radTech Newbies 400

X-ray physics intro for starting x-ray school, a step by step guide for new radiologic technologists (radiographers).

If you are a student in training or totally new to x-ray physics are you feeling:

  • overwhelmed or confused with the all the terminology and physics concepts
  • pressured or embarrassed that you don’t know the answers to questions from senior technologists during your clinicals
  • unsure of radiation effects and nervous about mass media coverage you have seen about radiation

Take a breath and get some good brain food while you are studying. I prefer sharp cheddar or dark chocolate, but generally not together.

Remember when you learned to play soccer, basketball or tennis. The first day that you picked up a ball you were not able to actually play a match or game. It took a long time to learn and you probably don’t remember the early days when you learned the basics.

Let’s think about learning x-ray physics in the same way where we take dedicated steps to understand x-ray physics every day. 

DO NOT try to do everything at once.

Take small steps so that YOU CAN GAIN CONFIDENCE. But DON’T SKIP STEP and DON’T JUMP AROUND learning a little of this and a little of that until you really understand the subject you are learning at the time.

Also if you are studying try to read this on a computer where you can concentrate and TURN OFF YOUR PHONE and HIDE IT FROM YOURSELF. Don’t worry your friends will still love love you if you miss a text or update from time to time. 

We first want to start with the basics here for x-ray physics. Just like when you learned tennis day one wasn’t step onto the court and serve the ball or when you learned to play basketball day one wasn’t shoot a three pointer. In the same way on our first time looking at x-ray physics we shouldn’t expect to be a master. We need dedicated practice and learning time. It doesn’t hurt to start with the physics early too since this is an area that can be more challenging.

As you are new to x-ray we want to help take you from a newbie who really wants to help patients but is feeling overwhelmed and confused by x-ray physics to a confident student in FIVE NOT SO HARD STEPs. I don’t want to sugar coat it and make it sound totally simple but if you put in some FOCUSED time it is very doable.

I suggest that you get out the old pen or pencil and paper and write down these questions. Then as you go through the learning material on the basics of x-ray physics you can write the answers down as well. This isn’t all that you need to know for x-ray physics, but if you can answer these questions as you go then you know that you are spending the time learning the material.

Another reminder, DO NOT try to learn this all at once. Make sure to take breaks in between your learning sessions and space it out. That way when you come back to it you will be able to focus more easily. I will put a table here for your reference when you come back but remember go through STEP BY STEP and DO NOT SKIP AROUND.

What should radiologic technologists know about Unit Conversion?

Go back to the basics. Before you dive into details that are specific to x-ray radiography make sure that you are familiar with scientific units. If you want to know how wide your phone screen is to see if it will fit in the pocket of a new jacket you are looking at you won’t be measuring it in units of kilometer (km). You probably will use units of centimeter (cm) or millimeter(mm).

Take a look at your phone and estimate how wide it is in mm? Actually that is a trick question, you are supposed to be concentrating now so you shouldn’t be able to see your phone. Hide that thing for real this time.

Just as in units of distance if we are referring to the current used in an X-ray tube or the effective radiation dose of a diagnostic procedure we will be using units of milliAmperes (mA) or milliSieverts (mSv) respectively. 

One of my personal heroes in life is Sal Khan at the Khan academy and he has a nice video on scientific units, please make sure you have that down before moving on. 

  • If your x-ray exposure is 250 mA (milliAmperes) how would you express that in units of A (Amperes)?
  • Which is greater 30 mSv or 0.04 Sv?
  • If the average energy of our x-ray beam is 60,000 eV (electron Volts) how many keV (kiloelectron Volts) is it?

Before going on to step 2 make sure that you are comfortable with unit conversions especially in SI units. If you need a refresher that is totally fine. 

What should radiologic technologists know about x-ray generation?

The next thing you need to know is how x-rays are generated in a diagnostic X-ray tube. This can go by multiple names including x-ray generation or x-ray production. All radiography and CT equipment have an X-ray tube that generates the x-rays in essentially the same way. This is why you need to understand the basics of x-ray generation, such as:

  • How are electrons are generated?
  • What pulls them over to the x-ray target?
  • What happens to the electrons when they hit the target?
  • What are the two interactions that can generate x-rays?
  • What are the main two controls for x-ray generation?

For answers to these questions and more see our post on X-ray generation.

