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Thread Subject:
MTF related

Subject: MTF related

From: Rajesh

Date: 12 Oct, 2010 08:16:03

Message: 1 of 2

Hello there,

I am trying to find the modulation transfer function (MTF) of a digital radiography system using an 'edge method'. The pixel size is 127 micron ( 0.127mm).

For this, first i get the Edge response function of a sharp edge of a metal from its radiograph. its nothing but the line profile across the edge. the grey values plotted against pixel number. Then i am supposed to find the Line Spread Function (LSF) by taking the first order darivative of ERF. Then do an FFT (fast Fourier) on the LSF to get the MTF.

I then normalise the MTF to 0-100% range.
Now,
 the question is if i have to plot this MTF against spatial resolution of the system in lp/mm (line pair per mm or cycles per mm) how should i calibrate the abscissa using the pixel size given above.
(since all along i have found the ERF, LSF using pixel numbers and therefore the MTF is obtained with spatial frequency expressed in cycles/pixel.
What i mean is If i directly multiply the abscissa with pixel/mm, a constant(1/0.127), will it be correct.
Or Am i suppose to do this conversion much earlier i.e. at the calculation of ERF or LSF stage?
or is it something other than the two above
hope i am clear.

regards.

ps- may be this is more about mathematics than matlab but since i am using matlab for the purpose that i thought people might have some answers here.

Subject: MTF related

From: Patrick Granton

Date: 1 Nov, 2010 10:41:03

Message: 2 of 2

hey Rajest, I made a script to do this:

It can be found here

http://www.mathworks.com/matlabcentral/fileexchange/28631

Regards

Patrick



"Rajesh " <rv_acharya@rediffmail.com> wrote in message <i915g3$m5i$1@fred.mathworks.com>...
> Hello there,
>
> I am trying to find the modulation transfer function (MTF) of a digital radiography system using an 'edge method'. The pixel size is 127 micron ( 0.127mm).
>
> For this, first i get the Edge response function of a sharp edge of a metal from its radiograph. its nothing but the line profile across the edge. the grey values plotted against pixel number. Then i am supposed to find the Line Spread Function (LSF) by taking the first order darivative of ERF. Then do an FFT (fast Fourier) on the LSF to get the MTF.
>
> I then normalise the MTF to 0-100% range.
> Now,
> the question is if i have to plot this MTF against spatial resolution of the system in lp/mm (line pair per mm or cycles per mm) how should i calibrate the abscissa using the pixel size given above.
> (since all along i have found the ERF, LSF using pixel numbers and therefore the MTF is obtained with spatial frequency expressed in cycles/pixel.
> What i mean is If i directly multiply the abscissa with pixel/mm, a constant(1/0.127), will it be correct.
> Or Am i suppose to do this conversion much earlier i.e. at the calculation of ERF or LSF stage?
> or is it something other than the two above
> hope i am clear.
>
> regards.
>
> ps- may be this is more about mathematics than matlab but since i am using matlab for the purpose that i thought people might have some answers here.

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