test 1: lecture 3 Flashcards
Cathode has ___ charge
anode has ___ charge
negative
positive
the kinetic energy from electrons striking the anode turn into ___
Bremsstrahlung <1%
Heat production 99%
mAs
of electrons that flow from cathode to anode
increasing mAs increases # of electrons but not overall energy created
→ increased # of xrays produced
kVP
change in voltage from cathode to anode, the bigger the change the stronger the Xray produced
increasing both the # of photons and the overall energy
increased quality and quantity
two types of attenuation
Photoelectric effect = Absorption
photon removed from beam
Compton effect = Scattering
photon changes direction, can fog the detector (decreases contrast) and can expose personnel (=radiation hazard)
compton effect
Compton effect = Scattering
photon changes direction, can fog the detector (decreases contrast) and can expose personnel (=radiation hazard)
photoelectric effect
= Absorption
photon removed from beam
low kVp increases the change of what type of attenutation
photoelectric effect
(absorption)
high kVP increases the chance of ___
compton scatter (foggy)
photoelectric effect increases with ___ materials and ___ energy Xrays
high atomic number (bone high)
low energy (low kVp)
___ gives Xrays contrast
photoelectric effect (absorption- high atomic number and low kVp)
compton scatter increases with ___ tissues and ___ energy Xrays
higher density
high
how does analog work
film incased in two intensifying screens
screens will convert Xrays to visible light photons
these will interact with the film and provide a picture
During analog, energy absorbed from X-ray photons is released as ___ in crystals within screen of cassette. X-ray film is usually most sensitive to green, blue, or UV light.
visible light photons
limitations of analog
•Narrow exposure latitude,
•Need for chemical processing
•Incompatibility with electronic transmission
•No image enhancement
•Higher costs for film materials and labor
what does narrow exposure latitude mean?
the amount of settings where you get a good xray is limited
too low exposure → underexposed
too high → overexposed
___: wide latitude and ability to compensate for underexposures and overexposures with image preprocessing and postprocessing capabilities that are not possible with film.
DIGITAL DETECTORS
digital detectors have wide latitude, meaning
there is a wide range in which you can get a good quality xray
how are xrays stored online?
Picture Archiving and Communications System (PACS)
two types of digital xray
computed
direct digital
steps for computed radiography
xray still needs to be processed by a reader
steps of direct digital radiography
2 steps, very fast, no need for processing step
Computer radiography is on __ plate made of __.
flexible image
photostimulable storage phosphor
why do you have to process computer radiography quickly
Plate needs to be processed by the laser reader quickly after exposure as the latent image is stable for a short period of time
how are computed radiography made
X-ray photons strike cassette containing photostimulable storage phosphor: Electrons excited to higher energy level when interacting with photons
Cassette placed inside a laser reader where laser beam stimulates phosphor crystals to release trapped electrons → light energy emitted. The amount of light released is directly related to the intensity of x-rays that struck that portion of the cassette.
The information is spatially encoded and sent to computer for image reconstruction
direct radiography
flat panel detector
X-ray photons strike a flat panel detector containing a scintillator that creates visible light photons when struck by x-ray photons.
Light photons stimulate photocathode (light into electrical energy)
Electrical energy is spatially encoded by a thin film transistor and directly transmitted to computer for image reconstruction
digital radiography
flat panel detector
X-ray photons strike selenium plate and create charges (photoconductor)
Charges are spatially encoded and directly transmitted to computer for image reconstruction
→ xray directly into electrical charge
difference between the two types of digital radiography flat panel detectors
xray directly into readable electrical charge by selenium plate
xrays changed into visible light by scintillator then light into electric charge by photocathode, electrical charge processed by thin film transistor to computer
how does charged couple detectors work
xray hit scintillator and turn into visible light
lens minification (reduction)
CCD converts light into electrical charge
electrical charge → computer
why is minification needed in charged couple detectors
size of CCD is smaller then the plate. needs to be reduced to fit
advantages of digital radiography
Wide dynamic range: e.g. 12 bit system → 212 possible gray values (0-4095) → MANY MORE THAN FILM-SCREEN RADIOGRAPHY!!!!!
Digital storage and retrieval
Lower radiation dose often possible
Distribution and reproduction of multiple exact copies
Workflow efficiency gain even for CR
Post processing
Telemedicine and Teleradiology
CR or DDR
Computed Radiography: cheaper, takes longer- needs post processing
Direct Digital Radiography: faster
flat panel
or
charged couple detectors
both are direct digital radiography and do not need post processing
CCD: minification can increase noise, can’t take at an angle, may increase dose of radiation cause less efficient then flat, less expensive
FT: can take at any angle, efficient, expensive, mobile
Regarding digital radiography systems, which ONE of the following is FALSE:
Computed radiography systems are cheaper than flat panel systems
Computed radiography, flat panel systems and charged couple detectors systems all allow digital storage and retrieval of radiographs using a PACS system
Computed radiography, flat panel systems and charged couple detectors systems all produce images with thousands gray level values (wide dynamic range)
Radiographs obtained with digital systems can only be viewed on a computer monitor
Flat panel systems usually allow for more workflow improvement than computed radiography systems
Radiographs obtained with digital systems can only be viewed on a computer monitor
With radiographic film‐screen systems, what is needed to reveal the latent image?
An intensifying screen
A computer monitor
A processor
A scintillator
A computer plate
A processor
In a flat panel detector:
A scintillator is always present
X‐ray photons are always directly converted into electrical charges
A magnification process happens after exposure, in contrast with the minification process seen with CCDs
A charged couple detector spatially encodes and digitizes the informaion after conversion of the X‐ray photons into electrical charges
A thin film transistor spatially encodes and digitizes the information after conversion of the X‐ray photons into electrical charges
A thin film transistor spatially encodes and digitizes the information after conversion of the X‐ray photons into electrical charges
