1.
Image characteristics

2.
 A radiograph that faithfully reproduces
structure and tissue is identified as a
high quality radiograph.

3.
What is image quality?
 Good technique requires considerable skill. It can be.
 1)Acquired only by practice and experience..” Factors are time,
distance, milli amperage and voltage .
 2) Image must have adequate “density (the degree of blackness)
 3) “Contrast….. characteristic that permits differentiation
between” densities..
 4) “Detail( definition)…visual quality that depends upon
sharpness and contrast.”

4.
Characteristics of image
Noise
Contrast
Sharpness
Resolution

5.
Noise
 Noise mean any signal that does
not convey useful information of
the subject.

6.
Signal to noise ratio
 Optimum condition :magnitude of
signal > magnitude of noise
Signal to noise ratio is low
:loss of information

7.
 Scatter radiation-
 Un-useful part of x-ray beam, have no
use in diagnostic purpose.
 scattered radiation reaching to the
image receptor also increases noise to
radiographic image.
 Can be controlled by stationary or
moving grid

8.
contrast
 The brightness ratio of the lightest
to the darkest part of an image or
difference in density or luminance
 BOUNDRY BETWEEN DARK AND
LIGHT AREA APPEAR SHARPLY.
TYPES:
HIGH CONTRAST.
LOW CONTRAST.
OPTIMUM CONTRAST.

9.
High contrast; means harsh, with lots of
dense blacks and brilliant white

10.
LOW CONTRAST
 Contrast level at a
minimum
 Image appear dull,
lacking in any true
black and whites

11.
OPTIMUM CONTRAST
 Optimum contrast
level tends to be
neither very high
nor very low and is
different for
different subjects

12.
SHARPNESS
Sharpness is concerned with how
suddenly blackening changes at the
boundary between adjacent part

13.
UNSHARPNESS
 THE INABILITY OF FILM
SCREEN SYSTEM TO
RECORED THE SHARP EDGE.

14.
 IMAGE UNSHARPNESS MAY BE
EXPRESS IN FOLLOWINF WAYS;
 EDGE SPREAD FUNCTION.
 POINT SPREAD FUNCTION.
 LINE SPREAD FUNCTION.

15.
 EDGE SPREAD FUNCTION; THE
MICRO DENSITOMETER SHOWS
VARIATION IN IMAGE DENSITY
ACROSS A BOUNDRY IS CALLED
EDGE SPREAD FUNCTION

16.
POINT SPREAD FUNCTION
 MICRODENSITOMETER SHOWS
VARIATION IN IMAGE AT POINT.
 POINT STRUCTURE IN AN
OBJECT PRODUCE A SHARP
IMAGE.

17.
LINE SPREAD FUNCTION
 MICRODENSITOMETER TRACE
THAT SHOWING VARIATION IN
LINE WHICH PRODUCE A LINE
IMAGE..

18.
RESOLUTION
 It is the ability of the system to demonstrate
closely spaced structures in the subject as
separate entities in the image
 Spatial resolution- ability to image
small objects that have high subject
contrast.
 Ex- bone- soft tissue interface, breast micro-
calcification, calcified lung nodule.
 Contrast resolution- ability to image
anatomic structures of similar subject
contrast.
 Ex- liver –spleen & gray matter- white matter.

19.
 Lower noise results in a better
radiographic image, because it
improves contrast resolution.

20.
Modulated transfer function
 The object should contain a mesh or
grid of closely spaced
lines,alternatively radiopaque and
radiolucent.
 Spacing of the line pairs is expressed
as a spatial frequency

21.
Modulated transfer function
 Resolution of different imaging system
may be compared objectively by
reference to the modulated transfer
function.
 It is charectestic of imaging system
that as the detail in the object
becomes more finer , the ability of the
system to record the detail becomes
progressevely reduced

22.
MTF CAN NEVER BE GREATER THAN 1
 MFT = information recorded
information available

23.
DENSITY CONTRAST RESOLUTION
kvp Directly
proportional
Inversly
proportional
……
mA Directly
proportional
Directly
proportional
directly
THICKNESS Inversly
proportional
inversly inversly
FFD inversly inversly inversly
FOCAL SPOT
SIZE
directly inversly inversly

24.
 THANK U