Rating Charts and Cooling Curves (9/20/2023)

99% of the kinetic energy of electrons is converted to ___ during x-ray production

heat

Amount of heat given off is expressed in ___

Heat Units (HU)

Number of HU produced depends on ___ and ___

the type of generator and the exposure factors used

Explain alternating currents (AC)

current that alternates between positive and negative kv

Why are single phase alternation currents not ideal?

the negative kv is not useful for imaging

What type of wave/current does the image depict?

single phase alternating current

What type of wave/current does the image depict?

single phase rectified current

What type of wave/current does the image depict?

3 phase 6 pulse wave form

What type of wave/current does the image depict?

3 phase 12 pulse current

What type of wave/current does the image depict?

high frequency wave form

What type of wave/current is used in all modern equipment? Why?

high frequency wave form; has the least ripple and the highest energy

Define ripple

the fluctuation in voltage output (each bump on the graph)

What is heat load capacity?

the amount of heat that a tube can withstand without damaging the tube components

Heat is produced according to:

• technical factors selected

  • kVp, mA, time

  • focal spot size

• generator type

  • more powerful generator produces x-rays more efficiently

  • more powerful generator creates 1.4x more HU

What determines the “quality” of x-rays?

What determines the “quantity” of x-rays?

quality: kVp

quantity: mAs

Generator factor indicates ___

heat production in comparison to the single phase generator

The more efficient the generator, the ___ the HU produced during x-ray production

higher

What is the formula for calculating heat units?

HU = (kVp) (mA) (time in seconds) (generator factor)

What is the generator factor for a single phase generator?

1.00

What is the generator factor for a 3 phase 6 pulse generator?

1.35

What is the generator factor for a 3 phase 12 pulse generator?

1.41

What is the generator factor for a high frequency generator?

1.45

What are the 3 types of rating charts?

1. tube rating charts

2. anode cooling charts

3. housing cooling charts (not used as much)

What type of rating chart is shown in the image?

tube rating chart

What is the purpose of a tube rating chart?

determines the technical factors that can be used without overloading tube

What do the vertical axis, horizontal axis, and curved lines represent in a tube rating chart?

vertical axis: kVp

horizontal axis: time (s)

curved lines: mA

How are tube rating charts read?

find the intersection of kVp and time on the graph; any combination of factors at or under the curve is safe

What do the vertical axis, horizontal axis, and curved lines represent in an anode cooling chart?

vertical axis: total heat capacity (HU)

horizontal axis: time (minutes)

curved lines: starting point HU to end time of complete cooling

What is the purpose of an anode cooling chart?

calculates the time it takes for the anode to cool from a given exposure OR the time it will take the anode to cool enough to make an additional exposure

What are some ways you can extend tube life?

• warm up anode

• depress rotor in one motion

• avoid excessive HU production

• use lower mA when possible

• avoid repeats

• handle tube gently

• do not move tube when energized

• do not use tube if you hear a loud rotor noise