A novel simultaneous beta-and-coincidence-gamma imaging technique for imaging plant leaves

1971 Objectives Develop and validate a novel phoswich detector that will enable simultaneous acquisition of a beta image and a coincidence gamma image of a thin object such as a leaf of a plant. This system will provide high sensitivity (~40% for beta imaging) and high resolution (potentially sub-millimeter) with good quantification when imaging a leaf of a plant. It may enable molecular and functional plant imaging research using positron-emitting tracers. Methods A phoswich detector was constructed using a sheet of plastic scintillator (0.5 or 1.0 mm thick) and a LSO array coupled to a position-sensitive PMT. The plastic detects beta effectively to form beta image but is insensitive to 511 keV gammas. The LSO array detects gammas effectively and serves as a light guide for beta detection. With the different decay times of the 2 scintillators, pulse shape discriminator was implemented to identify the origin of detected signal using sampled PMT waveform. Phantoms made by F-18 absorbed cotton threads were imaged by this detector. Results We can easily separate events detected by plastic scintillator and LSO by taking the ratio of 2 waveform samples. A beta image of ~1.5 mm FWHM resolution and ~40% sensitivity was achieved using 0.5 mm thick plastic scintillator sheet. We are currently refining the design of the front end beta detector in order to achieve sub-mm beta images. Coincidence detection with another PET detector is inherently available by this design and will be presented at the conference. Conclusions The results show that the proposed phoswich detector can provide functional imaging with high sensitivity and high resolution. Simultaneously acquired beta and coincidence gamma image should improve the quantification of PET tracer when imaging a thin object such as a leaf of a plant. Research Support Office of Science (BER), U. S. Department of Energy, Grant DE-SC000515