Deriving attenuation coefficients from 3D CT data for SPECT Monte Carlo simulations

Quantitation of nuclear medicine data is a major goal in medical imaging. It implies that photon attenuation, scatter and depth dependent spatial resolution be corrected for. Realistic, anthropomorphic numerical phantoms are needed to understand how these phenomena degrade nuclear medicine images, and to validate correction methods. We developed a Monte Carlo simulator which simulates photon transport in an anthropomorphic phantom. The main feature of our phantom consists in estimating the attenuation coefficient for the three main types of physical interaction from CT data and tissue nature in each voxel. The simulated data obtained with this approach show how accurate in terms of geometry and attenuation coefficient, a phantom must be defined to properly simulate scintigraphic acquisitions. It highlights the importance of bone tissues in the formation of scatter as well as the influence of patient's morphology in attenuation phenomena.