Hi Everyone, I'm looking for help on deconvolving and the fitting of two gamma variates. I'm using MATLAB. My two gamma variates have the form: modelFun = @(p,x) ( p(1) .* ( (x-t0)./(p(2)-t0)).^ p(3).* exp(p(3).*(1-(x-t01)./(p(2)-t01))) .* heaviside2nd(x-t01)); Where P has to be given initial values to perform the fit. Here the function heaviside2nd is the modified version of the heaviside function where Y=1 at X=0 rather than NaN. In my project I have to deconvolve the gamma variate graph Cm with the gamma variate graph AIF. invF [ F(Cm)/F(AIF) ] The thoery says that the AIF (arterial input function) are the average of those brain pixel chosen which have a peak that arrives earlier than average and which have a breadth (FWHM) that is smaller than average, and also the maximum is as large as possible. These are the properties of a concentration bolus that passes through the brain arteries. I use the AIF to determine blood flow in the other regions. The blood flow in the other regions can only be determined if there is an instant injection of blood: hence this is the residue function. Please see: http://s153.photobucket.com/albums/s235/s1020099/?action=view¤t=Afb1.jpg This is a case in which it has gone right. The deconvolved curve shoots up almost instantly and gradualy decreases as the blood leaves the region. But it doesn't always look like this and I don't know why: http://s153.photobucket.com/albums/s235/s1020099/?action=view¤t=Afb2.jpg http://s153.photobucket.com/albums/s235/s1020099/?action=view¤t=Afb3.jpg In the last photo the deconvolved curves oscilates. Is this a sign of noise? But how can there be noise in my sampled analytical gamma varite function? Please help. Maybe I'm not fitting the gamma variate curve right. The curve is fitted to force the concentration to go back to zero. You see that after the main peak the points remain higher than before the peak started. Please can you help? I don't understand why the deconvolution sometimes works great and sometimes gives strange results. I would very much appreciate email contact with some expert in this field too if possible. Thanks. _____________________________________ Do you know a company who employs DSP engineers? Is it already listed at http://dsprelated.com/employers.php ?

# deconvolution and fitting of gamma variates

Started by ●May 24, 2007