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WEINER SPECTRUM
Q1.True regarding Weiner spectrum is/are
a. an objective way to measure total noise
b. microdensitometer is used to measure noise
c. microdensitometer detect quantum mottle only
d. a specially designed cassette is needed to measure film grain
e. White noise vary
linearly with spatial frequency
ANS====.abd----Weiner
spectrum is a measure of the total noise recorded by the film(the sum of the
grain noise and the quantum mottle) . The Weiner spectrum of a film- screen
system depict total system noise (quantum plus grain noise),film grain noise
and recorded noise . The lines depicting total (quantum plus grain noise ) and
grain noise are straight lines –that is the amount of noise is same at all
spatial frequencies ,and --that is known as white noise .Microdensitometer
detect not only quantum mottle but film
noise also. [Chapter 14,Page 215-16, 4th
edition ,1990 reprinted 2010 ,
Christensen’s Physics of Diagnostic radiology].
Q2.True regarding Weiner spectrum is/are
a.the ability of film –screen system to record noise
decreases as the spatial frequency increases
b.the inherent film grain white noise is greater for the
fast film than slow film
c.a sharp screen with a fast film has more noise than
that of less sharp(thicker) screen with a slower film
d.the point at which the total recorded noise curve
merges with the film grain noise level indicates the relative MTF of each
screen
e.the screen with better MTF record noise out to higher
frequencies
ANS===abcde[Chapter 14,Page 215-16, 4th edition ,1990 reprinted 2010 , Christensen’s Physics of Diagnostic radiology].
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