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Flashcards in X-Rays Deck (40):

Simple X-Ray Tube Labels (7)

  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


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)


Method of Producing X-Rays Step 2 

Accelerating Electrons

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


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


X-Ray Efficiency

1% of energy --> X-rays

99% of energy --> Heat


Energy of X-ray depends on the ...

... proximity of electron to nucleus


Maximum energy X-rays created when ...

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


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)


Charactersitic X-Ray Diagram (2)

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


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

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


What is a K-line?

The peak of an x-ray line


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


What does Filtration do? (2)

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


Cathode Assembly

Part - Material - Properties (2)


Coiled Tungsten

  • Good thermionic emitter
  • Hard wearing

Focusing Cup

Nickel/stainles steel

  • Poor thermionic emitter
  • High melting point



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.



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



Stationary Anode characteristics (3)

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



Types of Digital Image Receptors (2)

  • Radiography
  • Fluroscopy



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



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



Scanning Plates Diagram (6)

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



How to clear CR plate once read?

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


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



Why are CR Cassettes lead-backed?

For backscatter protection


What does DR stand for?

Digital Radiography


What is bit-depth?

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


Types of DR (2)

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



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



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



What does the Scintillator layer do?

Converts x-rays into light


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



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



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



Image Intensifiers (7)

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



Fluoroscopy Diagram (5)

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



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



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



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



What does CCD camera stand for?

Charge Coupled Device Camera

  • Digital spot images
  • Can also use for cine



Advantages of Flat Panel Fluoroscopy (3)

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