RADR 2209 - UNIT 2 EXAM

What are some things that the protective housing does? (3)

-absorbs most photons traveling in directions other than towards the patient -provides solid and stable mechanical support for the tube -electrical insulator for the tube and provides thermal cushion for the tube

What are good properties of rhenium

-added to tungsten because it increases thermal capacity and tensile strength

Define diode (1) and what is another name for it (3)?

-allows electrons to flow in only 1 direction -aka one way valve/solid state rectifier/rectifier

Why is a line compensator used with the main power switch?

-because of the incoming power supply -it is wired around the autotransformer and automatically adjusts the power supplied to the x ray machine

the anode radiates heat within the tube away from itself. List the 3 processes of heat transfer

-conduction of heat by heat tolerant materials -radiation of heat energy from the anode to the oil bath -convection of heat into the room via cooling fans

What are good properties of molybdenum

-has low thermal conductivity -light but strong (makes it easier for anode to turn)

What are good properties of tungsten

-has very high melting point -has excellent thermal conductivity

Name 2 notes of caution regarding the housing

-housing can become very hot -high voltage cables are not handles to maneuver the tube head assembly

Name the 3 technical factors of the tube rating charts

-kv peak -milliamperage -exposure time

What 3 things need to happen in order to produce an x ray

-large potential difference to give kinetic energy to the filament electrons (kVp setting) -a vehicle on which kinetic energy can ride (mAs setting) -place for interaction (target of anode)

What are the 2 major causes of tube failure

-maintain tube at high temps -prolonged excessive heating caused by prepping the rotor unnecessarily or arcing from filament

What are the 2 types of electromagnetic induction

-mutual -self induction

Name the 4 magnetic properties and examples for them

-nonmagnetic (glass, wood, plastic) -diamagnetic: weakly repelled by magnets (water, Au, mercury) -paramagnetic: weakly attracted by magnets (platinum, Al, Gd) -ferromagnetic: strongly attracted by magnets (Fe, Co, Ni)

Define a battery (3)

-produces electrons -keeps electrical charge for long term -provides electrical potential

Describe the rotating anode

-spreads heat over a larger surface area -has molybdenum rotating disc and coated with tungsten and mounted in a copper shaft

Define resistor (2)

-stops flow of electrons -regulates flow of electricity through part of circuit that it replaced

Define capacitor (2)

-stores electrical charge but only temporarily -cant provide new electrons

Describe the stationary anode

-target doesn't move -tungsten is embedded in a copper wire -damages easily because electrons hit the same target area over and over again -used in old x rays and some dental x ray machines

Describe how the 2 filament wires are done in the tube

-tiny coils of wire are housed in the cathode of the x ray tube -represented on operating console via a large focal spot and small focal spot

What is the MRI's range of magnets?

0.5 T - 5.0 T

Name the 3 laws of magnetism

1. every magnet has a north and a South Pole 2. like poles repel each other, opposite poles attract 3. the force of attraction or repulsion varies on the strength of the poles and inversely with the square of distance between them

Name the 5 principals of Electrostatics

1. like charges repel, unlike charges attract 2. Coulombs law 3. electric charges reside on external surface of conductors 4. the concentration of charges on a curved surface of a conductor is greatest where the curve is the greatest 5. only negative electrons are allowed to move in the solid conductors (NOT protons)

Name the 3 characteristics of flux

1. lines of flux travel from South Pole to North Pole inside the magnet and north to south outside of the magnet (this creates elliptical loops) 2. lines in the same direction repel each other, lines in opposite directions attract each other 3. magnetic fields are distorted by magnetic materials and unaffected by non-magnetic material

What is the correction factor for a single phase

1.0

What is the correction factor for a 3 phase 6 pulse

1.35

What is the correction factor for a 3 phase 12 pulse

1.41

What is the correction factor for a high frequency

1.45

What percent ripple is a single phase full wave

100%

What percent ripple can be used depending on the number of rectifiers

13% (3 phase 6 pulse) - 3.5% (3 phase 12 pulse)

How many filament wires are in a radiographic tube

2

Most tubes have how many filaments? What is another word for them?

