Susanoo Flashcards
Glass envelope
Actual tube that conatins vacuum to allow electrons to flow without colliding with gas atoms
Window
Part of glass envelope where xrays passs through on their way down to patient
Made out of thinner glass
Tube Housing(Lead Casing)
Contains oil, aids in electrical insulation, keeps tube cool
Cathode
Negative terminal, contains focusing cup with negative charge around filament
Anode
Made of tungsten, attachted to rotor, rotates disk
Exposure button
Filament heats up and releases electron
Anode rotates from 3000-20000 rpm
positive charge is applied to rotating anode
Positive charge pulls electrons, electrons strike anode, xrays are produced
Collimator
Limits xray field reigon of interest
Xrays cannot be:
Seen
Smelled
Felt
Heard
xrays travel:
At speed of light
Grid
Between patient and IR, absorbs scatter xrays
Primary beam allowed to pass through grid
Detent
Mechanism that tends to stop a moving part in a specific location; vetically, transversally, longitudinally
Grid cutoff
Occurs when grid and IR are not in alignment, causes image that is at the edges
Grid cutoff causes
Tube not in detent Innocent SID Grid upside down IR at an angle to CR Result: image is to light at edges or down the down the center
Thermonuclear emission
Current creates heat and increases emission of electrons
Higher mA=hotter filament=more electrons emitted (directly proportional)
APR
Anatomically programmed radiography
A control that is programmable so exposure factors from conventional technique chart are available within computer
Select body part and technique will appear
Law of reciprocity
mAs=mAs
All combos of mA x S will produce the same amount of density
mAs
Quantity of X-rays produced
Increase mAs=increase number of X-rays produced
Distortion
Misrepresentation of true size or shape of object
Types=
Size-magnification
Shape- foreshortening & elongation
OID
Object to image distance
OID and size distortion-direct relationship
greater OID=greater magnification
magnification causes unsharpness/loss of detail
increase SID to offset magnification
SOD
Source to object distance
Closer the source to object the greater the magnification
If you increase OID or decrease SOD, increase SID
Motion
Not distortion, but is undesirable
Voluntary: lack of clear instructions, breathing, children, elderly
Involuntary: heart beat, peristalsis, tremor, chill, pain
Penumbra
blurring at edges of a structure
Factors: SID, OID, SOD, motion, patient factors
Spatial Resolution
Ability of imaging system to differentiate between two near-by objects
Factors: OID, SID, motion, focal spot size, patient factors, quality of system (pixels)
CR Systems
Computed radiography, cassette/IR has photostimulable phosphor plate
cassette placed into CR reader to create visible image
Half the radiation exposure of film screen
each image needs separate cassette
