The Generator

The production of x-rays starts with electricity. This is the same electricity that you get from of the outlets at home.  There are 2 types of electrical current, alternating current and direct current.  The current you use at home is alternating current, or AC current.  AC current can be demonstrated with the graph below.

 

AC graph

Electricity that we all use is simply the flow of electrons on a wire.  In alternating current, potential moves ("up" and "down", "backwards" and "forwards", "positive and negative").  In other words, the electrons oscillate.  Up and down or positive and negative are just terms used to describe the oscillation of the current in a wire (electrons need to move in order to create electricity).  This oscillation occurs 60 times per second in home outlets.  The oscillations can also be viewed as "pulses".  Anybody who has ever been shocked and felt the pulses of electricity, can relate to this.  In X-ray production, the generator can only use half of the provided current.  For this demonstration, we'll call "up" the positive side. 

 

AC X-ray

Every time current peaks on the positive side, voltage is sufficient to produce x-rays.  In the diagram above, x-rays are produced in 2 separate pulses.  In the medical imaging world, this is not very efficient.  In order to maximize efficiency in x-ray production, the generator also rectifies the current.

 

rectification

Rectification is the process of reversing half of the alternating current.   By "flipping" the negative half of this current, we have doubled the number of positive peaks that can be used, essentially doubling the number of x-rays that can be produced by a given current.  Rectification is the process of converting alternating current into direct current.


Types of Generators

Now that you've seen how rectification increases x-ray efficiency, we can describe how generator types control efficiency.  There are:

  1. Single phase generators
  2. 3-phase generators - there is 3-phase 6 pulse and 3-phase 12 pulse generators
  3. High frequency

So far in the demonstrations, we have talked about single phase generators.


 

3-Phase Generators

3 phase 

In a 3-phase generator, they stack 3 single phases together, making the system even more efficient.  You can see there are significantly more peaks to be used for x-ray production.  The above graph is a 3-phase unit that has been rectified.


High Frequency Generators

In a high frequency generator, there is a near constant supply of peaks, which make this the most efficient generator for producing x-rays.  Below is an actual graph of a high frequency generator, the red line.

high frequency

What Else Does the Generator Do? 

Transformer

Another very important function within the generator is the transformer. When we use electricity at home, we are using voltage at around 110 v (110 volts).  Some garages, shops, and hospital outlets provide 220 v.  In order to create x-rays in the medical diagnostic range, you need between 20 kv and 150 kv.  That's 20,000 to 150,000 volts!  In order to do that, the voltage needs to be "stepped up", hence we have what's called a step up transformer within the generator.  You'll be happy to know that I will not require you to know any formulas regarding how this is performed.  Just know that:

  1. The generator rectifies current to make it more efficient for x-ray production.
  2. The generator "steps up" the voltage so that x-rays in the diagnostic range can be produced.