EIDORS: Electrical Impedance Tomography and Diffuse Optical Tomography Reconstruction Software

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Modifying EIDORS data structures and models

EIDORS Stimulation patterns

In this tutorial, we explore using different 16 electrode configurations for 3D EIT. Assume that we have a 16 electrode adjacent stimulation, adjacent measurment system. Of course, the electrodes can be placed anywhere, and the corresponding images reconstructed.

% Explore Stimulation Patterns
% $Id: tutorial030a.m 1535 2008-07-26 15:36:27Z aadler $

% 3D Model
imdl_3d= mk_common_model('n3r2',16);
fmdl= imdl_3d.fwd_model;

% Show opposite pattern
fmdl.stimulation=mk_stim_patterns(16,2, '{op}','{op}', ...
             {'meas_current','no_redundant'} );
subplot(121)
display_meas(fmdl,'ya')

% Show adjacent pattern
fmdl.stimulation=mk_stim_patterns(16,2, '{ad}','{ad}', ...
             {'no_meas_current','do_redundant'} );
subplot(122)
display_meas(fmdl,'ya')

print -r75 -dpng tutorial030a.png;

Figure: Two layer 16 ring FEM models with different stimulation patterns.

Using 16 electrodes from a 32 electrode model

% Explore Stimulation Patterns
% $Id: tutorial030b.m 1535 2008-07-26 15:36:27Z aadler $

% We have a 16 electrode EIT machine with adjacent drive
adjdrv= mk_stim_patterns(16,1, '{ad}','{ad}', ...
             {'no_meas_current','do_redundant'} );

% Arrange 16 electrodes in a zigzag
zigzag_mdl= fmdl; zigzag_mdl.stimulation= adjdrv;
zigzag_pat= [ 1:2:15;
             18:2:32]; 
zigzag_mdl.electrode= fmdl.electrode( zigzag_pat(:) );

subplot(131); display_meas(zigzag_mdl,'y')

% Arrange 16 electrodes as planar
planar_mdl= fmdl; planar_mdl.stimulation= adjdrv;
planar_pat= [ 1:2:15;
             17:2:32]'; 
planar_mdl.electrode= fmdl.electrode( planar_pat(:) );

subplot(132); display_meas(planar_mdl,'y')

% Arrange 16 electrodes as planar-opposite
pl_ops_mdl= fmdl; pl_ops_mdl.stimulation= adjdrv;
pl_ops_pat= [ rem( (0:7)*3, 8)*2+1;
              rem( (0:7)*3, 8)*2+17]'; 
pl_ops_mdl.electrode= fmdl.electrode( pl_ops_pat(:) );

subplot(133); display_meas(pl_ops_mdl,'y')

print -r75 -dpng tutorial030b.png;

Figure: Three different ways to place 16 electrodes on a 32 electrode phantom. Left: Zigzag, Middle: Planar, Right: Planar-opposite,

Reconstruct images with different electrode placements

% Explore Stimulation Patterns - and reconstruct images
% $Id: tutorial030c.m 1535 2008-07-26 15:36:27Z aadler $

% Define an image
sim_img= eidors_obj('image', 'stimulation image');
sim_img.elem_data= ones( size(zigzag_mdl.elems,1) ,1);

% Simulate homogeneous measurements
sim_img.fwd_model= zigzag_mdl;
zigzag_data_h= fwd_solve( sim_img );

sim_img.fwd_model= planar_mdl;
planar_data_h= fwd_solve( sim_img );

sim_img.fwd_model= pl_ops_mdl;
pl_ops_data_h= fwd_solve( sim_img );

% Create targets in image
sim_img.elem_data([390,391,393,396,402,478,479,480,484,486, ...
                   664,665,666,667,668,670,671,672,676,677, ...
                   678,755,760,761])= 1.15;
sim_img.elem_data([318,319,321,324,330,439,440,441,445,447, ...
                   592,593,594,595,596,598,599,600,604,605, ...
                   606,716,721,722])= 0.8;

% Simulate inhomogeneous measurements
sim_img.fwd_model= zigzag_mdl;
zigzag_data_i= fwd_solve( sim_img );

sim_img.fwd_model= planar_mdl;
planar_data_i= fwd_solve( sim_img );

sim_img.fwd_model= pl_ops_mdl;
pl_ops_data_i= fwd_solve( sim_img );


%Add 25dB SNR noise to data
noise= std(zigzag_data_i.meas - zigzag_data_h.meas) ...
       / 10^(25/20) * randn(size(zigzag_data_h.meas));

zigzag_data_i.meas= zigzag_data_i.meas + noise;
planar_data_i.meas= planar_data_i.meas + noise;
pl_ops_data_i.meas= pl_ops_data_i.meas + noise;


%Reconstruct and show images
slices= [inf,inf,2.0,1,1; inf,inf,1.0,1,2];

subplot(131)
imdl_3d.fwd_model= zigzag_mdl;
img= inv_solve(imdl_3d, zigzag_data_h, zigzag_data_i);
show_slices(img, slices);

subplot(132)
imdl_3d.fwd_model= planar_mdl;
img= inv_solve(imdl_3d, planar_data_h, planar_data_i);
show_slices(img, slices);

subplot(133)
imdl_3d.fwd_model= pl_ops_mdl;
img= inv_solve(imdl_3d, pl_ops_data_h, pl_ops_data_i);
show_slices(img, slices);

print -r75 -dpng tutorial030c.png;

Figure: Reconstructions with three different ways to place 16 electrodes on a 32 electrode phantom. Left: Zigzag, Middle: Planar, Right: Planar-opposite. As expected, image quality is worse (at 25dB SNR) than for the 32 electrode case a 20dB SNR.