digital imaging Flashcards
analogue images
- have a continuously varying density across them
digital images
- Have discrete pixels with numerical density values
digital imaging series
- generation
- processing
- archiving
- presentation
types of digital radiography
computed radiography
digital radiography
computed radiography
- uses imaging plates which need developing in a processor
digital radiography
- acquires an image directly without using a processor
main digital image detector functions
- capture - absorbing x-rays
- coupling - linkage between the capture element and converter
- conversion - change of x-ray energy into an electrical signal which can be read
advantages of digital radiography
- time-efficient - receive image immediately
- ## reduction of unsharpness - no spread of light
advantages of indirect imaging
- can reduce dose/exposure
digital imaging (DR)
- Image does not need to be procecessed
- the image is sent to the computer via wireless connection
- the imaging detectors can either be fixed plates in a vertical or table bucky or portable cassettes
Selenium drum detector system
- the photoconductor is made of amorphous selenium ( generates an electrical charge
- has a detector drum
- A-D converter - readout process
In ….. x-ray energy is converted directly into electrical signal
DDR
a simple conversion process of x-rays to electronic signal reduces noise in……
DDR
one advantage for ….. is good image resolution
DDR
one advantage for… is reduction in patient dose, since x-ray exposure can be reduced
CR
…. can give a salt and pepper appearance
CR
one advantage of… is amplification of signal
CR
one advantage of … is image sharpness
DDR
One disadvantage of …. is that the extra energy conversion process produces image noise
CR
in…. X-rays first strike a light-producing layer, light is then used to produce an electrical signal in the detector plate
CR
Dose creep occurs in …
DDR
….. gives a lower dose to the patient
CR
…. uses cassettes, containing imaging plates which need processing
CR
…. Acquires an image without using a cassette or processor
DDR
………. can be linked via PACS
Both CR and DDR
…. is a direct method
DDR
…. is an indirect method
CR
one disadvantage of …. is that the light spread produces image fuzziness
CR
….. has a photoconductor of amorphous selenium
DDR
……. has a scintillation crystal made of caesium iodide activated with Thalium
CR
a simple conversion process of x-rays to electronic signal reduces spatial blurring in ……
DDR
purpose of a photoconductor
- absorbs light and then produces an electrical charge
flat-panel detector system
the photoconductor is made of Amorphous selenium
uses a TFT Array read-out process.
flat-panel detector system
the photoconductor is made of Amorphous selenium
uses a TFT Array read-out process.
flat-panel detector system
the photoconductor is made of Amorphous selenium
uses a TFT Array read-out process.
types of Amorphous Selenium DR systems
- selenium drum detector system
- flat-panel detector system
indirect DR
- each cell in the detector has a top layer of a scintillation crystal (made of CsI (caesium iodide) activated with thallium - which produces light when hit by x-rays
- below this, an amorphous silicon photodiode converts the light into an electric charge
types of CCD indirect radiography systems
lens-coupled CCD based system
Slot scan CCD based system
lens-coupled CCD based system
x-rays are converted into light by the scintillation crystals
- light passes through an optical lens and light is received by the charged-couple device
Amorphous silicon indirect DR system
x-rays are converted into light by the scintillation crystals
- this light is received by the Amorpous silicon photodiode
- light energy is converted to electrical energy and is received by the TFT array
what is quantum mottle
at very low mAs values, random fluctuations in x-ray intensity beam start to show
- image can appear grainy
CR system
x-rays hit the first storage phosphor IP and are stored
a laser is emitted and hits the second storage phosphor IP
a blue light is then emitted and is received by the photomultiplier
then the photomultiplier sends this light to an A/D converter where an electrical charge is produced
what is image noise
- random fluctuations in signal, due to imperfections in image recording/transfer process
sources of noise
- background scatter
- detector faults
- random electrical fluctuations
- quantum mottle
