function x = mri_timecourse(images, roi, ref_frame, filter);

x = []; 
for i= 1:length(images),
    x = [x, sum(images(i).data(roi))];
end;
if (nargin>2) & (ref_frame>0),
    x = (x./sum(images(ref_frame).data(roi))-1)*100;
end;

if (nargin>3) & (filter>0),
    lp = exp(-(-4:1/filter:4).^2/2); lp = lp/sum(lp);
    baseline = conv(x, lp);
    w = (length(lp)-1)/2;
    x = x - baseline(w: length(x)+w-1);
end;

% plot(x);