how to fuse image

Dear all,

this is my code to view CT image by slice

P = zeros(256, 256, 72);
for K = 1 : 72
    petname = sprintf('I4%03d.dcm', K);
    P(:,:,K) = dicomread(petname);
end
imshow3D(P)

then, this is my code for view SPECT image by slice,

Noted: all my 512 slice SPECT image stored in one file.

[spect map]=dicomread('128x128');
info = dicominfo('128x128');
gp=info.SliceThickness;
spect=(squeeze(spect));%smooth3

aa=size(spect);aa=aa(3);

imshow3D(spect);

Anybody can help me to fuse both SPECT and CT images?