image fusion dicom spect ct

Hi all, Please help me. i want to fuse image between spect and ct. but my problem is the image fused does not match each other. Below is my coding. Here i attached also my result picture.

let say my image info like:

spect = I4049.dcm, dimension 256x256

ct =128x128, dimension 128x128

A = dicomread('I4049.dcm');
RA = imref2d(size(A));
B = dicomread('128x128'); 
B1 = imresize(B,[256 256]);
RB1 = imref2d(size(B1));
RB1.XWorldLimits = RA.XWorldLimits;
RB1.YWorldLimits = RA.YWorldLimits;
C = imfuse(A,B1,'falsecolor','Scaling','joint','ColorChannels',[1 2 0]);
C = imresize(C,0.5);
imshow(C)
[D,RD] = imfuse(A,RA,B1,RB1,'ColorChannels',[1 2 0]);
D = imresize(D,0.5);
imshow(D)

[Muhammad Rehan Afzal]

it may be due to slice thickness and other parameters are different.

i think try registration of images first then apply image fusion