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Flashcards in X-Rays Deck (40):
1

Simple X-Ray Tube Labels (7)

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  1. High Potential Difference
  2. Thick walled glass chamber to maintain a high vacuum
  3. Heated metal filament cathode
  4. Outer tube housing of steel, lined with lead
  5. Useful beam of X-rays
  6. Thin window to allow emission of X-rays
  7. Electrical connection

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2

Method of Producing X-Rays Step 1 (3)

Producing Electrons

  • Cathode, tungsten filament (similar to lightbulb)
  • Heat filament by passing electric currentthrough it
  • Electrons "boil" off filament and produce a cloud of electrons (known as thermionic emission)

3

Method of Producing X-Rays Step 2 

Accelerating Electrons

  • Apply a large P.D between cathode and anode, creating electric field

4

Method of Producing X-Rays Step 3 (3)

Decelerating Electrons

  • Smash high energy electrons into anode target material (rapid deceleration)
  • Electrons interact with nucleus of target atom to produce a continuous x-ray spectrum
  • Known as Bremsstrahlung - breaking radiation

5

X-Ray Efficiency

1% of energy --> X-rays

99% of energy --> Heat

6

Energy of X-ray depends on the ...

... proximity of electron to nucleus

7

Maximum energy X-rays created when ...

... all electron's energy lost in the collision with nucleus

8

What are Characteristic X-Rays? (6)

  • Alternative to bremsstrahlung
  • An inelastic interaction with orbiting electrons
    • Electrons ionize an orbital electron of target atom
    • Inner shell electron rearrange to fill vacancy
    • Change in energy produces a line spectrum of photons
    • (Energy depends on binding energy)

9

Charactersitic X-Ray Diagram (2)

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  1. Collision of electrons, emission of delta-ray & creation of vacancy
  2. Fillin of vancancy by outer electron, emission of X-Ray

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10

Shape of Diagnostic X-ray spectrum depend on what factors? (5)

  • Potential applied across x-ray tube
  • Current
  • Filtration
  • Z
  • Waveform

11

What is a K-line?

The peak of an x-ray line

12

Spectrum Characterisitics of Max & Min Energy (2)

Max Energy - potential applied across X-ray tube

Min Energy - depends on absorption of low energy X-rays in:

  • anode
  • Exit port of tube
  • Cooling Oil
  • Any additional filters

13

What does Filtration do? (2)

  • Unwanted soft radiation removed to save skin dose, therefore hardened beam
  • Attenuator preferentially absorbs lower energy (soft) photons

14

Cathode Assembly

Part - Material - Properties (2)

Filament

Coiled Tungsten

  • Good thermionic emitter
  • Hard wearing

Focusing Cup

Nickel/stainles steel

  • Poor thermionic emitter
  • High melting point

 

15

What is the focussing cup? (2)

  • Fits around filament to direct electrons to a small focal spot on the anode
    • Otherwise large focus and poor resolution
  • Focusing cup may be biased or unbiased
    • Biased = tighter potential lines, tighter electron projectory.

 

16

Electrics of X-Ray Tube

Part - Description (3)

Filament Current

  • Boils electrons off cathode filament
  • ~5A @ 10V
  • controls # X-rays produced

High Voltage

  • attracts -'ve e from cathode to anode
  • 000's of volts
  • controls max x-ray energy

Tube Current

  • current of e crossing X-ray tube to produce X-rays
  • mA fluroscopy, 100mA for radiography

 

17

Stationary Anode characteristics (3)

  • Small tungsten target
  • Coppy block coducts heat way from target efficiently
  • Anode face angled to spread out heat

 

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18

Types of Digital Image Receptors (2)

  • Radiography
  • Fluroscopy

 

19

Photo-Stimulated Luminescence (3)

  • X-rays absorbed
  • elctrons:
    • excited from valence band to cond band
    • some fall back into electron traps
    • stay in traps until stimulated by laser light
    • leave traps & return to valence band
  • light emitted

 

20

Scanning CR Plates method (3)

  • laser scans across plate
  • trapped electrons released, causing light to be emitted
  • light is collected & converted from analog to digital signal

 

21

Scanning Plates Diagram (6)

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  1. Laser
  2. Collimator
  3. Galvo
  4. Fiber Optic
  5. Photo Detector
  6. Phosphor Image Plate

 

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22

How to clear CR plate once read?

