19. X-RAY DETECTORS: COMPUTED RADIOGRAPHY Flashcards
1
Q
- What are two examples of Indirect Systems?
A
- Computed Radiography Systems (CR)
- Indirect Digital Radiography Systems (IDR)
2
Q
- What do both of these indirect systems utilise?
A
- Cassettes
3
Q
- What happens with the Cassette in Indirect Digital Radiography Systems?
A
- the information from the cassette is directly converted
into an X-Ray image - there is no intermediate step of converting the X-Rays
into light - the emergent X-Rays will directly cause the system to
produce an electrical signal
4
Q
- What happens with Indirect Imaging?
A
- the X-Rays are absorbed
- they are then converted into light
- they are then converted once more to an electrical
signal
5
Q
- How does the Computed Radiography System (CR) work?
A
- this is a system that produces digital Radio-graphical
images - it does this in a very similar method to Film Screen
Technology
6
Q
- What does the Computed Radiography System not generally require?
A
- it does not require modifications to the X-Ray
equipment
7
Q
- What happens when a Computed Radiography system receives an Exposure?
A
- the CR imaging plate retains the latent image
- this is similar to what happens in film technology
THE DIFFERENCE OCCURS:
- when the latent image is processed
- the latent CR image is scanned using a laser beam
- it is digitised using a CR reader
WHEREAS:
- the latent image is processed chemically using film
technology
8
Q
- In a Computed Radiography system, what happens to the data that was digitised using the CR Reader?
A
- the data is sent to the computer
- it is displayed
- it is manipulated
- it is archived
9
Q
- What is the currently the most common imaging system?
A
- Computer Radiography
- that makes use of imaging plates
- these are known as Photostimuable Phosphors (PSP)
10
Q
- What do typical CR Resolutions range between?
A
- they range from 100 to 200 µm
- the spatial resolution is lower than that of fine or
detailed film screen technology
11
Q
- What does this image show?
A
- it shows how the latest systems can employ multiple
parallel lasers - they also have many light detectors and scanners
12
Q
- What are the two main systems of Indirect Digital Radiography?
A
- Those based on Thin Film Transistor (TFT)
Technology - Those based on Charged Coupled Device (CDC)
Technology
NB:
- both designs make use of phosphors and scintillators
- these produce light when exposed to X-Radiation
13
Q
- What is the difference between the 2 Indirect Digital Radiography systems?
A
- the differences revolve around how light is
detected - as well as how light is converted into a useful electrical
signal
14
Q
- Do these images make sense?
A
- yes
15
Q
- What is the magnitude of the Resolution System for Indirect Digital Radiography?
A
- 100 and 200 µm
16
Q
- What are some design considerations when it comes to Charged Coupled Device Technology (CCD)?
A
- how to connect the CCD array
- where to place the CCD array
17
Q
- What happens when any X-Ray reacts with a CCD?
A
- they create a false signal
- this is because CCDs are sensitive to X-Rays
- this means that the CCD array cannot be positioned in
line with the Scintillator Crystal - because this is where the X-Ray rays may interact with
it
18
Q
- How else can we position the CCD array to avoid
X-Ray sensitivity based issues ?
A
- we can use fibre optical tapers
- we can use a mirror and an optical lens arrangement
19
Q
- How do the detectors in Direct Digital Radiography work?
A
- they work in a similar way to ionisation chambers
20
Q
- What happens when Incident Radiation Passes into the sensitive volume?
A
- it causes electrons to be liberated from their orbits
- this creates positive and negative ions
- these ions carry charge from one electrode to the
other - these ions are attached to their respective electrode
- this creates a current
21
Q
- What does the Image Acquisition System do?
A
- it converts X-Rays to an electrical signal
- it does this without the need for first converting the X-
Rays to light
22
Q
- What does this image show?
A
- a flat panel detector
- this is the most modern form of Direct Digital
Radiography - it is used with regards to fluoroscopic materials
23
Q
- What are the advantages of Computed Radiography (CR)?
A
- this is an indirect mechanism
- it has greater versatility
- it can be used with unmodified equipment
- it is available in different Cassette Sizes