2 filaments referred as dual focus tubes (represented by large and small focal spot options)

What degrees are used in the target angles

7-18 degrees in a tube (12 is the most common)

What is current measured in?

Amperes (A)

What is the AEC and where is it located

Automatic Exposure Control -in the bucky measures the amount of radiation leaving the patient and stops exposure once a quantity of radiation has been reached

Who identified electric induction first?

Faraday

What is the HU equation

HU = kVp x mA x s x c (exposure time)

Give an example of mutual induction

Imagine 2 coils. Coil A is the primary coil connected to an AC power source. Coil B is the secondary coil, and as the fluctuating magnetic field from A moves back and forth through the turns of B, a secondary current is induced

Using the crystals, how do electrons move

ONLY from N to P

Who identified electromagnetism first?

Oersted

What is resistance measured in?

Ohm (O)

What crystals are used to make rectifiers

P and N crystals

What is the strength of magnets measured in?

Tesla (T)

What is electric potential measured in?

Volts (V)

When the kV is applied to the x ray rube, what does it create?

a large positive charge on the anode and large negative charge on the cathode

Define electric potential

ability to do work because of a separation of charges

What is the p crystal made of

abundance of electron traps

What is the n crystal made of

abundance of freely moving electrons

How is the autotransformer controlled

adjustable via the kVp selector on the operating console and is controlled by the radiographer

Define rheostat (1)

adjustable/variable form of a resistor

What does the kVp do

adjusts the autotransformer and determines the number of turns on the secondary side necessary to produce voltage through self induction, that will be sent to the step up transformer

Define AC

alternating current flows in both directions

Define self induction

an induced current flows in the direction that opposes the action that induced it - the action being the change in magnetic field

Define anode heel effect

angle causes intensity of x ray beam to be less on anode side because of the heel of the target is in the path of the beam and some x rays are absorbed in the target heel

What does the anode consist of (2)

anode target induction motor (1/2 inside and 1/2 outside protective housing)

What is the anode target face used for

anode target face is angled to make use of the line focus principle

Which is the positive and negative side of the x ray tube

anode: positive cathode: negative

Define actual focal spot

area being bombarded by filament electrons -the size of the electrons depended on the size of the filaments (the smaller the electron stream, the greater the heat generated in a small area)

Describe the electron cloud

attracted to the anode target because of the huge potential difference and flows from the cathode to anode and is a continuation of the flow of electricity through the x ray circuit -as the flow of electrons penetrate the target surface, these filament electrons interact with the atoms of tungsten, generating heat and x rays

Define thermionic emission

boiling off electrons

Define suntanning

bronze discoloration on glass

Describe the line focus principle

by angling the face of the anode target, a large actual focal spot can be maintained and small effective focal spot size can be created (goal is balance between heat and focal spot)

What is the effect of lowering the intensity on the anode side of the beam

can cause the image to be lighter on that end

Define transformer (1)

can increase or decrease voltage by a predetermined amount

What would happen to the tube if electrons were in the air

cause arcing and damage

What kind of pathway is an electric current?

closed pathway

What is the focusing cup connected to

connected to secondary circuits

Define grounding

connecting an electrical device to the earth via a conductor

What is the rheostat controlled by

controlled by the mA selector on the operating console the higher the mA, the lower the resistance

What do motors do?

convert electrical energy to mechanical energy

What do generators do?

convert mechanical energy to electrical energy

Name 3 examples of good conductors/bad resistors

copper gold water

_______ flows with the arrows and _______ flows against the arrows

current electrons

In an x ray tube, where does the current flow

current MUST always flow from anode to cathode this is done by the rectifier

Following the sequence of events through the filament circuit, where does current flow to

current flows from the autotransformer to the rheostat, to the step down transformer, and to the selected filaments within the cathode of the x ray tube