Exposure with very bright white light (removes any electrons still in traps)

23

Imaging Chain method (5)

  • image plate (IP) exposed to radiation
    • absrobs X-rays & "stores" image
  • IP put into reader
    • remove phosphor IP from cassette
    • scanned by laser beam
    • emits visible light
  • reader collects light
    • sends dark/light signals to computer
  • image displayed on monitor
  • IP cleared for re-use

 

24

Why are CR Cassettes lead-backed?

For backscatter protection

25

What does DR stand for?

Digital Radiography

26

What is bit-depth?

Mapping images to different levels of gray (higher bit-depth = more number of levels)

27

Types of DR (2)

  • Indirect (most common)
  • Direct (used in mammography)

 

28

Benefits of DR Detectors (3)

Direct o/p of electronic signal for digitisation

  • no manual cassette handling
  • no separate exposure & readout stages
  • image almost instantly produced on screen

 

29

Method of Indirect DR (5)

  • X-rays converted into light at the scintillator
  • Light converted to electric chrge in the photodiode
  • Electric charge detected & stored in a 2D pixel array
  • Stored charge forms a latent image
  • Charge read out to create the image

 

30

What does the Scintillator layer do?

Converts x-rays into light

31

Reasons for pre-processing of DR Images (3)

  • Raw image data is pre-processed to:
    • minimise difference in response between pixel elements
    • correct for broken pixels
    • remove offset errors
  • Pre-processing uses pixel correction maps & measurements taken during detector calibration
  • Detector must be calibrated regularly

 

32

Direct DR method (4)

  • X-rays converted directly into electric charge in the photoconductor
  • Electric charge detected and stored in a 2D pixel array - a flat panel array
  • Stored charge forms a latent image
  • Charge read out to create the image

 

33

Advantages of DR over CR (3)

  • Direct readout of latent image in electronic form, with no need to:
    • handle cassettes
    • separate reader
    • faster image production
    • higher patient throughput
  • Higher Detective Quantum Efficiency than standard CR
    • potential for patient dose savings
  • Similar spatial reslution to standard CR
    • inferior spatial resolution to High Res CR systems

 

34

Image Intensifiers (7)

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  1. Video Camera
  2. Aperture
  3. Anti-scatter grid
  4. Table
  5. Collimation
  6. Filters
  7. X-ray Tube

 

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35

Fluoroscopy Diagram (5)

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  1. Path of electrons
  2. Electrodes of the electron lens
  3. Output fluorescent screen
  4. Input fluorescent screen
  5. Photo Cathode

 

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36

What is S-Distortion? (3)

  • S-shaped distortion across image
  • Caused by external magnetic fields
    • stray field from surroundings
    • Earth's magnetic field
  • Usually negligible

 

37

What is Minification Gain?

  • Large image on i/p focused to small image on o/p
  • Intensity of light amplified
  • Gain increases with increasing diameter of i/p phosphor

 

38

What is Maginification Mode? (5)

  • Uses largest FoV limited by physcal size of ||
  • Can use magnified FoVs
  • X-ray field reduced
  • Voltages applied to electrodes in || changed
  • Brightness gain decreases --> i/p exposure rate increased to compensate

 

39

What does CCD camera stand for?

Charge Coupled Device Camera

  • Digital spot images
  • Can also use for cine

 

40

Advantages of Flat Panel Fluoroscopy (3)

  • Smaller & Lighter
  • Less Bulky detector
    • better access to patient
  • Less geometric distortion
    • ability to reconstruct in 3D