Recent Progress on Single Photon and Positron Emission Tomography - From Detectors to Algorithms -

In the last few years, great efforts have been made to achieve higher sensitivity, higher spatial resolution, better image quality and quantification. In the SPECT, collimators and scanning methods have been improved. 180° sagittal scan is proposed for brain imaging. Practical correction methods for uniform attenuation are compared from a view point of noise propagation. In the PET system, current status of TOF-PET, high resolution PET are reviewed. CsI(Br) scintillator is a candidate of a new PET detector. For stationary PET using discrete detectors, an iterative method is preferable for the image reconstruction, because it does not need to satisfy the conventional sampling requirement for projections. Recent ECT technology tends to be sophisticated both in data acquisition and processing. It needs more powerful and versatile algorithms. Iterative reconstruction methods should be reconsidered as a tool of routine use. The EM algorithm is attractive, but it seems to need a trick to accelerate the convergence. A fast maximum likelihood algorithm is proposed, which can provide satisfactory images by a few iterations.