Image Production Flashcards
What conditions are required to produce x-rays?
- source of electrons
- means to accelerate electrons
- sudden stoppage of electrons against target material
What is the Autotransformer?
single coil of wire with an iron core
What does the Autotransformer do?
Determines the voltage applied to the xray tube (kVP selection controls transformer
Where is the Autotransformer located?
beginning portion of the control counsel in the circuit
What is the voltage of the primary turns in the autotransformer?
220V
What is the voltage of the secondary turns in the autotransformer?
selected by radiographer
What is the Line compensator?
Measures the voltage provided to the xray machine imaging system and adjusts it to 220V
What is the kVP meter (aka prereading voltmeter)
Allows voltage be monitored before an exposure
Where is the kVp meter (aka prereading voltmeter) located?
between the autotransformer and high voltage transformer
What is the timing circuit (exposure timer)
regulates the duration of x-ray exposure
Where is the exposure timer (timing circuit) located in the circuit?
between the autotransformer and high voltage transformer
What are the 4 types of timing circuits
- synchronous
- electronic
- mAs
- automatic exposure control
What is an AEC back up timer
- a backup timer that can terminate exposure in event of malfunction
- protects patient exposure and tube heating
- setting too short a time will result in underexposed images
name the parts of the primary circuit
- Line compensator
- autotransformer
- major and minor kvp selector
- kVp meter
- timing circuit
- primary side of step up transformer
What is a step up transformer?
- Used to increase the voltage from the autotransformer to the kV needed
What is the high voltage generator
respondsible for increasing the output voltage from the autotransformer to the kV
What are the three parts of a high voltage generator
- high voltage (step up transformer)
- filament transformer
- rectifiers
What type of current is required for a step up transformer?
alternating current
The primary side of the step up transformer is measured in what? secondary side?
volts -> kilovolts
What is the mA meter?
monitors the x-ray tube current
Which ciruit is the mA meter located in?
secondary circuit
What is a rectifier?
changes AC to DC
What does a rectifier consist of?
solid state semiconductor diode (contains two electrodes)
Where is the rectifier located?
In the secondary circuit between the step up transformer and the xray tube
Define half wave rectification
- voltage does not swing negatively during cycle
- 0,1,2 diodes
- long exposure time ( waste of power)
Define Full Wave rectification
- negative half of cycle is inverse voltage making anode always positive
- 4 diodes
- exposure time cut in half
What is a diode
an electronic component that acts as a one-way switch for current in a circuit, allowing it to flow in one direction but not the other.
Single phase power
- results in pulsating x-ray beam
- low energy
- low penetrability
Three phase power
-multiple waveforms that maintain a nearly constant high voltage
- voltage never drops to zero during exposure
Define ripple
the energy that fluctuates from zero to the max voltage (peak of wave)
Which has more ripple single phase or 3 phase?
Single phase has %100 ripple 3 phase has significantly less (3.5-13%)
Which of the following will be more consistent in producing the kVP that is selected? (6 pulse or 12 pulse) only for three phase power
12 Pulse
What kind of current does the x-ray tube require?
Direct current DC
what is the voltage ripple for High frequency generator
around %1 = %99 of produced kVp is the selected amount
- results in lower patient dose
What is the mA meter?
measures tube current in milliamperes
Where is the mA meter located?
between the rectifier and x-ray tube
What is the Filament circuit
controls the degree and duration the filament is heated
What is the unit of measurement for resistance?
Ohms
What is the unit of current?
Amperes
What is the unit of voltage?
volts
Define resistance
a quantity that measure the reduction of electric current through a device or material
Define Current
The measure of the amount of electric charge transferred per unit of time
Define voltage
The electric potential between two points in an electric field
Equation to Find resistance?
(R) resistance = (V) voltage / (I) current
What is Ohm’s law?
The current along a conductor is proportional to the potential difference (V = I x R)
What is coulombs law?
The force between two charges is inversely proportional to the square of the distance between them
F = ((Q1 x Q2)/ (d^2)) k
What is the energy formula?
Used to calculate the energy of a photon of electromagnetic energy
(E = hf)
- h = plancks constant
What is wave formula
used to calculate the wavelength (frequency) of electromagnetic energy
(C = f(wave length)
What is Faraday’s law?
An electric current is induced in a circuit if some part of that circuit is in a changing magnetic field
What does the step down transformer do?
reduces voltage and increases current
The x-ray tube consists of what?
Cathode
Anode
protective housing and glass envelope
The high voltage section consists of what?
