Novel light-guide-PMT geometries to reduce dead edges of a scintillation camera

• Published in: Physica medica Vol. 48; pp. 84 - 90
• Main Authors: Wang, Beien, Kreuger, Rob, Beekman, Freek J., Goorden, Marlies C.
• Format: Journal Article
• Language: English
• Published: Italy Elsevier Ltd 01.04.2018
• Subjects: Dead edge; Gamma Cameras; Gamma-ray detectors; Light; Maximum likelihood estimation; Photomultiplier tube; Scintillation Counting - instrumentation; Maximum likelihood estimation; Photomultiplier tube; Gamma-ray detectors; Dead edge
• ISSN: 1120-1797; 1724-191X; 1724-191X
• DOI: 10.1016/j.ejmp.2018.04.004

•Cost-effective solution to reduce dead edges for Anger camera.•Unconventional PMT-lightguide layout, absorptive edges, and maximum likelihood positioning.•Evaluated with Monte Carlo simulation toolkit GATE. Anger cameras based on monolithic NaI scintillators read out by an array of PMTs are predominant in planar gamma imaging and SPECT. However, position estimation of gamma interactions is usually severely degraded near the edges of the scintillator which can be extremely undesirable for applications like breast imaging. Here we propose a relatively cost-effective solution based on the use of scintillators with absorptive edges with an unconventional light-guide-PMT layout employing a maximum likelihood positioning algorithm. The basic design on which we aim to improve consists of a monolithic NaI(Tl) scintillator read out by 3 × 5 square PMTs (conventional layout, CL) that could be suitable for molecular breast imaging. To better detect gamma interactions near the crystal’s critical edge, we tried different set-ups: we replaced the 5 large PMTs near the edge by 11 smaller PMTs (small-sensor layout, SSL); we emulated rectangular PMTs along the critical edge by inserting a row of 5 rectangular light-guides that direct the light toward square PMTs placed behind (shifted layout, SL); we inserted rectangular light-guides alternatingly, such that the PMTs are in an interlocking pattern (alternating shifted layout, ASL). The performance of our designs was tested with Monte Carlo simulations. Results showed that SSL, SL, and ASL gave better spatial resolution near the critical edge than CL (3.4, 3.6, and 4.1 mm near the edge compared with 5.3 mm for CL), and thus resulted in a larger usable detector area. To conclude, for applications where small dead edges are crucial, our designs may be cost-effective solutions.