*Exam 2: Chapters 5, 6, 7, 8, & 17
Photoelectric Effect:
- An orbital electron is ejected from its atom by absorbing all of the energy of an incoming light photon - Here, light is found behaving more like a particle than a like a wave as if a "collision" knocks the orbital electron out
Functions of the Main Circuit:
- Consists of: Primary & Secondary circuit - Supplies power to the X-ray tube so that x-rays are produced - Modifies incoming current to produce x-rays - Boost the voltage to the necessary range of x-ray production - Permit the radiographer to adjust technical factors - Incorporate appropriate circuitry to increase x-ray production efficiency
3. Wavelength:
- Defined as the distance between two points, such as the distance from the top of one crest to the top of the next crest - One completion of wave form before it repeats itself is called a "cycle" (each cycle consists if two pulses: one positive and one negative) & it's when the two pulses superimpose they form a complete circle
What did Oersted discover?
- Electricity moving through a wire created a magnetic field - All moving electric charges develop magnetic fields around them - Eventually led to the development of both motors and generators
Electrostatics:
- Study of electric charges at rest - An object is electricity any time there is an excess or a deficiency of electrons
Functions of the Filament Circuit:
- Supplies power to the filament of the X-ray tube so that the filament supplies enough electrons by thermionic emission - Modifies incoming line power to produce thermionic emission from the filament wires - Filament circuit adjusts the mA ratings (50, 100, etc.) - After mA selection, current sent to step-down transformer to modify amps that reach - Controls X-ray tube current & voltage is supplied by transformer
2. Amplitude:
- The maximum displacement of the medium (the "height" of waves) - Also, loss of amplitude allows the inverse square law: for each doubling of the distance traveled the amplitude drops to one-quarter of the original
An example of a transverse wave is? Longitudinal (compressional)?
- Transverse: Water wave - Longitudinal (compressional): Sound wave
Medical application of waves in medical imaging:
- X-rays: CT & radiography - Gamma rays: NM & radiation therapy - Waves: MRI, ULS, & laser surgery (Computed radiograph readers: an exposed photostimulable plate is scanned by a laser beam, freeing trapped electrons {from exposure} to fall back into their atoms. The energy lost as they fall is emitted as light, causing the plate to grow)
Electromagnetic waves:
-Include: radio and TV waves (AM & FM), radar, microwaves, infrared light, visible light, UV lights, x-rays, gamma rays, and cosmic rays - These are all a form of transverse waves and behave just like water waves in every wave EXCEPT: water in waves can travel at different speeds BUT electromagnetic waves always travel the same speed in a vacuum such as outer space, a velocity we commonly refer to as the speed of light
Any meaningful electrical circuit must have 3 components:
1. A conductor (source of electrons) 2. Source of EMF (electromotive force) 3. A device (ex: light bulb)
The Filament Circuit consists of:
1. BEGINS with rotor switch 2. Resistors (aka rheostat): controlled by the mA selector & they control filament temp and the rate at which electrons are boiled off 3. Step-down transformer: KV to V- inversely proportional; decreases voltage from the primary to secondary coil and increase current in the same proportion 4. Filaments: controlled by the focal spot selector - Large focal spot - Small focal spot
Electrification in 3 different ways:
1. Friction 2. By contact (conduction) 3. Induction
Magnetic field follows 2 basic laws of behavior:
1. Like poles repel each and opposite poles attract 2. Gauss' Law
What are the 3 types of changes that increases electrical resistance within a wire?
1. Longer length 2. Narrower diameter 3. Poor conducting material or poor circulation
What the Primary Circuit (Control Console) consist of:
1. Main power switch: the switch that generates the power to the X-ray tube 2. Circuit breaker 3. Line voltage compensator: adjusts the power supplied to the x-ray machine to 220 volts 4. Autotransformer (kVp control) 5. Exposure switch with exposure timer: - Exposure switch: a remote control device that permits current to flow through the circuit - Timer: device used to end the exposure at an accurately measure preset time 6. Pre-reading kVp meter volts, amps 7. Rotor switch (physically attached to the exposure switch but leads to the filament circuit) 8. Resistor bank for setting mA (mA control) 9. ENDS with the primary coil of the step-up transformer
What are the 3 types of magnets?
1. Natural 2. Permanent or artificial 3. Electromagnets
4 types of material:
1. Non-magnetic: completely UNaffected by magnets (wood & rubber) 2. Paramagnetic: SLIGHTLY attracted to strong magnets (oxygen & sodium) 3. Ferromagnetic: STRONGLY attracted to magnets (iron & nickel) 4. Diamagnetic: REPELLED away from magnets (glass & water)
What are the 2 general types of circuit layouts?
