Single Plane Compton Imaging for Radionuclide and Prompt Gamma-Ray Imaging

The contribution reports on first attempts to prove the concept of Single Plane Compton Imaging (SPCI), which was recently proposed in [1]. SPCI combines electronic collimation as known from conventional Compton cameras with a much simpler detector design: Multiple scintillator pixels are arranged alongside in a single detection plane. Imaging information is encoded in a set of ‘conditional’ spectra meaning energy deposition distributions in single pixels obliged with the condition of a coincident detection in another (adjacent) pixel. The activity distribution is iteratively reconstructed from the measured projections (the bin contents of the conditional spectra) by using the Maximum Likelihood Expectation Maximization (MLEM) algorithm.
This concept has been approached experimentally with three distinct setups addressing the application fields of radionuclide imaging in nuclear medicine, and of prompt-gamma based range verification in radiooncology with proton beams.
The first setup consists of two Directional Gamma-Ray Detectors [2], each consisting of two monolithic CeBr3 scintillators of 2”x1” and 2”x2”, arranged facing each other in close geometry. Those were exposed to prompt gamma radiation produced by a 90 MeV proton beam in a beam-stopping polymethyl acrylate (PMMA) target.
The third setup, aiming to be applied in radionuclide imaging, is a combination of a 4×4 pixel array of about 7 × 7 × 20 mm3 GAGG scintillator pixels read out with a Philips STEK module comprising 4×4 digital silicon photomultiplier dies. Data were taken with radioactive point sources arranged in few-cm distance from the scintillator pixels. Though data analyses are not yet finished, the effects enabling imaging are clearly visible. Preliminary plots exemplify the applicability of SPCI in both applications. The experimental activities have been closely accompanied with appropriate imaging methods and modeling using the Geant4 toolkit.

Bibliography

[1] G. Pausch, C. Golnik, A. Schulz and W. Enghardt, "A Novel Scheme of Compton Imaging for Nuclear Medicine," in IEEE Nuclear Science Symposium, Medical Imaging Conference and Room-Temperature Semiconductor Detector Workshop (NSS/MIC/RTSD), Strasbourg, 2016.
[2] A. Gueorguiev, J. Preston, l. Hoy, G. Pausch, C. Herbach and J. Stein, "A novel method to determine the directionality of radiation sources with two detectors based on coincidence measurements," in IEEE Nuclear Science Symposuim & Medical Imaging Conference, Knoxville, 2010.