Xray physics: The Xray Tube (ch.7 Bushong) & Xray production (Ch.8)

what is leakage radiation?

any x-rays, other than the primary beam, that escape the tube housing

T/F: it is okay to rest patient limbs on tube to obtain a better image

F

what does it mean to say that radiation is emitted isotropically?

it is emitted in equal intensity in all directions

what is the purpose of high voltage receptacles

to protect against accidental electrical shock

the glass envelope is a diode containing the ____________ and _____________

cathode and anode

the glass envelope is made of a special kind of glass known as

pyrex (heat resistant)

the (cathode/anode) is the negative side of the xray tube

cathode

the cathode contains the ____________ and the ____________ ___________

filament

focusing cup

the cathode (receives/absorbs) electrons emitted

receives

the filament is made of which element

tungsten

the focusing cup is (negatively/positively) charged

negatively

the focusing cup is comprised of _______________ or _______________

molybdenum or nickel

what is the purpose of the focusing cup

to focus the electrons from the filament as they travel to the cathode and prevent the electrons from spreading out and creating a larger focal spot

T/F: focusing cups provide more efficient xray production

true

what amperage is required for thermionic emission to occur

3-6

term for the cloud of electrons that collect around the filament

space charge effect

the space charge effect limits the amount of electrons that can be emitted by the filament due to

electrostatic repulsion

the space charge effect makes it difficult to produce exposures with (high/low) mA

high

what is the older term for the space charge effect

blooming

when does saturation current occur

when the maximum number of electrons has been produced at the filament

T/F: increasing kVp will increase mA

T

T/F: most modern xray tubes contain both small and large filaments

T

T/F: only small filament size can be used at lower mA stations (300 or less)

F; both can be used

T/F: both filaments can be used for higher mA stations

F; only large

small focal spot filament size

0.1-0.5

large focal spot filament size

0.4-1.2

the positive side of the xray tube

anode

T/F: anodes can be either stationary or rotating

T

what are three functions of the anode

electrical conductor

mechanical support

thermal conduction

T/F: and anode made of copper will be less noisy than one made of molybdenum

F

which materials allow for easier rotation of the anode

molybdenum/tungsten

graphite/tungsten

this is the area of the anode on which electrons from the cathode strike

target

which modality of xray does not use tungsten as its target material

mammography

atomic number of tungsten

74

melting point of tungsten

3400 degrees C

rotating anode rpm range

3,400-10,000

rotating anodes are driven by

an induction motor

the ______________ ____________ principle increases the area of target on which electrons can strike

line focus principle

the actual focal spot (increases/decreases) with increased anode angle

increases

target angles vary from ____ to ____ degrees

5-15

the focal spot projected onto the patient

effective focal spot

the line focus principle (increases/decreases) production of radiation and (improves/reduces) detail

icreases

improves

the spot on the target where electrons actually strike

actual focal spot

the smaller the effective focal spot, the (better/worse) the detail

Better

the larger the target angle, the (smaller/larger) the effective focal spot

larger (less detail)

what is the disadvantage of the line focus principle

anode heel effect

the anode heel effect results from (increasing/decreasing) target angle

decreasing

radiation intensity on the cathode side is (greater/lesser) than on the anode side

greater

T/F: you can compensate for the anode heel effect

T; patient positioning

saying for patient positioning to counteract the anode heel effect

fat cat

T/F: anode heel effect is a bigger issue on DR rather than film

F; film

what is flat fielding

when digital system evens out the image brightness

term for radiation produced other than at the focal spot

extrafocal radiation

is extrafocal radiation diagnostic?

no

extrafocal radiation (increases/decreases) contrast

decreases

tube failure is caused by (6):

excessive heat

cracking of anode

long exposure times

filament vaporization

pitting and bubbling

arcing

what would cause the anode to crack?

applying too much heat before it is properly warmed up

describe arcing

when tungsten vaporizes on the inside of the glass envelope and attracts electrons (produces a popping sound)

T/F: xray tube life is controlled by the manufacturer

F; the radiographer controls tube life

T/F: you can use maximum exposure factors on a cold anode as long as it is one the first exposure

F; dont do that

the _____________ rating chart is the most important

radiographic

radiographic rating charts will determine if particular ______________ ___________ are safe for a particular radiographic unit

exposure factors

focal spot size is (directly/indirectly) proportional to heat produced

directly

for single phase unit, HU (heat units) =

kVp x mA x seconds

for 3 phase (6 or 12 pulse) and high frequency units, HU (heat units) =

kVp x mA x seconds x 1.41

1.41 is the correction factor

where to find max amount of heat units the anode can handle on an anode cooling chart

where the cooling curve intersects with the y axis

where to find how long it will take to completely cool the anode after it has reached max heat on an anode cooling chart?

where the line intersects the x axis

T/F: you need to wait until the anode is completely cool to make a new exposure

F

this determines the time it takes for the protective housing to cool

housing cooling chart

it takes ___-____hrs for the protective housing to cool from max heat capacity

1-2hrs

T/F: an overheated protective housing determines if an exposure can be taken

F

the primary function of the xray tube is to accelerate electrons from the ____________ to ___________

cathode to anode

electrons travel ______ times the speed of light

1/2

the electron-target interaction converts _____________ energy into ____________ energy

electrical to electromagnetic

KE=

1/2m x v^2

increasing kVp increases electron _____________ energy

kinetic

during heat production, _____% of kinetic energy is converted to heat- less than ___% results in xray production and infrared light

99; 1

isotropically means

equal intensity in all directions

only the radiation that is directed through the _____________ is considered useful

window

radiation other an that which is directed through the window is absorbed by the _______ _______ or ______ inside the xray tube

protective housing

oil

any radiation that emerges from the xray tube other than through the window

leakage radiation

interaction of projectile electrons with the inner shell electron of the target atom

characteristic radiation

T/F: the target atom is ionized through characteristic radiation

T

energy of the projectile electron must be (greater than / less than / equal to) the EBE of the target atom in characteristic radiation

greater than or equal to

why is it called *characteristic radiation

very specific energy levels produced are characteristic of the target material used

in characteristic radiation, the production of an xray photon is the result of

an outer shell electron filling the vacancy of the inner shell

photon energy (Kev) =

(inner shell EBE) - (filled vacancy shell EBE)

characteristic radiation produced as a result of ionization of inner (k) shell

k xrays

only form of characteristic radiation that is useful in radiology

k xrays

why is other characteristic radiation (L, M, N...) non diagnostic

the energy levels are too low

formula for maximum electrons existing in an orbital shell

2n^2

kVp less than 69 with tungsten as the target material would produce a ___ shell vacancy

L (not diagnostic) (characteristic not produced)

for characteristic radiation to be produced, the PE must conatin at least ____ keV

69

german word for breaking or slowing down

Bremsstrahlung

T/F: ionization occurs with bremsstrahlung radiation

F

___________ radiaiton interacts with the nucleus of the target atom

bremsstrahlung

the projectile electron bypasses the orbital electrons in ______________ radiation

bremsstrahlung

the projectile electron (gains/loses) kinetic energy in bremsstrahlung radiaiton

loses

in bremsstrahlung radiation, the xray photon equals

the amount of energy lost by the projectile electron

the projectile electron (slows/speeds up) and changes direction in bremsstrahlung radiation

slows