X-Ray Machine Flashcards
What are the 3 parts that compose the x-ray machine?
Tubehead
Control Panel
Arm of the machine
What are the two types of elecric current
Direct current and alternating current
What is direct current?
DC
Current flows in only one direction in an electric circuit
What is alternating current?
AC
Current flows in one direction and then flows in the opposite direction in the circuit
What is a cycle (in AC)?
refers to the flow of current in one direction, then the reversal, and flowing of the current in the opposite direction
60 cycles/sec
What is voltage?
Describes the electric potential or force that drives an electric current through a circuit
Volt= the unit of measurement kVp= max peak or voltage in AC
What is amperage?
amount or quantity
What is an ampere?
Measures the amount of current flowing through a circuit
Milliampere (mA)= 1/1000 of an ampere
What is a transformer?
Regulates voltage. Can increase or decrease the voltage in an electric current
What is a step up transformer
when the transformer increases the voltage (from 110/220 to 65,000-100,000)
What is a step down transformer?
When the transformer decreases the voltage (from 110/220 to 3-5v)
What does an autotransformer do?
Serves as a voltage compensator that corrects minor fluctuations in the current
What is a coolidge tube used for?
Thermionic emission tube invented by Dr. W.D. Coolidge
3 Basic elements of an x-ray tube used to produce x-rays
- Source of electrons within the tube
- High voltage potential to accelerate electrons across the tube
- Target to stop the electrons
What are the 2 sides of the x-ray tube?
Negative side= cathode
Positive side= anode
Current flows from cathode to anode
Devices on control panel for regulating the x-ray beam
On/off switch
Activating button
Regulating devices- kVp regulator, mA regulator, timer
What is the main source of electrons in the x-ray tube?
Tungsten filament found at the cathode
As the filament becomes hotter, what is happening?
More electrons are being produced at the cathode
Emits electrons at a rate proportional to the temperature of the filament
What is Thermionic Emission Effect?
Production, or boiling off, of electrons from the heated tungsten filament
How big is the tungsten filament? How is it mounted?
2mm in diameter, 1cm or less in length.
Mounted on 2 stiff wires
What does the milliamperage dial do?
Controls the amount of current in the filament circuit and the number of electrons that boil off
What is the molybdenum focusing cup?
Negatively charged, concave reflector that surrounds the tungsten filament and directs electrons towards the anode that contains the target
Parabolic shape. Electrostatically focuses the electrons into a narrow beam
What is the tungsten target/focal spot?
Small rectangular area on the anode.
Electrons move in this direction and are repelled by the negatively charged cathode and attracted to the positively charged anode
Characteristics of tungsten
High atomic number
High melting point
Low vapor pressure
Does not have a high degree of thermal conductivity– embedded in a copper stem to carry the heat generated away to the cooling system
What does the on/off switch do?
Completes the filament circuit
Heats tungsten filament
What do the milliamperage settings do?
Low voltage current, controls the number of electrons (quantity)
Controls temperature of the tungsten coil
the higher the mA, the hotter the coil; the greater the # of electrons produced in the cloud to be propelled to the target
What does the kVp setting do?
High voltage current, regulates the speed of the electrons (quality) traveling from the tungsten coil to the target
The higher the kVp, the faster the electrons will travel
What is the exposure time of one impulse?
1/60 of a second
What creates the formation of electron cloud at the cathode as filament circuit is activated?
X-ray tube
What is the electron cloud?
The electrons that stay at the filament
What is the cathode ray?
Stream of electrons crossing the tube from the cathode to the anode
What are soft x-rays?
lower energy or less penetrating x-rays
Do not penetrate tissue; produce secondary radiation
Filtered out before they leave the tube
What is used in the tube head for filtration?
An aluminum disc placed below the porte
2.5mm thick
What is collimation?
The x-ray beam is limited before it leaves the tube head
Diameter of the beam is limited by a lead diaphragm
Opening is 2.75” and collimator is placed below the aluminum disk
What is the central ray?
x-rays located at the center of the divergent beam
What is penumbra?
That part of a shadow of an object which is larger than a point and yet represents a single point on the object
Area of partial shadow
The unsharpness of the image
What is umbra?
Area of total shadow
What is the ideal kVp for viewing carious lesions?
65-70 kVp
Higher than this results in an image with a broad scale of contrast making viewing caries more difficult
What is density?
The degree of blacking on an xray image
Controlled by milliamperage and exposure time
What is contrast?
The difference in densities between adjacent areas
Primary controlling factor for contrast is kVp. High or low contrast images can be produced
Properties of a high contrast image
Great deal of black and white with little gray
Produced by low kilovoltage- 45-50kVp range
Properties of low contrast image
Also referred to as long scale contrast
High kilovoltage range 90-100 kVp
Many tones of gray in addition to whites and blacks
What is fogging?
Overall grayness on a radiograph resulting from secondary radiation
