Development of a multi-purpose, flexible and scalable data acquisition system for DOI-PET

1840 Objectives Depth-of-interaction (DOI) measurement, which reduces the parallax error, is desirable not only for reducing resolution loss at the peripheral region but also for enabling unusual, dedicated detector-arrangement in PET. However practical use of DOI detectors has not been achieved in clinical scanners. In this paper, therefore, we develop a multi-purpose, flexible and scalable DOI detector system, and it is used to develop two world’s first PET scanners, the OpenPET and the helmet-chin PET. OpenPET, which consists of two axially separated detector rings, is originally proposed for in situ visualization of irradiation field in particle therapy. On the other hand, the helmet-chin PET, in which additional “chin strap” detectors assist a hemisphere detector unit, is proposed as the most efficient geometry for brain imaging. Methods For both scanners, the DOI detectors consist of 1024 Zr-doped GSO crystals which are arranged in 4 layers of 16 × 16 arrays, coupled to a 64-ch flat panel PMT. Each crystal element is 2.8 × 2.8 × 7.5 mm3. Front-end circuit equipped only resister chain and amplifier and the data acquisition (DAQ) system was separated from the gantry by 15-m coaxial cables for protecting electronics circuits from radiation damage by secondary particles. Also, the DAQ system has no coincidence circuit and only the singles list-mode DAQ circuits. Singles data are multiplexed and stored in a single PC through the optical cable. The assumed maximum data transfer rate of this DAQ system is 100 Mcps. The DAQ system makes a judgment on coincidence based on software. Results For the whole-body OpenPET, count rate performance was measured by the cylinder phantom. This phantom activity was 257 MBq. Measurement time was 60 s at 20 min intervals. Singles data loss was under 8%. Also, calculation time of the coincidence process was less than the measurement time less than 250 MBq. Conclusions We developed the flexible DAQ system and showed that the DAQ system had sufficient performance. Research Support In the whole-body OpenPET, this scanner design has 2 separated rings. Each ring has 2 detector rings of 40 detector blocks. The ring diameter is 660 mm, and the distance between separated rings, which can be controlled, is 90 mm. In the Helmet-Chin PET, 47 DOI detectors were used to form a hemisphere of 25 cm inner diameter and 50 cm outer diameter, and 7 DOI detectors were used for the chin strap.