chapter 5 physics Flashcards
at what voltage do x ray systems operate at?
25 to 150 kVp
what is the operating x ray system tube current?
100 to 1200 mA
what is the purpose of couches in OR?
they hold the cassette and potter Bucky and they reduce patient dose
what are the parts of the X-ray imaging system and at what order do they go in the circuit?
Operating Console, high- voltage generator and the X-ray tube
what are other names for operating console?
primary circuit, low voltage circuit, and control panel
what are other names for the high voltage generator?
secondary circuit, high voltage circuit and lead box
what are other names for the X- ray tube?
X- RAY TUBE LOL
what does the low voltage circuit control?
current and voltage aka mAs and kVp
Radiation quantity measured in what ?
mGya/mAs
radiation quality measured in what ?
kVp or half-value layer
what is the line-compensater, where is it located and and where does it fall in the X-ray circuit?
it adjust voltage to 220v or 440v b/c voltage will not always come in at that voltage. it is located in the primary circuit and is after the breaker before the autotransformer.
what is the auto-trasformer, where is it located and where does it fall in the X-ray imaging system?
it adjusts kVp to the necessary technique. it is located in the low voltage circuit. Is located after the line-compensater.
how does the Auto-transformer work?
through self-induction and electromagnetic induction
what kind of relationship does voltage and the number of turns ratio have?
direct relationship; meaning as voltage goes up number of turns ratio goes up
exposure switch and its place in the circuit
it is found in primary circuit after the timing circuit. responsible for heating up the thoriated tungsten filament to thermionic temp. to create a space charge.
types of timers and their location?
electronic timers, synchronous timers, mAs timers, AEC
what is the AEC?
its a backup timer that protects the patient and the unit. and should be set at 150% of the anticipated mAs.
what is sunburn
vaporization of the thoriated tungsten filament and rhenium tungsten target
step- down transformers other names ?
filament transformer or isolating transformer
how can sun burn affect the beam intensity?
it can decrease it via attenuation
what material and in what order are traversed by the photons as they exit the tube?
Glass envelope (handles heat produced)>oil (coolant)>Aluminum (added filtration)
in the anode do tube interactions cause ionization?
not bremsstrahlung; only characteristic
which tube interaction goes through cascading?
Characteristic
what is caused at the anode by repeated heating from multiple exposures?
Anode pitting
what is caused by exposure without tube warmup?
cracking of the anode
where are X rays more intense?
cathode side
what anatomical part goes under the cathode side?
thicker anatomical part
what are the most common anode angle?
7-17; 5-20; most common is 12
anode heel affect predominates when
small target angle, shorter SID, NO collimation, large field size
what is off- focus radiation
when electrons don’t hit the focal track on the anode when created into photons
what do you note when looking at a tube rating chart
rpm, unit phase, FSS, and Target angle
Anode/ hosing cooling chart
how long it takes the anode to cool down completely
single phase heat unit calculation formula
mA X Time X kVp
three phase 6 pulse heat unit calculation formula
mA X Time X kVp X 1.35
three phase 12 pulse heat unit calculation formula
mA X Time X kVp X 1.41
what rpms are required for a stator and the rotor to rotate
2300-10000
what type of material is the anode made of
rhenium tungsten
Whereis the mA selector located and what does it do?
it is located in the primary circuit on the filament circuit; selects mA
what are the parts of the high voltage section?
- step-up transformer; high tension transformer
- step down transformer; low tension transformer; filament transformer; isolating transformer
- rectifier
what are other names for the step-up transformer?
high tension transformer
what are other names for the step down transformer?
low tension transformer; filament transformer; isolating transformer
how does the step up transformer work?
it converts a low voltage/ high current into a high voltage/low current so that way we are able to use kV instead of V
how does the step down transformer work?
it covers low current/ high voltage into high current/ low voltage in order to change mA to Amps so the filament can reach thermionic temp. (2200 c)
what is the rectifier and where is it located in the x-ray circuit; and at what point in that circuit?
this is what converts AC to DC in order to have enough voltage to power the x ray tube and is after the step up transformer
what is the relationship between voltage (V) and number of turns (N)?
direct relationship
what is the relationship between voltage and current?
indirect relationship
what type of induction is a step-down transformer?
mutual induction
what type of induction is a step-up transformer?
mutual induction
what type of induction is an auto-transformer
self induction
what do falling generators allow?
allow high mAs and short exposure time
how does a falling generator allow high mAs and short exposure time?
it accomplishes this by starting at a high mA at 0 ms then the intensity decreases to allow a short exposure time with a high mA.
what is the p-n junction when p-type+, n-type-?
solid-state Diolde
what is a p-type?
have holes with no electrons
what is an n-type?
loosely bound electrons
what are what are p-type and n-type ?
Diodes
what is a voltage ripple?
the ampere
single-phase ripple % and image quality
100% ripple/ 0 to max value
3-phase, 6 pulse ripple % and image quality
14% ripple/ doesn’t fall under 86% of the max value
3-phase, 12 pulse ripple % and image quality
4% ripple/ doesn’t fall under 96% of max value
high frequency ripple % and image quality
1% ripple/ best quality and quantity
what generator is best for the imaging system?
high voltage generator
where is DC created? and at what circuit?
in the rectifier in the high voltage circuit
what is thermionic emission
when the electrons in the cathode filament are boiled off and are ejected from outer-shell
what is a cloud of electrons ?
space charge
what is saturation current
kVp will continue to increase even though mAs hits its max
what mA is required for a small focal spot
300mA or lower
what mA is required for a large focal spot
400 mA or higher
coast time?
the time it takes the rotor to completely stop its rpm
what is the target angle for an effective focal spot?
5-20
what are the three ways heat is dissipated
radiation, conduction, convection
radiations related to heat dissipation
heat is transferred to infrared
conduction
transfer of energy from one object to another
conviction
transfer of energy though movement of headed substance from one place to another
radiographic rating chart
determines which techniques are safe and unsafe
anode cooling chart
tracks heat so that it does not exceed head storage capacity
housing cooling chart
determines cooling time after max heat capacity
synchronous timers
keeps the shaft at 60 revolutions per sec.
electronic timers
time required to change a capacitor through a variable resistance
mAs timers
production of mA and time (s)
AEC (automatic exposure control
automatically terminates exposure when intensity (mAs) is reached
whats a Diode in a single phase generator
the hump of the current which is called the Apere
two Diodes in a single phase generator result in what ?
negative pulse which is not read b/c its only a half eave which only accounts for the + side of the apere
Four diodes in a single phase generator result in what?
negative pulse is flipped so both are read b/c it takes both +,- into account
does single phase power ever drop to zero?
yes, b/c it has 100% ripple
what is three-phase power?
three waves that are spaced out evenly; one wave starts before the other is depleted
does the wave form of a three phase power ever drop to zero?
no because another wave form is already coming back up
does the individual voltage of a three phase power drop to zero?
yes
how many diodes are in a three-phase, 6-pulse waveform?
6
how many diodes are in a three-phase, 12-pulse waveform?
12
how many pulses/second are recognized in a single-phase half-wave?
60
how many pulses/second are recognized in a single-phase full-wave?
120
how many pulses/second are recognized in a three-phase 6-pulse?
360
how many pulses/second are recognized in a three-phase 12-pulse?
720
how many pulses/second are recognized in a high frequency?
we no longer see pulses b/c there are too many
