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  • 1. Aykac, M.
    et al.
    Bauer, F.
    Stockholm University, Faculty of Science, Department of Physics.
    Williams, C.W.
    Loope, M.
    Schmand, M.
    Timing performance of Hi-Rez detector for time-of-flight (TOF) PET2006In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 53, no 3, p. 1084-1089Article in journal (Refereed)
    Abstract [en]

    Positron emission tomography (PET)-based on time-of-flight (TOF) is desired to enhance the image quality by improving the noise variance in the reconstruction. This benchtop study evaluates the timing performance of the current Hi-Rez detector which is based on a 13/spl times/13 LSO array of 4 mm/spl times/4 mm/spl times/20 mm crystals and not optimized for TOF PET applications. A Hamamatsu R9779, fast, 51-mm-diameter PMT was used for some experiments in this study as a reference PMT and its time resolution was measured to be 160 ps with a plastic scintillator. The average crystal time resolution of two Hi-Rez detectors, coupled to a 2/spl times/2 array of Hamamatsu 25-mm-diameter R8619 PMTs at +1050 V, in coincidence was measured to be 733 ps. The average crystal energy resolutions for two detectors were measured 13.1% and 13.2%. The average crystal time resolution of two Hi-Rez detectors improved from 733 ps to 642 ps when the PMT voltage was increased to +1300 V. The Hi-Rez detector was originally optimized for good energy resolution to reduce scatter and high packing fraction to obtain high sensitivity and improved spatial resolution for clinical PET.

  • 2.
    Bauer, F.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Aykac, M.
    Loope, M.
    Williams, C. W.
    Eriksson, L.
    Stockholm University, Faculty of Science, Department of Physics.
    Schmand, M.
    Performance Study of the New Hamamatsu R9779 and Photonis XP20D0 Fast 2" Photomultipliers2007In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 54, no 3, p. 422-426Article in journal (Refereed)
    Abstract [en]

    The focus of this paper is the evaluation of the new fast 51 mm-diameter, 8-stage Hamamatsu R9779 photomultipliers (PMTs) with an acceleration-ring at the front-end and the Photonis XP20D0 PMTs with a screening grid in front of the anode. The following performance characteristics are presented: Timing resolution, anode-scan-uniformity and transit-time spread. The unfolded timing resolution for two R9779 was 192 ps and 210 ps using plastic scintillators. The individual timing resolutions for two XP20D0 using plastic scintillators are 181 ps and 154 ps, respectively. The variation in time resolution across the windows of the two R9779 ranged between 117 ps and 171 ps, and 79 ps and 73 ps for the two XP20D0 PMTs.

  • 3.
    Bauer, F.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Corbeil, J.
    Schmand, M.
    Henseler, D.
    Measurements and Ray-Tracing Simulations of Light Spread in LSO Crystals2009In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 56, no 5, p. 2566-2573Article in journal (Refereed)
    Abstract [en]

    We report on measurements of the absolute light output from LSO crystals for irradiation with 511 keV gamma rays as a function of interaction position, reflector arrangement, detector coupling geometry and optical coupling to an adjacent crystal. The light output for this series of geometrical configurations is simulated with the ZEMAX ray-tracing software. By fine-tuning the optical parameters of the bulk and at the interfaces of the crystal, a model is obtained which yields good agreement with experimental data for all configurations. The resulting parameter set is applied to calculate the light distribution in a 12$,times,$ 12 crystal block detector. A comparison of measured and calculated block position profiles shows good agreement, demonstrating the potential of the simulation model to predict block detector performance data and provide guidelines for future array designs.

  • 4.
    Bauer, F.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Zhang, N.
    Schmand, M.
    Loope, M.
    Eriksson, L.
    Stockholm University, Faculty of Science, Department of Physics.
    Aykac, M.
    Dynode-Timing Method for PET Block Detectors2008In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 55, no 1, p. 451-456Article in journal (Refereed)
    Abstract [en]

    The focus of this paper is the investigation of a new dynode-timing technique optimized for PET block detectors. This method allows utilization of dynode signals from single but especially multiple photo-multiplier tubes (PMTs), operated with negative high-voltage. The technique will provide an event-timing trigger without deteriorating the anode signal. A printed circuit board has been developed and built for this investigation. Benchmark measurements have been performed, comparing timing of the anode signal with timing of the inverted last-dynode signal and timing of the dynode signal extracted via a newly developed LVPECL-logic based board. Timing measurements were performed with plastic as well as LSO scintillators. From single PMT measurements we find a 30 ps improvement with the dynode-timing method compared to the standard anode timing with two Photonis XP2020Q PMTs with LSO (10 mmtimes10 mmtimes10 mm). For a quad-PMT block detector, assembled of four Hamamatsu R9800 with a Hi-Rez block, the timing-resolution improves ~10%, by 43 ps compared to the standard anode timing.

