rtkProjectionsDecompositionNegativeLogLikelihood.h

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 *  Copyright RTK Consortium
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 *  you may not use this file except in compliance with the License.
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#ifndef rtkProjectionsDecompositionNegativeLogLikelihood_h
#define rtkProjectionsDecompositionNegativeLogLikelihood_h

#include <itkSingleValuedCostFunction.h>
#include <itkVectorImage.h>
#include <itkVariableLengthVector.h>
#include <itkVariableSizeMatrix.h>
#include "rtkMacro.h"

namespace rtk
{
// We have to define the cost function first
class ProjectionsDecompositionNegativeLogLikelihood : public itk::SingleValuedCostFunction
{
public:
  ITK_DISALLOW_COPY_AND_MOVE(ProjectionsDecompositionNegativeLogLikelihood);

  using Self = ProjectionsDecompositionNegativeLogLikelihood;
  using Superclass = itk::SingleValuedCostFunction;
  using Pointer = itk::SmartPointer<Self>;
  using ConstPointer = itk::SmartPointer<const Self>;
  itkNewMacro(Self);
  itkTypeMacro(ProjectionsDecompositionNegativeLogLikelihood, SingleValuedCostFunction);

  //  enum { SpaceDimension=m_NumberOfMaterials };

  using ParametersType = Superclass::ParametersType;
  using DerivativeType = Superclass::DerivativeType;
  using MeasureType = Superclass::MeasureType;

  using DetectorResponseType = vnl_matrix<double>;
  using MaterialAttenuationsType = vnl_matrix<double>;
  using IncidentSpectrumType = vnl_matrix<float>;
  using MeasuredDataType = itk::VariableLengthVector<double>;
  using ThresholdsType = itk::VariableLengthVector<int>;
  using MeanAttenuationInBinType = itk::VariableSizeMatrix<double>;

  // Constructor
  ProjectionsDecompositionNegativeLogLikelihood()
  {
    m_NumberOfEnergies = 0;
    m_NumberOfMaterials = 0;
    m_Initialized = false;
  }

  // Destructor
  ~ProjectionsDecompositionNegativeLogLikelihood() override = default;

  MeasureType
  GetValue(const ParametersType & itkNotUsed(parameters)) const override
  {
    long double measure = 0;
    return measure;
  }
  void
  GetDerivative(const ParametersType & itkNotUsed(lineIntegrals),
                DerivativeType &       itkNotUsed(derivatives)) const override
  {
    itkExceptionMacro(<< "Not implemented");
  }
  virtual void
  Initialize()
  {}

  virtual itk::VariableLengthVector<float>
  GetInverseCramerRaoLowerBound()
  {
    // Return the inverses of the diagonal components (i.e. the inverse variances, to be used directly in WLS
    // reconstruction)
    itk::VariableLengthVector<double> diag;
    diag.SetSize(m_NumberOfMaterials);
    diag.Fill(0);

    for (unsigned int mat = 0; mat < m_NumberOfMaterials; mat++)
      diag[mat] = 1. / m_Fischer.GetInverse()[mat][mat];
    return diag;
  }

  virtual itk::VariableLengthVector<float>
  GetFischerMatrix()
  {
    // Return the whole Fischer information matrix
    itk::VariableLengthVector<double> fischer;
    fischer.SetSize(m_NumberOfMaterials * m_NumberOfMaterials);
    fischer.Fill(0);

    for (unsigned int i = 0; i < m_NumberOfMaterials; i++)
      for (unsigned int j = 0; j < m_NumberOfMaterials; j++)
        fischer[i * m_NumberOfMaterials + j] = m_Fischer[i][j];
    return fischer;
  }

  virtual void
  ComputeFischerMatrix(const ParametersType & itkNotUsed(lineIntegrals))
  {}

  unsigned int
  GetNumberOfParameters() const override
  {
    return m_NumberOfMaterials;
  }

  virtual vnl_vector<double>
  ForwardModel(const ParametersType & lineIntegrals) const
  {
    vnl_vector<double> attenuationFactors;
    attenuationFactors.set_size(m_NumberOfEnergies);
    GetAttenuationFactors(lineIntegrals, attenuationFactors);

    // Apply detector response, getting the lambdas
    return (m_IncidentSpectrumAndDetectorResponseProduct * attenuationFactors);
  }

  void
  GetAttenuationFactors(const ParametersType & lineIntegrals, vnl_vector<double> & attenuationFactors) const
  {
    // Apply attenuation at each energy
    vnl_vector<double> vnlLineIntegrals;

    // Initialize the line integrals vnl vector
    vnlLineIntegrals.set_size(m_NumberOfMaterials);
    for (unsigned int m = 0; m < m_NumberOfMaterials; m++)
      vnlLineIntegrals[m] = lineIntegrals[m];

    // Apply the material attenuations matrix
    attenuationFactors = this->m_MaterialAttenuations * vnlLineIntegrals;

