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  • 1.
    Bauer, F.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Aykac, M.
    Loope, M.
    Williams, C. W.
    Eriksson, L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmand, M.
    Performance Study of the New Hamamatsu R9779 and Photonis XP20D0 Fast 2" Photomultipliers2007Ingår i: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 54, nr 3, s. 422-426Artikel i tidskrift (Refereegranskat)
    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.

  • 2.
    Bauer, F.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zhang, N.
    Schmand, M.
    Loope, M.
    Eriksson, L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Aykac, M.
    Dynode-Timing Method for PET Block Detectors2008Ingår i: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 55, nr 1, s. 451-456Artikel i tidskrift (Refereegranskat)
    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.

  • 3.
    Bauer, Florian
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Aykac, Mehmet
    Eriksson, Lars
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmand, Matthias
    Depth of interaction with a 3-dimensional checkerboard arrangement LSO-LSO block2010Ingår i: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 57, nr 3, s. 971-975Artikel i tidskrift (Refereegranskat)
    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

  • 4.
    Bauer, Florian
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Loope, Michael
    Schmand, Matthias
    Eriksson, Lars
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Evaluation of a Micro-Channel Plate PMT in PET2006Ingår i: Nuclear Science Symposium Conference Record, 2006, IEEE, 2006, s. 2503-2505Konferensbidrag (Refereegranskat)
    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.

  • 5.
    Cantillana, T
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljökemi.
    Eriksson, Lars
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    (2S)-1,1-dichloro-2-(2-chlorophenyl)-2-(4-chlorophenyl)ethane2009Ingår i: Acta Crystallographica Section E: Structure Reports Online, ISSN 1600-5368, E-ISSN 1600-5368, Vol. 65(Pt 1), s. m9-m10Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    In the mol­ecule of the title compound, [HgCl2(C10H9N3)], the HgII atom is four-coordinated in a distorted tetra­hedral configuration by two N atoms from the chelating di-2-pyridylamine ligand and by two Cl atoms. In the crystal structure, inter­molecular N—HCl hydrogen bonds link the mol­ecules into centrosymmetric dimers. There is a π–π contact between the pyridine rings [centroid–centroid distance = 3.896 (5) Å].

  • 6. Conti, Maurizio
    et al.
    Eriksson, Lars
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Karolinska Institute, Sweden; Siemens Healthcare Molecular Imaging, USA; University of Tennessee, USA.
    Physics of pure and non-pure positron emitters for PET: a review and a discussion2016Ingår i: EJNMMI Physics, ISSN 2197-7364, Vol. 3, nr 1, artikel-id 8Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    With the increased interest in new PET tracers, gene-targeted therapy, immunoPET, and theranostics, other radioisotopes will be increasingly used in clinical PET scanners, in addition to F-18. Some of the most interesting radioisotopes with prospective use in the new fields are not pure short-range beta(+) emitters but can be associated with gamma emissions in coincidence with the annihilation radiation (prompt gamma), gamma-gamma cascades, intense Bremsstrahlung radiation, high-energy positrons that may escape out of the patient skin, and high-energy gamma rays that result in some e(+)/e(-) pair production. The high level of sophistication in data correction and excellent quantitative accuracy that has been reached for F-18 in recent years can be questioned by these effects. In this work, we review the physics and the scientific literature and evaluate the effect of these additional phenomena on the PET data for each of a series of radioisotopes: C-11, N-13, O-15, F-18, Cu-64, Ga-68, Br-76, Rb-82, Y-86, Zr-89, Y-90, and I-124. In particular, we discuss the present complications arising from the prompt gammas, and we review the scientific literature on prompt gamma correction. For some of the radioisotopes considered in this work, prompt gamma correction is definitely needed to assure acceptable image quality, and several approaches have been proposed in recent years. Bremsstrahlung photons and Lu-176 background were also evaluated.

