1. Producing An Image
Lavin: Chapter 6
CTVT:

2. To review… Elements & electrons – The electromagnetic spectrum –
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
Shorter WL’s have higher energy, and penetrate farther

3. Electromagnetic Spectrum

4. What do we mean by the “image receptor” in film-based processing?
To review…
What do we mean by the “image receptor” in film-based processing?
What 3 main components make up the receptor?
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

5. 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

6. To review…
What within the image receptor can cause a reduction in sharpness on the radiograph?

7. Poor Film/Screen Contact

8. In review… Regarding the cassette itself, discuss:
Handling – both open & closed
How to open
How to get the film out
How to reload
Cleaning

9. In review…
What are some examples of lead blockers, and how are they used in radiography?

10. In Review…
What is an intensifying screen, and what is its purpose in film-based processing?
vs. grid - An X-ray grid is the part of an X-ray machine that filters out randomly deflected radiation that can obscure or blur an image produced by the machine. It was invented in 1913.

11. 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.

12. Producing an Image
“The main objective of all imaging systems is to demonstrate the differences in tissue density.”

13. 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.

14. 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

15. 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
4 factors of radiographic exposure and how each impacts the production of a diagnostic image.
Kilovoltage (kV), milliamperes (mA), time (seconds), distance
Might need to increase kVp:
Can’t tell bones from soft tissue
Mostly light or dark
Can’t see “into” the patient

16. 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

17. 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 doesn’t yield a proportional result

18. What is Scatter Radiation?
“Secondary radiation”
Lower-energy x-ray photons that have undergone a change in direction after interacting with structures in a patient’s body
Is of concern because:
Decreases image quality
Increases radiation exposure
The primary source of exposure for technicians
Darkens radiograph & decreases contrast

19. 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 kVp’s as low as possible
Careful collimation
Avoiding retakes
Use of a grid
Grid – filters out scatter/random radiation

20. Optimizing Kilovoltage
The 15% Rule – A “rule of thumb”
Used to optimize kV’s and enhance contrast
Doesn’t impact density
To increase penetration – increase kV’s 15%
To decrease penetration – decrease kV’s by 15%
Don’t forget to adjust mA’s if you change kVp’s:
Increasing kV = Divide mA’s by 2
Decreasing kV = Multiply mA’s by 2
“The power behind the cue stick”

21. Adjusting kVp’s
Not enough Contrast
Optimized Contrast

22. 2nd Factor of Radiographic Exposure: MilliamperagemA
“Quantity” of X-Rays – How many
Impacts density or darkness
Directly proportional – doubling doubles density
A very simple concept
4 factors of radiographic exposure and how each impacts the production of a diagnostic image.
Kilovoltage (kV), milliamperes (mA), time (seconds), distance

23. “Increases the number of balls in play”
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”

24. 3rd Factor of radiographic Exposure: Time (mA’s)
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
4 factors of radiographic exposure and how each impacts the production of a diagnostic image.
Kilovoltage (kV), milliamperes (mA), time (seconds), distance

25. mAs: Too High & Too low

26. Troubleshooting Technical Factors
If image isn’t coming out right:
Reposition & re-measure
Adjust mA’s first, as long as tissue is penetrated
An easy change to make & measure…
Adjust kVp’s 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

27. 4th Factor of Radiographic Exposure: 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.
4 factors of radiographic exposure and how each impacts the production of a diagnostic image.
Kilovoltage (kV), milliamperes (mA), time (seconds), distance

28. Anatomic Considerations
Skull & Cervical Spine
High contrast bone & tissue – higher kVp’s not required
Chest, thorax, abdomen
Homogeneous density, so scatter possible if high kVp’s used
Keep KVp’s as low as possible and increase mA’s
Extremities
Body parts thin, and tissue-to-bone ratio high
Low kVp’s indicated
Birds & pocket pets
Similar technical factors to extremities

29. Evaluating Radiographs
The technician needs to have the ability to properly evaluate a radiograph.
If you don’t know what’s good, then it will be hard to attain a good quality image on film.
Will help to minimize re-takes

30. Assessing a Radiograph
Taking a second radiograph is sometimes unavoidable.
If you can figure out what’s wrong, you can make corrections so that the second attempt is the last attempt.
Radiographic quality depends on the technologist’s understanding of the concepts and variables that produce a good radiograph.
Danger of non-diagnostic?
Treatment errors
Retakes
Increased exposure
Fractious animals
Time
Supplies
Equipment wear

31. Exposure Factors & 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 kVp’s.
kVp’s control the quality/penetration of x-rays
The collision produces heat and x-radiation.

32. 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.

33. Film View Position V/D or D/V: Lateral: Limbs:
Film position on the illuminator matters:
V/D or D/V:
Head at the top of the view screen
Handshaking position
Lateral:
Head at viewer’s left
Spine on top
Limbs:
Proximal end up

34. 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 kVp’s

35. Is there proper penetration?
If there is inappropriate penetration of the x-rays, change kVp’s
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.

36. 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%.

37. 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.

38. 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***

39. Creating a Technique Chart
Provides suggested techniques of anatomy and positioning… Without it, new calculations would have to be taken before every radiograph.

40. 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

41. 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 mA
Other 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 = mAs
Spine: 300 mA X 1/30 secs = 10 mAs

42. Creating a Technique Chart
Step 3: Select your initial kVp
Calculate initial kVp using Sante’s Rule
Formula: 2 x thickness grid factor
If a grid is used, add 10 to total
Grid is usually indicated for measurements > 9 cms
Example: Body Part = 8 cms
(2 X 8) + 40 = 56 kVp
No grid necessary since < 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 **

43. Sante’s 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).

44. Creating a Technique Chart
Step 4: Expose the perfect film
Use the exposure factors calculated above as a starting point
If you can’t 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 can’t 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 you’re 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

45. Creating a Technique Chart
Step 5: Make the technique chart
Complete kVp’s 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)

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

47. 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