Producing An Image

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Producing An Image

• Lavin Chapter 6
• CTVT 529-532

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To review

• Elements electrons
• Structure what happens when they become
  unstable
• The electromagnetic spectrum
• Which waves penetrate farther? Shorter or longer
  wavelength?
• Electrification induction
• Induction uses force fields to cause a reaction
  without contact
• The parts of the x-ray unit
• Functions safety measures
• Creating images on film
• Cassettes, screens, and film

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Electromagnetic Spectrum
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To review

• What do we mean by the image receptor in
  film-based processing?
• What 3 main components make up the receptor?

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Producing Radiographs

• The image receptor receives the produced x-rays
  and produces the actual image.
• Receptor components in film-based imaging
• Cassette/film holder
• Intensifying Screen
• Film

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To review

• What within the image receptor can cause a
  reduction in sharpness on the radiograph?

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Poor Film/Screen Contact
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In review

• Regarding the cassette itself, discuss
• Handling both open closed
• How to open
• How to get the film out
• How to reload
• Cleaning

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In review

• What are some examples of lead blockers, and how
  are they used in radiography?

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In Review

• What is an intensifying screen, and what is its
  purpose in film-based processing?

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Intensifying Screens

• Purpose
• Reduces the amount of radiation required
• Only 5 of exposure results from ionization of
  x-rays. The remainder is due to light emitted
  from intensifying screens.
• Reduces mAs needed
• Decreases radiation dose to the patient
• Decreases exposure potential to the technician
• Enhances contrast
• The screens in an x-ray cassette sandwich the
  film.

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Producing an Image

• The main objective of all imaging systems is to
  demonstrate the differences in tissue density.

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Learning Objectives Chapter 6

• List understand the 4 factors of radiographic
  exposure and how each impacts the production of a
  diagnostic image.
• Kilovoltage (kV), milliamperes (mA), time
  (seconds), distance
• Understand how milliamperage (quantity) and
  kilovoltage (quality) of x-rays can impact a
  radiograph
• Define scatter radiation and understand its
  impact on radiographic quality and radiation
  exposure of personnel.
• Define the 15 rule, and be able to use it to
  fine-tune a radiographic image.
• Understand how to create and use a technique
  chart to create diagnostic radiographs.

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The Four Factors of Radiographic Exposure

• These must be manipulated so tissue absorption of
  radiation is exactly correct to demonstrate
  anatomy/pathology and minimize artifacts.
• The 4 factors
• Kilovoltage (kV) quality or contrast
• Milliamperes (mA) quantity or darkness
• Time (seconds) exposure time
• Distance

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1st Factor of Radiographic Exposure Kilovoltage

• Kilovoltage Peak (kVp) - the maximum value of
  x-ray tube voltage during x-ray production
• Quality of the x-rays
• Directs x-ray penetration
• Increase Increase in contrast
• More contrast
• Darks vs lights
• Fewer shades of gray in-between
• Can distinguish between structures
• Can impact density, since too high will darken
  film

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Technical Factors of Exposure

• kVp Power behind the cue stick
• Ma Number of balls in play
• Energy is transferred as balls bounce off each
  other

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Optimizing Kilovoltage

• Use the lowest setting that will penetrate region
  of interest, enhance tissue contrast, and
  minimize scatter radiation.
• Kilovoltage is energy, so not directly
  proportionate to tissue thickness
• Tissue Fluence - Variations in tissue absorption
• Calculate a starting point, but be ready to
  adjust
• Changing a setting doesnt yield a proportional
  result

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What is Scatter Radiation?

• Secondary radiation
• Lower-energy x-ray photons that have undergone a
  change in direction after interacting with
  structures in a patients body
• Is of concern because
• Decreases image quality
• Increases radiation exposure
• The primary source of exposure for technicians
• Darkens radiograph decreases contrast

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Managing Scatter Radiation

• Is directly impacted by increases in
• Kilovoltage
• Thickness of the part being radiographed
• Size of the field
• Can be managed by
• Reducing kVps as low as possible
• Careful collimation
• Avoiding retakes
• Use of a grid

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Optimizing Kilovoltage

• The 15 Rule A rule of thumb
• Used to optimize kVs and enhance contrast
• Doesnt impact density
• To increase penetration increase kVs 15
• To decrease penetration decrease kVs by 15
• Dont forget to adjust mAs if you change kVps
• Increasing kV Divide mAs by 2
• Decreasing kV Multiply mAs by 2
• The power behind the cue stick

