A novel scheme of Compton imaging for nuclear medicine

The paper introduces a novel concept of gamma imaging, the Single-Plane Compton Imager (SPCI). An SPCI is a compact array of scintillation crystals with separate light readouts, arranged for example in a checkerboard configuration. The passive collimation of conventional gamma cameras is replaced by kind of a “soft” electronic collimation derived from the Compton kinematics. In contrast to Compton cameras, where individual scattering angles are determined event-by-event from coincident energy depositions in separate detector planes, the SPCI reconstructs activity distributions from accumulated “conditional” spectra by using Maximum Likelihood Expectation Maximization algorithms. The condition is a coincident energy deposition in two (adjacent) detector elements of a single plane, which occurs most likely due to Compton scattering in one element followed by absorption in the other one. The SPCI could overcome drawbacks of Anger and Compton cameras: (i) Image resolution and detection efficiency are no competing factors. Both improve with increasing detector area. (ii) The fraction of valid events per hit exceeds that of passively collimated systems or Compton cameras by orders of magnitude. (iii) A single detector construction could fit to a wide range of gamma energies. Last not least, optimal SPCI pixels sizes fit with pixel dimensions in PET scanners. SPCI could thus be based on recent detector developments for PET-MRI featuring individual Si-based pixel readouts.