Xray Tube Design

Question 1

What is the basic function of the x-ray tube?

Answer 1

Produces electrons, harnessed from electricity, which can be used to create photons

Question 2

Name the 5 basic elements of the x-ray tube and a basic function

Answer 2

1. Pyrex glass envelope - Gas free enclosure
2. Tungsten filament - where electrons are generated
3. Molybdenum anode - where electrons strike
4. Photon - x-ray beam
5. Beryllium window - exit for x-ray beam

Question 3

Describe power to the x-ray tube

Answer 3

A step up transformer is used to increase 240 volts from wall
Thousands of volts are required

Question 4

Describe Alternating current in relation to the x-ray tube

Answer 4

X-ray tube requires direct current
Energy needs to flow from cathode to anode
When wave inverts, x-ray production stops - why direct current is needed

Question 5

Describe rectification

Answer 5

Process that removes negative portion of the wave, making it positive
There is still a ripple effect

Question 6

Describe mAs

Answer 6

Number of photons or x-rays in the beam

Question 7

Describe kVp

Answer 7

The power that the photons are going to have

Question 8

Describe the 2 parts of the exposure button

Answer 8

1. top half - creates space charge
2. bottom half - allows electrons to be accelerated across a potential difference, electrons strike focal track and x-rays are produced

Question 9

Describe the structure of the anode

Answer 9

Disk Shaped, mounted on a spindle
Focal track inlaid to molybdenum
Rhenium combined with tungsten for alloy
Back filled with graphite - makes it lighter

Question 10

Describe anode rotation

Answer 10

Rotating anode spreads heat over wider area
Induction motor used with ball bearings
Stator copper windings allow induced current

Question 11

Describe the anode heel effect

Answer 11

Limitations of the machine can be used
Radiation protection - less intensity at anode side, put patients head here
Image quality - can create clearer image by positioning thicker parts near more intense beam

Question 12

What is the line focus principle?

Answer 12

Describes relationship between actual and effective focal spots

Question 13

What are actual and effective focal spots

Answer 13

Actual - area on anode struck by electrons
Effective - same area but viewed below x-ray tube

Question 14

What is the difference between large and small focal spots

Answer 14

Large - can withstand more heat, suffers from penumbra
Small - better image quality

Question 15

Describe the structure and function of the tube housing

Answer 15

Lead housing place over glass, filled with oil, to cool machine
Function - X-rays are emitted 360 degrees, so lead blocks excess x-rays

Question 16

Describe how x-rays are produced

Answer 16

-Electrons accelerated to positive anode
-Electrons slam into heavy metal atoms in anode
-Electrons transfer energy to target
-Electrons interact with either orbital electrons or nucleus
-As well as k shell electrons, electrons also interact with outer shell electrons - excitation causing heat