (rectified) waveform current on the X-ray spectrum

A
  • increases average energy
  • Increases quantity of x-ray photons
  • same maximum keV
51
Q

Describe and illustrate the spectrum of x-ray energies produced by an X-ray tube

A

The resulting spectrum of x-ray photon energies released is shown in the graph. At a specific photoenergy there are peaks where more x-rays are released. These are at the characteristic radiation energies and are different for different materials. The rest of the graph is mainly Bremsstrahlung, in which photons with a range of energies are produced. Bremsstrahlung accounts for the majority of x-ray photon production.

52
Q

Discuss the process by which X-rays are produced

A
  1. A current is applied through tungsten filament at cathode.
  2. Heats up filament to produce enough energy to overcome binding energy of electrons (thermionic emission).
  3. Electrons released from filament.
  4. Tube voltage is applied across the x-ray tube.
  5. Electrons, therefore, are accelerated towards positively charged anode, which
    gives them a certain energy.
  6. The electrons strike the anode and the energy released via interaction with the anode atoms produces x-ray photons.
  7. These x-ray photons leave the x-ray tube through the window in an x-ray beam towards the patient.
  8. They pass through the patient to the detector to produce the x-ray image
  • How X-rays are produced ? Key words- Current, filament, voltage, focusing cup, anode, bremstraulang and characteristic radiation
53
Q

Distinguish between Bremstraulang and characteristic x-rays

A

P - %
I - interaction
R - radiation release due to what
R - radiation released of what energy
X - X-ray photon energy dependent on what

54
Q

What is the difference between kV, keV and kVp

A

kV - tube potential
keV - photon energy
kVp (kilovolt peak) - maximum photon energy

55
Q

What is the anode heel effect

A

Describes the variation in x-ray intensities between the cathode and anode side of an x-ray field.

Due to the distances that the x-rays have to travel when leaving the anode.

Need to travel more distance through anode side. Therefore cathode side has more penetrating beam “

The phenomenon by which more target material is traversed at emission angles perpendicular to the electron beam (closer to the anode) than at those more parallel to it (closer to the cathode).

This increase in material leads to more resorption of the x-rays by the target material resulting in fewer x-rays reaching the field at angles perpendicular to the electron beam.

  • therefore cathode side has more penetrating beam - should be placed over area of greatest intensity
  • decreased anode angles gives smaller effective focal spot (useful in imaging) but larger anode heel effect - less uniform and more attenuated beam
  • Because x-rays are produced deep in the target material they must traverse back out of it before they can proceed to the target field.

Three parameters than can change to manipulate heel effect:

  1. Anode angle
  2. SID - source to image distance - reduced effect when increased SID (detector more inferior to X-ray tube) by less variation of X-ray intensities
  3. Field size - collimate - removes X-rays on cathode an anode side of field
56
Q

What is the line focus principle

A

Shows the relationship between the anode angle and our actual and effect focal spots

The line-focus principle tells us that a steeper (smaller) anode angle will reduce the size of the effective focal spot while an anode angle greater than 45° will increase the size of the effective focal spot in comparison to the width of the electron beam.

Application of the line-focus principle allows us to obtain the best possible resolution while spreading out the heat created by the electron interactions on a larger portion of the anode surface

  • choice of target angle is a compromise between tube loading, geometric unsharpness, and desired area to be covered by the useful beam. For practical purpose, at 40” FFD the anode angle should be no smaller than 15 degrees. A decrease in angle below six degrees will result in anode heel effect
  • Steeper target angles create a greater amount of anode-heel effect.

*focus film distance (FFD)

57
Q

What is an X-ray tube rating

A

Tube ratings are the defined input parameters (kVp, mA, exposure) that can be safely used during its operation without causing damage to the x-ray tube itself and unique to each individual x-ray tube model. An x-ray tube rating is the maximum allowable kilowatts (kW) in 0.1 second

By creating tube ratings the operator can ensure that the parameters set are appropriate for the examination whilst minimising the risk of damage to the x-ray tube. Typical x-ray tube ratings are between 5-100kW

Factors affecting - focal spot size - larger - higher heat capacity - better tube rating, anode angle, anode rotation speed, kV waveform, heating and cooling curves of anode body , constant electrical potential- uniform heat distribution- better tube rating

58
Q

Explain information on the tube rating charts

A
59
Q

What is AEC

A

A feature in radiography that allows phototimers/ionisation chambers to terminate the exposure once the radiation detector receives a predetermined signal of radiation (which indirectly means the image receptor is sufficiently exposed).

