Maximum likelihood reconstruction for cone beam SPECT with camera tilt

Iterative maximum-likelihood (ML) reconstruction techniques are extended to the cone-beam SPECT (single-photon-emission computed tomography) geometry with the camera head tilted relative to the axis of rotation. The resulting code is an extension of a previous cone-beam ML code for the untilted case. The details of the code development, which included the variable camera sensitivity but excluded resolution, attenuation, and scatter, are described. The code is tested as a function of iteration in comparison with an existing tilt-angle filtered-backprojection (FBP) code, which has known distortions due to an incomplete theory. For a variety of point sources, as well as for a brain phantom, the tilt-angle cone-beam ML code (TCBML) performs visually and quantitatively better than cone-beam FBP (CB-FBP), and it removes the distortions inherent in CB-FBP. The TCBML code requires substantial computation time, which depends on the source geometry being reconstructed and varies in the present work from 3.5 to 50 times longer than the CB-FBP code