x ray Image quality

1. IMAGE QUALITY

2. Radiographic Quality
 Radiographic Quality refers to the fidelity
with which the anatomic structures being
examined are imaged on the film.
 Three main factors:
 Film Factors
 Geometric Factors
 Subject Factors

3.  Characteristic of radiographic quality:
 Spatial Resolution (Recorded Detail)
 Contrast Resolution (Visibility of Detail)
 Noise (Visibility of Detail)
 Artifacts

4. Spatial Resolution
 Resolution is the ability to image two
separate objects and visually
distinguish one from the other.
 Spatial Resolution is the ability to
image small structures that have high
subject contrast such as bone-soft
tissue interface.
 When all of the factors are correct,
conventional radiography has
excellent spatial resolution.

5. Contrast Resolution
 Contrast resolution is the ability to
distinguish structures with similar subject
contrast such as liver-spleen, fat-muscle.
 Computed tomography and MRI have
excellent contrast resolution.
Conventional radiography is fair to poor.

6. Noise
 Noise is an undesirable fluctuation in
optical density of the image.
 Lower noise results in a better
radiographic image because it improves
contrast resolution.
 Two major types:
 Film Graininess- no control over
 Quantum Mottle- some control over

7. Film Graininess
 Film graininess refers to the distribution
in size and space of the silver halide
grains in the film emulsion.
 Similar to structure mottle that refers to
the size and shape of the phosphors in
the intensifying screens.
 Inherent in image receptor, and are
not under the control of technologist,
and they contribute very little to
radiographic noise.

8. Quantum Mottle
 Quantum mottle refers to the random nature
by which x-rays interact with the image
receptor.
 Principal contributor to radiographic noise.
 Image produced with few x rays will have
higher QM than image produced with from
large number of x rays. use of very fast
intensifying screens results in increased QM.
 The use of high mAs , low kVp settings and of
slow image receptors reduces quantum
mottle.

9. Quantum Mottle
 Very fast screens have higher quantum
mottle because it takes fewer x-rays to
make the image.

10. Speed
 Resolution and noise are intimately
connected with speed.
 While the speed of the images receptor is
not apparent on the image, it influences
both resolution and noise.

11. Radiographic Quality Rules
 Fast Image receptors have high noise and
low spatial and contrast resolution.
 High spatial and contrast resolution
require low noise and slow image
receptors.
 Low noise accompanies slow image
receptors with high spatial and contrast
resolution.

12. Film Factors of Quality
 Characteristic curve
 Density
 Contrast
 Latitude
 Processing
 Time
 Temperature

13. Sensitometry
 Sensitometry is the study of the
relationship between the intensity of
exposure of the film and the blackness
after the film is processed.
 Unexposed film is clear with a blue tint
after processing.
 Properly exposed film appears with
various shades of gray.
 Heavily Exposed film is black after
processing.

14. Sensitometry
 Two principles involved.
 Exposure of the film
 Amount of light transmitted through the
processed film of optical density.
 Used to describe the relationship of
radiation exposure and blackness or
optical density on the film.

15. Characteristic Curve
This relationship is
called the
characteristic curve
or H & D curve of
the film.
H & D stands for
Hurter and Driffield.

16. Parts of the Characteristic Curve
Toe and shoulder
low and high ,
exposure levels,
where large
changes in
exposure results in
small changes in
OD.

17. Parts of the Characteristic Curve
 The straight line or
intermediate area is
where very small
changes in exposure
results in large changes
in density.
 This is the important
part of the curve in
radiography,where
properly exposed
radiographs appear.

18. Log Relative Exposure (LRE)
 X-ray films responds to a
wide range of exposure
from 1 mR to 1000 mR.
 It is not the absolute
exposure that is of interest
but rather the change in
OD over each exposure
interval
 Exposure is represented
on logarithmic
manner(log relative
exposurer).

