Fluoroscopy & Image Intensifiers

Question 1

What is fluoroscopy?

Answer 1

Fluoroscopy procedure is an imaging technique that gathers real-time moving images using a fluoroscope of internal structures of patients.

Question 2

What is an image intensifier?

Answer 2

It is a device which amplifies the visible light resulting from fluoroscopic process.
Contained within an evacuated glass or ceramic envelope surrounded by a metal housing preventing light from getting into the tube

Question 3

What are the three main components of an image intensifier?

Answer 3

Input screen
Electron focusing electrodes
Output screen

Question 4

What are the system components in order?

Answer 4

Monitor
Video camera
Optical coupling
Image intensifier
Grid
Patient
Table
Filtration
Collimator
X-ray tube
X-ray generator

Question 5

What is II input window?

Answer 5

It’s provides protection for sensitive and precise components of the Tube and maintains the vacuum.
It is usually made of aluminium or titanium foil to allow x-ray Beam to enter with minimum attenuation. Convex metal shield that covers the input base of the II.

Question 6

What are the main principles of fluoroscopy?

Answer 6

II Input window
Input phosphor
Photocathode

Question 7

What is input phosphor?

Answer 7

Layer of sodium activated caesium iodide for good x-ray absorption efficiency channelled into tiny and needle-like crystals with fibreoptic-like characteristics deposited on a thin aluminium substrate
Each x-ray photons produces 3000 light photons in the blue spectrum

Question 8

What happens in a photocathode?

Answer 8

Fluorescent emission from the phosphor gets absorbed in a light-activated photocathode.

Absorption of the fluorescent light and photons releases a pattern of electrons in the body of the II tube, approximately 200 electrons released per absorbed x-ray photon

Question 9

What is the process of image intensification?

Answer 9

Primary x-ray beam exit the patients as strikes The inputs phosphor of the vacuum IQ tube.

Inputs phosphor fluorescent screen absorbs the x-ray photons and Emits lights photons, proportional to the amount absorbed.

Photocathode absorbs light photons and uses their energy to promote energy of existing electrons within the material so that are electrons are emitted.

Electrons accelerated from photocathode toward the anode and the output of phosphor (fluorescent screen) by the potential difference between them (25kv).

Electrostatic lenses used to accelerates and focus electrons. Acceleration of the electron beam increases energy and ability to emit light at the output screen.

Focusing of the electron beam intensifies the image into a smaller area. When they strike the anode which is a thin aluminium coating on the output phosphor, the outputs phosphor Emits many light photons, due to their high level of kinetic energy.

Question 10

What is the process of the image display?

Answer 10

1) An electron beam scans over the photoconductive target, depositing electrons
2) When the light photons hit the photoconductive target they increase the conductivity. The more lights photons the more conductivity increases the higher the leakage of charge.
3) The electron beam keeps scanning over the targets. It replenishes the areas of low charge (few electrons). The areas with a high number of electrons (high charge) will not accept anymore.
4) The flow of charge through the resistor creates a voltage. This is a video signal.

Question 11

What is automatic brightness control (ABC) and the purpose?

Answer 11

ABC controls the amount of radiation by taking the input signal from the light intensity of the output screen.
The purpose of the ABC is to maintain constant view condition independent of examination.
Changes and light intensity are fed back to the generator and increases in either KV or mA or both are made
The need to alter the mA or KV is determined by the electronic sampling the video signal or by measuring the II light input with a photo-sensor

Question 12

Why is ABC essential in fluoroscopy?

Answer 12

It is essential as manual control is not practical because the region of the patient being imaged may change throughout the course of the examination and absorption may change rapidly with administration of contrast

Question 13

What are the different modes used for ABC?

Answer 13

Minimum patient dose rate mode
Standard patient dose rate mode
High patient dose rate mode (high image quality)

Question 14

What is input screen size?

Answer 14

Screen size may vary between 150- 400mm

Question 15

How is II magnification achieved?

Answer 15

By moving the focal points near to the input screen, “tube magnification” is achieved so that the central image fills the whole of the outputs phosphor

Question 16

How many different magnification values can a unit have?

Answer 16

4
Diameter range from 20cm to 40cm, depending on application

Question 17

What are the positives and negatives of the II magnification?

Answer 17

Modification results in better resolution
However, it reduces the brightness on the output screen
Therefore to restore brightness exposure factors are increased
Thus the patients skin dose is also increased

Question 18

How are doses reduced In fluoroscopy?

