Meaghan Piretti Study Guide 1-100

What side of the x-ray tube positive

Anode

What side of the x-ray tube is negative

Cathode

What is the role of the glass envelope

Containment and maintains the vacuum. Maintains a vacuum inside the X-ray tube, allowing electrons to travel freely from the cathode to the anode without interacting with air molecules.

What is the role of the tube housing

Prevents leakage and insulates

What end of the tube has the filament and focusing cup

Cathode

What are the types of anodes

Rotating and Stationary

What is the anode made of

Tungsten

Why is Tungsten the chosen material for the anode

Has a high atomic number meaning it has a high melting point

Describe the induction motor

Stator on the outside and Rotor on the inside

What is a stator

Electric motor that turns the rotor at high speed

Rotating magnetic field when energized

What does the rotor do

Spins the anode allowing heat to be spread out across a larger area

What do the bearings of the induction motor do

Support and enables rotation

Define Anode heel effect

Variation in x-ray intensity between anode and cathode sides of the tube

What side of the x-ray tube has the more intense beam

Cathode

Why is the beam more intense on the cathode end

X-rays produced deeper within the anode must pass through more material which absorbs some of the beam, the absorption reduces intensity on the anode side

If the degree of anode angle decreases what will happen to the anode heel effect

It increases, a smaller angle means x-rays have to travel through more anode material to exit

Define the line focus principle

Large Actual focal spot that spreads heat while maintaining a small effective focal spot for better image detail

What is larger, the actual focal spot or effective

Actual focal spot is larger. effective is smaller

Where is the actual focal spot located

On the surface of the anode target

Which focal spot goes towards the pt, actual or effective

Effective

If you decrease anode angle (choose small focal spot) how will that affect the effective focal spot size

It also decreases

Define off focus radiation

Radiation produced outside the actual focal spot which causes blurred edges or ghost images

Define tube loading

The amount of heat energy generated in the x-ray tube during an exposure, heat units

What is the formula for heat units

HU= kVp x mA x time (s) x wave form factor

What is the average wave form factor

1.4

What is the wave form factor for single phase

1

What is the wave form factor for 3 phase 6 pulse

1.35

What is the wave form factor for 3 phase 12 pulse

1.41

What is the wave form factor for high frequency

1.45

wrap up of heat units in order

Single-phase 1.00

Three-phase, 6-pulse. 1.35

Three-phase, 12-pulse 1.41

High-frequency 1.45

HU = kVp × mA × time × correction factor

Describe the difference between series and parallel circuits

Series: 1 path, if 1 breaks the entire circuit stops like x-mas lights

Parallel: multiple paths, other branches still work even if one breaks

Define amperes

Aka Amps

a measure of the flow of electric current in a circuit

Define voltage

The electrical potential difference between two points in a circuit

The pressure that pushes electrons through

Define resistance

Measured in Ohms

How much a material resists or slows down the movement of electrons

List the components in the primary circuit

Main power switch, Circuit breaker, Autotransformer, kVp selector, Exposure switch, Timer circuit, and the primary side of the step up transformer

What is purpose of the circuit breaker

Protects against electrical overloads

What is the purpose of the autotransformer

Adjusts the incoming voltage and supplies it to the step-up transformer

What is the purpose of the kVp selector

Allows the user to choose the desired kilovoltage

What is the purpose of the step-up transformer

It begins the process of increasing voltage to create the potential difference needed for x-ray production

List the components of the secondary circuit

Secondary side of the step-up transformer, mA meter, rectifiers, x-ray tube

What does the Secondary side of the step-up transformer do

Converts low voltage into high voltage

What is the purpose of the mA meter

measures the current flowing between the cathode and anode during exposure

What is the purpose of the rectifiers

To convert AC to DC so the current will flow in only 1 direction

List the components of the filament circuit

Step-down transformer, Filament (Cathode), and mA selector aka Rheostat

What is the purpose of the step down transformer

Reduces voltage while increasing current to heat the filament

What is the purpose of the filament (cathode)

The heated wire that emits electrons when current passes through

What is the purpose of the mA selector or rheostat

Controls the amount of current flowing to the filament, adjusting filament temperature and thus the quantity of electrons

What is the incoming voltage coming into the circuit

220 volts AC

What transformer comes first in the circuit

Autotransformer

The autotransformer works on what type of induction

Self induction, 1 winding coil

The step-up and step-down transformers work on what type on induction

Mutual induction, 2 separate coils one for the primary side and one for the secondary side

What works on AC in the x-ray circuit

Autotransformer, Step up & down transformer, and the incoming power supply

What works on DC in the x-ray circuit

X-ray tube, and rectifiers

When a tech increases the mA on the control panel, what factors will also increase

Filament current, Thermionic emission, Tube current, Quantity of x-rays produced, and Pt dose

Define tube current

The flow of electrons from the cathode to the anode within the x-ray tube, measured in mA, more x-rays produced think Quantity