    // Compute the negative exponential
    for (unsigned int energy = 0; energy < m_NumberOfEnergies; energy++)
    {
      attenuationFactors[energy] = std::exp(-attenuationFactors[energy]);
    }
  }

  itk::VariableLengthVector<double>
  GuessInitialization() const
  {
    itk::VariableLengthVector<double> initialGuess;
    initialGuess.SetSize(m_NumberOfMaterials);

    // Compute the mean attenuation in each bin, weighted by the input spectrum
    // Needs to be done for each pixel, since the input spectrum is variable
    MeanAttenuationInBinType MeanAttenuationInBin;
    MeanAttenuationInBin.SetSize(this->m_NumberOfMaterials, this->m_NumberOfSpectralBins);
    MeanAttenuationInBin.Fill(0);

    for (unsigned int mat = 0; mat < this->m_NumberOfMaterials; mat++)
    {
      for (unsigned int bin = 0; bin < m_NumberOfSpectralBins; bin++)
      {
        double accumulate = 0;
        double accumulateWeights = 0;
        for (int energy = m_Thresholds[bin] - 1;
             (energy < m_Thresholds[bin + 1]) && (energy < (int)(this->m_MaterialAttenuations.rows()));
             energy++)
        {
          accumulate += this->m_MaterialAttenuations[energy][mat] * this->m_IncidentSpectrum[0][energy];
          accumulateWeights += this->m_IncidentSpectrum[0][energy];
        }
        MeanAttenuationInBin[mat][bin] = accumulate / accumulateWeights;
      }
    }

    for (unsigned int mat = 0; mat < m_NumberOfMaterials; mat++)
    {
      // Initialise to a very high value
      initialGuess[mat] = 1e10;
      for (unsigned int bin = 0; bin < m_NumberOfSpectralBins; bin++)
      {
        // Compute the length of current material required to obtain the attenuation
        // observed in current bin. Keep only the minimum among all bins
        double requiredLength = this->BinwiseLogTransform()[bin] / MeanAttenuationInBin[mat][bin];
        if (initialGuess[mat] > requiredLength)
          initialGuess[mat] = requiredLength;
      }
    }

    return initialGuess;
  }

  itk::VariableLengthVector<double>
  BinwiseLogTransform() const
  {
    itk::VariableLengthVector<double> logTransforms;
    logTransforms.SetSize(m_NumberOfSpectralBins);

    vnl_vector<double> ones, nonAttenuated;
    ones.set_size(m_NumberOfEnergies);
    ones.fill(1.0);

    // The way m_IncidentSpectrumAndDetectorResponseProduct works is
    // it is mutliplied by the vector of attenuations factors (here
    // filled with ones, since we want the non-attenuated signal)
    nonAttenuated = m_IncidentSpectrumAndDetectorResponseProduct * ones;

    for (unsigned int i = 0; i < m_MeasuredData.GetSize(); i++)
    {
      // Divide by the actually measured photon counts and apply log
      if (m_MeasuredData[i] > 0)
        logTransforms[i] = log(nonAttenuated[i] / m_MeasuredData[i]);
    }

    return logTransforms;
  }

  virtual vnl_vector<double>
  GetVariances(const ParametersType & itkNotUsed(lineIntegrals)) const
  {
    vnl_vector<double> meaninglessResult;
    meaninglessResult.set_size(m_NumberOfSpectralBins);
    meaninglessResult.fill(0.);
    return (meaninglessResult);
  }

  itkSetMacro(MeasuredData, MeasuredDataType);
  itkGetMacro(MeasuredData, MeasuredDataType);

  itkSetMacro(DetectorResponse, DetectorResponseType);
  itkGetMacro(DetectorResponse, DetectorResponseType);

  itkSetMacro(MaterialAttenuations, MaterialAttenuationsType);
  itkGetMacro(MaterialAttenuations, MaterialAttenuationsType);

  itkSetMacro(NumberOfEnergies, unsigned int);
  itkGetMacro(NumberOfEnergies, unsigned int);

  itkSetMacro(NumberOfMaterials, unsigned int);
  itkGetMacro(NumberOfMaterials, unsigned int);

  itkSetMacro(IncidentSpectrum, IncidentSpectrumType);
  itkGetMacro(IncidentSpectrum, IncidentSpectrumType);

  itkSetMacro(NumberOfSpectralBins, unsigned int);
  itkGetMacro(NumberOfSpectralBins, unsigned int);

  itkSetMacro(Thresholds, ThresholdsType);
  itkGetMacro(Thresholds, ThresholdsType);

protected:
  MaterialAttenuationsType       m_MaterialAttenuations;
  DetectorResponseType           m_DetectorResponse;
  MeasuredDataType               m_MeasuredData;
  ThresholdsType                 m_Thresholds;
  IncidentSpectrumType           m_IncidentSpectrum;
  vnl_matrix<double>             m_IncidentSpectrumAndDetectorResponseProduct;
  unsigned int                   m_NumberOfEnergies;
  unsigned int                   m_NumberOfMaterials;
  unsigned int                   m_NumberOfSpectralBins;
  bool                           m_Initialized;
  itk::VariableSizeMatrix<float> m_Fischer;
};

} // namespace rtk

#endif