1. Series circuit: all the devices are connected in a row within the same line or wire, one after another; if a light bulb burns out then it breaks the circuit and the entire strand no longer works (ex: Christmas lights) 2. Parallel circuit: uses branches of wire, which spilt off from the original incoming wire and connect across to the outgoing wire; if one branch breaks, the other branches are not affected
*4 characteristics of a wave:
1. Speed 2. Amplitude 3. Wavelength 4. Frequency
What are the 2 types of waves?
1. Transverse 2. Longitudinal (compressional)
5 laws of electrostatics:
1. like charges repel: unlike charges attract 2. in solid objects, only negative (which electrons) can move 3. in solid objects, electrical charges only on the surface of the object 4. in solid objects, charge will concentrate at the greatest curvature of the surface 5. the force of electrical charge follows coulomb
What the Secondary Circuit (high-voltage section) consists of:
10. BEGINS with the secondary coil of the step-up transformer (the high-voltage step-up transformer) V to KV: used to increase voltage from primary to secondary coil & decrease current in the same proportion 11. mA meter: monitors the X-ray tube current & wires go to control console 12. LAST STEP is the Rectifier Bridge: converts AC to DC!!!! + within the X-ray tube, current must always flow from ANODE (+) to CATHODE (-) and electrons from cathode to anode, so rectifiers are used 13. X-ray tube: DC ONLY!
The speed of light ("c"):
3 x 10^8 meters per second or about 186,000 miles per second
For a high-frequency x-ray machine, what is the average kV as a percentage of the kVp?
99%
What will create the most resistance?
A long wire with a small diameter
Radiopaque:
A material that does NOT allow x-rays to through easily (like lead or bones)
Radiolucent:
A material that x-rays can easily pass through (like air in the lungs)
What are the 2 components of every motor?
A stator and a rotor
AC vs. DC current
AC: Electrons oscillate back and forth DC: Electrons always flow in the same direction in a steady stream (Need both in the X-ray tube for the productions of x-rays)
What is the type of current where electrons oscillate back and forth?
Alternating current
What is a rectifier?
An electrical device that converts alternating current to direct current
Radiography is made possible because part of the x-ray beam makes it through the body and part of it does not. This is referred to as ______ of the x-ray beam.
Attenuation
What is partial absorption of some of the energy of a single incoming x-ray or some of the intensity or quantity of x-ray within an x-ray beam?
Attenuation
What contains an iron core and a single winding or wire; is used in the x-ray circuit to provide a small increase in voltage before that step-up transformer?
Autotransformer
At the x-ray machine console, the kVp controls are the setting for what?
Autotransformer (kVp control) (The kVp major & minor controls on the x-ray machine set the autotransformer; kVp meter actually measures the amount of voltage (measured with a pre-reading) selected from the autotransformer before it is stepped up; it connected in parallel is between the autotransformer & the step-up transformer)
A technologist has control over which of the following? A) anode angle B) filament size C) actual focal spot
B & C
Why would a self-rectified x-ray unit only produce one-half the exposure of a single-phase x-ray machine?
Because negative pulses of electricity are completely blocked from reaching the X-ray tube, so there are only 60 pulses per second instead of 120
Why must the filament current be separate from the main circuit?
Both high voltage and high amperage cannot be produced in the same circuit because there is a limited amount of electrical power available
What protects the electronic components of the x-ray machine from over-heating by kicking off if there is an overload or short-circuit in any part of the system?
Circuit breaker
Which is a material that electricity easily flows through?
Conductor (Insulators: RESIST the flow of electricity)
What are the 3 general sections of the x-ray machine circuit?
Control console circuit, high-voltage section, and X-ray tube filament circuit
The large, solid part of the transformer is best known as the:
Core
What is the unit for electrical charge?
Coulomb
What is the type of current where electrons always flow in the same direction in a steady stream?
Direct current
Plank's formula:
E=hf E=the amount of energy in a particular h= Plank's constant (4.15 x 10^-15 volts-seconds) f= the frequency of its waveform (Energy is directly proportional to frequency; EX: X-ray is an example of quantum = if the energy {the voltage} of the x-ray doubles then its frequency as an electromagnetic wave must also double)
What is the closed pathway composed of wires and circuit elements through which electricity may flow?