- step up transformer
- mA meter
- focal spot selector
- rectifier
Describe the Cathode
- located in x-ray tube
- negatively charged
- contains the focusing cup and tungsten filament
What is the tungsten filament of the cathode
- produces electrons after heating
What is the focusing cup of the cathode
concentrates the electrons to aim at small area of anode
Describe the anode
- positively charged
- consists of tungsten target, stem/neck, and rotor and stator
What is the tungsten target of the anode?
a means to stop electrons connected to the rotor by the anode stem
The area electrons hit the target is called the?
focal spot
What is the purpose of the target angle?
larger actual focal spot and smaller effective focal spot and heat dissipation
What is the effective focal spot?
the portion that is seen by the IR
What is the line focus principle?
- The angling of the anode results in the effective focal spot being smaller than the actual focal spot
- allows for a large area for heating while maintaining a small focal spot
Larger angle = larger effictive focal spot = actual focal = decrease spatial resolution
What is the anode heel effect?
The radiation intensity on the cathode side of the x-ray field is higher than that of the anode side
Decreasing the anode angle does what to the heel effect?
Increases heel effect
(angle and effect are inversely proportional)
Deceasing the SID does what to the heel effect?
increases the heel effect
(SID and Effect are inversely proportional)
Increasing the field size does what to the heel effect?
increases the heel effect
(proportional)
What are the two types of x-ray productions?
Bremsstrahlung and Characteristic
What is the difference between xray productions and xray interactions?
Productions are the creations of x-rays, interactions are the x-rays coming into contact with matter
Describe bremsstrahlung radiation
- incident electron moves towards atoms nucleus
- electron is (-) nucleus is (+) causing electron to slow
- the braking of the electron speed releases energy as x-ray photon
- majority of diagnostic x-rays are brems
Which production interaction makes up a majority of x-ray photons?
Bremsstrahlung
Describe Characteristic radiation
- incident electron collides with inner shell electron of anode target
- removes the inner shell electron from orbit and ionizes atom
- vacancy from inner shell electron is filled from adjacent outer shell electron
- in the process outer shell electron sheds energy in form of x-ray photon
- process continues to fill the next vacancy
- x-ray photons energy is equal to the difference in binding energies of the two shells
What x-rays in Characteristic radiation are sufficient to be used in diagnostic radiography?
k-shell only
At what kVp are characteristic x-rays produced?
kVp higher than 70
Define wavelength
the distance from peak to peak of a wave
Define Frequency
The number of waves passing a given point per unit time
What is the relation between wavelength and frequency?
Inversely proportional
What wavelength is more penetrating?
short wavelength
An x-ray beam containing many different energies is termed what?
heterogeneous
Best ideal for anode angle
Small effective spot large actual focal spot
what is the minimum for the total filtration of the x-ray tube
at least 2.5 mm aluminum equivalent
Removing low energy “soft” rays does what?
- hardens beam
- lowers patient skin dose
Define half value layer
amount of filtration that reduces the beam intensity by half
What is the equation to find the heat unit of a single-phase, full wave rectified equipment
kVp x mAs
What is the equation to find the heat unit of a three-phase 6 pulse full wave rectified equipment?
kVp x mAs x 1.35
What is the equation to find the heat unit of a three- phase 12 pulse full wave rectified equipment?
kVp x mAs x 1.41
What is the process of automatic adjustment of kVp and mA in fluoroscopy?
Automatic brightness control (ABC)
- aka automatic brightness
- aka automatic gain control
What is the image intensifier?
converts x-ray energy into visible light and then into an electronic signal that is displayed on a monitor
- used in fluoroscopy
Define input phosphor
receives exit rays from the patient and converts the rays into visible light
Describe the process that occurs in the image intensifier (fluoroscopy)
- input phosphor receives exit rays and converts into visible light
- visible light strikes photocathode
- photocathode releases electrons
- electrons directed towards anode end of image intensifier
- electrons strike output phosphor
- ## energy of electrons converted to much greater amount of visible light
Define flux gain
gain in brightness caused by the acceleration of electronic beam inside of image intensifier (fluoro only)
Define minification gain
gain in brightness caused by the minification of the image at the output phosphor compared to that of the input phosphor
A flat panel IR is provides better resolution of large or small anatomy?
smaller anatomy
What is the difference of digital fluoroscopy vs conventional
- Digital has all equipment similar to conventional but adds an operating console and computer workstation
- image intensifier is replaced by a flat panel IR
- patient dose is lower due to pulse fluoro
- utilizes analog to digital converter
- allows for posprocessing
- ABC still utilized in both
What is the accuracy requirement for collimator/ light to field alignment?
within 2%
What is the accuracy for effective focal spot size?
Within 50%
What is the required accuracy for kVp?
within 5% of what is displayed on the indicator
Which utilizes a cassette? DR or CR?
CR
What is the layering of the IR in computed radiography (CR)
1) Protective layer
2) Photostimulable Phosphor plate (PSP): Barium fluorohalide / Europium
3) conductive (antistatic): reduce electron charge
4) support base
5) reflective (light shield): reflects light
6) protective layer
