Fdi 2-3

Front 1

Beam Filtration
• 2 Main Types

Back 1

o Inherent Filtration
o Added Filtration

Front 2

o Inherent Filtration

Back 2

 Inherent to the x-ray tube & housing
• Glass Envelope
• Oil surrounding the tube
• Collimator Mirror
 No energy below 15keV allowed to pass

Front 3

o Added Filtration

Back 3

 Added to the port of the x-ray tube
 Aluminum (Al) primarily used
 Absorbs low energy but allows high energy to pass
Inherent

Front 4

Total Filtration

Back 4

•
o Sum of Added + Inherent filtration
o Current U.S. standard
 X-ray tubes operating over 70kvp must have a minimum total filtration of 2.5 mm of Aluminum (Al) equivalent

Front 5

• Selective / Special / Compensating Filtration –

Back 5

between x-ray beam/collimator & patient
o Added to the primary beam to alter its intensity
o Examples: Gonadal shielding, Eye shielding, Trough (double wedge filter)
o Most common type: Simple Wedge Filter
 Thick Side & Thin Side
 Made of aluminum or lead
o Also used to “even out” an image

Front 6

Heat Units (HU)

Back 6

• Amount of heat produced by any given exposure
• mA x Time (S) x kVp x Generator factor = HU
o High Frequency Generator Factor = 1.45

Front 7

Tube Rating Charts

Back 7

• Describes exposure limits of the x-ray tube
• Most modern machines will not allow for tube-damaging exposures
o Theoretically, you can’t burn anode

Front 8

Interactions with Matter

Back 8

5 Main types of interactions with matter

• 3 Within Diagnostic Range
Compton
Photoelectric
Coherent (Classic) Scattering

2 Outside
o Pair production
o Photodisentigration

Front 9

• 3 Within Diagnostic Range
Compton
Photoelectric
Coherent (Classic) Scattering
2 Outside
o Pair production
o Photodisentigration

Back 9

• 3 Within Diagnostic Range
o Compton = outer shell – creates scatter
o Photoelectric = interacts with k shell (inner shell) – most desired for film
o Coherent (Classic) Scattering – Non–ionizing - never ejects an actual electron from shell
• 2 Outside Diagnostic Range (Nuclear interactions)
o Pair production
o Photodisentigration

Front 10

Scatter increases film density –

Back 10

Creates fog

Front 11

Differential Absorption
•

Back 11

Process where some of the x-ray beam is absorbed in the tissue & some pass through a given object
• Different tissues absorb differently (listed from radiolucent [BLACK] to radiopaque [WHITE])
• 5 Radiographic Intensities
o Inherent / Endogenous – Normally found in Human body
1. Air
2. Fat
3. Water (H2O)
4. Bone
o Exogenous – NOT normally found in Human body
5. Metal

Front 12

• 5 Radiographic Intensities

Back 12

o Inherent / Endogenous – Normally found in Human body
1. Air
2. Fat
3. Water (H2O)
4. Bone
o Exogenous – NOT normally found in Human body
5. Metal

Front 13

Beam Attenuation
•

Back 13

The energy reduction of a primary x-ray beam as it passes though a given object
• 3 processes occur
1. Absorption – Good
2. Scattering – NOT good – only degrades image quality
3. Transmission – doesn’t interact with anything

Front 14

Field Size

4 Types of Beam-Restricting Devices

Back 14

o Cones
o Cylinders
o Aperture Diaphragms
o Collimators – most commonly used in diagnostic radiology

Front 15

Primary Ways to Control (Prevent) Production of Scatter
3 ways

Back 15

1. Field size (example: collimator)
2. kVp (lower kVP = less scatter)
3. Patient Thickness (Anatomical Part thickness / Size) – Dr. has least amount of control over
a. Methods to reduce patient size
i. Can lay patient down
ii. Use compression bands

Front 16

Focal Film Distance (FFD)

Back 16

• Air-Gap Technique - Increase Object-Image Distance (OID)
o Move image receptor away from the patient (create gap), less scatter reaches the image receptor

Front 17

Grids
formula?
Grid Ratio?