19. Optical Density
 It is not enough to say that OD is the
degree of blackening of a radiograph,or
that a clear area of the radiograph
represent low OD and a black area
represent high OD.
 OD density has a pre size numeric value
that can be calculated if the level of light
incident on a processed film(Io)and the
level of light transmitted through that
film(It) are measured.
 OD=log10 Io/It

20. Optical Density Range
 The optical density
range is from 0.0 to
4.0 corresponding to
clear and absolute
black repectively.
 Useful range in
general radiography
is from 0.5 to 2.25.
 Image range is 0.5 to
1.25 OD

21. Fog density and base density
 Most unexposed and processed film has an
OD in the range of 0.1 to 0.3,corresponding to
79% and 50% transmission, respectively.these
ODs of unexposed film are due to base
density and fog density.
 Base density is inherent in the base of the film
and is due to the composite of the base and s
the tint added to the base.
 Fog density results from development of silver
grains that contain no useful
information.higher fog density reduces the
contrast of the image.

22. Base fog or base density
The tint of the base
of the film and the
inadvertent
exposure of the
during processing.
Range is from 0.1 to
0.3. Should be never
above 0.30 most is
.21 OD

23. Items that Impact Base Fog
 Film storage
 Film exposure to wrong spectrum of light
or light intensity.
 Chemical contamination.
 Improper processing.
 High Base fog levels reduce contrast.

24. Contrast
The variations in the OD in the
radiograph is called radiographic
contrast.
Marked differences in OD----High
contrast radiograph.
OD differences are small----Low
contrast radiograph

25.  Radiographic Contrast is the combined
result of image receptor contrast and
subject contrast.
 Image receptor contrast refers to the
contrast inherent in the film and
influenced by the processing of the film.

26. Contrast
 Subject contrast is determined by the size,
shape and x-ray attenuating
characteristics of the subject being
examined and the energy (kVp) of the x-
ray beam.

27. Image Receptor Contrast
 Inherent to the film and screen
combination but is influenced by:
 Range of Optical Density
 Film Processing Technique
 Film type is determined by the type of
intensifying screens used.
 Film-screen images always have higher
contrast compared with direct exposure
images.

28. Image Receptor Contrast
The slope of the
straight line portion
of the H & D curve is
the receptor
contrast.
The average
gradient is a straight
line drawn between
the densities of 0.25
and 2.00 + base
fog.

29. Average Gradient
The average
gradient is a straight
line drawn between
0.25 OD and 2.0 OD
above base plus
fog.
This is the useful
range of optical
density in on most
radiographs.

30. Speed
Speed is the ability
of the receptor to
respond to low x-ray
exposure.
The H & D curve is
useful in comparing
speed when
selecting film or
screens.

31. Speed
 A relative number of 100 given to Par
Speed Calcium Tungstate Screens.
 High Speed Calcium Tungstate has a
speed of 200. Half of the exposure is
needed to produce the same image.
 Rare earth screen film combinations
range is speed from 80 to 1600.

32. Speed
 By knowing the Speed, sometimes
referred to as the Relative Speed Value, it
is easy to convert the technical factors for
one speed to another speed.
 When image receptors are replaced,a
change in mAs setting may be necessary
to maintain the same OD,e.g if image
receptor speed is doubled, the mAs must
be halved.no change is required in kVp.

33. LATITUDE
Latitude can be
observed on the H
& D curve.
Latitude refers to
the range of
exposure that will
produce a
diagnostic range
OD.

34. Latitude
Latitude and
Contrast are
inversely
proportional.
Wide latitude has a
wide gray scale or
low contrast. (B)
Narrow latitude has
a short scale or high
contrast. (A)

35. Latitude
 Latitude is designed into some screen and
film combinations. With wide latitude, the
error factor in technique is wider.
 Latitude can also be impacted by the
technical factors.

36. Film Processing
Radiographic
Quality is impacted
by film processing
parameters.
The developer must
be at the proper
concentration and
at the correct
temperature.

37. Film Processing
The film must also
spend the correct
amount of time in
the developer.
This is the time &
temperature
relationship.

38. Processing
 Speed and base fog increase with the
temperature.
 Contrast will increase to a point and then
drop with the base fog increase.
 Manufactures set processing parameters
to optimize speed, contrast and low base
fog.

39. THANKS