Fundamentals of digital radiography Flashcards
CR imaging plate layers
Protective Phosphor Conductor Support Light Shield Protective backing
Protective layer
protects the phosphor layer
Conductor layer
grounds imaging plate from electro-static charge
light shield layer/backing layer
prevent unwanted light and background radiation from affecting unexposed latent image
Phosphor layer
- made of bromides (85% barium flourohalides, 15% europium iodides)
- store and release energy to create latent image
CR digitizer
device used to convert CR latent image into digital radiograph
components of CR digitizer
laser - splitter - focusing lens - mirror - photo-multiplier tube - analog to digital converter
laser
helium-neon laser interacts with phosphors on imaging plate, releasing light photons
photo-multiplier tube
collects photons, sending to ADC
analog to digital converter
converts analog (light) signal to digital (binary) signal
CR CCD reader
acts as a PMT, but collects and converts to digital all in one step (no ADC needed)
photo-stimulating light
erases imaging plate through bright, white light which releases any remaining stored photons
DR direct conversion
conversion system with semiconductor and TFT only
DR indirect conversion (TFT)
scintilation layer
photodiode layer
TFT array
DR indicrect conversion (CCD)
cassetteless conversion system without photocathode or TFT
scintillation layer
- made of Cesium Iodide (CsI) rods
- incoming photons converted into light photons
photodiode layer
- made of amorphous silicone
- converts light photons into electric charge, transfer to TFT
Thin film transistor layer
made of DELs
-converts electric charge to binary
sensor chip in CCD system
light photons converted directly to binary and sends to computer for processing
semiconductor layer
- amorphous selenium
- interaction between high voltage charge and xray photons causes release of electrons in selenium atoms, which can then go to TFT for processing
Pixel size formula
FOV
Pixel size = —————-
Matrix size
dynamic range
the range of exposures that can be captured by a detector
exposure latitude
the range of exposures that produce quality images at an appropriate patient dose
bit depth
total number of brightness levels that can be assigned to any given pixel
calculating bit depth
2^(bit system)
8-bit system
2^8 = 256 shades of gray
contrast resolution
the smallest exposure change that can be detected and displayed by the system
PACS
picture archiving and communication system
-networking and storage system
PACS servers
maintain image archives for long-term storage
DICOM
digital imaging and communication in medicine
-imaging format that functions on all PACS systems, regardless of vendor or facility
EMR
electronic medical record
-contains standard medical data within an office or site
EHR
electronic health record
-contain and share information from all providers, not just one office or site
server based PACS networking system
imaging equipment
to PACS servers
to reading stations
server based PACS networking system
advantages
- any exam can be opened from any PACS workstation
- only one rad can open the exam to interpret it
- all prior exams are immediately accessible to rads
server based PACS networking system
disadvantages
- PACS server failure=system failure
- data flow can bog-down
web based PACS networking system
imaging equipment
to PACS servers
to reading stations (through the web)
web based PACS networking system
advantages
-exams can be accessed from any computer with internet access
web based PACS networking system
disadvantages
- desktop monitors may not be of diagnostic quality
- speed of this system is dependent on internet speed
- PACS server failure=system failure
distribution PACS networking system
imaging equipment
to PACS servers and directly to reading stations
distribution PACS networking system
advantages
- PACS server failure does not mean system failure
- multiple copies of images
distribution PACS networking system
disadvantages
- technologist must send images to correct reading station
- rad can only read from their PACS station, would need to physically move to another station to get different images (such as other modalities)
