Tuesday 18 February 2014

FRCR MCQ --- WEINER SPECTRUM

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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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