Answer 18

Pulsed fluoroscopy

Question 19

What is pulsed fluoroscopy?

Answer 19

Voltage switched on and off at regular intervals to give pulses of x-ray from the tube
– x-ray delivered in rapid succession of pulses – exposure reduction
– range of frame rates available - choose lowest rate that provides acceptable image quality

Question 20

What are some additional radiation protection measures? (Out with PPE) (Fluro)

Answer 20

Additional added filtration
Beam shaping filters and wedges
Automatic brightness control (ABC)
Fluoroscopy programmed radiography
Collimation

Question 21

What is additional added filtration?

Answer 21

Reduction of entrance skin dose by automatic or manual selection of additional filters (usually copper), depending on patient size/ examination type

Question 22

What is beam shaping filters and wedges?

Answer 22

Patients naturally asymmetric; allows contour of x-ray beam to compensate
Improves image quality and reduces dose

Question 23

What is automatic brightness control (ABC)?

Answer 23

Monitors light output from II and increases x-ray output if levels falls

Question 24

What is fluoroscopy programmed radiography?

Answer 24

The goal is high image quality at low dose
Exposure parameters of particular sequence used to predict exposure factors or subsequent acquisition, for optimal image quality

Question 25

What is a flat panel detector (FPD)?

Answer 25

X-ray energy falls on the detector array and is converted into an electronic output signal

Question 26

How many types of different FPD systems are there and what are they?

Answer 26

2
Indirect and Direct System

Question 27

What are the advantages of II?

Answer 27

Well tested technology and lower costs

Question 28

What are the disadvantages of II?

Answer 28

Some image distortion due to curved construction of photocathode (magnification at the edges of the image field)
Degradation of image quality with time
Bulkier and heavier than FPD

Question 29

What are the advantages of FPD?

Answer 29

Potential for dose reduction due to increased signal efficiency
No geometric distortion and uniform response across FOV
Smaller and lighter than II with same field size
Potentially no degradation of image quality during lifetime of FPD

Question 30

What are the disadvantages of FPD?

Answer 30

More expensive to purchase and replace
Long-term reliability in clinical use largely unknown, to date

Question 31

What are the four main system components?

Answer 31

X-ray generator - choice depends on number and type of procedures being done
X-ray tube assembly, incorporating - collimator to direct and define area of x-ray beam
Beam filters to reduce patient dose
X-ray table (couch)
Detector- converts x-ray to image for display on monitor
May be image intensifier (II) or flat panel detector

Question 32

What is the line Focus principle?

Answer 32

Explains the relationship between the anode surface and the effective focal spot size
The smaller the focal Point size the better the image detail

Question 33

Apart from heat what other factors influence the tube rating?

Answer 33

Target size
Target thickness
Speed of target rotation

Question 34

What are the modern-day types of image intensifiers?

Answer 34

Solid-state flat panel detector (FPD)
O arm
Mini C arm

Question 35

What is the C arm or U-arm normally designed for?

Answer 35

Specialists procedures ie Angiography

Question 36

What is digital subtraction angiography?

Answer 36

It’s when the images of the bones and soft tissues are electronically removed to produce clearer images of contrast filled blood vessels

Question 37

What are some components of mobile II?

Answer 37

Ideal for Theatre
Needs to be connected to monitor unit
Operate exactly as static fluoroscopy unit
Narrower field of view (FOV), limited by the size of its input phosphor
Obviously needs to apply mobile radiation protection practises (temporary controlled area)
Have either a fused plug or a dedicated socket in the theatre (often connected to a warning light) that has a separate fuse
Have a key (kept locked away) to prevent unauthorised use

Question 38

What are the advantages of a Mini C-arm?

Answer 38

May or may not reduce screening time
Radiation safety and documentation
Reduced Radiographer workload as surgeon operated
Limited application of swallow FoV-distal limbs, eg below elbow /knee

Question 39

What are indirect systems?

Answer 39

Layer of phosphor material (e.g. caesium iodide) - conversion of x-ray energy to light photons (image amplification)
Some image resolution is lost in the process due to the light spreading that occurs, although low radiation dose

Question 40

What are direct systems?

Answer 40

Amorphous selenium photoconductor absorbs x-ray photons directly and emits electrons (bypasses x-rays to light and light to electrons stages)
High image resolution but likely also higher radiation dose

Question 41

What is a photocathode made of?

Answer 41

The photocathode is compromised of a very thin layer of antimony caesium alloy that has a spectral sensitivity well matched to the blue light emission of the sodium activated caesium iodide (Csl:Na).