Help Needed - Shift observed on reconstructed slices

[alex-feb]

Hi
I came across this algorithm recently and I tried to reconstruct using FBP algorithm. The reconstructed images has the objects in every slices in shifted manner. My object size is around 55mm and tried to reconstruct into 110 slices each of 0.5mm. My machine parameters are shared below in the parameter settings. The image are taken from the machine with a static detector. I am sharing the projection data as mat file along with a reconstructed slice in jpg format. It would be helpful for if you can provide me some inputs for resolving this.

The projection data is available in below link
https://www.sendspace.com/file/emnp03

%% Physical Parameters Settings
% Breast voxels density
parameter.nx = 2304; % number of voxels (columns)
parameter.ny = 2945; % number of voxels (rows)
parameter.nz = 110; % number of voxels (slices)

% Detector panel pixel density
parameter.nu = 2304; % number of pixels (columns)
parameter.nv = 2945; % number of pixels (rows)

% Single voxel real size (mm)
parameter.dx = 0.098;
parameter.dy = 0.098;
parameter.dz = 0.5;

% Single detector real size (mm);
parameter.du = 0.098;
parameter.dv = 0.098;

% X-ray source and detector distances
parameter.DSD = 650; % Distance from source to detector (mm)
parameter.DSO = 608; % Distance from source to the top of object (mm)
parameter.DDR = 12; % Distance from detector to pivot (mm)
parameter.DSR = parameter.DSD - parameter.DDR; % Distance from source to pivot (mm)
parameter.DAG = 1; % Distance of Air Gap (mm)

% Detector and object full real sizes (mm)
parameter.sx = parameter.nx.*parameter.dx;
parameter.sy = parameter.ny.*parameter.dy;
parameter.sz = (parameter.nz.*parameter.dz)+parameter.DAG;
parameter.su = parameter.nu.*parameter.du;
parameter.sv = parameter.nv.*parameter.dv;

% Detector and object Volume grid settings
parameter.xs = (parameter.nx-1:-1:0)*parameter.dx;
parameter.ys = (-(parameter.ny-1)/2:1:(parameter.ny-1)/2)*parameter.dy;
parameter.zs = (0:1:parameter.nz-1)*parameter.dz + parameter.DAG;
parameter.us = (parameter.nu-1:-1:0)*parameter.du;
parameter.vs = (-(parameter.nv-1)/2:1:(parameter.nv-1)/2)*parameter.dv;

% Number of Projections
parameter.nProj = 7;

% Angle settings (Degrees)
parameter.tubeAngle = 12; % Tube Angle
parameter.tubeDeg = linspace(-parameter.tubeAngle/2,parameter.tubeAngle/2,parameter.nProj);

parameter.detAngle = 0; % Detector Angle
parameter.detectorDeg = linspace(-parameter.detAngle/2,parameter.detAngle/2,parameter.nProj);

%% General parameters

% Slice range to be saved
parameter.sliceRange = 1:parameter.nz;
% Region of interest (ROI) to store
parameter.iROI = 1:parameter.ny;
parameter.jROI = 1:parameter.nx;

% Bit number quatization
parameter.bitDepth = 16; % Load from dicom header

Regards

[rodrigovimieiro]

Hello, thanks for the report.

Are the projections already in terms of attenuation coefficients?

I will look into that.

Best.

[rodrigovimieiro]

I flipped the parameter.tubeDeg, because your data seems to be arranged coming from positive angles. Thats the output of the angles:

parameter.tubeDeg = 6 4 2 0 -2 -4 -6

Your object seems to be placed around 48.5mm on the Z axis. Is it right? It is coming in focus approximately at slice 97, as you can see in the figure:

I uploaded the results here.

Let me know if is that what you were expecting. Otherwise, we can analyze it further.

Best.