Physics exam #2

the exam of champions.

kinetic energy is converted to what for x-rays

electromagnetic energy

the function of an x-ray system is to

provide a controlled flow of electrons intense enough to produce an x-ray beam appropriate for imaging

diagnostic units operate btw what kvp

25-150

why is the bottom number of the kVp range of diagnostic units 25

because of mammo

general purpose rooms usually have what imaging

fluro and radio

the fluro tube usually resides

under the table and fixed

medical x-rays are

diagnostic or therapeutic

the x-ray table is made of

carbon fiber

30 degree tilt on a table is

trendelenburg

90 degree tilt on a table is

reverse trendelenburg/ fowler

3 principle components of imaging system

operating console

xray tube

high voltage generator

operating console is used to

establish conditions of the exposure

the console must display

conditions of exposure

there are controls available to control

major and minor kVp adjustments

mA

Exposure time

all except how many circuits connecting the meters and the controls are low voltage to protect hazardous shock

one

a schematic drawing is

not a picture of what it looks like its a picture of what it acts like

what is line compensation used for

to provide consistent voltage to the autotransformer

technical factors must have very _______ voltage

precise

input voltage can vary as much as

5%

vacillation means

theres not constant voltage

Line compensation controls what

the # of turns on the primary side of the autotransformer

what are the 2 main circuits

main and filament

the main circuit does what

modifies incoming voltage to produce x-rays

what does the main circuit consist of

line compensator, autotransformer, kVp controls, High voltage transformer, rectifiers, tube

what does the filament circuit consist of

wire compensator, autotransformer, mA selector, filament transformer,

the kVp meter is connected to the what terminals of the autotransformer

output

the mA controls mA by controlling the

temperature of filament

mA selector is

a bank of varied resistors

filaments operate on what A

3-6 A

the transformer voltage is

fixed

if the transformer voltage is fixed how do we raise current

decrease resistance

what are the three exposure timers

synchronous timers, electronic timers, mA timers, and the AEC

what is the Hz of american power

60

electronic timers allow for how long exposures

1ms

mAs timers are found where

portable machines

mAs timers do not work with

AEC

Three main parts of a high voltage generator

high voltage transformer

filament transformer

rectifiers

high voltage generators are usually immeresed in

oil

the turns ratio for a high voltage generator is

500:1 or 1000:1

the waveform from the secondary side will differ from the waveform on the primary side in what

amplitude

high voltage generators must have what to function

alternatic current

rectifiers do what

convert AC to DC

what is a rectifier

device which allows electrons to flow in only one direction

the 2 types of rectifiers

vacuum tube and solid state

Half wave rectifers usually have how many diodes

2 or none

single phase full wave rectifiers have how mant rectiifers

4 or more

generator types

single phase

three phase

high frequency

Above the 0 line of the graph of rectifiers means the electrons are flowing to what

toward the anode

single phase half wave rectified has how many pulses per second

60

single phase full wave rectified has how many pulses per second

120

the ripple effect is

the measure of efficiency of the system and the lower the # the more efficient

what is the voltage ripple of half wave

100%

what is the voltage ripple of full wave

100%

why are both half wave and full wave 100%

they fall 100% of the way back to 0 on the graph

what is the voltage ripple of three phase 6 pulse

13-14%

what is the voltage ripple of three phase 12 pulse

4%

what is the voltage ripple of high frequency

<1%

three phase power has how many waveforms

three

what makes three phase power more efficient

while one wavelength goes down, the other goes up

high frequency consists of

full wave rectified converted to high frequency

what does high frequency convert 60 Hz to

500-25,000

what chops DC current into smaller square pulses

inverters

what makes high frequency so great

cheaper, smaller, most efficient

the high voltage transformer does what to voltage

steps up

the filament transformer does what to voltage

steps down

the filament transformer does what to current

steps up current

the autotransformer can be

step up or step down

the line compensator

adjusts # of terms on the primary side of the autotransformer to maintain constant voltage

the line compensator essential removes

vasilation

the kVp selection is a

compensator for the secondary side

the resistor bank or mA selector changes resistance to change

Intensity

x-rays are produced in equal intensity in all directions or

produced isotropically

x-rays emitted from any other part other than the window are called

leakage radiation

shielding protects from specfically

leakage radiation

the x-ray tube housing protects from

leakage radiation and shock

the three external components of the x-ray tube are

x-ray tube support

protective housing

glass or metal envelope

proper tube must have leakeage less than or equal to

1mGya/hr (100 mR/hr) at 1 meter

the glass of the glass envelope is

pyrex

metal envelopes are used to prevent

bronzing

the cathode is not always

negative

the cathode is only negative

at the time of exposure

the space charge effect limits

thermionix emission by electrostatics

the saturation current is

the max electrons boiled off at a certain mA and the highest mA is the tube saturation

the anode is only positive at

exposure

the anode serves three functions which are

thermal radiator

conducts electrons

provides mechanical support for target

higher tube currents and shorter exposures times are possible with which anode

rotating

the target is made of

tungesten rhenium

the line focus principle states

a purposeful angle at the target to maximize area of bombardment and minimize effective focal spot size

the effective focal spot size is also known as

projected/apparent focal spot

as the target angle becomes more vertical, the effective spocal spot size

decreases

if the effective focal spot size decreases, the spatial resolution

increases

the anode heel effect is due to

line-focus principle

what three things cause the anode heel effect to manifest

large field size

short SID

large focal spot

the anode heel effect technically occurs by

x-rays attenuating on the anode side due to going through the target to the angled angle

the effective focal spot is smaller towards the

anode

extra focal radiation is

x-rays produced outside the focal spot

extra focal radiation is also called

off focused radiation

what are the 4 problems caused by extra focal/off focused radiation

extends size

increases skin dose

reduces image contrast

exposes unintended tissues

what helps minimize off focus radiation

diaphragm and window

what is the primary cause of tube failure

heat