Attenuation map segmentation without reconstruction using a level set method in nuclear medicine imaging

In nuclear medical imaging, attenuation maps are images of the set of the linear attenuation coefficients of the observed body region. They are reconstructed from transmission SPECT (single photon emission computed tomography) acquisitions (the projections). The geometrical information of attenuation maps is crucial. We make the reasonable hypothesis that they are composed of homogeneous regions limited by straight edges. Thus, an accurate segmentation of attenuation maps is an important challenge. Instead of reconstructing an attenuation map and then segmenting it, we propose two methods to achieve its segmentation directly from the projections, without reconstructing it. Both are curve evolution algorithms using a level set technique. However, the first one is based on a geodesic search whereas the second one involves a more heuristic evolution speed definition. The methods are applied to 2D attenuation map segmentation from 1D transmission acquisitions in a fan beam geometry