Week 1 Lecture 1

Question 1

what are the three components of x-ray imaging systems that influence the flow of electrons?

Answer 1

1. operating console
2. generator
3. x-ray tube

Question 2

what does the operating console consist of?

Answer 2

specialized keyboards that control the intensity and quality of the radiation used during imaging

Question 3

why are high voltage generators preferred?

Answer 3

• production of near constant-potential
• produces greater x-ray quantity and quality
• compact in size

Question 4

where do you find the generators on new CT equipments?

Answer 4

built into the scanners because they are so small

Question 5

why is the production of greater x-ray quantity and quality important?

Answer 5

it improves the image quality and decreases patient dose

Question 6

x-ray tube

Answer 6

• electronic vacuum that produces x-ray photons
• focuses useful beams of radiation through a window
• help with heat dissipation

Question 7

what are the 2 components that make up the x-ray tube?

Answer 7

1. anode
2. cathode

Question 8

protective housing

Answer 8

contains the x-ray tube

Question 9

what are the 3 functions of the protective housing?

Answer 9

helps to prevent:
1. electric shock
2. exposure to leaking radiation
3. damage to internal components

Question 10

what is the role of metal and glass envelopes?

Answer 10

to maintain the vacuums inside the tube as well as providing structural support

Question 11

why is the vacuum important for the tube?

Answer 11

• maintains the tube’s current
• allows for more efficient x-ray production and longer tube life

Question 12

in modern ct tubes, which is preferred? metal or glass envelopes?

Answer 12

metal

Question 13

why is oil found between the housing?

Answer 13

to dissipate heat

Question 14

what causes arcing?

Answer 14

deposits from tungsten vaporization

Question 15

why are metal envelopes preferred over glass ones?

Answer 15

metal envelopes:
- prevent arcing
- enables higher tube currents
- improves heat dissipation

Question 16

window on the envelope

Answer 16

• emits useful x-ray photos from the tube
• enables maximum emission of x-ray photons with the least amount of of absorption

Question 17

where do you find the window?

Answer 17

near the target – on the anode side

Question 18

cathode

Answer 18

negatively charged portion of the x-ray tube

Question 19

what is the purpose of the cathode?

Answer 19

• produces electrons
• directs the electrons to a specific location on the anode

Question 20

how does the cathode produce electrons?

Answer 20

thermionic emission

Question 21

what are the two primary parts to the cathode?

Answer 21

1. filament
2. focusing cup

Question 22

filament

Answer 22

thoriated tungsten coils that boils off electrons when it is heated

Question 23

why are there two filaments in an x-ray tube?

Answer 23

difference in the filament size used affects spatial resolution and impacts the heat capacity of the anode

Question 24

coil size of the filament correlates to what?

Answer 24

focal spot sizes

Question 25

both filaments can be used at once. t/f

Answer 25

false

Question 26

larger filaments are _____ and _____.

Answer 26

longer and wider

Question 27

focusing cup

Answer 27

- metal canal that surrounds the filament to electrostatically confine electrons - ensures the electrons will strike the anode target at the right spot

Question 28

why is the focusing cup negatively charged?

Answer 28

to prevent the electrons from spreading out

Question 29

anode

Answer 29

positively charged portion of the x-ray tube

Question 30

what are the 3 purposes of the anode?

Answer 30

1. produces x-rays 2. conducts electricity 3. provides mechanical support for the target

Question 31

what are the 3 components of the anode?

Answer 31

1. bearing assembly 2. rotor 3. target/disk

Question 32

where is the bearing assembly found?

Answer 32

it is covered by the rotor + covered in oil

Question 33

what is the purpose of the bearing assembly?

Answer 33

- to provide and ensure smooth rotation of the anode disk - conducts heat away from the x-ray tubes

Question 34

liquid bearing method vs. silver ball-bearing technology

Answer 34

liquid bearing method improves anode disk rotation reduces the vibration and noise

Question 35

what is the purpose of the rotor?

