linearity of x-ray film/autorads

Leonard N. Bloksberg bloksber at pilot.msu.edu
Mon Jan 24 12:02:00 EST 1994


In Article <1994Jan21.181718.27088 at galileo.cc.rochester.edu> "DSCT at BPHVAX.BIOPHYSICS.ROCHESTER.EDU (DAVID SCOTT)" says:
> We qould like to know across what range x-ray film (autorads) are
> going to be linear in signal. Example. We are looking at differant
> methods of scanning autoradiograms, and quantitating signal. We are
> looking at northerns and genomic southerns. Scanners can handel from
> 1.7 to 4.0 O.D. (depending on method of scanning, $ spent), so
> we are wondering what the film can handle. Buying a scanner that is
> more accurate than the film seems like a waste of money. Comments 
> or answers would be greatly aprecciated.
> 		-Gavin Fischer
> 		University of Rochester Cancer Center
> 
.
First, it is VERY important to remember that the response of X-Ray film is 
absolutely NOT linear.  In order to make the film response linear, you must
first pre-flash the film.  Amersham used to publish a wonderful primer on
the subject, fully referenced, with elegant graphs to show the response of
x-ray film under various conditions.  I believe it is Amersham bulletin 
#23.  In it, they explain that film can be preflashed with a standard camera
flash, calibrated to darken the film to 0.2 to 0.4 absorbence units at 540nm.
Only then will the film respond in a linear manner to the the sygnal from
your blot.  Good Luck.
.
	Leonard N. Bloksberg
	bloksber at pilot.msu.edu
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