Tube current= electron flow = x-ray quantity

How does mA relate to the number of x-rays produced

Directly proportional

How does mA relate to thermionic emission

Directly proportional

How is mAs calculated

mA x time (s)

What is the reciprocity law

The same radiographic density will be produced if the mAs is the same regardless of the combination of mA and time (s) used

Define tube potential

The voltage difference between the cathode and anode in the x-ray tube and is measured in kVp

How does kVp relate to the energy of the electron beam

Directly proportional

How does kVp relate to the beam quality

Directly proportional

Can kVp also change the intensity of the beam

Yes, kVp increases not only energy (quality) but also the number (quantity) of photons produced, this is because higher-energy electrons can interact more effectively with the anode generating more x-rays overall

How does kVp relate to pt dose

Directly and Indirectly, higher kVp= higher energy x-rays meaning less absorption by the pt so doses can be lower and because higher kVp creates more penetrating beam a tech can typically reduce the mAs to get the same image quality, lower mAs= fewer photons = lower dose

increase of kVp & decrease of mAs = decreased dose, but increase in kVp and the same mAs = increase dose

Describe the 15% rule

Increasing the kVp by 15% will double the exposure to the image receptor and to maintain the same exposure you must halve the mAs

What does SID stand for

Source to image distance

How does increasing the distance affect intensity

Decreases according the the inverse square law

Simply put, define the inverse square law

As you move farther from the source your dose will decrease

Where is the AEC located in the x-ray room

Behind the patient but in front of the IR and is usually built into the Bucky

Describe how AEC works

Automatic exposure control works by measuring the amount of radiation that passes through the pt and automatically stops the exposure once the preset amount has been detected

This ensures that there is a consistent image density regardless of the patient size or tissue thickness

What does AEC control

Time

What is the backup timer used for on AEC

It terminates the exposure if the AEC fails to do so within a safe time limit

What is the minimum response time for AEC

The shortest possible time the system needs to detect radiation and terminate the exposure after reaching the proper amount

Usually between 1-2 ms

When would a tech use density controls

To compensate for unusual anatomy or pathologies, or to intentionally lighten or darken an image

What is the disadvantage of AEC

Positioning sensitivity, wrong detector selection, or when imaging small anatomy

What is considered a tech error when using AEC

Selecting the wrong detector or improper positioning over a chamber

What are the density controls used for in AEC

Allows for a tech to manually adjust the exposure

How will increasing kVp change the seconds during exposure

If using AEC time will decrease

How will increasing mA change the seconds during exposure

Decrease, reciprocity law

How will decreasing mA change the seconds during exposure

Increase, reciprocity law

How will increasing the density setting by +1 change the seconds during exposure

Increase, the exposure will go on for longer adding the +1 tells AEC to allow for more radiation to reach the IR before stopping

What is the purpose of a grid

Reduce scatter radiation before it reaches the IR, improving image contrast

Where will you find a moving (oscillating) grid in the x-ray room

In the upright bucky

What types of exams would you use a stationary grid

Portable or table top exams requiring a grid

What factor should you increase when using a grid

mAs

How will grids affect pt dose

Increases because of the use of excess mAs

What is the grid ratio formula

height of the lead strip/distance between strips

What is the grid conversion formula

New mAs= og mAs x (new grid factor/ old grid factor)

What is the grid ratio conversion factor for no grid

1

What is the grid ratio conversion factor for 5:1 grid

2

What is the grid ratio conversion factor for 6:1 grid

3

What is the grid ratio conversion factor for 8:1 grid

4

What is the grid ratio conversion factor for 12:1 grid

5

What is the grid ratio conversion factor for 16:1 grid

6

What is grid cut off

Unintended absorption of useful (primary) x-rays by the grid which result in a lighter (unexposed) area on the image

What are the possible grid errors

Off level, Off angle, Off center, Off focus, Upside down

With the reciprocity law, if you increase seconds how should the mA be adjusted

Decreased

List the steps of the CR imaging process

1.) Exposure, PSP plate absorbs the x-ray energy and stores it as a latent image

2.) The PSP plate contains barium fluorohalide crystals that trap electrons in a high energy state forming the latent image

3.) The cassette is placed into a reader and a laser scans the plate in a rasta pattern, releasing the stored energy as visible light

4.) The emitted light is captured by a photomultiplier tube (PMT) then the light is converted into an electrical signal then digitized into a pixel based image

5.) The digital image appears on a computer for review and analysis

6.) Plate erasure, the plate is exposed to bright white light to erase any residual data

What type of phosphor is used in CR

Barium fluorohalide

List the layers of a CR Plate

Protective layer that protects the phosphor from damage, Phosphor layer, Reflective layer, Conductive layer (helps eliminate static electricity that could cause an artifact), Support layer made of polyester, Backing layer (includes barcode and provides physical protection)