Holger Nöldgen

PhenoPET: A dedicated PET scanner for plant research based on digital SiPMs (DPCs)

In the framework of the German Plant Phenotyping Network (DPPN) we developed a novel PET scanner for imaging plants and crops. The observation of the carbon transport within the plant becomes possible by using 11CO2 as PET tracer. The use of the rather short living isotope C-11 asks for a scanner with high dynamic range. That means fast timing and high data rates are important features which let us choose the Philips Digital Photon Counter (DPC) as photo detector. Due to the fast photo detectors and the special crystal matrix arrangement the system will allow measurements with rather high activities. We could measure a coincidence resolution time of ~ 250 ps FWHM between two detector elements. This opens the opportunity to employ time-of-flight information for the first time on a PET scanner of this size. This paper presents very first results from a prototype single-ring system with a FOV of 18 cm diameter and 6.5 cm axial height.

Read-out electronics for digital silicon photomultiplier modules

This work has its focus on the development of fast read-out electronics for digital silicon photomultipliers (dSiPM -called Digital Photon Counter (DPC) by Philips).

PET scintillator arrangement on digital SiPMs

A typical high resolution PET detector consists of a matrix of scintillator elements which are connected to a light guide in order to spread the light onto the pixels of a photo detector. In this work we introduce a matrix that works without light guide but has defined internal light leaks in order to allow controlled light sharing between the individual scintillator elements. This is especially useful when used together with the Philips digital SiPM DPC 3200. We show that better position determination is achieved and in addition higher count rates should be possible compared to a classical light guide solution.

Position reconstruction in monolithic block detectors

In high resolution PET systems the detector generally uses a scintillator which consists of individual pixel elements. The scintillation light of such a pixel element will be identified and thus the interaction is localized by the pixel position. Consequently, the delivered position of such a detector can only take discrete values. A different approach is the monolithic scintillator detector. A continuous scintillator block spans over an area of several photodetector pixels and the position is reconstructed from the recorded light distribution. Manufacturing of this detector is easier and the sensitivity is generally higher as no scintillating material is wasted for optical isolation between the pixels. But the challenge is to find a dedicated algorithm in order to identify the interaction position with sufficient resolution. We will present measurements of a monolithic scintillator detector (21×18×10mm3 LYSO) and compare different reconstruction methods. Already a Least Square Optimization algorithm based on a rather simple model delivers a resolution similar to an Artificial Neural Network approach but which requires pre-registered data for training. The comparison of the resolution to that of a pixelated detector of similar size and 2×2×10mm3 pixels shows the superior performance of the continuous block.

Development and characterization of a 4 × 4mm2 pixel neutron scintillation detector using digital SiPMs

This work describes the development of the first demonstrator device for neutron detection based on a 6Li-glass as a scintillator and silicon photomultipliers (SiPM) as photodetector. For the first characterization, the scintillator was pixelated with a one to one correspondence between scintillator and SiPM pixels, and optical cross-talk between pixels was minimized. Measurements in a high luminosity neutron beam show the functionality of the device and allow for partial characterization. The position resolution is 4 × 4mm2 and the detection efficiency of neutrons is 91(6)% relative to the active area. The device is linear up to at least 600 kcps.

PhenoPET — results from the plant scanner

Within the German Plant Phenotyping Network (DPPN), we developed a novel PET scanner based on Philips Digital Photon Counters (DPCs, or dSiPMs = digital Silicon Photomultipliers). The scanner is dedicated for plant research and provides functional information on carbon transport within the plant. To this end the detector ring is oriented horizontally. It provides a Field-of-View of 18 cm dia. and 20 cm in height. The read-out electronics cluster hits from different photodetector pixels when they originate from the same scintillation event. These single events are written via USB 3.0 with up to 300 MB/s to the computer system. Crystal identification, energy discrimination and coincidence detection is realized in software. The spatial resolution in the center Field-of-View (CFOV) could be estimated to approx. 1.6 mm from measurements of a dedicated hot rod phantom. Preliminary sensitivity measurements result in a peak sensitivity of 4.04% (ΔE = 250-750 keV) in the CFOV and a Coincidence Resolving Time of 298 ps could be achieved.

The use of USB 3.0 for fast data transfer in a PET detector

The Research Centre Juelich is developing a PET detector for plant phenotyping together with Philips Digital Photon Counting, Aachen. The scientific goal is to study the carbon transport in plants. To detect the photon pairs we use a ring of digital photon counters recently developed by Philips. For the prototype we decided to use a Xilinx Kintex evaluation board for data concentration and processing of the coincidences. It is assumed that the necessary data rate from the FPGA to the acquisition computer is about 300 MByte/s. As data link a 10-gigabit Ethernet link would be preferred, but the evaluation board contains a USB 3.0 interface already, therefore we chose to use this one in order to reduce the development costs.