Iterative reconstruction with attenuation compensation from cone-beam projections acquired via non-planar orbit

Single photon emission computed tomography (SPECT) imaging with cone-beam collimators provides improved sensitivity and spatial resolution for imaging small objects with large field-of-view detectors. It is known that Tuy's (1983) cone-beam data sufficiency condition must be met in order to obtain artifact-free reconstructions. Even though Tuy's condition was derived for attenuation-free situation, the authors hypothesize that an artifact-free reconstruction can be obtained even if the cone-beam data are attenuated, provided the imaging orbit satisfies Tuy's condition and the exact attenuation map. In the authors' studies, emission data are acquired using nonplanar orbit such as circle-and-line orbit to acquire sufficient data for cone-beam tomographic reconstruction. An iterative conjugate gradient reconstruction algorithm is used to reconstruct projection data with a pre-acquired attenuation map. Quantitative accuracy of the attenuation corrected emission reconstruction is significantly improved. The authors observe that the cone-beam iterative algorithms are very sensitive to the projection and backprojection models, because each voxel is sampled anisotropically. Sampling artifacts (i.e., aliasing artifacts) sometimes are very severe for non-planar orbit data acquisition geometries. Better voxel models and sampling geometries are required in further investigations.