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The 3 X-ray Tube Rating Charts

There are three (3) x-ray tube rating charts that are very important in order to prolong tube life. They are listed below:

  1. Radiographic Tube Rating Charts
  2. Anode Cooling Chart
  3. Housing Cooling Chart


Radiographic Tube Rating Charts

radiographic tube rating chart

The rating of an x-ray tube is based on maximum allowable kilowatts (kW) at an exposure time of 0.1 second.

  • A guide regarding the most common technical factor combinations that can be used without overloading the tube.
  • When you use the Radiographic Tube Rating Charts for the X-Ray machine you want to make sure that the kVp setting and the time of the exposure intersect below the mA reading.
  • The mA is graphed as a curved line.
  • Any combination of kVp and Time below the line should be safe for a single exposure.

Anode Cooling Chart

anode cooling chart

It takes approximately 15mins. to completely cool down the anode.

  •       Shows the thermal capacity of an anode and its heat dissipation characteristics
  • Permits the calculation of the time necessary for the anode to cool enough for additional exposure to be taken.
  • The anode has a limited capacity for storing heat.
  • Thermal energy in x-ray is measured in Heat Units (HU)
  • HU= kVp x mA x time (s)
  • The cooling is rapid at first but slows as the anode cools. Usually, it take approximately 15 minutes to completely cool down the anode.
  • When you need to find out how long it will take to cool the anode so that you can make more exposures you need to follow the instructions below.

1. Find the total heat units applied on the vertical scale.
2. Read from the heat units over to the cooling curve and then down to read the corresponding time.
3. Calculate the time necessary for the anode to cool to any desired level and subtract the corresponding time of the initial exposure.


Housing Cooling Chart

housing cooling chart

It takes approximately 1 - 2 hours before the tube housing completely cools down.

  •       It indicates the heat unit capacity and cooling characteristics of the housing.
  • The tube housing cooling chart is very similar to the anode cooling chart.
  • The tube housing will generally have a capacity of about 1 to 1.5 million HU.
  • Complete cooling time may take 1 to 2 hours.

Photo credits: Stewart Bushong (^_^)


The author is a Radiologic Technologist, currently in the academic field, hoping to mold and produce future Radiologic Technologists who will be theoretically and technologically competent.

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