A radiograph that faithfully reproduces
structure and tissue is identified as a
high quality radiograph.
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
4) “Detail( definition)…visual quality that depends upon
sharpness and contrast.”
Characteristics of image
Noise mean any signal that does
not convey useful information of
Signal to noise ratio
Optimum condition :magnitude of
signal > magnitude of noise
Signal to noise ratio is low
:loss of information
Un-useful part of x-ray beam, have no
use in diagnostic purpose.
scattered radiation reaching to the
image receptor also increases noise to
Can be controlled by stationary or
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.
High contrast; means harsh, with lots of
dense blacks and brilliant white
Contrast level at a
Image appear dull,
lacking in any true
black and whites
level tends to be
neither very high
nor very low and is
Sharpness is concerned with how
suddenly blackening changes at the
boundary between adjacent part
THE INABILITY OF FILM
SCREEN SYSTEM TO
RECORED THE SHARP EDGE.
IMAGE UNSHARPNESS MAY BE
EXPRESS IN FOLLOWINF WAYS;
EDGE SPREAD FUNCTION.
POINT SPREAD FUNCTION.
LINE SPREAD FUNCTION.
EDGE SPREAD FUNCTION; THE
MICRO DENSITOMETER SHOWS
VARIATION IN IMAGE DENSITY
ACROSS A BOUNDRY IS CALLED
EDGE SPREAD FUNCTION
POINT SPREAD FUNCTION
VARIATION IN IMAGE AT POINT.
POINT STRUCTURE IN AN
OBJECT PRODUCE A SHARP
LINE SPREAD FUNCTION
THAT SHOWING VARIATION IN
LINE WHICH PRODUCE A LINE
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
Ex- bone- soft tissue interface, breast micro-
calcification, calcified lung nodule.
Contrast resolution- ability to image
anatomic structures of similar subject
Ex- liver –spleen & gray matter- white matter.
Lower noise results in a better
radiographic image, because it
improves contrast resolution.
Modulated transfer function
The object should contain a mesh or
grid of closely spaced
lines,alternatively radiopaque and
Spacing of the line pairs is expressed
as a spatial frequency
Modulated transfer function
Resolution of different imaging system
may be compared objectively by
reference to the modulated transfer
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
MTF CAN NEVER BE GREATER THAN 1
MFT = information recorded