  • 7. Conti, Maurizio
    et al.
    Eriksson, Lars
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Siemens Healthcare Molecular Imaging, USA; Karolinska Institute, Sweden; University of Tennessee, USA.
    Rothfuss, Harold
    Sjoeholm, Therese
    Townsend, David
    Rosenqvist, Göran
    Carlier, Thomas
    Characterization of Lu-176 background in LSO-based PET scanners2017Ingår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 62, nr 9, s. 3700-3711Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    LSO and LYSO are today the most common scintillators used in positron emission tomography. Lutetium contains traces of Lu-176, a radioactive isotope that decays beta(-) with a cascade of. photons in coincidence. Therefore, Lutetium-based scintillators are characterized by a small natural radiation background. In this paper, we investigate and characterize the Lu-176 radiation background via experiments performed on LSO-based PET scanners. LSO background was measured at different energy windows and different time coincidence windows, and by using shields to alter the original spectrum. The effect of radiation background in particularly count-starved applications, such as Y-90 imaging, is analysed and discussed. Depending on the size of the PET scanner, between 500 and 1000 total random counts per second and between 3 and 5 total true coincidences per second were measured in standard coincidence mode. The LSO background counts in a Siemens mCT in the standard PET energy and time windows are in general negligible in terms of trues, and are comparable to that measured in a BGO scanner of similar size.

  • 8. Conti, Maurizio
    et al.
    Eriksson, Lars
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Westerwoudt, Victor
    Estimating Image Quality for Future Generations of TOF PET Scanners2013Ingår i: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 60, nr 1, s. 87-94Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Images taken with time-of-flight (TOF) positron emission tomography (PET) scanners are of improved quality compared to equivalent non-TOF images. This improvement is dependent on the scanner time resolution. The present generation of commercial TOF scanners has a time resolution in the range of 500-600 ps full width half maximum. In this work we investigate how the image characteristics will improve for future generations of TOF PET. We performed a Geant4 simulation of a 30-cm uniform cylinder containing hot spheres, with time resolution ranging from 600 to 200 ps. Data were reconstructed using TOF filtered back projection (FBP) and TOF ordered subsets expectation maximization (OSEM), with nonTOF reconstruction as a reference. Images were compared in terms of contrast recovery and variance in the image. The TOF gain was evaluated for both reconstruction methods. The TOF gain was also evaluated vs. counts in the scan, in order to understand the behavior of such gain at very low statistics. Using TOF FBP, it was shown that the TOF gain can be used as a sensitivity amplifier, reducing (according to the expected TOF gain) the number of counts necessary to produce an image of the same characteristics. Some limitations in the TOF gain were observed at very low counts, particularly if using iterative methods.

  • 9.
    Eriksson, Lars
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Conti, M.
    Melcher, C. L.
    Townsend, D. W.
    Eriksson, M.
    Rothfuss, H.
    Casey, M. E.
    Bendriem, B.
    Towards Sub-Minute PET Examination Times2011Ingår i: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 58, nr 1, s. 76-81Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The main performance parameters in positron camera system design are sensitivity and spatial resolution. This paper concerns sensitivity, which is a function of the scintillation material, the solid angle subtended by the detector array, and the scintillator packing fraction. The solid angle can be increased by extending the axial extent of cylindrical detector systems. Most commercial positron camera systems are based on rings of detector blocks with lutetium oxyorthosilicate, LSO:Ce or LYSO:Ce, as the scintillator of choice. By adding more rings, the solid angle and thus the absolute sensitivity increases while the singles detection efficiency remains fairly constant assuming the same crystal thickness. It has been shown that Ca co-doping of LSO:Ce reduces the scintillation decay time to similar to 30 ns with a light output over 30000 ph/MeV. This improvement may give a time-of-flight (TOF) advantage with time resolution of 500 ps or less. If the count rate sensitivity of a large axial field-of-view (AFOV) system is combined with the TOF sensitivity increase, we have the means to create examination times in the sub-minute range with no compromise in image quality. In the present study we have compared the existing Siemens molecular CT (mCT) systems to future 6, 8, 12, 20 and higher block ring systems with and without TOF. The mCT 4 block ring system has been used as a reference. The time for acceptable image quality with this system is then extrapolated to other systems based on planar sensitivity. However, the planar sensitivity is related to the solid angle, and reaches saturation for large AFOVs. This implies that there is an upper count rate sensitivity limit. A 20 block ring system may cover a 70 cm examination range at a certain planar count rate and could provide acceptable quality images in approximately 10 seconds by combining the high planar sensitivity count rate provided by the multi-ring feature, the high stopping power of LSO and the TOF gain due to the improved timing resolution. The increased sensitivity may be used to reduce patient dose.

