Sensors and Digital Imaging Flashcards
in 2016 and 2017 survey of practicing dental assistants in the US estimate that up to ____% of dental offices use digital radiology
90%
what are the contents of film packets
- outer cover
- lead foil
- black, light proof paper wrapper
- film
what are the sizes of film and what are they each for
size 0- pediatric
size 1- PA, pediatric
size 2- standard
size 4 - occlusal
what is the film composition
- supercoat- thin layer of hard plastic
- emulsion - gel and Ag- halide crystal
- adhesive
- base - plastic
what is Ag formed from
silver halide salt
chemical changes are ____,_____,_____ dependent
time, temperature, and concentration
how is a digital image made
a digital image is a table with columns and row which each cell (pixel) is assigned a number value which is then assigned a gray intensity. the composite collection of pixel values are used by a computers software processing ability to construct an image for visual display
what is the word pixel derived from
PEL- picture element
what is a pixel
the smallest portion of a sensor, image or display that is capable of being recorded and then printed or displayed
what are the general steps in digital image formation
- X ray shadow
- electric shadow signal is detected by digital sensor
- numerical pixel values sent to the computer
- digital image on the computer screen
how is the electric shadow signal detected by digital sensor
- pixels are electrified
- each pixel has a pre exposure electrical charge
- X ray photons that make it to the sensor change the electric charge in those pixels
- the thicker/denser the body part adjacent the sensor, the less the x-photons can affect the electrical charge
- the net effect is that there is a shadow of electric charges on the sensor reflective of the thickness/density of the body part
what are the types of historic/indirect digital radiography
- flatbed scanner
- slide scanner
- digital scanner
what are the types of indirect/ semidirect digital radiography
phosphor storage plate (PSP)
- aka photostimulable phosphor storage plate (PPSP)
what are the types of direct digital radiography
- charge coupled device (CCD)
- complementary metal oxide semiconductor (CMOS)
why is indirect digital radiography not preferred
loss or alteration of information due to partial volume averaging
what are the components of semidirect digital system
- laser scanner
- PSP plate
- X ray source
- screen monitor
- CPU, server or PACS
- printer, EPR, PACs
what are the principles of PSP detector
- X ray
- PSP plate coated with crystalline halide emulsion made up on BaFBrEu2+ producing a latent image of ionized phosphors
- scanned with red laser beam
- emits fluorescent light from excitation of valence electrons in ionized fluorophosphors
- intensified by a photomulitplier tube
- light intensity converted to digital data
- expose to strong light to erase residual images by neutralizing charges in ionized fluorophophors
- resuse
what are the componenets of direct digital system
- screen monitor
- CPU, server or PACS
- printer EPR PACs
- analog to digital converter to CCD
- digital interface cord
- CCD/CMOS
- X ray source
how big are XDR size 1 sensors
3.5mm x 2 mm
how big are XDR size 2 sensors
4mm x 2.5mm
what are the components of sensors
- electronic substrate
- CMOS imaging chip
- fiber optic face plate (FOP)
- CSI scintillator
what are the portions of the CCD/CMOS area
- external size
- internal active area- the portion of the sensor producing the image
in a sensor, each pixel is like a tiny battery with its charge equal to the number of ______
electrons trapped inside
what is the thickness of sensors
4-6mm
what are the shapes of sensors
square, rounded or cut
what are the types of sensors
CMOS and CCD
what is the principle of the CCD detector
- Xray -> scintillating material -> light photos -> silicon -> electrons deposited in electron wells -> transferred in a sequential manner (charge-coupling) -> read out amplifier -> images on monitor
describe CMOS compared to CCD
- CMOS is newer technology
- require less power
- superior image quality
what is bit depth
the number of colors that a pixel is able to show
what are the benefits to digital imaging
- less radiation
- better image
- lower costs
- reduced patient chair time
- no cost for film and chemicals
- no darkroom needed
- environmentally friendly- less toxic chemicals disposed in sewage
why SHOULD digital imaging be appealing
- electronic communication improves efficiency
- rapid acquisition
- image portability
how do CCD/CMOS sensors work
- cesium iodide scintillator converts x rays into visible light
- photosensitive pixels convert scintillator’s light into electrical signals. on chip circuitry turns electrical signals into digital output
- digital data is sent to a computer
describe digitization in CCD,CMOS types
X ray photons cause ionization of pixel silicone; ejected electrons are trapped in the pixel similar to the charge in a battery. the computer records the charge in each pixel and converts it to a gray value
what is the size of pixels in sensors
15 microns or 15 x 10^-3 mm
describe CCD sensors compared to CMOS
- older technology
- require an additional power via an adjunct box
- need additional power to convert the photon energy to an electrical digital signal
when was the first CCD system created and by who
- 1988
- Dr. Francis Mouyen
describe the prinicple of CMOS detector
- X ray -> scintillating material -> light photos -> silicon -> electrons deposited in electron wells and converted to voltage in each pixel ->smoother signal digitization -> software processing -> images on monitor
what is the power consumption, sensitivity to XR, cost to manufacture, readout, pixel signal, chip output of CMOS
- 40 mW
- low
- medium
- simple
- voltage
- bit/digital
what is the system complexity and sensory complexity of CCD and CMOS
- CCD: high and low
- CMOS: low and high
what types of extraoral digital radiography have been applied in panormaic and plain skull images
CCD and PSP plates
describe extraoral digital radiography
- similar spatial resolution as film based format 4Ip/mm
- inferior contrast resolution possibly compensated by manipulation functions
what is the actual and line pair resolution of sensor image wuality
- actual: visible >20 Ip/mm
- theoretical- calculated >26 Ip/mm
what are the brand of CMOS sensors
- AFP imaging
- Planmeca
- XDR
