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Radioactive sources of 241Am, 125I, 153Gd, 170Tm, and 57Co were used to measure the attenuation coefficient muL of various body tissues (gray and white matter, fat, liver, pancreas, and muscle), fluids (water, cerebrospinal fluid, plasma, and red blood cells), and cerebral lesions (blood clots, edematous brain tissue, and eight types of brain tumors) at 16 different energies in the range 18-136 keV. Experimental accuracy was about 0.1-0.3% and 0.2-0.4% in the energy ranges 18-60 keV and 60-136 keV, respectively. Comparisons with values determined in vivo and in vitro with an EMI scanner showed excellent agreement. It is hoped that these findings will provide a better understanding of the photon interactions at the sensitivity level of computed tomography.
Phelps et al. (Mon,) studied this question.