Hi,
i worked several weeks with et_project et_backproject using matlab with normal volume sizes(N = 192 )without problems. I decided to move to higher resolutions, but wrong results returned when N increased to 256 using ET_DEMO_MLEM.
Are you normally able to work with N>192?

here is my results for CPU(left) and GPU(right).
CPU parameters:
N = 256;
N_cameras = 120;
cameras = linspace(0,2*pi,N_cameras)';
psf = ones(5,5,N);
N_counts = 50e6;

iter_mlem = 2;
GPU = 0;

phantom_type = 1; % 0 for 'brain FDG PET'; 1 for 'sphere in uniform background'

GPU parameters:
N = 256;
N_cameras = 120;
cameras = linspace(0,2*pi,N_cameras)';
psf = ones(5,5,N);
N_counts = 50e6;

iter_mlem = 2;
GPU = 0;

phantom_type = 1; % 0 for 'brain FDG PET'; 1 for 'sphere in uniform background'

I build my own niftyrec(msvc2008, matlab 64bit, cuda 4.1.28). There was linking problem with m.lib so i removed this file from additional dependencies.
I changed my video card from old GF 8800GT 512MB to GF 670 4GB. Am afraid that is possible, that old drivers wasn't uninstalled perfectly. I used standard nvidia uninstall to remove old drivers before changing a card and installed new drivers after rebooting with new card.

Hi I didn't tried 256x192x256.

What I tried is several experiments with different cube size(NxNxN),different cuda version and different niftyrec version, there is my results:

Niftyrec 166, Cuda 4.2 64bit, matlab 64bit, N = 64,128,192 OK, 256-448 Constant output(same as on previous picture), 512 - error due the memory allocation(seems that memory requirement was higher than my 4GB on the card)

Niftyrec 168, Cuda 4 64bit, matlab 64bit, N = 64 artifacts in the image,N=128 OK, N=192 artifacts in the image, N= 256 matlab crush

Niftyrec 168, Cuda 5 64bit, matlab 64bit, N = 64,128 OK, N= 192 artifacts in the image, N= 256 matlab crush

Do you still want the 256x192x256 experiment? My codes does not work with non cubic volume. Do you have working example?

I hope this will be usefull for you.

Hi Stefano,
there is output of et_demo_mlem_noncube.m

??? Error using ==> et_backproject_mex
niftyrec: ERROR - unspecified error.

Error in ==> et_backproject at 96
image = et_backproject_mex(sinogram, cameras, attenuation, psf, use_gpu, background, background_attenuation,
truncate_negative_values);

Error in ==> et_demo_mlem_noncube at 39
norm = et_backproject(ones(N,m,length(cameras)), cameras, attenuation, psf, GPU) ;

Same result for N= 192;m = 128; and N= 256;m= 192;

This function does not end with error for N= 64;m= 64; but output is constant "white".

Sorry for late

Lukas