Diagnostic Imaging - Interaction of Ionizing Radiation w/ Tissue (Image Production Processing) Flashcards
What are the different digital processing systems for images?
CR - computed radiography processing
DR - digital radiography processing
Compare CR and DR.
CR: cheaper, more time consuming, need to remove/replace IR, less efficient QDE, more artifacts, less portable, cassettes easier to replace, prone to dust, damage of CR reader/PSP
DR: more expensive, faster, no need for repositioning, better QDE, less artifacts, very portable, IR sensitive to cold/damage, better qlty image
Describe the process of CR.
Primary excitation: xray passes through upper layer to phosphor, reacts w/ electrons w/i phosphor, exciting them to higher energy levels, majority of electrons drop back to initial state, remaining get trapped, stores image w/i plate.
Secondary excitation: plate removed from cassette & scanned by laser beam, beam stimulates trapped electrons, causes light photons to be emitted. Light produced channeled to photomultiplier using optics
Photomultiplication
Digitisation
Plate erasure
The number of light photons produced by secondary excitation is directly proportional to
the number of electrons that were trapped in the storage phosphor (in CR)
How should an imaging plate be maintained?
- store away from radiation
- store cassettes in an upright position
- check imaging plates for damage
- dust-free environment
- erase imaging plates before use
- screen cleaning
- dirt on intensifying screens or PSP plates can appear as artefacts & mimic pathology
What are practical disadvantages of CR?
slower than DR
not as portable, less useful for off-site imaging
CR reader artefacts
PSP need to be replaced/maintained
need to erase cassettes prior to using
need to keep PSP clean & dust free
need to be processed relatively quickly
prone to scatter radiation
IDR stands for…
indirect digital radiography
IDR transforms x-ray energy to
light, then transforms light into an electric impulse
What are the two types of IDR?
Charge-coupled device
Flat panel detector
What two chemical compounds are used in a scintillator?
Gadolinium oxysulfide (Gadox)
Cesium iodid (CsI)
Flat Panel Detector uses
photodiode and TFT
photodiode converts light into
an electrical signal
TFT converts electrical charge into
an image displayed on monitors
How should flat panel detectors be maintained?
- wireless system batteries/ tablets must be charged
- may need to warm up detector to required temp
- careful handling systems/ electric board
What is DDR?
Direct digital radiography
What takes place in DDR?
Photodiode converts x-ray energy to electrical signal which is then converted to TFT to produce digital image. Then sent to PACS
What are characteristics of the optimal image?
- demographic info
- correct markers
- good positioning and centering
- geometric integrity/sharpness
- radiation safety/protection
- optimal exposure, brightness, contrast & grey scale, with minimal noise
- no preventable artefacts
How is the spatial resolution in CR?
Size of pixels detected by field of view
how is the spatial resolution in DR?
array of detectors linked together to form matrix, in which individual detector elements form the pixels of the matrix
Contrast is affected by
- exposure factors - kVp/mAs
- subject region of interest
- dynamic range of imaging system
- artefacts
- quantum mottle/noise
In digital systems, contrast is a result of…
selecting appropriate look-up table setting, providing an appropriate scale of displayed contrast for exam selected
Image contrast is affected by…
subject contrast
Contrast digital processing means
the dynamic range is wider, copes better w/ wider range of exposure
Underexposure means the image has a…
grainy appearance/quantum mottle
