finding unfiltered backprojection and laminogram

I have to generate a sinogram of a phantom image and use back projection to plot my laminogram. I cannot use Radon or iRadon matlab functions. I am able to generate the sinogram but I am having difficulty finding the laminogram. Where am I going wrong? My code is:

clc;
close all;
clear;
% The radon transform of Circle Phantom
image=imread('CirclePhantom.tif');
% pad the image with zeros
padimage = [2,2];
image= padarray(image,padimage);
% Original image
subplot(2,3,1)
imagesc(image);
colormap('gray');
title('Circle Phantom')
xlabel('X')
ylabel('Y')
% Theta is 0:180 with the increment of 0.5 degrees
freq = 0.5;
thetas = 0:freq:180;
% compute sinogram / radon transformation
gtheta  = length(thetas);
gl = size(image,1);
sinogram = zeros(gl,gtheta);
% loop for the number of angles
for i = 1:length(thetas)
   tmpImage      = imrotate(image,-thetas(i),'bilinear','crop');
   sinogram(:,i) = sum(tmpImage);
end
subplot(2,3,2)
imagesc(sinogram);
title('Circle Sinogram');
xlabel('l');
ylabel('\theta');

% The inverse radon transform with only 1 back projection that is theta = 0
thetas=0;
Fl = size(sinogram,1);
Ftheta  = length(thetas); 
% convert thetas to radians
thetas = (pi/180)*thetas;
% set up the backprojected image
g0 = zeros(Fl,Fl);
% find the middle index of the projections
Fmid = ceil(Fl/2);
% set up the coords of the image
[x,y] = meshgrid(ceil(-Fl/2):ceil(Fl/2-1));

% loop over each projection
for i = 1:Ftheta
    % Using the back projection formula
    rotCoords = Fmid+round(x*sin(thetas(i)) + y*cos(thetas(i)));
%     % check which coords are in bounds
%     indices   = find((rotCoords > 0) & (rotCoords <= Fl));
%     newCoords = rotCoords(indices);
    % summation
    rotCoords=floor(abs(rotCoords));
    g0 = g0 + sinogram(rotCoords,i)./Ftheta;
end
subplot(2,3,3);
imagesc(g0);
title('Simple backprojection')
xlabel('X')
ylabel('Y')

Answer 1

[Simon]

Did you solve this problem? Can you please point it out?