1. Exposure Factors or Prime Factors

2. What is “technique” ? How does it affect the “image”
PRIME FACTORS
What is “technique” ?
How does it affect the “image”

3. Objectives Identify Exposure or Prime Factors.
Describe how Prime Factors affect image quality
Identify other factors to consider to receive best image possible.

4. Terms and Abbreviations
kVp – Kilovolt Peak (controls “quality” of X-ray)
mAs – milliAmpere second (controls “quantity” of X-ray)
SID/FFD – Source to Image Distance/Focal Film Distance (Distance from X-ray tube to film)
OID/SFD – Object to Image Distance/Subject to Film Distance (Distance from part to be imaged and film)
IR – Image Receptor (Film)
OD – Optical Density (darkness of the film)

5. Exposure Factors – 3 or 4 The four prime exposure factors are:
Voltage = kVp*
Current = mA*
Exposure time = seconds or fractions of a sec*
Source-to-image distance = SID (FFD)

6. PRIME FACTORS
KVP
MAS
DISTANCE

7. kVp Kilovolts controls how fast the electrons are sent across the tube
kVp controls energy (quality) of X-ray beam
Controls, quality, penetrability & contrast
Increasing kVp also increases scattered photons reducing image quality
Does kVp influence OD?

8. “SHORT” VS “LONG” SCALE

9. kVp
Low kVp (50 – 60)
Short scale
High contrast
“Bone work”

10. kVp
High kVp (90 – 120)
Long scale
Low contrast
“Chest images”

15. mA
Determines the number of photons, radiation quantity, OD & patient dose
Changing mA does not change the kinetic energy of e-
Available mA stations are usually 50, 100, 200, 300, 400 & 600 (Focal Spot Size)

17. Exposure Time mA X s = mAs mAs controls OD
Should be kept as short as possible, for most examinations. To minimize the risk of patient motion
mA X s = mAs
mAs controls OD
mAs determines the number of photons in the primary beam

18. Focal Spot Size Smaller x-ray beam width will produce a sharper image.
Fine detail = small focal spot (i.e. small bones)
General radiography uses large focal spot
Beam from penlight size flashlight vs. flood light beam

19. Focal spot size of the cathode

20. Line-focus principle

21. Penumbra
Edge “unsharpness”

23. Focal-Spot Changes - Penumbra

27. Distance Affects exposure of the IR because of the Inverse Square Law
SID (FFD) largely determines the intensity of photons at the IR (Film)
Distance has no effect on radiation quality but does affect film quality

28. INTENSITY IS SPREAD OUT…

29. Inverse Square Law Formula
Distance #2 - Squared
Intensity #1
Distance #1 - Squared
Intensity #2

30. SID Changes

31. Direct Square Law
New mAs = New distance 2
Old mAs Old distance 2

32. Producing optimal radiographs … key for diagnosing disease

33. How much of the radiation received by the patient
Actually reaches the IR ?

34. About 1%

35. Creating the IMAGE
When x-rays pass through a patient's body, three things can happen:
(1) the x-ray photon is transmitted, passing through the body, interacting with the film, and producing a dark area on the film;
(2) the x-ray photon is absorbed in an area of greater tissue density, producing lighter areas on the film; or
(3) the x-ray photon is scattered and reaches the film causing an overall gray fog.

37. IMAGES DENSITY = THE AMOUNT OF BLACKENING “DARKNESS” ON THE RADIOGRAPH
CONTRAST – THE DIFFERENCES BETWEEN THE BLACKS TO THE WHITES

38. mAs Changes
at least % mas change needed to see a visible change in density

39. mAs DOUBLED = DENSITY DOUBLED

40. + 25% % mas

41. mAs Changes

42. Tube voltage (kVp) Determines the maximum energy in the beam
spectrum and affects the quality of the output spectrum
Efficiency of x-ray production is directly related to tube voltage

43. Influencing factors: kVp
15% rule:
15% kVp = doubling of exposure to the film
 15% kVp = halving of exposure to the film
15% rule will always change the contrast of the image because kV is the primary method of changing image contrast.
Remember :
15% change ( ) KVP has the same effect as doubling or ½ the MAS on density

44. kVp Changes
The kVp setting must be changed by at least 4% to produce visual changes an image

45. kVp Changes

46. + 15% kvp % kvp

47. kVp Changes

48. 4% kVp Changes

49. Determining Radiographic Technique The Patient Factor
The most difficult task for technologists… evaluating your patient
The patient size, shape, and physical condition greatly influences the technique selection

50. 4 general states of body habitus

51. Radiographic Technique
Technique charts are based on the “average patient”
The thicker the part the more x-radiation is required to penetrate. Calipers should be used
Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

52. Technique In general, Soft tissue = low kVp and high mAs
Extremity (soft tissue & bone) = low kVp
Chest (high subject contrast) = high kVp
Abdomen (low subject contrast) = middle kVp

53. Low Subject Contrast

54. OD = amount of black on image

55. Film Screen Overexposed
Referring to a radiograph that is too dark because too much x-radiation reached the image receptor
Underexposed
Referring to a radiograph that is too light because too little x-radiation reached the image receptor

56. Technique - Pathology
Pathology can severely affect the technologist technique selection
Always question your patients about health status
If prior images are available…check them!

57. Pathology Can appear with increased radiolucency or radiopacity
Some pathology is destructive causing tissue to be radiolucent
Others can be additive causing tissue to be radiopaque

58. OD vs tissue attenuation

59. Technique selection – Fixed kVp
For each anatomic part there is an optimum kVp
mAs is varied based on part thickness or pathological condition

60. QUESTIONS ABOUT TECHNIQUE ?