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Adjusting kVps
Not enough Contrast
Optimized Contrast
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2nd Factor of Radiographic Exposure Milliamperage

• mA
• Quantity of X-Rays How many
• Impacts density or darkness
• Directly proportional doubling doubles density
• A very simple concept

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Advantages of high mA

• Allows for shorter time setting with the same
  number of x-rays produced
• Shorter time possibility of motion is decreased
• Decreases exposure for restraining personnel
• More x-rays produced
• Allows for examination of thicker anatomic areas
• Increases the number of balls in play

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3rd Factor of radiographic Exposure Time (mAs)

• Adds in time factor
• mA X seconds mAs
• Suitable mA setting depends on the thickness and
  type of tissue being radiographed
• mA time are inversely related but often
  combined settings on the x-ray machine
• Changes in mAs
• Increased x-ray becomes blacker in color
  overall
• Decreased x-ray becomes lighter in color
  overall

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mAs Too High Too low
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Troubleshooting Technical Factors

• If image isnt coming out right
• Reposition re-measure
• Adjust mAs first, as long as tissue is
  penetrated
• An easy change to make measure
• Adjust kVps using 15 rule
• If film is light, check temperature of chemicals
• If image is dull gray, look for light leaks in
  darkroom or improperly exposed film in box
• Have the unit serviced recalibrated

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4th Factor of Radiographic Exposure Distance

• Distance
• The Inverse Square Law
• The intensity of radiation at a
• location is inversely proportional to
• the square of its distance from
• the radiation source
• In most clinics, the distance between the x-ray
  tube and receptor/cassette is fixed at 40 inches.

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Anatomic Considerations

• Skull Cervical Spine
• High contrast bone tissue higher kVps not
  required
• Chest, thorax, abdomen
• Homogeneous density, so scatter possible if high
  kVps used
• Keep KVps as low as possible and increase mAs
• Extremities
• Body parts thin, and tissue-to-bone ratio high
• Low kVps indicated
• Birds pocket pets
• Similar technical factors to extremities

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Evaluating Radiographs

• The technician needs to have the ability to
  properly evaluate a radiograph.
• If you dont know whats good, then it will be
  hard to attain a good quality image on film.
• Will help to minimize re-takes

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Assessing a Radiograph

• Taking a second radiograph is sometimes
  unavoidable.
• If you can figure out whats wrong, you can make
  corrections so that the second attempt is the
  last attempt.
• Radiographic quality depends on the
  technologists understanding of the concepts and
  variables that produce a good radiograph.

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Exposure Factors X-Ray Generation

• X-ray generation
• mAs (current) is applied to the filament in the
  cathode.
• mAs control the quantity/total number of x-rays
• Generates an electron space cloud
• The electrons are directed to the anode target by
  kVps.
• kVps control the quality/penetration of x-rays
• The collision produces heat and x-radiation.

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Viewing a Radiograph

• Viewed on an evenly lit view box in a
  semi-darkened room.
• View box should be clean, and all light bulbs
  should be in working order.

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Film View Position

• Film position on the illuminator matters
• V/D or D/V
• Head at the top of the view screen
• Handshaking position
• Lateral
• Head at viewers left
• Spine on top
• Limbs
• Proximal end up

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Evaluation of Radiographic Technique

• Two basic questions
• Is the film too light or too dark?
• More exposure blacker film overall
• Increase kVp or mAs to darken
• Decrease kVp or mAs to lighten
• Is there proper penetration/differentiation?
• If cannot see contrast between structures
• Adjust kVps

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Is there proper penetration?

• If there is inappropriate penetration of the
  x-rays, change kVps
• If film is dark, should be decreased.
• If film is light, should be increased.
• If penetration of x-radiation is satisfactory,
  then mAs should be adjusted.

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If film is too light

• Is the film under penetrated?
• If no Increase mAs 30-50
• If yes Increase the kVp 10-15
• Is the film over penetrated?
• If yes Decrease kVp by 10-15
• If no Decrease mAs by 30-50.

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What Determines Adequate Penetration?

