X-Rays Flashcards

(40 cards)

1
Q

Simple X-Ray Tube Labels (7)

A
  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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Method of Producing X-Rays Step 1 (3)

A

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)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Method of Producing X-Rays Step 2

A

Accelerating Electrons

  • Apply a large P.D between cathode and anode, creating electric field
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Method of Producing X-Rays Step 3 (3)

A

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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

X-Ray Efficiency

A

1% of energy –> X-rays

99% of energy –> Heat

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Energy of X-ray depends on the …

A

… proximity of electron to nucleus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Maximum energy X-rays created when …

A

… all electron’s energy lost in the collision with nucleus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are Characteristic X-Rays? (6)

A
  • 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)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Charactersitic X-Ray Diagram (2)

A
  1. Collision of electrons, emission of delta-ray & creation of vacancy
  2. Fillin of vancancy by outer electron, emission of X-Ray
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

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

A
  • Potential applied across x-ray tube
  • Current
  • Filtration
  • Z
  • Waveform
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is a K-line?

A

The peak of an x-ray line

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Spectrum Characterisitics of Max & Min Energy (2)

A

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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What does Filtration do? (2)

A
  • Unwanted soft radiation removed to save skin dose, therefore hardened beam
  • Attenuator preferentially absorbs lower energy (soft) photons
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Cathode Assembly

Part - Material - Properties (2)

A

Filament

Coiled Tungsten

  • Good thermionic emitter
  • Hard wearing

Focusing Cup

Nickel/stainles steel

  • Poor thermionic emitter
  • High melting point
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the focussing cup? (2)

A
  • 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.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Electrics of X-Ray Tube

Part - Description (3)

A

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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Stationary Anode characteristics (3)

A
  • Small tungsten target
  • Coppy block coducts heat way from target efficiently
  • Anode face angled to spread out heat
18
Q

Types of Digital Image Receptors (2)

A
  • Radiography
  • Fluroscopy
19
Q

Photo-Stimulated Luminescence (3)

A
  • 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
Q

Scanning CR Plates method (3)

A
  • laser scans across plate
  • trapped electrons released, causing light to be emitted
  • light is collected & converted from analog to digital signal
21
Q

Scanning Plates Diagram (6)

A
  1. Laser
  2. Collimator
  3. Galvo
  4. Fiber Optic
  5. Photo Detector
  6. Phosphor Image Plate
22
Q

How to clear CR plate once read?

A

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

23
Q

Imaging Chain method (5)

A
  • 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
Q

Why are CR Cassettes lead-backed?

A

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)
1. Video Camera 2. Aperture 3. Anti-scatter grid 4. Table 5. Collimation 6. Filters 7. X-ray Tube
35
Fluoroscopy Diagram (5)
1. Path of electrons 2. Electrodes of the electron lens 3. Output fluorescent screen 4. Input fluorescent screen 5. Photo Cathode
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