X-ray tube heating and cooling

Question 1

How is x-radiation produced?

Answer 1

Relatively large amounts of electrical energy must be transferred to the x-ray tube

Question 2

What is the limitation on the use of x-ray apparatus?

Answer 2

Only a small fraction (typically less than <1%) of the energy deposited in the x-ray tube is converted into x-ray

Question 3

How can x-ray tube be damaged?

Answer 3

If excessive heat is produced in the x-ray tube, the temperature will rise above critical values

1. melted anode
2. Ruptured tube housing

Question 4

How to prevent the damage of the x-ray tube ?

Answer 4

Operator needs to be aware of the heat produced and its relationship to the heat capacity of the x-ray tube

Question 5

Where and how is heat produced ?

Answer 5

1. focal spot area

2. bombarding electrons from the cathode

Question 6

Quantity of heat produced in the focal area

Answer 6

Heat (J) = KVe x MAS

or

Heat (J) = w x KVp x MAS.

Question 7

What is the waveform factor value determined by?

Answer 7

Waveform of the voltage applied to the x-ray tube

Question 8

What are the values for most waveform encountered in diagnostic x-ray machines?

Answer 8

1, constant potential 1.0

2. three-phase - 12 pulse, 0.99
3. three-phase - 6 pulse, 0.96
4. single phase 0.71

Question 9

What is the relationship between a quantity of heat expressed in heat units and in juoles?

Answer 9

Heat (HU) = 1.4 x heat (j)

Question 10

What is the rate at which heat is produced in a tube equivalent to?

Answer 10

Electrical power

Power (watts) = w x KVp x MA.

Question 11

What Temperature is the physical quantity associated with?

Answer 11

An object that indicates its relative heat content

Question 12

Heat capacity

Answer 12

Temperature = heat / heat capacity.

Question 13

What is the heat capacity of an object proportional to?

Answer 13

1. size
2. mass
3. characteristic of the material - specific heat

Question 14

What is the temperature of an object determined by?

Answer 14

Relationship between heat content and heat capacity

Question 15

What area has the smallest capacity?

Answer 15

Focal spot area or track

Question 16

How is heat removed from the tube housing?

Answer 16

Transfer to the surrounding atmosphere

Question 17

How can damage occur?

Answer 17

If the heat content of any area exceeds its maximum heat capacity

Question 18

What is the major limiting factor with single exposures?

Answer 18

The maximum heat capacity of the focal spot area

Question 19

How can the anode surface melt?

Answer 19

If quantity of heat delivered during an individual exposure exceeds the track capacity

Question 20

What is the total heat developed during an exposure the product of?

Answer 20

1. power

2. exposure time

Question 21

What are x-ray tubes often given?

Answer 21

single power ratings (in kilowatts, kW)

Question 22

What is used for specifying a tube’s power rating?

Answer 22

Exposure time of 0.1 second

comparing tubes and operating conditions

Question 23

What is the significance of a power rating?

Answer 23

specifies the maximum rate energy can safely be applied to a tube

Question 24

What can power rating limit?

Answer 24

how short exposure times can be made to reduce motion blurring

Question 25

What is the focal spot track?

Answer 25

surface area of the anode that is bombarded by the electron beam

Question 26

What is required to produce the desired x-ray images with minimum blur?

Answer 26

small focal spot

Question 27

What does a small focal spot tend to do?

Answer 27

concentrate heat and give the focal spot track a lower heat capacity

Question 28

what does anode angle range from

Answer 28

7° to 20°

Question 29

What is inversely related to anode angle?

Answer 29

track width and heat capacity

Question 30

What gives maximum heat capacity?

Answer 30

anodes with small angles

Question 31

What does high-speed rotation generally increase?

Answer 31

power capacity of a tube by approximately 60%

Question 32

What does the constant potential operation increase?

Answer 32

effective focal spot track heat capacity

Question 33

In comparing three-phase or constant potential and single-phase operation, three factors should be considered

Answer 33

1. Constant potential operation permits a tube to be operated at a higher power level because of the uniform distribution of heat.
2. Constant potential operation produces more x-radiation and increased penetration at a given KV and MAS setting.
3. Constant potential operation produces more heat for a given KV and MAS setting.

Question 34

What is the highest power capacity obtained by?

Answer 34

using three-phase power and high-speed rotation