Electric Circuit (PPT also states: this pathway for electricity must be closed (complete) for electricity to flow & an open circuit is one in which the pathway is broken, such as when a switch is turned off)
The source of electromagnetic waves is a vibrating or oscillating __________ ___________.
Electrical charge
If you take a solenoid (a coil of wire) that has an electrical current running through it, and wrap it around an iron bar creates what?
Electromagnet
The push and pull of electric charges and magnets are so similar because they are different manifestations of the same force:
Electromagnetic force (Any electrically charged particle which is moving generates a magnetic field around it along with its electrical field; the magnetic and electrical field are always perpendicular to each other)
True or False: For x-rays, their energy and wavelength are always directly proportional to each other (Ex: the higher the voltage (kVp), the longer the wavelength)
False
Gauss vs. Telsa:
Gauss (G): used for small magnets Telsa (T): used for very large magnets
As a device in which the electrons in the wire try to follow the spinning magnet?
Generator
What uses a moving magnet to induce electricity to flow by converting mechanical energy into electrical energy?
Generator
What is the amount of a specific absorbing material needed to reduce the intensity of the beam precisely one half of the original x-ray output from the tube?
Half value layer (HVL)
What is thermionic emission?
Heating of the filament before making an exposure to "boil" electrons off of it
Unit for frequency is:
Hertz (Hz) (one cycle per second is the definition for this unit; 1 Hz = 1 cycle/second)
What are ways to minimize static electricity?
Humidity kept above 40%, use of an insulator, and grounding
A compressional wave has its amplitude or strength measured:
In the same direction as the motion of the wave
1. Inherent filtration (within the x-ray tube & anode itself):
Includes: 1. Glass of X-ray tube, oil in the tube housing, and the beryllium window above 2. The mirror and plastic windows in the collimator 3. The anode itself through the anode heel effect
2. Added filtration
Includes: 1. Slabs of pure aluminum installed between the X-ray tube housing and the collimator or in a slot in the upper portion of collimator 2. All machines capable of operation above 70 kVp are required to have a minimum total filtration equivalent 2.5 mm of aluminum
Power switch:
Incoming lines form the power plant which normally carry AC electricity at 220-240 volts; it shown as a break in the wires to whole x-ray machine
The glass of the x-ray tube envelope, the oil surrounding it, and the beryllium window are all examples of:
Inherent filtration
What are the 2 types of protective filters?
Inherent filtration and added filtration
Voltage and amperage have what type of relationship in the transformer?
Inversely proportional relationship (The relationship between electrical resistance, pressure, and flow are summed up into a simple formula called the Ohm's law: V = IR..... V= Voltage I= Amperage R= Resistance .....cover R and you see that V and I are proportional (V=I) which means the electricity pressure increases so does the current, pushing harder results in more flow)
What law states that the induced current flows in a direction that opposes the action that induced it, therefore the induced magnetic field will lie opposite to the original?
Lenz's law describing self-induction (which is the autotransformer)
A greater amount of wire winding on the primary side of the transformer will produce:
Less voltage
In order for a transformer to increase voltage it must have:
Less wire winding on the primary side
What has energies measured in the range of 2 to 3 volts?
Light waves (& diagnostic x-rays are 30,000 to 150,000 volts (as the energy) and the wavelength is 0.1 to 0.5 angstroms)
What compensates for fluctuations in the incoming voltage so radiographic techniques can be consistent?
Line voltage compensator
What is a displacement of a medium that is parallel to the direction of wave travel?
Longitudinal (compressional)
Who is the father of quantum theory that hypotheses that the energy in atomic wheels is found only in certain predictable amounts, each with an associated wavelength and frequency?
Max Planck
What does half value layer (HVL) measure?
Measures beam penetration (PPT says: reduces beam intensity by half-that's how you know the beam is working)
Which electromagnetic radiation has a wavelength about the width of your smallest fingernail?
Microwave
What is a device in which the magnet of the rotor tries to follow the electrons circulating around it?
Motor
What uses the constant changing magnetic field around the wire carrying AC current to cause a magnet to spin, it converts electrical energy to mechanical energy?
Motor
What induction describes the induction of electricity in a secondary coil by a moving magnetic field & when a moving magnetic field is placed near a secondary coil, electricity is induced to flow in that coil?
Mutual induction (which is the step-up & step-down transformers)
The amplitude of a series of water waves is the:
One-half the vertical distance from crest to trough
A three-phase x-ray machine produces more remnant exposure at the receptor plate both because of increased ________ and increased _____.
Penetration; intensity
The electrical wave and the magnetic wave components of an x-ray are always __________ to each other.
