Radiographic factor

1. Dr Saket Jain

2. 

Degree of blackening within the image
Defined more accurately when type of
image receptor is considered
1- Photographic film
2- Digital image capture

3. 

1)
2)
3)
Difference in density between structures of
interest within the image .
Built up in three main stages
Subject contrast
Radiographic contrast
Subjective contrast

4. 

1)
2)
3)
4)
Feature of object (subject) under examination
Factors that influence
The region of body under examination
Contrast media
Pathology
Kilo voltage

5. Is the difference in optical density on different
parts of the processed film or differences in
computer screen brightness and depends on
1) Subject contrast
2) Scattered radiation reaching the image
receptor
3) Image acquisition device
4) Film fog
5) Exposure
6) Development


6. The personal appreciation of the contrast in
the image
 Depends on
1) Radiographic contrast
2) The observer
3) Viewing condition
4) Computer screen / monitor


7. 

For a given FFD (focus to film distance) the
greater the distance between the object and
the film the greater will be the magnification
of the image .
image size
FFD
Magnification =
=
object size
FOD
FOD – focus to object distance

9. 
Distorted image will be produced if not all
parts of the image are magnified by the same
amount .

Beam is right angle to object = distorted
elongated image is produced

Beam is right angle to image receptor than
the foreshortened image is produced

11. The aim is to produce an image that is as
sharp as possible in order to resolve fine
detail within the image
 Important for looking subtle fractures
 Factor lead to UNSHARPNESS
1) Geometry
2) Movement
3) Absorption
4) Photographic / acquistion factors


12. 
Degree increases by increased focal spot size
and increased object to film distance
object to film distance
x focal spot size
object to focus distance

14. 
Sharpness can be increased by using a
shorter exposure time (lower mAs with
higher KVp , higher mA or greater tube
loading time) by small object to film distance
& immobilisation .

16. The choice of factors will depend on the region
being examined .
 Exposure factors to be selected are
1) The mAs
2) The kilovoltage
3) The FFD – focus to film distance


17. 



MA = tube current = number of electrons and
quantity of x-rays produced Intensity
X-ray tube current and exposure time (sec)
Density is diectly related
General rule – mA should be as high as
possible with a short time , to reduce the risk
of movement unsharpness

18. 


KVP = Energy of x-rays = higher penetrability,
it moves through tissue Density directly but
not linearly related
Contrast depends
Halving or doubling mAs is equivalent to
increasing or decreasing kVp by 10-15%

19. 



X-ray tube not to be too closed
Short FFD could give unacceptable geometric
unsharpness
FFD not to be excessive otherwise the large
increase in mAs required would mean high
tube loading
Most radiographic examinations are carried
out at 100 cms

20. Focus to Film distance :
new dist 2
New mAs
x original mAs
old dist 2


21. 

Undesirable fluctuation in optical density of
the image .
If image acquisition device is used , then an
insufficient mAs will manifest as noise or
mottle .

22. 
Radiographic variables Density
Contrast
Increase MAS
Decrease MAS
increase KVP
decrease KVP
increase FFD
decrease FFD
increase OID
decrease OID
no change
no change
decrease
increase
no change
no change
increase
decrease
increase
decrease
increase
decrease
decrease
increase
decrease
increase

23. increase collimation
decrease collimation
decrease
increase
increase
decrease

24. 200 cm
150 cm
100 cm

28. GEOMETRIC
MOVEMENT
PHOTOGRAPHIC
A
Use fine focus,
standardized(large) FFD
Use short exposure time
with high tube loading
Use fine grained screens,
single sided emulsion
B
Use small OFD , avoid
equipment vibration
Use small OFD ;
Ensure all cassettes
immobilization ; make
maintain good film /
patient comfortable ; give screen contact
clear instructions to
patient about keeping
still
OFD – object to film distance