What does a step down transformer do?

decreases voltage

Define DC

direct current flows in 1 direction

Describe what is inside the x ray tube

electric vacuum that consists of an anode, cathode, and induction motor all incased in a glass or metal envelope (enclosure)

Define Ohm

electrical resistance equal to the resistance between 2 points along a conductor

In an x ray tube, where does electrons flow

electrons MUST flow from cathode to anode this is done by the rectifier

Define electrodynamics

electrons in motion

Define ripple

energy fluctuates from the 0 (on the line) to the max voltage (peak of the wave)

What must the filament circuit do to produce the correct number of x ray photons for an exposure

filament circuit must work with the exposure timer in the primary circuit

Define current

flow of electrons in a conductor

What does the cathode consist of (2)

focusing cup filaments

What does the cathode consist of? (2)

focusing cup filaments

Name the 2 protective devices

fuse circuit breaker

Name 2 examples of bad conductors/good resistors

glass plastic

Define fuse (1)

glass encased wire that melts if current flow rises excessively, thus opening the circuit

Define half wave rectification

half the AC cycle flows through the x ray tube and the other half that would flow the wrong way in the x ray tube is blocked

Describe what the rotor is made of

has an iron core that is surrounded by coils

What do enclosure types have and why

have a target window for the desired exit point of the x rays produced made to minimally interfere with (absorb) the x rays

Define circuit breaker (1)

if the current flow rises, the internal switch of the breaker is tripped (opened) stopping the flow of electricity

How can you tell if a thing is safe or not

if the point is on or above the specified mA line, it is UNSAFE

What do transformers do?

increase or decrease voltage

What does a step up transformer do?

increases voltage

Describe what the stator does

induces an electric current with the rotor in a magnetized field -the rotor aligns with the stator as the stator magnetizes and a net electric current and magnetic field is induced, causing the rotor to turn

Define mutual induction

induction of electricity in a secondary coil by moving a magnetic field

Where is the stator and what is it made up of

is outside the tube enclosure made up of electromagnets

What is the tube assembly made of

lead

Describe the protective housing

lead lined metal structure with 2 large electrical cables that securely attach to the x ray tube through special high voltage receptacles

The anode side needs ______ exposure

less exposure

What is the goal of the filament circuit

literally boil off electrons out of the filament wire

Where is the timer switch/circuit located and why?

located in primary circuit because its easy to control a low voltage vs a higher one

What is the focusing cup made of and what does it do

made of nickel surrounds each filament on its back side leaving the front open and facing the anode target receives a negative charge from the secondary circuit that forces the electrons together on a cloud as they are boiled off of the filament via electrostatic repulsion

Define flux

magnetic field consisting of lines of force in space

What items are in the primary circuit? (5)

main power switch circuit breaker autotransformer timer circuit primary side of step up transformer

What is the main purpose of the cathode

maintain a vacuum within the tube

What does resistance depend on? (4)

material length temperature cross-sectional area

Electric charge is a property of ______

matter

What is the significance of electric timers

measures time as a device

What does the mA meter do

monitors the x ray tube current

The cathode side needs _____ exposure

more exposure

Why are rectifiers necessary in the x ray circuit

necessary to route the electricity through the x ray tube correcly

Define main power switch

on/off switch for the unit and is connected to the incoming power supply (around 220V)

When is the exposure terminated in the primary circuit

once the programmed magnitude of electric charge is reached

What is another name for a rectifier

one way valve/diode

Define switch (1)

opens circuit therefore breaking the pathway closes circuit therefore forming a pathway

Define effective focal spot

origin of the x ray beam and is seen from the patients perspective (the smaller the area is, the sharper the image will be)