Perpendicular
A positive & negative image:
Positive image: dark details against a light background Negative image: light details against a dark background
Protection filtration only affects the _________ beam
Primary
The effect of filtration on the beam spectrum show a decrease in the _________ of x-rays, but an increase in the _______ kV for the primary beam.
Quantity; average (quality)
Rectifiers & the Rectifier Bridge:
Rectifiers: is an electrical device that converts AC TO DC - 2 types: 1. Half Wave Rectifiers: pass half of the AC through one or more diodes 2. Full Wave Rectifiers: generally use four diodes to function, changing the entire current into DC Rectifier Bridge: - It is essential that rectification be the last step in preparing the high-voltage current to enter the X-ray tube - Energy from this current must flow from filament to anode
HVL is defined as the amount of absorber required to _________________.
Reduce the intensity of the primary beam to one-half the original
What is absorption?
Refers to an x-ray or a ray of light being completely stopped
What is transmission?
Refers to its passing completely through without any loss of energy or intensity
What describes a materials ability to remain magnetized?
Retentivity
What spins that is part of a motor and is attached to wheels or some other device?
Rotor
When considering the electromagnetic spectrum, the higher the frequency the:
Shorter the wavelength
What decreases voltage from primary coil and increases current in the same proportion, has more turns on primary than secondary coil and used in the filament portion to increase current flow to the cathode?
Step-down transformer
At the x-ray machine console, the mA controls are the setting for current fed into what?
Step-down transformer (The mA meter on a console measures the milliamperage of the current which actually flows across the X-ray tube, not the current that heats up the filament; the filament current (the step-down transformer must be used in) , which set by the mA station selected, determines how hot the filament burns)
What increases voltage from the primary coil to the secondary coil and decreases current in the same proportion and has more turns on the secondary coil than on the primary coil and also used to increase voltage to the kilo voltage level?
Step-up transformer
Filtration (Added) results in:
The "hardening" of the x-ray beam, increasing average energy & penetration, and lowering patient exposure
Voltage to the filament circuit is provided by:
The autotransformer
What is differential atteuntion?
The different ratios of absorption and transmission characteristic of each different tissue in the body
Permeability is?
The ease in which a material can be penetrated by a magnetic field, or how susceptible it is to being magnetized
Milliamperes is the unit to measure?
The flow of electrons in a circuit (Unit: Ampere or Amp, abbreviated A or I)
What happens when rectification improves and generator power increases?
The quantity and quality of electrical current improves
What is the part of the motor that has stationary coils of wire surrounding the root that has electrical current passing through the wires to cause the rotor to spin?
The stator
What generator has a ripple of about 14%?
Three phase 6- pulse
What is the purpose of filtering the x-ray beam before it reaches the collimator?
To eliminate unnecessary patient exposure
What is the purpose of the filament circuit?
To provide high average current to the X-ray tube filament to heat it to extremely high temperature where high friction is needed (PPT says: supplies power to the filament of the X-ray tube so the filament supplies enough electrons by thermionic emission)
What alters the voltage or the amperage of electrical current?
Transformer
What is a displacement of the medium that is perpendicular to the direction of wave travel?
Transverse waves
True or False: X-rays are like particles and waves
True
What is the step-up transformer used for?
Used to increase the voltage from the autotransformer to the kVp necessary for x-ray production (primary circuit ends with the primary coil of the step-up transformer)
Ohm's Law:
V=IR V= Voltage I= Amperage R= Resistance
Visible light vs. X-rays:
Visible light: - Double transverse waves but with DIFFERENT energies - Energy between 2 and 3 volts - Follows the law of reflection and refraction (the bending of light as it passes through an interface {boundary} between two materials - Glass lenses focus light - Behaves like a WAVE but sometimes like a particle X-rays: - Double transverse waves - Are NOT refracted by a glass lens but pass right through in straight lines - X-rays pass through the glass without any effect - Higher energy, behave like a PARTICLE most of the time, but can behave like a wave (What determines the behavior they manifest is the specific conditions around them)
The role of the transformer is to increase or decrease what?
Voltage
Electromotive force is expressed in what unit?
Volts
What is a disturbance in any medium which transports energy from one place to another without causing any permanent change in the medium?
Wave
*What are the 3 factors that determine x-ray beam penetration?
kVp, generator type, and filtration
Which formula expresses the total number of electrons, or the total amount of electricity, used for an x-ray exposure?
milliAmperes per second
The wave formula:
v=fλ v= velocity or speed f= frequency λ= wavelength (velocity/speed and frequency are directly proportional to each other)