Structure and Function of an X-ray Machine

In vet med we always want as _____ an exposure time as possible because of what two things?

-Short -1. Animal movement 2. Safety

What three things does an x-ray tube rating dictate?

-The maximum kVp, mA and exposure time that can be used without overloading the tube (causing damage)

The x-ray tube is designed so the ____ and _____ of the x-rays produced can be _____

-amount -energy -varied

How fast do rotating anodes rotate?

approx. 3350 times per minute

To produce quality radiographs with a variety of subjects both the ____ (___) and the ______(___) must be controlled and manipulated. This is controlled by altering mA, kV and the ___ of ____

--intensity(mA) -energy(kV) -length of exposure

What is the collimator?

-Adjusatable lead shutters that control the size and shape of the primary beam -It has a light source which allows the visualization of the beam size and shape

Where are stationary anodes found?

-In dental and small portable units

Where are rotating anodes found?

-In large/stationary x-ray machines

Describe the stucture of the x-ray tube

-It consists of an outer metal casing with a glass "tube" or envelope inside

What does good collimation prevent?

-It prevents unnecessary irradiation of the patient and x-ray personnel and reduces scatter radiation

What is the focal spot? Why does it's size matter?

-Its the area of the target where the electons collide -if smaller the image is clearer, but also must be large enough to accomodate the high temperatures generated

What specific practices are portable units used in? What is their man advantage?

-Practices frequently out of clinic: equine or large animal -They are small portable and durable

Why is a cooling system needed in the x-ray tube and what are the three components it's made of?

-because of the great amount of energy produced in the form of heat (99%) 1. Copper: conducts heat away from the target do the metal of the target doesn't melt 2. Oil: surrounds the glass tube to transfer heat away from the anode 3. Heat exchanger: the oil may be circulated through a heat exchanger to cool it

Stationary machines have the power to radiograph __, ___, ___ and _____. They offer the greatest variety of ____ and _____, but they are very _____ and require the patient to be brought into the hospital

-chests, pelvis, skulls and abdomens -positions and exposures -expensive

Energy measured in __ is used to produce an ____ ______ between the cathode and the anode

-electrical potential

Where is the focal spot on a stionary anode?

-embedded in a copper cylinder

The electrons smash in the ___ ___ on the anode

-focal spot

The production of kVp to provide the larger electrical potential between the anode and cathode requires ____ voltage (____). This requires a step __ transformer

-high voltage (kilovolts) -up

The faster the e- are travelling when they collide with the target , the ____ ___ ____ of the x-rays produced and the better _____ of x-ray beam

-higher the energy -quality

Where is the focal spot in rotating anodes?

-it is incorporated in a rotating disc 3" in diameter, providing a small focal spot

What does the metal casing portion of the x-ray tube do?

-it prevents the escape of stray radiation and also protects the glass envelope from physical damage

What are x-ray tube ratings expressed in? What four things are they based on?

-kilowatts 1. Focal spot size 2. Target angle 3. Type of anode/anode speed 4. Electrical current

The production of mA for heating the filament requires ___ voltage, therefore a step __ transformer is used to change the line voltage from ___ to ___

-low -down -220V to 10V

Energy measured in ___ is used to heat the _____ in the cathode and _____ are produced

-mA -filament -electrons

The higher the kVp the more high energy x-rays that are produced and the greater ____ _____ of the x-ray beam

-penetrating power

What is mA? What is it a measure of?

-the amount of energy required to heat the filament so that electrons are released. The quantity of e- released depends on the amount of heat so the higher mA=more heat=more electrons -a measure of the intensity of the x-ray beam (the number of x-rays produced)

Unnecessary use of the pre-exposure button means that the anode is spinning and producing heat which can do what?

-the heat can build up and shorten the life of the anode bearings

What is the cathode? What does it do?

-the negative electrode -it produces electrons and directs them toward the target (anode)

In order to manipulate the mA, kV and length of exposure the incoming electrical current must be changed and manipulated. This is accomplished through the use of ________, the ____ ____, and the ____ ___

-transformer -timer switch -control panel

Transformers change the incoming line ____

-voltage

What are the advantages of the rotating anode?

1. Because it rotates it distributes heat over a larger area while still maintaining the small focal spot so it is able to withstand more heat 2. The continual rotation provides a cool target area

What are some drawbacks of the staionary anode (2)

1. Small capacity for x-ray production 2. Unable to withstand large amounts of heat because the anodes may be damaged/pitted and then they make lighter than expected radiographs

What are the two main types of anodes?

1. Stationary 2. Rotating

What three things does the timer switch control?

1. The amount of time during which kV is applied across the tube 2. The length of time over which an x-ray is produced 3. The length of exposure of the radiographic film to x-rays

What does the x-ray tube filter decrease? (2)

1. decreases the total amount of x-rays bombarding the patient and therefore decreases hazard 2. decreases the scatter radiation and therefore increases radiographic detail

List six common components of the x-ray machine control panel

1. on/off switch 2. kV selector 3. mA selector 4. timer 5. exposure button/foot pedal 6. warning light

Whatare the two means of directing x-rays to a subject?

1. the spot angle on the anode direects the x-ray beam downwards 2. the collimator

1 kV= ____ volts

1000

How can the electrons travelling between the anode and cathode be accelerated?

By making the anode more positively charged which increases the electrical potential

What adjusts the incoming line voltage so it remains constant before being sent to any transformer?

Line voltage compensator

What does mA stand for?

Milliamperage

What does depressing the pre-exposure button frequently before actually exposing the film tend to do?

Shorten the filament life

What does the cathode contain? What is this objects purpose?

The cathode contains the filament which when heated emits electrons -It is made of tungsten because it has a high melting point and a high atomic number so it provides alot of electrons

What is kV used to measure?

The electrical potential between the cathode and anode which effects the speed the electrons travel toward the anode and collide with the target.

What is the x-ray tube filter?

a thin sheet of aluminum placed over the window of the x-ray tube which absorbs low energy x-rays

How can you compensate for the heel effect?

by having the thicker side of the animal on the cathode side

For each x-ray tube there are two rated limits what are they?

electrical and thermal limits

Where is the filament in the cathode housed?

in a molybdenum focusing cup which directs the electrons towards the anode

What does the vacuum inside the glass envelope of the x-ray tube do?

it allows e- to travel fast and eliminates any air molecules which could be obstacles

What is the anode made of?

it is made of a bevelled tungsten target on a cylindrical copper base

What is the anode?

it is the positive electrode -The electrons produced by the cathoed are attracted the the positve anode and when they hit the anode energy (E) is released (99% heat, 1% x-rays)

What does kV stand for?

kilovoltage

What is kVp?

kilovoltage peak- the maximum energy available at a partivular kV setting

What is found inside the glass envelope of the x-ray tube?

the anode and cathode are inside the tube where a vacuum is maintained

What is kV directly related to?

the quality/ amount of energy of the x-ray beam

What is the heel effect?

the variation in intensity of the primary x-ray beam between the cathode side and the anode side. The beam on the cathode side is mroe intense due to the anode angle

How do x-rays escape from the x-ray tube"?

through a window

The electrons accelerate toward the anode; this is enhanced by the ____ that is maintained in the glass envelope

vacuum