X-ray machines

Question 1

what is contained within the negative cathode?

Answer 1

filament

Question 2

what is contained within the positive anode?

Answer 2

tungsten target

Question 3

how do you heat up a cathode?

Answer 3

pass a current through it

Question 4

what happens when you heat a cathode?

Answer 4

e- in outer shell gets enough energy to escape (emits e-)

Question 5

Where is the focusing cup located?

Answer 5

negative cathode

Question 6

How is an x-ray formed?

Answer 6

hitting target

Question 7

what does the negative focusing cup do?

Answer 7

focuses e- into a narrow beam toward anode (e- don’t diffuse away)

Question 8

where is the tungsten target located?

Answer 8

copper stem in anode

Question 9

what is the function of tungsten target?

Answer 9

converts kinetic energy of colliding e- into x-ray photons

Question 10

what is the function of the copper stem?

Answer 10

dissipates heat produced

Question 11

Once e- hits target, most of the energy is converted to –

Answer 11

heat (>99%)

Question 12

Once e- hits target, some of the energy is converted into –

Answer 12

x-rays (1%)

Question 13

increase likelihood that e- hits target by – (e- move towards target faster)

Answer 13

high potential difference between cathode and anode (70 kwatts)

Question 14

x-rays are – by calcified tissues (bones)

Answer 14

blocked

Question 15

x-rays are – by soft tissues

Answer 15

absorbed

Question 16

clearer images from a – source of radiation

Answer 16

point (small)

Question 17

umbra =

Answer 17

sharp

Question 18

penumbra =

Answer 18

fuzzy

Question 19

focal spot size of dental x-ray tubes

Answer 19

0.4 to 0.7 mm

Question 20

what kind of anode is mostly used?

Answer 20

stationary

Question 21

why do you angle target?

Answer 21

seemingly smaller source of radiation –> clearer image

Question 22

unlike visible light, x-rays are not –

Answer 22

reflected (produce at 360 degrees)

Question 23

How does a rotating anode decrease heat buildup at the anode?

Answer 23

e- hit a different surface on anode

Question 24

panoramic, CT, and cone-beam use what kind of anode?

Answer 24

rotating

Question 25

best to use -- anode for radiographs that have extended time periods

Answer 25

rotating

Question 26

rotating anodes make x-rays from a -- point

Answer 26

narrow

Question 27

describe energy x-ray photons

Answer 27

broad spectrum of energy

Question 28

e- attracted to positive nucleus in anode but the orbiting e- forces the incoming e- to --

Answer 28

deviate

Question 29

e- that hit closer to the nucleus give off -- energy

Answer 29

more

Question 30

All x-ray photons produced are not monoenergetic describes -- radiation

Answer 30

Bremsstrahlung

Question 31

x-ray photons with discrete energies describes -- radiation

Answer 31

characteristic

Question 32

describe e- movement in characteristic radiation

Answer 32

incoming e- collides with e- in orbit outer shell moves in inner shell is lost

Question 33

the difference between the outer and inner shell of a characteristic radiation has -- energy

Answer 33

discrete

Question 34

Ideal range of photon energy that can be blocked by bone but not tissue

Answer 34

20-50 keV

Question 35

How can you control the energy produced?

Answer 35

``` milliamperage (mA) exposure time (seconds) peak kilovoltage (kVp) ```

Question 36

What is mA

Answer 36

how much current goes thru filament

Question 37

What happens when you heat filament more?

Answer 37

more electrons produced/liberated --> more x-ray photons

Question 38

How long is the general exposure time?

Answer 38

0.1-0.4 seconds

Question 39

What happens when you increase the kVp (diff b/t cathode and anode)?

Answer 39

more electrons produced --> more photons

Question 40

How can you increase mA?

Answer 40

heat filament more

Question 41

What happens when you double mA?

Answer 41

double photons but same energy (keV)

Question 42

Why is it better to increase mA than exposure time to get more photons?

Answer 42

same radiation but lower patient movement

Question 43

Adjusting kilovolt (peak) depends on --

Answer 43

size of object (hand vs skull)

Question 44

What influences both energy and number of photons?

Answer 44

kVp

Question 45

How should you adjust kVP if it's the same amount of bone but less calcified?

Answer 45

lower kVp

Question 46

describe useful energy

Answer 46

sufficient energy to penetrate tissue and reach film (cause some ionization but w/o these there's no image)

Question 47

What is the function of Al filter?

Answer 47

removes low energy photons

Question 48

describe low energy photons

Answer 48

absorbed by tissue (damaging) and no image

Question 49

What is the function of collimation?

Answer 49

limit radiation beam to examined region

Question 50

what does collimation reduce?

Answer 50

radiation exposure and scatter radiation

Question 51

inverse square law

Answer 51

beam intensity is inversely proportional to square of distance from radiation source