decay_correction_factor.h

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//
//
/*
    Copyright (C) 2005- 2009, Hammersmith Imanet Ltd
    This file is part of STIR.

    SPDX-License-Identifier: Apache-2.0

    See STIR/LICENSE.txt for details
*/
#ifndef __stir_decay_correction_factor_H__
#define __stir_decay_correction_factor_H__

#include "stir/common.h"
#include <cmath>

START_NAMESPACE_STIR


inline double
decay_correction_factor(const double isotope_halflife, const double start_time, const double end_time)
{
  assert(end_time - start_time > 0);
  const double lambda = std::log(2.) / isotope_halflife;

  return std::fabs(lambda * (end_time - start_time)) < .01
             ? std::exp(start_time * lambda) // if very short frame, we can ignore the duration
             : lambda * (end_time - start_time) / (std::exp(-start_time * lambda) - std::exp(-end_time * lambda));
}


inline double
decay_correction_factor(const double isotope_halflife, const double rel_time)
{
  return std::exp(rel_time * std::log(2.) / isotope_halflife);
}

END_NAMESPACE_STIR

#endif