X-ray Tube Construction

Question 1

Milliampere (mA) and Time (s) controls?

Answer 1

Quantity and Density

Question 2

How does Milliampere (mA) control quantity?

Answer 2

Amount of electrons emitted at the filament by process of thermionic emission

• more # of electrons = more # of x-rays being emitted
• less # of electrons=less # of x-rays being emitted

Question 3

How does Time (s) control quantity?

Answer 3

determines length of time electrons are allowed to flow from cathode to anode

• more time -> more electrons> more x-ray
• less time-> less electrons-> less x-ray

Question 4

The combination of Milliampere (mA) and Time (s) is?

Answer 4

mAs (milliampere seconds)
-treated as one unit

Question 5

Kilovoltage (kV) controls?

Answer 5

• Quality
• Penetrating power
• Energy
• Density and Contrast

Question 6

What is Contrast?

Answer 6

difference b/w black and white

ex)
- The higher the kV the darker the image
-The lower the kV the lighter the image

Question 7

What is Density?

Answer 7

Overall degree of darkness

ex)
- too strong of kV the blacker the image will get
-too light of kV the whiter the image

Question 8

There are three different types of External and Mechanical Support in a X-ray Room Structure. What are they?

Answer 8

1. Ceiling
2. Floor-to Ceiling
3. C arm

Question 9

Ceiling support

Answer 9

• most common
• freely moves in all directions : transverse

Question 10

Floor-to- Ceiling support

Answer 10

• Multi-directional
• Requires effort to move

Question 11

C arm Support

Answer 11

• Nearly limitless in tube position
• Robotic and fluid in motion
• Angiography

Question 12

Protective Housing is considered to be_____?

Answer 12

Isotropic

Question 13

The useful beam-emitted through the window of protective housing is also called?

Answer 13

Primary beam

Question 14

Anything else which escapes the protective housing is called?

Answer 14

Leakage radiation or Secondary beam

-non-diagnostic
- unnecessary exposure to both patient and technologist

Question 15

Protective housing is lined with what material?

Answer 15

Lead

Question 16

Why is protective housing lined with lead? and why is protective housing important?

Answer 16

1. reduce leakage radiation (<100 mR/hr @1meter)
   2.
   -Provides mechanical support
   - Protects from damage caused by rough handling

Question 17

Protective housing contains ________ to insulate from shock and dissipate heat.

Answer 17

Oil

Question 18

Electron to x-ray efficiency is __%

Answer 18

1%

-99% is heat

Question 19

What is Pyrex glass and why is it important?

Answer 19

• withstands large amounts of heat
• Vacuum
  • more efficient x-ray production
  • Longer tube life

Question 20

What is a Cathode ?

Answer 20

Negative Electrode Filament
-(2) coils of wire (toaster vs x-ray filament)

Question 21

What is Dual Focus?

Answer 21

Refers to Large FSS and Small FSS

Question 22

What does FSS stand for?

Answer 22

Focal Spot Size

Question 23

Dual Focus Cathode contains 2 filaments. What are they?

Answer 23

1. Small Filament
2. Large Filament

Question 24

Small focal spot size filament uses ____mA or less

Answer 24

200

-provides better detail
- best for small body parts

Question 25

Large focal spot size filament uses _____mA or more

Answer 25

300 -larger body parts -can withstand more heat

Question 26

What is a Focusing Cup?

Answer 26

Negative charge that surrounds the filament on the cathode -confines electron beam to small area of anode

Question 27

What is Thermionic Emission?

Answer 27

When electrons are boiled off

Question 28

What is the space-charge effect?

Answer 28

Prevents subsequent electrons from being boiled off due to electrostatic repulsion (same charges repel)-Coulomb's Law

Question 29

What is an Anode?

Answer 29

Positive electron

Question 30

What is a stationary Anode?

Answer 30

* High tube current and power not required * Used in dental offices, clinics, portables, simple x-ray units * Has a copper Anode and Tungsten Target

Question 31

What is a Tungsten Target?

Answer 31

* In the middle of copper anode * Most important primary material

Question 32

What is a con to a stationary anode?

Answer 32

Pitting can occur

Question 33

What is Pitting?

Answer 33

wear and tear of the Tungsten Target which can also lead to tube failure

Question 34

What does a Rotating Anode help do?

Answer 34

x-ray tubes capable of producing high-intensity x-ray beams in shorter time periods -Has Copper, Molybdenum, Rotating Tungsten Target, Target Track

Question 35

The rotating anode has________ to ________ RPM?

Answer 35

3,600 to 10,000 RPM (Rotations Per Minute)

Question 36

Why is a Rotating Anode better compared to a Stationary Anode?

Answer 36

* Better for heat dissipation * Higher tube currents with shorter exposure time (more efficient) * Increased heat loading abilities

Question 37

What is a Target (track)?

Answer 37

Area of disc that the electrons strike, and are converted into x-rays

Question 38

Disc is composed of 3 layers. What are they?

Answer 38

1. Tungsten/rhenium 2. Molybdenum 3. Graphite

Question 39

Why is Tungsten used?

Answer 39

* High atomic #(74) * Higher Efficiency * Thermal Conductivity * Better at heat dissipation * High Melting Point * Minimize occurences of pitting

Question 40

What is the high melting point of Tungsten?

Answer 40

3410 °C (6170 °F)