A Fully 3D Maximum Likelihood Estimator Algorithm with Attenuation and Scatter Correction Adapted to a Limited Angle Positron Camera


A Fully 3D Maximum Likelihood Estimator Algorithm with Attenuation and Scatter Correction Adapted to a Limited Angle Positron Camera

Pönisch, F.; Enghardt, W.

The in beam dual head positron camera BASTEI (Beta+ Activity meaSurements at the Therapy with Energetic Ions) is used to monitor and control the applied dose distributions simultaneously to the irradiation of the therapeutic carbon ion beam at the experimental heavy ion therapy facility at GSI Darmstadt. Therefore, the PET system is mounted directly at the treatment site. A fully 3D reconstruction algorithm based on the Maximum Likelihood Estimator algorithm has been developed and adapted to a strongly spatially-varying imaging situation. A scatter and attenuation correction is applied to the measured listmode data prior to the image reconstruction. The scatter correction method uses the subtraction of scattered data from measured data.
In this particular PET-application the fluence of registered events at the detector surface is in the order of 10 to 102 cm-2 compared with about 102 to 103 cm-2 in conventional PET in nuclear medicine. The emission data are acquired in a 3D list mode. Since less than 100,000 out of approximately 4 millions coincidence channels typically contribute to the reconstruction all detected events have to be utilized. In addition, they cannot be sorted into sinograms because the necessary interpolation procedures would generate additional noise. Therefore the reconstruction algorithm takes the original emission data as input. The non-zero elements of the 3D transition matrix are calculated at run-time using a Monte-Carlo code that models the individual crystal responses along each coincidence channel. Results of the performance studies as well as examples of use are presented.

  • Poster
    Proc. F3D-2001 The Sixth International Meeting on Fully Three-Dimensional Image reconstruction in Radiology and Nuclear Medicine, Pacific Groove, USA (2001)
  • Contribution to proceedings
    Proc. F3D-2001 The Sixth International Meeting on Fully Three-Dimensional Image reconstruction in Radiology and Nuclear Medicine, Pacific Groove, USA (2001)

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Publ.-Id: 5531