xray system design

Question 1

what is faradays law

Answer 1

states that a current will be induced in a conductor which is exposed to a changing magnetic field

Question 2

what is flemings right hand rule

Answer 2

thumb = force
first finger = magnetic field
=middle finger = current

Question 3

what is electromagnetic induction

Answer 3

production of an electromotive force (emf) across an electrical conductor in a changing magnetic field. Alternating …

Question 4

1 cycle = 1 Hz = 1 rpm

Question 5

how do you transform voltage? (between 2 circuits)

Answer 5

1. coils of wire (provide AC current flowing thru primary circuit thats wrapped around a core)
2. magnetic flux ( induced by flow of current)
3. magnetic flux is induced into the coil of the secondary circuit and when the number of windings on secondary side is greater than the primary, voltage increases

Question 6

what does SST stand for

Answer 6

solid state transformers

Question 7

why are SST’s preferable

Answer 7

using small high power, high frequency semi-conductors they are more efficient and reliable for power transformation

they can also transform AC into DC

Question 8

what is a generator cabinet

Answer 8

cabinet that sits in xray room supplying all electrical needs

converts power circuits into low or high voltages and amperage and its a high frequency generator

Question 9

what is a watt

Answer 9

1 volt x 1 amp

Question 10

what 6 things are in xray tube housing and what do they do

Answer 10

1. steel outer casing to be robust
2. lead shielding to protect from leakage
3. output port for primary beam
4. insulated high-voltage cable sockets
5. oil which insulates against electrical shock and circulates to help dissipate heat
6. expansion bellows which disable the exposure switch when tube gets too hot

Question 11

what is shown on the exit port of the light beam diagphragm

Answer 11

DAP dose area product

measures radiation exiting tube (not radiation reaching patient)

cGyxcm^2

Question 12

what is on the back of the LBD

Answer 12

tube suspension, which can rotate

Question 13

whats on the sides of the LBD

Answer 13

locks
electromagnet
switches to engage motor

Question 14

what is the envelpe of the xray tube made of

Answer 14

borosilicate glass (pyrex) with beryllium window

Question 15

why is the envelope made of borosilicate glass

Answer 15

heat resistant
strong
electrical insulator
radiolucent

Question 16

what 2 main things are found in the glass envelope

Answer 16

cathode with heated filament and focusing cup

anode on a spindle

Question 17

why do most tubes have 2 filaments

Answer 17

to give large and small focal spot

2 foci provide choice of quick exposures or high resolution

Question 18

what are the filaments made out of?

Answer 18

thoriated tungsten

Question 19

what amps do the filaments carry?

Answer 19

3-4 amps

Question 20

why does the cathode have 2 electrical circuts

Answer 20

1 for high voltage current to make X-rays

2 to heat the filament and make it hot

Question 21

what does the focusing cup do

Answer 21

electrostatic ally confines electrons to keep them ready to be used

Question 22

what is the focusing cup made of

Answer 22

nickel

Question 23

how does the filament get hot

Answer 23

large CURRENT thru thin wire, thickness of wire and material cause resistance.

electrical resistance is limiting affect which gives off heat and when heated enough the wire will give electrons via thermionic emission

Question 24

what is a gridded tube/ what is its use?

Answer 24

controls the electron flow electrostatic ally by having an electronic grid on the cathode, switching from the focussing cup

Question 25

why might a focussing cup need additional electrostatic charge

Answer 25

when imaging using short and rapid exposures, need precision of switching and generating electrons

Question 26

what are the 3 different types of anodes and give examples of what they are used in

Answer 26

stationary anode (metal or mobile applications) rotating anode (standard tube) heavy-duty anode, ceramic envelope (angiography or CT tube)

Question 27

what are the 2 different types of anode targets used in mammography and why

Answer 27

molybdenum ( get k shell to match breast tissue) rhodium (for higher k shell energies for thicker breasts)

Question 28

why is the target at an angle

Answer 28

to reduce apparent focal spot size and decrease unsharpness

Question 29

what is the cylinder of a stationary anode made of

Answer 29

copper

Question 30

what are the 4 things that construct an anode

Answer 30

1. disc (tolerate heat loading) ( molybdenum) 2. track (tolerate head loading and characteristic radiation) (tungsten-rhenium alloy) 3. head-radiant backing (removes heat) (graphite) 4. thin spindle (reduce heat conduction to bearings) (molybdenum)

Question 31

flemings left hand rule is used only in MOTORS

Answer 31

apply current to wire place in external magnetic field force perpendicular to current and magnet formed causing spinning

Question 32

magnitude of EMF induced in coil is proportional to rate of change of magnetic field

Answer 32

SO the faster you change the magnetic field, the faster it turns

Question 33

What 3 things can make an xray classified as broken

Answer 33

- anode is pitted and xrays to consistent - bearings seize - glass cracks and hot oil goes everywhere

Question 34

why might a xray tube break

Answer 34

-problems in manufacture - overheating due to either large exposures or not long enough cooling time

Question 35

what will the xray machine do when it is overheating

Answer 35

expansion due to heat connects the warning circuit warning light on generator beeping noise system cuts out until it has cooled OR limits the amount of rays to complete procedure

Question 36

what 2 things does heating affect

Answer 36

size (expansion or contractions) transfer of heat (conduction, convection radiation)

Question 37

what are the positive and negative things that heating affects in xray?

Answer 37

ADV: - heats cathode filament - anode expansion to expected size DIS: - anode over-loaded due to frequent or high mAs exposures - LBD (light sticks on) - bearings wear in rotor

Question 38

what are 2 ways xray machines are cooled

Answer 38

internally - via oil externally - via air or water (chiller)

Question 39

what is the use of a collimator

Answer 39

to limit the beam

Question 40

collimation is manual or motor-drive by automatic format collimation system e.g bucky

Question 41

what 5 components make up the light beam diaphragm

Answer 41

1. added filtration 2. entrance shutters 3. mirror 4. light source (light field) 5. lead shutters

Question 42

What are the ADV and DIS of having a ceiling suspended tube

Answer 42

adv: - useful in large room for trauma, orthopaedics etc dis: - may not go very low if ceiling is high - only travels along length of track in each direction - cant be used if ceiling cant take the weight

Question 43

what are the ADV and DIS of having floor mounted tube

Answer 43

adv: - cheaper - can reach distance that a ceiling one would have difficulties reaching dis: - not as hygienic

Question 44

what is the typical ration found in a moving grid within a bucky system

Answer 44

12:1

Question 45

what dimensions are the detector that is permenantly within the wall stand and table?

Answer 45

43cm x 43cm

Question 46

what type of grids are used in integrated flat detectors

Answer 46

stationary grids

Question 47

how do digital tomography and ct differ

Answer 47

dt is simpler/ simple version of ct