What new radiologic technologists should know about x-ray image formation?

After we generate the x-rays they can be used to make x-ray images of your patients. A digital x-ray image is just made up of the signal in many detector elements that can then be shown to you, the radiologist and the patient. In each detector element a signal is measured and the contrast in the images comes from the different between neighboring detector elements in the images.

Contrast media is also something that can be injected in order to enhance or boost the contrast in an image, but here we are talking about x-ray contrast as the difference between the signal in neighboring detector elements.

To understand how the signal is generated in x-ray images you should be able to explain:  

  • What are the interaction mechanisms as the x-rays pass through the body?
  • The next key point that you need to understand is how image contrast is generated using x-rays? 
  • Which interaction mechanism is responsible for most of the x-ray image signal?
  • Which interaction mechanism causes background haze in the x-ray images?
  • Why is the contrast in images so heavily dependent on the Z of the material?
  • Why is increasing the kVp necessary in practice even though the contrast is better at low kVp?

To understand the answers to these questions check out our posts on X-ray interactions and X-ray signal generation.

What a new radiologic technologist should know about x-ray techniques, i.e. the technical parameters influence on x-ray exposure?

Remember to be taking some study breaks especially if you are brand new to this x-ray physics stuff. And when you are fueled up we will jump into the next step away from being a Rad Tech newbie.

As you learned in the x-ray generation section above the two main controls when making an x-ray image are the x-ray kVp (tube voltage) and the mA (tube current). These are controls of the x-ray tube parameters. Along with these parameters the exposure time (s) impact the exposure achieved on the detector.

In addition to the x-ray tube parameters there are other technical parameters which affect the exposure on the detector. As we learned in the basic x-ray properties section the x-ray beams travels in straight lines and are divergent. Therefore, the concentration of x-rays will be reduced as the source to image distance (SID) is increased.

Finally, we note that a mechanism that reduces image contrast is x-ray scatter in the images. One of the most powerful ways to combat the influence of x-ray scatter is to use an x-ray scatter grid. However, there is no free lunch so we need to use a higher x-ray exposure when a grid is used. The factor that determines how much extra exposure is needed on the detector is referred to as the Bucky Factor.

These are the five factors that you need to know about and each one has a simple relationship with the exposure at the image receptor.

As you go through our example which includes an online calculator please keep in mind

  • Which technical factor has the largest contribution to the exposure, and does this technical factor also affect the image contrast?
  • Which technical factor is most often used to modify the exposure?
  • Which technical factors are inversely proportional to the exposure so that as these increase the exposure actually decreases?

By studying these five simple relationships that come together into one golden equation you can dominate when it comes to questions on x-ray technical factors that influence the x-ray exposure. And you can walk a little taller at work when you know the technical details behind your x-ray technique selection.

What should new radiologic technologist learn first about radiation dose?

Congratulations on making it through the golden equation and mastering the relationships that drive x-ray exposure using the online calculator. Since you know you aren’t supposed to be skipping around I know that you have gone through the golden equation and are ready to own your technical parameters.

With x-ray generation, image formation and technical parameters in hand we just have one more big topic to free you from being a Rad Tech Newbie. The last topic is the one that your family and friends are most likely to ask you about, which is radiation dose.

There have been several waves of media reports in the popular press around radiation dose and hence much concern around radiation dose for those who are not in the radiography field.

The field of radiation biology is large and eventually during the course of your X-ray program you will go through all of the posts that we have on radiation biology for the ARRT prep. But as part of this quick start guide you should get your feet wet but don’t need to dive deep into all of the details.

Coming fresh into this field you may have questions such as:

What happens when x-rays interact with the body which can cause harm to the tissues in the body?

We know that the x-rays interact via Photoelectric Effect and Compton interactions but then what?

What actually causes damage to the DNA in the body?

What the heck does LD50 mean?

What is the difference between a radiation dose effect that is stochastic vs deterministic?

Get out your pen/pencil and paper again and spend some dedicated time with our post Introduction to Radiation Biology where you will learn the answers to these questions and much more.

After you go through the Introduction to Radiation Biology post for extra credit please take a look at the post which summarizes the background radiation sources and specifically the comparison between the radiation dose levels of diagnostic x-ray and CT procedures and background radiation which we are all constantly receiving.

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