Back 17

o Height of lead strips / Distance between the lead strips
o Ex: 6:1, 8:1, 10:1, 12: 1, 16:1
o 10:1 or 12:1 ideal ratios to be used for diagnostic imaging

Front 18

• Types of Grids

Back 18

1 Linear Grid
2 Crossed Grids
3 Focused Grids - Focused grids follow beam divergence
 Linear Focused Grids – Most commonly used in diagnostic radiology
 Crossed focused Grids

Front 19

• Grid Performance

Back 19

o Purpose is to increase radiographic contrast, reduce scatter, but reduces density so additional mAs is required
o Grid conversion factor (aka Bucky factor) used to determine adjustment of mAs needed
o Mathematically expressed
 Bucky factor = mAs with the grid/mAs without a grid

Front 20

• Frequency (# of lead lines / unit length)

Back 20

o Typical: 40 lines/cm or 103 lines/inch for diagnostic radiology

Front 21

• Grid Cut-off (most only occur with focused grids )

Back 21

o Off-Center Grid
 Lateral decentering
o Off-Focus Grid
o Upside-Down (Focused) Grid
 A focused grid placed upside-down
 Appears as significant loss of density along the edges
• Dark Middle but Nothing on the SIDES of image
o Off-Level Grid – MOST COMMON
 X-ray beam is angled across the lead strips
 Occurs with both focused & parallel

Front 22

• If a part measures 10 cm or Greater thickness –

Back 22

Use a grid

Front 23

• Increase patient dose – ?
• Advantages vs Disadvantages

Back 23

• Increase patient dose – because MaS must be increased to maintain density

Front 24

Cassettes

Radiographic Film
•

Back 24

Construction (Layers of Film)
1 Supercoat
 Protective outer layer
 Made of gelatin

2 Emulsion
 Radiation/light-sensitive layer
 Active ingredient: Silver halides
• Dominant Silver halide: Silver Bromide (AgBr) 90-99%
• Silver iodide (AgI) only 10-1% of emulsion layer

3 Adhesive Layer

4 Base
 Blue dye or tint added - to reduce eye strain

Front 25

Latent Image –

Back 25

Image that exists on the film after exposure, but prior to processing (aka prior to development)
• Formed by: Gurney-Mott Theory
• Can’t be seen with eyes
• After developing film Latent Image becomes Manifest image

Front 26

• After developing film Latent Image becomes ?

Back 26

Manifest image

Front 27

Manifest Image –

Back 27

image that exists on film after exposure & developing
• The Radiographic Image

Front 28

Crossover

Back 28

o A problem unique to having 2 layers of emulsion (Double emulsion or Duplitized film)
o Light produced by the intensifying screen exposes the back emulsion, crosses over the base layer & exposes the front emulsion
o Blurs the Image
o Modern film has built in t-grain technology & anti-crossover layers that virtually eliminate crossover

Front 29

3 Types of Film
•

Back 29

Direct Exposure (Non-screen)
o Intended for cardboard holder without an intensifying screen
• Screen Film
o Most widely used
o Used with one-two intensifying screens
o More light sensitive
o Single Emulsion
o Double Emulsion (aka Duplitized)
• Duplicating (aka Copy film)– designed to allow a copy of an original film
o Solarization – process by which copy film acts (opposite/ the reverse) as it should to light

Front 30

o Solarization –

Back 30

process by which copy film acts (opposite/ the reverse) as it should to light

Front 31

Exposure Latitude –

Back 31

aka Forgiveness of the film
 Range of exposure techniques (kVp & mAs) that will produce an acceptable image

Front 32

• Contrast & Latitude

Back 32

= Inverse Relationship
o High contrast film = Narrow (low) latitude
o Low contrast film = Wide (high) latitude
 Wide Latitude = more favorable for diagnostic imaging
• It’s more forgiving
• Don’t have re-x-ray patient as much because there are a wider range of exposures that fit

Front 33

• Characteristic curve (aka H&D curve or Sensitometric curve)

Back 33

o Graphically demonstrates (plots):
 Film speed
 Contrast
 Latitude
o Describes the relationship between Optical Density & Radiation Exposure

Front 34

Object-Image Distance –

Back 34

between object being x-rayed and image receptor
• Increase in OID = increase contrast (ie: air-gap technique)
o Scatter doesn’t have enough Energy to get to the film

Front 35

Intensifying Screens

Back 35

 Primary function: Reduce patient dose

• Active layer: Phosphor layer
Modern intensifying screens
• Factors that effect screen speed
• Luminescence
• Quantum Mottle
• Efficiency
• Conversion Ratios
• Spectral Matching
Calcium tungstate screen speed
Faster screen
Faster screen

Front 36

• Active layer: of fiilm?

