mri_vol_data.cpp

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//=============================================================================================================
 
//=============================================================================================================
// INCLUDES
//=============================================================================================================
 
#include "mri_vol_data.h"
 
//=============================================================================================================
// USED NAMESPACES
//=============================================================================================================
 
using namespace MRILIB;
using namespace Eigen;
 
//=============================================================================================================
// DEFINE MEMBER METHODS
//=============================================================================================================
 
MriVolData::MriVolData()
: version(0)
, width(0)
, height(0)
, depth(0)
, nframes(0)
, type(MRI_UCHAR)
, dof(0)
, rasGood(false)
, xsize(1.0f)
, ysize(1.0f)
, zsize(1.0f)
, x_ras(-1.0f,  0.0f,  0.0f)   // FreeSurfer defaults when goodRASflag is false
, y_ras( 0.0f,  0.0f, -1.0f)   // See: https://surfer.nmr.mgh.harvard.edu/fswiki/FsTutorial/MghFormat
, z_ras( 0.0f,  1.0f,  0.0f)
, c_ras( 0.0f,  0.0f,  0.0f)
, TR(0.0f)
, flipAngle(0.0f)
, TE(0.0f)
, TI(0.0f)
, FoV(0.0f)
{
}
 
//=============================================================================================================
 
bool MriVolData::isValid() const
{
    return (version == MRI_MGH_VERSION && width > 0 && height > 0 && depth > 0);
}
 
//=============================================================================================================
 
Matrix4f MriVolData::computeVox2Ras() const
{
    //
    // Build voxel-to-surface-RAS transform (FreeSurfer convention).
    //
    // The direction cosine matrix Mdc stores the orientation of each voxel axis
    // (columns are x, y, z directions). Scaling by voxel size gives the actual
    // spacing matrix M:
    //
    //   M = Mdc * diag(xsize, ysize, zsize)
    //
    // The origin P0 in RAS coordinates is:
    //
    //   P0 = c_ras - M * (dim/2)
    //
    // The full 4x4 vox2ras matrix is:
    //
    //   | M   P0 |     (in mm, then converted to meters for FIFF)
    //   | 0    1 |
    //
    // Reference: https://surfer.nmr.mgh.harvard.edu/fswiki/FsTutorial/MghFormat
    //
 
    // Construct M = Mdc * D (scale direction cosines by voxel sizes)
    Matrix3f M;
    M.col(0) = x_ras * xsize;
    M.col(1) = y_ras * ysize;
    M.col(2) = z_ras * zsize;
 
    // Compute center voxel
    Vector3f center(static_cast<float>(width)  / 2.0f,
                    static_cast<float>(height) / 2.0f,
                    static_cast<float>(depth)  / 2.0f);
 
    // Compute P0 = c_ras - M * center
    Vector3f P0 = c_ras - M * center;
 
    // Build 4x4 matrix in meters (FreeSurfer uses mm, FIFF uses meters)
    Matrix4f vox2ras = Matrix4f::Identity();
    vox2ras.block<3, 3>(0, 0) = M / 1000.0f;
    vox2ras.block<3, 1>(0, 3) = P0 / 1000.0f;
 
    return vox2ras;
}