Gabriela Jazvac is presenting our latest work on PET detector design at the 14th International Conference on Position Sensitive Detectors (PSD14), held this week at Queen Mary University of London. PSD is a triennial conference series running since 1986, bringing together the latest developments in position sensitive radiation detectors from research groups worldwide across a broad range of scientific disciplines. The poster sessions run alongside the industry exhibition on 2–3 September. Qmul

The poster, A Single-Ended Multiplexed DOI-Capable PET Detector with 4-to-1 Crystal-to-Pixel Coupling and Edge-Effect Mitigation: An Optical Simulation Study, appears in the X-ray & Gamma Ray Detectors session.

The problem. Positron emission tomography systems achieve high spatial resolution by using a large number of readout channels, which drives up both cost and system complexity. Multiplexed light-sharing readouts reduce the channel count, but they introduce a well-known penalty: crystals at the edge of the scintillator matrix experience a different light-sharing geometry than those at the center, degrading spatial resolution and signal-to-noise ratio precisely where the field of view needs it.

Our approach. We have developed a single-ended, depth-of-interaction (DOI) capable PET detector with 4-to-1 multiplexing that mitigates these edge effects by design. The scintillator matrix is coupled to light guides and a silicon photomultiplier (SiPM) array on opposing ends. The multiplexing scheme couples adjacent crystal pairs at the matrix center and distant pairs at the matrix edge. Sharing scintillation light between exactly two SiPM pixels enables DOI determination, while the distant pairing at the edges restores the light-sharing symmetry that conventional schemes lose there.

What the simulations show. DOI capability was evaluated through optical simulations, recording the number of photons incident on each of the two coupled pixels across a range of interaction depths. The pixel corresponding to the interaction crystal always receives more photons than its coupled counterpart, allowing the interaction crystal to be identified unambiguously. The ratio between the two increases exponentially with depth of interaction, and — critically — this behavior is preserved for the edge crystals. Ratio values span three orders of magnitude for both center and edge pairs, indicating favorable DOI performance across the entire scintillator matrix.

Team. The work was presented by Gabriela Jazvac (PhD candidate), with co-authors Dr. Ana Marija Kožuljević, Dr. Luka Lotina, and Dr. Luka Pavelić, all of the Institute for Medical Research and Occupational Health, Zagreb.