Sunday 16 February 2014

FRCR MCQ--Line spread function

Line spread function 

Q.True regarding line spread function graphs is/are.
a. relative density increases with distance away from slit line
b. microdensitometer is needed to read micro variation in               density over large area
c. the less the light diffusion ,the sharper will be image
d. the image will be sharper with slower screen rather than fast      screen

e. the LSF of x ray film exposed without screens is more easy to measure


ANS====cd----In line spread function graphs relative density decreases with distance away from slit line source of x ray.The photographic effect of the x-ray beam is spread over a total distance of 800 or more micron while width of slit is 10 microns.

Microdensitometer is needed to measure film density over such small area ,say 800microns .

The LSF of x ray film exposed without screens is difficult to measure because there is almost no diffusion of x rays and secondary electrons in the film,so the LSF is narrow.

 [Chapter 14,Page 209,  4th edition ,1990  reprinted 2010 , Christensen’s Physics of Diagnostic radiology].

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