Define leakage radiation

photons traveling in directions other than towards the patient

What is phase 2 of the 2 phase switch

prepping the rotor this phase initiates the x ray production process

Define circuit breaker

protects against short circuits and electrical shock

What does the metal envelope provide

provides a constant electric potential between the cathode and the disclosure

What does the cathode do

provides a source of electrons needed for x ray production

What 2 things are used to extend tube life

rating charts cooling charts

What items are in the filament circuit

rheostat step down transformer

How does an anode rotate

rotates by an induction motor that consists of a stator and rotor

What items are in the secondary circuit? (4)

secondary side of step up transformer/circuit mA meter rectifier bank x ray tube (except for the filaments)

What does the radiographer select the operating options for? (4)

selecting kVp mAs exposure time focal spot size

Describe properties of the anode

series of electrical thermal conductor and has a target window -all x rays that don't make it to the target window continue as a current flow through the x ray current

Define an autotransformer

set by a control panel and is self induction

What parts of the focusing cup affects how well it focuses the electrons on the target? (3)

size shape charge

Why are rectifiers used in pairs

so that the AC has an open path from each direction

What happens when the exposure switch is first pressed

some of the electricity is diverted to the induction motor of the tube to bring the rotor up to speed. with the rotor spinning, the selected filament is energized whirl the desired degree of thermionic emission is achieved

Define resistance

something in a current that resists/impedes the flow of electricity

What are the 2 types of anodes

stationary anode rotating anode

Define electrostatics

stationary electrons

Describe how the stator and rotor are situated

stator on the outside rotor on the inside

Who controls the filament circuit? (3)

technologist mA selector rheostat

What happens to the HU equation if multiple exposures are made

the answer from the equation is multiplied by the number of exposures

Define space charge. What does it do?

the charge is self limiting and once it reaches a size good for the current used, it becomes difficult for additional electrons emitted -the self limiting factor is the space charge effect -the focusing cup forms them to a cloud and becomes the space charge

What happens to the pathway if the circuit is broken?

the circuit becomes open (open circuit) EX: Turning on a switch, closes the pathway and turning off a switch opens the pathway

How is the anode target angle determined

the intended use of the tube and NOT by the radiographer

Define electromagnetic induction

the phenomenon of inducing an electric current in a conductor by moving a conductor through a magnetic field

What is the dividing line between the primary and secondary circuits

the step up transformer

What happens when the switch is pressed

the voltage from the autotransformer passes back to the step up transformer the voltage then passes through the rectifier bank before passing to the anode and cathode the x ray tube so that the anode is always positive and cathode always negative

What is part of the anodes job

to dissipate the heat that is massively produced here

Why is a step down transformer used

to increase current by reducing voltage that is applied to the filament

What surrounds the protective housing and why

tube is immersed in an oil bath and cooling fans that circulate air around the assembly and therefore protecting it from thermal damage

As the tubes age, what material can also be used to cause arcing and damage to the tube

tungsten

What are rectifiers used for

used to convert AC to DC

What is the step up transformer used for?

used to increase voltage from the autotransformer to the kV necessary for x ray production

What is the significance of the exposure timer

uses impulses of electricity to time the exposure

What is the significance of mAs timers

uses the mA on the control panel and automatically sets the mA to the largest setting and time to the shortest setting to obtain the desired quality of the x rays

What is Ohm's law and the equation for it?

voltage across the total circuit or any part of that circuit is equal to the current multiplied by the resistance V=IR

Following the sequence of events through the primary and secondary circuit, where does voltage flow to

voltage flows through the autotransformer to the step up transformer through the rectifiers to the x ray tube

When is full wave rectification used

when 4 rectifiers are used

Define magnetic materials

when orbital electrons of their atoms spin in 1 direction creating tiny magnets called magnetic dipoles

Define how a magnet works

when the dipoles form groups of similarly aligned atoms, they create domains. When magnetic materials are placed in a strong magnetic field, the domains align with the external field, which organizes them and magnetizes the material, thus creating a magnet

Using the crystals, when will the solid state diode conduct electricity

when there is a positive P and a negative N

Define three phase power

when we rectify each waveform as if they were a single waveform, the x ray tube sees a waveform