Answer 35

prevents transmission of heat from disk to the bearings

Question 36

what is the stator?

Answer 36

- tube-like structure that surrounds the rotor - makes the target rotate by electromagnetic induction

Question 37

where do you find the stator?

Answer 37

outside the metal envelope

Question 38

what is the purpose of the target?

Answer 38

collides with the electrons from the cathode

Question 39

how are x-rays created?

Answer 39

when fast moving electrons strike the metal target

Question 40

targets are designed to improve heat capacity and spatial resolution. how?

Answer 40

by the angles that are found on the targets

Question 41

how does the target move?

Answer 41

by the stator due to electromagnetic induction

Question 42

focal spot(s)

Answer 42

area of electron collision therefore site of x-ray emission

Question 43

where do you find focal spots?

Answer 43

on the angled portion of the targets

Question 44

larger or steeper angles = ?

Answer 44

larger or steeper angles of target will result in a larger surface areas larger surface areas will mean larger area of interaction which reduces the concentration of heat steeper angles also = ability to irradiate wider sections of anatomy = decrease spatial resolution

Question 45

does CT imaging or general radiography generate more heat?

Answer 45

CT imaging

Question 46

to manage heat production, what do CT tubes have in terms of FSS, target angles + size, and rotation speed?

Answer 46

larger fss larger angles on larger and thicker targets faster target rotation speeds

Question 47

what are the three designs for CT targets?

Answer 47

1. all-metal disk 2. brazed graphite 3. chemical vapour deposition (CVD) graphite disk

Question 48

what are limitations for all-metal disks?

Answer 48

- heavy - fixed targets - poor heat dissipation - short tube life

Question 49

*which target design was used in old/conventional scanners?

Answer 49

all-metal disks

Question 50

*which two target designs are more commonly found in helical/spiral ct scanners?

Answer 50

brazed graphite and chemical vapour deposition graphite disks

Question 51

*what is the difference between the brazed graphite targets and the CVD targets?

Answer 51

both have graphite bases, but the difference is brazed graphite's focal track is made of tungsten rhenium while the CVD's focal track just has the layer of tungsten r. over it

Question 52

what are the two advantages to brazed graphite?

Answer 52

1. capacity to withstand more heat (higher thermal capacity) 2. longer tube life

Question 53

what are the three advantages to CVD?

Answer 53

- allows for disks to be large and lightweight - large heat-storage capacity - fast cooling rates

Question 54

what are the steps to x-ray production?

Answer 54

operating console to engage generator generator sends current of electricity to x-ray tube cathode's filament is being heated which creates electrons potential difference develops (e- from cathode to anode) target on the anode gets bombarded with electrons production of heat (99%) and x-ray photons (1%)

Question 55

steps to getting a CT image.

Answer 55

1. perform scout 2. scan sequence 3. check for quality/accuracy - repeat scans if necessary 4. post-procedural care + dismiss patient 5. perform image post-processing

Question 56

protocols =

Answer 56

"how to scan" guide

Question 57

what are the four key considerations to achieve a ct image?

Answer 57

1. scan type (axial or helical) 2. patient positioning 3. use of contrast media 4. scan paramaters (technique selections - kVps, mAs)

Question 58

smaller filaments

Answer 58

increases spatial resolution decreases heat capacity

Question 59

larger filaments

Answer 59

used when imaging longer lengths of anatomy or hypersthenic patients

Question 60

hypersthenic

Answer 60

obese

Question 61

sthenic

Answer 61

"average" body

Question 62

hyposthenic

Answer 62

thin - below average

Question 63

asthenic

Answer 63

frail - "very thin"

Question 64

why does CT use a thicker target than GR x-ray tubes?

Answer 64

exposures are longer and produce more heat

Question 65

what is an important consideration in CT imaging?

Answer 65

overheating reduces maximum exposure times

Question 66

when would a large focal spot be preferred?

Answer 66

imaging larger body parts