exposure factors or prime factors
DESCRIPTION
Exposure Factors or Prime Factors. PRIME FACTORS. What is “technique” ? How does it affect the “image”. 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. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/1.jpg)
Exposure Factors or Prime Factors
1
![Page 2: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/2.jpg)
PRIME FACTORS
What is “technique” ?
How does it affect the “image”2
![Page 3: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/3.jpg)
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
3
![Page 4: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/4.jpg)
PRIME FACTORS
• KVP• MAS• DISTANCE
4
![Page 5: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/5.jpg)
kVp
Kilovolts controls how fast the electrons are sent across the tube
Controls, quality, penetrability & contrast
Increasing kVp also increases scattered photons reducing image quality
Does kVp influence OD?5
![Page 6: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/6.jpg)
“SHORT” VS “LONG” SCALE
6
![Page 7: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/7.jpg)
kVp
• Low kVp (50 – 60)
• Short scale
• High contrast
• “Bone work”
7
![Page 8: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/8.jpg)
kVp
• High kVp (90 – 120)
• Long scale
• Low contrast
• “Chest images”
8
![Page 9: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/9.jpg)
9
![Page 10: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/10.jpg)
10
![Page 11: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/11.jpg)
11
![Page 12: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/12.jpg)
12
![Page 13: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/13.jpg)
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
13
![Page 14: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/14.jpg)
14
![Page 15: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/15.jpg)
Exposure Time
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
15
![Page 16: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/16.jpg)
Distance
Affects exposure of the IR because of the Inverse Square Law
SID largely determines the intensity of photons at the IR
Distance has no effect on radiation quality
16
![Page 17: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/17.jpg)
INTENSITY IS SPREAD OUT…
17
![Page 18: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/18.jpg)
Inverse Square Law Formula
Intensity #1
Intensity #2
Distance #2 - Squared
Distance #1 - Squared
18
![Page 19: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/19.jpg)
SID Changes
19
![Page 20: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/20.jpg)
Direct Square Law
• New mAs = New distance 2
Old mAs Old distance 2
20
![Page 21: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/21.jpg)
Focal-Spot Changes
21
![Page 22: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/22.jpg)
Producing optimal radiographs … key for diagnosing disease
22
![Page 23: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/23.jpg)
How much of the radiation received by the patient
Actually reaches the IR ?
23
![Page 24: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/24.jpg)
About 1%
24
![Page 25: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/25.jpg)
25
![Page 26: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/26.jpg)
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; and
• (3) the x-ray photon is scattered and reaches the film causing an overall gray fog.
26
![Page 27: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/27.jpg)
IMAGES
• DENSITY = THE AMOUNT OF BLACKENING “DARKNESS” ON THE RADIOGRAPH
• CONTRAST – THE DIFFERENCES BETWEEN THE BLACKS TO THE WHITES
27
![Page 28: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/28.jpg)
mAs Changes• at least 20 - 30 % mas change
needed to see a visible change in density
28
![Page 29: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/29.jpg)
mAs DOUBLED = DENSITY DOUBLED
29
![Page 30: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/30.jpg)
+ 25% + 50 % mas
30
![Page 31: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/31.jpg)
mAs Changes
31
![Page 32: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/32.jpg)
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
32
![Page 33: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/33.jpg)
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
33
![Page 34: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/34.jpg)
kVp Changes
• The kVp setting must be changed by at least 4% to produce visual changes an image
34
![Page 35: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/35.jpg)
kVp Changes
35
![Page 36: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/36.jpg)
+ 15% kvp - 15% kvp
36
![Page 37: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/37.jpg)
kVp Changes
37
![Page 38: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/38.jpg)
4% kVp Changes
38
![Page 39: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/39.jpg)
Determining Radiographic TechniqueThe Patient Factor The most difficult task for technologists…
evaluating your patient
The patient size, shape, and physical condition greatly influences the technique selection
39
![Page 40: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/40.jpg)
4 general states of body habitus
40
![Page 41: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/41.jpg)
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)
41
![Page 42: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/42.jpg)
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
42
![Page 43: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/43.jpg)
Low Subject Contrast
43
![Page 44: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/44.jpg)
OD = amount of black on image
44
![Page 45: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/45.jpg)
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
45
![Page 46: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/46.jpg)
Technique - Pathology
Pathology can severely affect the technologist technique selection
Always question your patients about health status
If prior images are available…check them!
46
![Page 47: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/47.jpg)
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
47
![Page 48: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/48.jpg)
OD vs tissue attenuation
48
![Page 49: Exposure Factors or Prime Factors](https://reader033.vdocument.in/reader033/viewer/2022061606/56815c35550346895dca1c13/html5/thumbnails/49.jpg)
Technique selection – Fixed kVp For each anatomic part there is an optimum
kVp
mAs is varied based on part thickness or pathological condition
49