How to measure X-ray or CT Dose ( with Ion Chambers ) [Rad Techs]

How to measure x-ray or CT dose? A tool called an ion chamber is the most common method to measure radiation dose. We focus in this video on how ion chambers work as they are the basis for radiation dose measurements. The x-rays dose can be measured with an ion chamber that measures a signal that is proportional to the exposure (if measured in air) or the absorbed dose (if measured in a plastic phantom).

For more information on the physics behind radiology see our site:
https://howradiologyworks.com

Chapters:
00:00 Intro
00:28. Ionization in Free Air
01:37. Ion chamber measurements
04:27. Geiger counter (Radiation Survey Meter)

Ionization can occur from photoelectric or Compton interactions wherein stable uncharged molecules are transformed into ions when they loose their electrons. The idea behind and ion chamber is to use this effect in order to measure the radiation dose.

By establishing a potential or an electric field in the region where the ionizations are occuring, i.e. a chamber of gas, the electrons will flow towards the positively charged surface. This is called the anode, just like in the x-ray tube circuit where the electrons flow towards the anode as well.

As the electrons flow through the circuit a current meter can be used to determine the flow of electrons and since this is related to the number of ionization events which is in term related to the radiation dose a conversion factor can be established between the radiation dose and the current that is measured in the circuit.

Once we can measure that current of electrons, if the ion chamber and the electronic circuit is calibrated, the software with the ion chamber will calculate the exposure or if the measurement is made inside of a plastic phantom to mimic a patients attenuation it can be a measurement of absorbed dose (mGy).

For radiation survey meters, i.e. Gieger counters a higher potential is used. The concept of a radiation survey meter is that you would like to be sensitive to low levels of radiation and we don't need to know exactly how much radiation is there. The same concept of an ion chamber can be used except the voltage is increased so that the electrons generated by ionization can then multiply along their way to the anode.