X-Rays Flashcards
(40 cards)
1
Q
Simple X-Ray Tube Labels (7)
A
- High Potential Difference
- Thick walled glass chamber to maintain a high vacuum
- Heated metal filament cathode
- Outer tube housing of steel, lined with lead
- Useful beam of X-rays
- Thin window to allow emission of X-rays
- Electrical connection
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)
3
Q
Method of Producing X-Rays Step 2
A
Accelerating Electrons
- Apply a large P.D between cathode and anode, creating electric field
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
5
Q
X-Ray Efficiency
A
1% of energy –> X-rays
99% of energy –> Heat
6
Q
Energy of X-ray depends on the …
A
… proximity of electron to nucleus
7
Q
Maximum energy X-rays created when …
A
… all electron’s energy lost in the collision with nucleus
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)
9
Q
Charactersitic X-Ray Diagram (2)
A
- Collision of electrons, emission of delta-ray & creation of vacancy
- Fillin of vancancy by outer electron, emission of X-Ray
10
Q
Shape of Diagnostic X-ray spectrum depend on what factors? (5)
A
- Potential applied across x-ray tube
- Current
- Filtration
- Z
- Waveform
11
Q
What is a K-line?
A
The peak of an x-ray line
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
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
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
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.
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
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
- Laser
- Collimator
- Galvo
- Fiber Optic
- Photo Detector
- 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