Back 36

Phosphor layer
o Emits light during stimulation by x-rays
o Converts energy of x-ray beam into visible light
o Layer of crystals

Front 37

• Modern intensifying screens:

Back 37

Rare Earth phosphor Intensifying Screens
o Rare Earth phosphors (atomic number between 57 to 71)
 Gadolinium – produces green light when stimulated
 Lanthanum – Blue light when stimulated
 Yttrium – Ultraviolet/Blue light when stimulated

Front 38

• Factors that effect screen speed

Back 38

o Size of crystals
o Thickness of phosphor layer (crystal layer)
o Phosphor used
 Rare Earth phosphor Intensifying Screens
• Faster, More Efficient, Faster Conversion Ratio than Calcium Tungstate
• Conversion ratio – taking photons in and converting it to white light
o Intensification factor
 Exposure required without screens/Exposure required with screens

Front 39

 Rare Earth Ratio than Calcium Tungstate
• Conversion ratio – taking photons in and converting it to white light

Back 39

phosphor Intensifying Screens
• Faster, More Efficient, Faster Conversion

Front 40

o Intensification factor

Back 40

 Exposure required without screens/Exposure required with screens

Front 41

• Luminescence
o

Back 41

Florescence
 Type of Luminescence do intensifying screens produce

Front 42

o SCREENS Don’t use Phosphorescence

Back 42

 Produces screen after-glow or screen lag
 NOT favorable
 Would overexpose radiograph

Front 43

• Quantum Mottle

Back 43

o Image noise, “Noise in the film”
o Statistical fluctuation in the quantity of x-ray photons that contribute to image formation per square millimeter
o If you use too low of mAs the image may appear “salt & pepper” like
o Decreases recorded detail

Front 44

• Spectral Matching

Back 44

o Film should be sensitive to the same color as intensifying screen
 Spectral emission of the screen must match sensitivity of the x-ray film
 Example: Green screen, should use green sensitive film

Front 45

• Calcium tungstate

Back 45

screen speed - Standard screen speed or Par-Speed
o Speed at which other screens are measured against/compared to
o Speed: 100

Front 46

• Faster screen 

Back 46

increases Density

Front 47

• Faster screen 

Back 47

decreases (lowers) Detail (doesn’t affect contrast)

Front 48

Density

Back 48

• Controlling Factors
o Miliamperage (Ma)
o Exposure Time (S)

Front 49

Contrast

Back 49

• Controlling Factor:
o Kilovoltage(kVp)
• Inverse relationship to Contrast
• Example: High kVp = low Contrast
• Direct relationship to Gray Scale
• Example: High kVp = Long Gray Scale (Long-scale)
• Gray Scale Inverse relationship to Contrast
o Example: Long Gray Scale (long-scale) = low Contrast

Front 50

• Gray Scale relates to Contrast

Back 50

• Gray Scale Inverse relationship to Contrast
o Example: Long Gray Scale (long-scale) = low Contrast

Front 51

(kVp)
relates to Contrast & Gray Scale

Back 51

• Inverse relationship to Contrast
• Example: High kVp = low Contrast
• Direct relationship to Gray Scale
• Example: High kVp = Long Gray Scale (Long-scale)

Front 52

Inverse-Square Law
example 1

Back 52

• Relationship between FFD (aka SID – Source-Image Distance) & Density
• Density (intensity) of x-ray beam is inversely related to Square of Distance (Distance2)
o 2x FFD = MaS should be increased by 4x (factor of 4) to maintain same densitty
o Example #1: If distance is increased from 40in to 80in (double [2x] distance)
 Density of film will be ¼ of density that it originally was (at 40in)
 Must increase MaS by 4X to maintain original density

Front 53

Inverse-Square Law
example 1

Back 53

o Example #2: If distance is decreased from 60in to 30in
 MaS must be decreased by ¼ to maintain same Density
o Short FFD = increase Density
o Long FFD = decrease density
o Closer you are to SOURCE the darker the image should be

Front 54

Grids

Back 54

• Decrease density
• When using a grid: Must increase Time (S) to maintain Density (to prevent density from being lowered)
• Grid Ratio
o 10:1 or 12:1 ideal ratios to be used diagnostically
• Increase Contrast (limits/prevents/reduces Scatter hitting film)

Front 55

Collimation (field size)

Back 55

• Limits field size – limits area being radiated
• Increases Contrast (limits/reduces Scatter)

Front 56

Air Gap Technique

Back 56

• Increases Contrast (limits/reduces Scatter)