1. Chapter 4: Diagnostic X-Ray Production

2. Learning Objectives: Chapter 4
Understand the mechanical components both inside and outside of an x-ray unit
List & describe the parts of an x-ray tube and trace the creation of an x-ray
Describe the Line Focus Principle and its application in radiography
Define the focal spot, and understand problems that can occur with it
Define the anode heel effect

3. Steps in Creating a Radiograph
1. Getting power to the unit and tube
2. Heating the tube & producing energy
3. Converting energy to x-rays
4. Focusing the beam
5. Exposing the film

4. Getting Power to the Unit
Power (W) = current (I) x volts (V)
Unit of power is the watt
Toady’s x-ray units use a max. of 300 milliamperes and 125,000 volts
How many mA are in 1 ampere?
How many watts is this?
*Generators in clinics are rated at 30,000 W min.
How many kilowatts is this?

5. Equipment Relating to Power
Energy that is needed travels from a power plant to clinic generator
Transformers boost power along the way
Alternating current travels in 1 positive
and then 1 negative pulse
This provides low current, with high voltage
Cheaper and more efficient than direct current
Power goes to the circuit breaker first
Accepts the current into the unit (milliamperage)
Needs to have a ground wire for safety
*When would the circuit be interrupted?

6. Equipment Relating to Power
Wall switch- within reach of the x-ray unit
Required by law
On-off switch located on x-ray unit too
Brings power directly to the x-ray unit
Line voltage compensator
Increases/decreases incoming voltage
Won’t see this on new units
*Radiology uses mA to regulate the number of electrons used to produce x-rays*

7. Getting Power to the X-Ray Tube
3 transformers in an X-ray circuit:
1. Autotransformer – increases incoming voltage
Allows operator to select kV’s to produce a radiograph
2. High-voltage transformer
Final increase of voltage
From 220 volts to 125,000 volts (maximum)
3. Filament transformer
Produces voltage to the x-ray tube filament in the form of heat
Filament requires specific temp. for exposure to happen

8. X-Ray Unit 4 essentials to every unit: Control Panel/Generator
X-Ray tube
High-tension transformer
Dedicated power line

9. How are X-Rays Produced?
When electrons are slowed or stopped by the atoms of a target area, x-rays are produced.
This happens inside the x-ray tube, which is a vacuum environment.
Vacuum allows electrons to keep their energy
Once the electrons strike the target area, an x-ray beam of photons is created.

10. X-Ray Tube Where X-rays are generated
Transformers supply the power to here
We need 5 elements to produce x-rays:
Source of electrons
A way to accelerate the electrons
Obstacle free path
Target area
A heat-resistant glass envelope to provide a vacuum environment
Produces not only x-rays but a lot of heat

11. The X-Ray Tube

12. Cathode Two filaments made of tungsten
Provides a source of electrons and directs them towards a target area
Overall holds a negative charge
Circuit is activated  filament transformer sends electricity here  heats up  electrons leave the filament
Two filaments made of tungsten
Filaments emit electrons when heated electrons are held less tightly and become excited
Filaments are found in the focusing cup of the cathode
Point directly towards the target area on the anode

13. Rotating Anode Contains the target of the x-ray tube
Where the electrons are being sent to
Where are they coming from?
Target is mounted on an angled disc
Acts as an electrical conductor
Transmits the electrons back to the generator
Completes the circuit
Made of tungsten, tungsten molybdenum or tungsten/rhenium alloy
All heat resistant materials: which is best?
Rotates so photons are not always focused on the same spot
Dissipates the heat

14. Rotor Circuit Turns the rotating anode
More than 3000 revolutions/minute!
Activated when the filament transformer starts to heat the cathode
Prepares the anode to
receive electrons
Could be the source of loud
noise
Happens at the bearings

15. Stationary Anode Anode is fixed in place Made of copper
What is the concern here?
Operator must follow the warning lights on the machine!
Made of copper
Has a wide stem
Also composed of tungsten
To handle the x-ray conversion
When are these used?

16. The Line Focus Principle
The change of direction of the radiation due to the angle of the bevel on the anode.
Ideal bevel angle is <15° from vertical
This makes the x-ray
beam very narrow
Narrow beam = high
resolution image
Purpose is to make a small
“effective focal-spot size”.

17. Possible Focal Spot Issues:
1. Off-Focus Radiation:
Produced by electrons without great aim (hit outside of the target)
Bounce off the anode and to the patient outside of the focal spot
Collar of lead around tube normally prevents this
Can appear as artifact on film if the lead is not sufficient
*Prevent by having machine maintenance performed

18. Off-Focus Radiation

19. Possible Focal Spot Issues
2. Heat Bloom:
Target is exposed to radiation a great amount in a short time
Anode gets too hot and is not allowed to cool
Outer edges of focal spot expand
Enlarges effective focal spot size
Decrease in image resolution (Image loses sharpness)
*Can be eliminated by checking your anode cooling chart

20. Focal Spot Bloom

21. The Anode Heel Effect
Causes the intensity of radiation to be greater on the cathode side of the x-ray tube
Bevel of the angled anode
limits the amount of x-rays
produced on anode side
Place thicker end of patient
on the cathode side
Head usually to right

22. The Exposure Switch Usually 2-stages
Sets the events of producing an x-ray in motion
Usually 2-stages
1st stage activates the rotor, filament circuit, and transformers
2nd Stage causes the exposure through the tube
Can be hand controlled or via foot pedal
Exposure takes two movements
You must follow the light signals
“wait”, “ready”, etc

23. Exposure Concerns: You are now generating x-radiation!
Thoughts?
Be familiar with the noises
They may scare your patient – be ready!
May need to condition the patient
Sound of boiling liquid is bad – tube could rupture