• Abdominal radiograph
• Can see outlines of liver, spleen, kidneys and
  bowel
• Thoracic
• Heart clearly outlined, diaphragm boundary
  evident, bone differentiation clear
• Inadequate penetration areas almost completely
  white, and organs/bones cannot distinguished.

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Radiograph Too Dark

• If bone tissue is gray, with too little contrast
  between the bone and adjacent soft tissue, there
  was too much penetration.
• Decrease kVp by 10-15
• If bone tissue is relatively white, compared to
  surrounding tissues, then penetration is
  adequate.
• Decrease mAs 30-50
• Evaluating radiographs is an art, and often
  several changes can be made to improve the
  radiograph equally

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Creating a Technique Chart

• Provides suggested techniques of anatomy and
  positioning Without it, new calculations would
  have to be taken before every radiograph.

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Creating a Technique Chart

• Step 1 Prepare
• Service your processor and ensure screens and
  film match.
• Select a medium-sized dog of average weight.
• Step 2 Select your mAs
• Use the following for an average speed
  intensifying screen
• Extremity 2.5 mAs
• Thorax 5 mAs
• Abdomen 7.5 mAs
• Spine 10 mAs
• Remember mA secs mAs

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Creating a Technique Chart

• Step 2 Select your mAs (cont.)
• To achieve this mAs, the mA and time need to be
  set separately, and the machine will calculate
  the mAs for you.
• Use these as standard mA settings
• Extremity 150 mA
• Other 300 mA
• Calculate the time as follows
• Extremity 150mA X 1/60 secs (approx) 2.5 mAs
• Thorax 300 mA X 1/60 secs 5 mAs
• Abdomen 300 mA X 1/40 secs 7.5 mAs
• Spine 300 mA X 1/30 secs 10 mAs

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Creating a Technique Chart

• Step 3 Select your initial kVp
• Calculate initial kVp using Santes Rule
• Formula 2 x thickness 40 grid factor
• If a grid is used, add 10 to total
• Grid is usually indicated for measurements gt 9
  cms
• Example Body Part 8 cms
• (2 X 8) 40 56 kVp
• No grid necessary since lt 9 cms
• Note At VTI, we always use a grid for cats,
  and sometimes will use a grid as a way to achieve
  a clearer image, even if the animal is small

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Santes Rule Why 40?

• Represents the distance from the x-ray tube focal
  spot to the image receptor (film) in inches
• This distance can be referred to as the Focal
  Film Distance (FFD) or Source-image Distance
  (SID).

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Creating a Technique Chart

• Step 4 Expose the perfect film
• Use the exposure factors calculated above as a
  starting point
• If you cant see details of internal structures
  because the image is too dark, the radiograph has
  been over-penetrated (too much contrast), so
  decrease kVp by 15
• If you cant see details of internal structures
  because the image is too light, the radiograph
  has been under-penetrated, so increase kVp by 15
• Once the radiograph is close to perfect, reduce
  the changes to 5 increments until youre
  satisfied with the result.
• mAs can be adjusted up or down 50 as needed to
  alter density
• Once the exposure is right, go to step 5

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Creating a Technique Chart

• Step 5 Make the technique chart
• Complete kVps above and below the perfect
  entry as follows
• Subtract 2 kVp from the original kVp for each cm
  decrease from the original
• Add 2 kVp to the original kVp for each cm
  increase from the original kVp up to 80 kVp.
• Add 3 kVp for each cm increase that places the
  kVp above 80 and up to 100
• Add 4 kVp for each cm increase that places the
  kVp above 100
• Step 6 Create a Technique Chart for each
  different study (abdomen, thorax, extremity, and
  spine)
• Create an additional chart for body parts that
  may need to be radiographed using a grid (all but
  extremities)

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For example
Cm. kVp mAs
7 64 7.5
8 66 7.5
9 68 7.5
10 70 7.5
11 72 7.5
12 74 7.5
13 76 7.5
14 78 7.5
15 80 7.5
16 83 7.5
17 86 7.5
18 89 7.5
19 92 7.5
In this example, the perfect combination of kVp
and mAs for a sample 15 cm abdomen is shown in
pinkThe entries above and below are filled in
based on the previous rules.
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Technique Chart Homework

• Create a Technique Chart for each of the
  following
• Extremity No grid
• Thorax Grid
• Abdomen No grid
• Spine Grid
• Use the handout and previous slides