production of X Rays pt 1

Question 1

Control panel
can adjust?
type of button?
requires?

Answer 1

Control panel:
 Exposure time, kVp (energy) and mA (#xrays) selectors
 Exposure button (dead-man type)
 Requires Indicator light and audible signal

Question 2

Tube head components

Answer 2

Tube head: Power supply + x-ray tube
◦Glass envelope
◦Insulating oil
◦Metal housing
◦Tube window
◦Aluminum filters
◦Lead collimator

Question 3

power supplies within the tube head

Answer 3

step up (anode) and step down transformers (cathode)

Question 4

what is the state inside the x ray tube?

Answer 4

vacuum

Question 5

why do we need insulating oil

Answer 5

the heat produced by x-ray production must be dissipated

Question 6

purpose aluminum filter

Answer 6

remove low E x rays, not useful for imaging

Question 7

cathode of the x ray tube

Answer 7

negative charge (repel e), 2 parts: filament and focusing cup, uses low V power supply
◦ Filament:
◦ Made of tungsten
◦ Source of electrons
◦ Is heated with a low voltage source and emits electrons at a rate proportional to its
temperature (thermionic emission).

◦ Focusing cup
◦ Made of Molybdenum
◦ Negatively charged
◦ Focuses the electrons into an arrow beam directed to the focal spot (+).

Question 8

anode of x ray tube

Answer 8

positively charged= attracts e, high V power source, 2 main parts

◦ Tungsten target:
◦ Transform the kinetic energy of the colliding electrons into x-ray photons.
◦ Highly inefficient: produces 99% heat and 1% x-rays

◦ Copper stem:
◦ Works as a thermal conductor to remove the heat from the tungsten avoiding target
melting.

Question 9

Why is tungsten a good target material?

Answer 9

1. High atomic number: efficient production of x-rays
2. High melting point (3422°C): to withstand theheat produced
3. High thermal conductivity: to dissipate the heat produced away from the target
4. Low vapor pressure: helps maintain vacuum in the tube at high temperatures

Question 10

Conditions necessary for X-ray production in order

Answer 10

1.Separation of electrons
2.Production of high-speed electrons
3.Concentration of electrons
4.Sudden stoppage of electron steam

Question 11

Separation of electrons from the filament, also called?

Answer 11

◦ Low voltage filament current heats the tungsten filament to incandescence with
resultant separation of outer shell electrons from the tungsten atom (“boiling off”). This
separation of electrons is called thermionic emission

Question 12

Production of high-speed electrons
approx acceleration?

Answer 12

◦ High potential difference is produced between the cathode and anode by applying a high voltage between them.
◦ Electrons are accelerated to approx. 0.5 X speed of light increasing the voltage differential can increase the acceleration

Question 13

Concentration of electrons

Answer 13

◦ Electron beam is focused by the focusing cup (negative charge) and directed towards the focal spot.

Question 14

Sudden stoppage of electron steam

Answer 14

◦ Upon striking the focal spot in the anode, the electron stream is stopped abruptly, and the kinetic energy of the electron stream undergoes conversion to greater than 99% heat and less than 1% x-radiation.
◦ Cooper stem removes the heat from the tungsten

Question 15

focal spot, size implication for image quality?

Answer 15

◦ Area on the target to which the focusing cup directs the electrons and from which the
x-rays are produced.
◦ Size if the focal spot is important for image quality (smaller focal spot, higher spatial
resolution)

Question 16

◦ The smaller the focal spot →heat? how can this be overcome?

Answer 16

◦ The smaller the focal spot →more heat accumulates.
◦ 2 ways to overcome this problem:
1. Rotating anodes
2. Stationary anodes (line- focus principle)

Question 17

Rotating anode

Answer 17

Rotating anode
• Allows heat at the focal spot to spread out over a large surface (dark band)
• Medical devices

Question 18

Line-focus principle
(stationary anode)

Answer 18

• Angling the target to achieve a smaller effective focal spot than the actual focal spot
• Results in sharper radiographic image while maintaining the original surface area of the target for heat dissipation

Question 19

actual and effective focal spots of the line focus principle

Answer 19

• Actual focal spot: the projection of the focal spot perpendicular to the target
• Effective focal spot: the projection of the focal spot perpendicular to the electron beam
• Effective focal spot is always smaller than the actual focal spot.

Question 20

Power supply 2 principal functions:

Answer 20

◦ Provide a low-voltage current to heat the x-ray tube filament (step-down transformer)
◦ Generate a high potential difference to accelerate electrons form the cathode to the focal spot on the anode (step-up transformer)

Question 21

◦Transformer

Answer 21

◦Electromagnetic device that either increases (step-up) or decreases (step-down) the voltage in a circuit.

Question 22

transformers of the x ray unit

Answer 22

◦ Step-down transformer (filament transformer)
◦ Step-up transformer (high voltage)
◦ Autotransformer

Question 23

step down transformer

Answer 23

◦ Used to convert 110 or 220 volts to 3-5 volts to heat the filament (low voltage circuit)
◦ Regulated by the mA switch
◦ increasing mA setting will increase the number of electrons emitted

Question 24

step up transformer

Answer 24

◦ Used to convert 110 or 220 volts to 60,000-100,000 volts to move the electrons across the tube (high voltage circuit)
◦ Regulated by the kV setting
◦ Increasing the kV will increase the energy of the electrons traveling from the cathode to anode

Question 25

Exposure timer, time delay circuit, and timing circuit

Answer 25

◦ Determines amount of time the high voltage circuit is applied across the x-ray tube (amount of time x-rays are produced)
◦ Time delay circuit: delay of ½ second to heat the filament
◦ Timing circuit: Actual time of exposure

Question 26

kV on control panel

Answer 26

controls the acceleration of electrons from cathode to anode

Question 27

mA on control panel

Answer 27

controls heating of the filament

Question 28

exposure time on control panel

Answer 28

controls the time in which x-rays are produced