In radiography, the automatic exposure control device is placed in front of the image receptor. In mammography, the automatic exposure control device is placed underneath the image receptor. This is mainly due to the low energy requirement for mammography; if the AEC device was placed in front of the receptor, the device would produce an image on the receptor, confounding the mammogram.

How it works - Within the i Ionization chamber, photons ionize gas . Positive charge from gas neutralized by cathode. At anode - a signal produced to make image.

60
Q

What is the effect of rectification on an X-ray spectrum

A
  • increases mean photon energy
    as fewer photons of lower energy
  • increased x-ray output - stays closer to maximum for longer
  • shorter exposure - as output higher can run exposure for shorter time to get same output
  • lower patient dose - increase mean energy means fewer low energy photons that do not contribute to final image

three phase supply - 3 electrical supplies applied at different times

high frequency generator- constant potential switched on and off rapidly at 14 Hz

  • rectification: conversion of alternating current to direct current - negative to positive voltage needed - standard sinusoidal wave needs to be converted into positive constant square wave by full wave rectification
  • generation smooths out current in secondary circuit. Primary circuit converts alternating current to direct current that flows in one direction in the secondary circuit
61
Q

Describe the process of ionization and excitation of a photostimulable phosphor (PSP)

A

They are materials that store absorbed energy within excited electrons and release it in the form of light on exposure to laser energy.

Process of X-ray interaction:

  1. X-ray/ gamma photon interacts with phosphor then releases high energy electrons through PE and Compton scatter
  2. These secondary electrons excite surrounding electrons from valence to conduction bands through beastie collisions until the secondary electron has lost all kinetic energy
  3. electrons excited to the conduction band fall into empty electron traps within the forbidden zone, which are created by impurities in the material
  4. in order to return to the valence band, the electrons require excitation energy to overcome the trap
  5. in PSP the energy required to return to overcome the trap is high enough that they require laser light energy to do so
  6. the electron from the conduction band then returns to the valence band and due to the energy difference must lose energy in the form of an emitted photon.
    Application
    PSPs are used to record and reproduce a latent x-ray image by absorbing the radiation, then releasing the stored energy as light photons when stimulated by a HeNe laser. The emitted photons are detected by a photomultiplier tube, and an electronic signal is produced which is converted to a digital image for viewing on PACS.

Structure
PSP materials are crystal lattices, which give near uniform characteristics to electron bands, and impurities, which alter the electron bands to induce electron traps in the forbidden zone. One of the materials of choice is barium fluorobromide doped with europium (2+ valence), however many others exist with their own unique properties.

The material itself needs certain properties to satisfy a number of criteria in order for it to be useful in image acquisition:

release the stored energy when exposed to a wavelength produced by common lasers
release the stored energy in a photon wavelength readily absorbed by common photomultiplier tubes
retain the latent image without significant signal loss over time due to phosphorescence

62
Q

What is the impact of field size, kVp and patient thickness on scattered radiation

A
  • higher kVp produce a greater proportion of higher-energy scattered x-rays compared with examinations using low kVp
  • the larger the x-ray beam field size, the greater the amount of scatter radiation produced
  • the thicker the part being imaged, the greater the amount of scatter radiation produced
63
Q

Distinguish between atomic excitation vs ionization

A

Excitation is the addition of a discrete amount of energy to a system such as an atomic nucleus, an atom, or a molecule. It is the result of energy being given to an electron moving it to a higher energy level.

Ionization potential is the amount of energy required to remove the most loosely bound electron from a neutral, gaseous atom. If enough energy is given to the electron to remove it from the atom ionization has occurred.

64
Q

What is X-ray luminescence in context of a PSP

A

X-ray luminescence is the physical mechanism by which x-ray energy is converted into light in a phosphor screen. It involves two mechanisms that both occur to some degree when a phosphor screen is irradiated:

ƒ X-ray fluorescence: the immediate emission of light. This is the mechanism that predominates in screen film radiography

ƒ X-ray phosphorescence: this is when the emission of light is delayed over a timescale of many minutes, hours or days and can be accelerated by shining specific coloured light onto the phosphor. This is the mechanism exploited in CR. It allows x-ray energy to be temporarily stored in a phosphor screen to be read-out later.