Find execution time of parallel program

I have written parallel program for HYPR algorithm. Basically it reconstructs an image with slices with the help of radon and iradon functions.It takes more time to reconstruct an image (60s). I have written parallel program for it using to workers and the execution time is 39s.( I have found execution time using tic and toc). Now when i try with workers 3 and more there is no significant change in time. MY laptop is i2 core. How to find an execution time of parallel program?

my code is: clear all; % M=input('Enter the number of time frames:'); % N=input('Enter the number of projections:'); Theta_in=0; Theta_end=360; Composite=0; Z_1=0;Z=0;

Theta=0; Theta1=72; Theta2=168;

% divide angles from initial to end in M*N equal divisions % Theta=linspace(Theta_in,Theta_end,M*N);

% Read dicon images files = dir(fullfile(pwd,'*.dcm')); j=1; k=5; l=9; z=0; time1=0; matlabpool open local 3 PP = Composite(); PP1 = Composite(); PP2 = Composite();

spmd % Composite Image tic for i= 1:12 if labindex==1 && j<=4 img = dicomread(fullfile(pwd,files(j).name)); for z= 1:24 FP=radon(img,Theta); FBP=iradon(FP,Theta); f=fspecial('gaussian'); fil=imfilter(FBP,f);

            % padding of image
                  padimg= padarray(fil,[50 50],0,'both');
            % Rotating image
                  Rotate=imrotate(padimg,Theta,'crop');
                     Theta=Theta+1;
            % Formation of composite image      
               PP= PP+ Rotate;

            end;
              j=j+1; 

    end;

     if labindex==2 && k<=8

    img = dicomread(fullfile(pwd,files(k).name));
            for z=1:24
            FP=radon(img,Theta1);
             FBP=iradon(FP,Theta1);
             f=fspecial('gaussian');
             fil=imfilter(FBP,f);

            % padding of image
                  padimg= padarray(fil,[50 50],0,'both');
            % Rotating image
                  Rotate=imrotate(padimg,Theta1,'crop');
            % Formation of composite image      
               PP1= PP1+ Rotate;
                  Theta1=Theta1+1;

            end;
        k=k+1;

     end;

        if labindex==3 && l<=12

     img = dicomread(fullfile(pwd,files(l).name));
             for z=1:24
             FP=radon(img,Theta2);
              FBP=iradon(FP,Theta2);
              f=fspecial('gaussian');
             fil=imfilter(FBP,f);

             % padding of image
                   padimg= padarray(fil,[50 50],0,'both');
             % Rotating image
                   Rotate=imrotate(padimg,Theta2,'crop');
             % Formation of composite image      
                PP2= PP2+ Rotate;
                   Theta2=Theta2+1;

             end;
         l=l+1;

       end;

    % lab2=lab2+toc;
end;
toc
end;

%PP2=PP{1}+PP1{2}; %PP2=PP2/12; figure,imshow(PP{1},[]); title('labindex 1'); figure,imshow(PP1{2},[]); title('labindex 2'); figure,imshow(PP2{3},[]); title('labindex 3'); PP2=(PP{1}+PP1{2}+PP2{3}); figure,imshow(PP2,[]); title('Combined'); matlabpool close;