  • 5.
    Bauer, Florian
    Stockholm University, Faculty of Science, Department of Physics.
    Detector Considerations for Time-of-Flight in Positron Emission Tomography2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Positron-Emission-Tomography (PET) is a modern imaging technique in nuclear medicine providing quantitative 3D distribution of a radioactive tracer substance in the human body. The gamma-detector is the first link in the chain of components that constitutes a PET. It converts incoming radiation into optical light pulses, which are detected by photo multiplier tubes. Here the light is converted into electric pulses, to be further processed by the acquisition electronics. Improving detector sensitivity and resolution is of great value in research and in clinical practice.

    The focus of this work is to improve the detector to give it time-of-flight (TOF) capabilities, in order to further improve sensitivity, which in turn leads to increased image quality, faster scan time and/or reduced dose exposure for the patient.

    Image quality has improved over the years, but losses in image quality have been reported for heavy patients, due to increased attenuation, and more dispersed counts over a larger volume. Instrumentation limits are still significant in heavy patient images, but the incorporation of TOF information promises to alleviate some of the limitations.

    In order to improve the timing resolution of the detector fast photo-multipliers and a novel scheme to extract the event timing trigger from a detector by using the summed dynode signal were investigated.

    When designing new PET detectors, it is important to have detailed understanding and control of the light sharing mechanisms in the crystal arrays. Therefore it was necessary to perform optical simulations and single crystal light output measurements to derive a model for an LSO block detector.

    Another way to improve the image quality is to use the depth-of-interaction (DOI) of the gamma ray within the detector. It is shown that a multi-layer phoswich detector comprised of LSO with different decay times and TOF capability, combines the benefits of TOF and DOI in one detector, maximizing the effective sensitivity gain.

  • 6.
    Bauer, Florian
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Aykac, Mehmet
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Physics.
    Schmand, Matthias
    Depth of interaction with a 3-dimensional checkerboard arrangement LSO-LSO block2010In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 57, no 3, p. 971-975Article in journal (Refereed)
    Abstract [en]

    In order to improve image quality in Positron Emission Tomography (PET) different routes are being pursued such as fast timing resolution for time-of-flight PET, higher spatial resolution by the use of smaller scintillator pixels and the use of depth-of-interaction information. The detection of the depth-of-interaction (DOI) of a gamma ray within a detector, deploying pulse shape discrimination (PSD), has been used to increase sensitivity and spatial resolution, especially at the edge of the field of view (FOV). The DOI information is used to reduce the parallax error; thus improving spatial resolution. Commonly, different scintillator materials with different decay times and light output and other differentiating factors, such as density, emission spectra, etc. are used for DOI detectors. We present a multi-layer phoswich detector comprised of LSO with different decay times in the range from 30 ns to 47 ns. The difference in decay times is achieved by co-doping LSO:Ce with Ca, resulting in short decay times of ~ 30 ns [1]. The use of a cut light guide allows the use of regular Photomultiplier tubes, giving the opportunity of a potential DOI detector replacement for current detectors. We were able to identify each pixel in the different detector layers

  • 7.
    Bauer, Florian
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Loope, Michael
    Schmand, Matthias
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Physics.
    Evaluation of a Micro-Channel Plate PMT in PET2006In: Nuclear Science Symposium Conference Record, 2006, IEEE, 2006, p. 2503-2505Conference paper (Refereed)
    Abstract [en]

    The focus of this paper is the evaluation of micro-channel plate PMTs for PET detectors. Several properties of MCPs make them interesting for PET applications, such as fast time response, high spatial resolution, compact size, low susceptibility to magnetic fields, high gain and low power consumption. The preliminary tests in this paper are performed with the 51 mm times 51 mm square Burle 85011-501 assembly with 64 anodes (8 times 8). A new version of this MCP will be examined for the full paper. Initial measurements have been performed with a pulsed LASER (Hamamatsu Picosecond Light Pulser PLP-10 with M8903 Laser diode head). The engineering sample of the 85011 exhibited a time resolution of 26 ps. Further measurements will be performed, such as transit time measurements and timing measurements with scintillators. Single-photon timing measurements were presented earlier in [Ref. 1], from the old version as well as the suitability of the device in Cherenkov detectors in [Ref. 2]. For the full paper it is also planned to develop a circuit which allows lossless splitting of the anode signal.

  • 8.
    Melcher, C.
    et al.
    University Tennessee.
    Eriksson, L.
    Stockholm University, Faculty of Science, Department of Physics.
    Aykac, M.
    Bauer, F.
    Stockholm University, Faculty of Science, Department of Physics.
    Williams, C.
    Loope, M.
    Schmand, M.
    Current and Future Use of LSO:Ce Scintillators in PET2006In: Radiation detectors for medical applications / [ed] Stefaan Tavernier, Dordrecht: Springer , 2006, , p. 243-257p. 243-257Conference paper (Refereed)
    Abstract [en]

    Single crystal scintillators of Lu2SiO5:Ce (LSO:Ce) were first developed about 15 years ago and have been in commercial use in positron emission tomography systems for more than five years. Annual production now exceeds 10,000 kg. We review the development of LSO:Ce and its implementation in PET, and summarize the current understanding of the scintillation characteristics and mechanisms. In addition, we present the evolution of LSO:Ce detector design and consider the potential performance of future imaging systems. In particular, coincidence timing measurements are presented and time-of-flight systems that take better advantage of the timing characteristics of LSO:Ce are discussed.

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