  • 10.
    Eriksson, Lars
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Conti, M.
    Melcher, C. L.
    Zhuravleva, M.
    Eriksson, M.
    Rothfuss, H.
    LuYAP/LSO Phoswich Detectors for High Resolution Positron Emission Tomography2013Ingår i: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 60, nr 1, s. 194-196Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The spatial resolution in positron emission tomography (PET) can be improved by the addition of depth-of-interaction (DOI) information. This can be achieved by using the phoswich approach in which depth identification relies on differences in scintillation decay time and pulse shape discrimination techniques. In this paper we have looked at a special phoswich combination LuAP/LSO or LuYAP/LSO. This combination of scintillators is especially interesting since LuAP and LuYAP have emission in the excitation band of LSO, which may have an impact on the timing resolution of the detector. As will be shown in this paper, the phoswich concept based on these two scintillators can be utilized, however, with some limitations. This paper is an extension of our previous phoswich investigation [3].

  • 11.
    Eriksson, Lars
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Karolinska Institutet, Sweden; Siemens Healthcare Molecular Imaging, USA; University of Tennessee, USA.
    Conti, Maurizio
    Randoms and TOF gain revisited2015Ingår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 60, nr 4, s. 1613-1623Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Time-of-flight (TOF) positron emission tomography (PET) typically reduces the variance in the images by a factor that is proportional to the size of the object to be scanned, and inversely proportional to the time resolution of the PET scanner. Attempts to better characterize this relationship and understand its limits have been published, showing that such gain also increases with random fraction. In this paper, new experimental and simulated data are analyzed and old results are incorporated in the study. The proportionality of TOF gain with time resolution is confirmed, the proportionality constant is measured, the effect of the randoms is validated, and the limit of the model for small objects is investigated.

  • 12.
    Melcher, C.
    et al.
    University Tennessee.
    Eriksson, L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Aykac, M.
    Bauer, F.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Williams, C.
    Loope, M.
    Schmand, M.
    Current and Future Use of LSO:Ce Scintillators in PET2006Ingår i: Radiation detectors for medical applications / [ed] Stefaan Tavernier, Dordrecht: Springer , 2006, , s. 243-257s. 243-257Konferensbidrag (Refereegranskat)
    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.

  • 13. Watson, Charles C.
    et al.
    Eriksson, Lars
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kolb, Armin
    Physics and applications of positron beams in an integrated PET/MR2013Ingår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 58, nr 3, s. l1-L12Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In PET/MR systems having the PET component within the uniform magnetic field interior to the MR, positron beams can be injected into the PET field of view (FOV) from unshielded emission sources external to it, as a consequence of the action of the Lorentz force on the transverse components of the positron's velocity. Such beams may be as small as a few millimeters in diameter, but extend 50 cm or more axially without appreciable divergence. Larger beams form 'phantoms' of annihilations in air that can be easily imaged, and that are essentially free of gamma-ray attenuation and scatter effects, providing a unique tool for characterizing PET systems and reconstruction algorithms. Thin targets intersecting these beams can produce intense annihilation sources having the thickness of a sheet of paper, which are very useful for high resolution measurements, and difficult to achieve with conventional sources. Targeted beams can provide other point, line and surface sources for various applications, all without the need to have radioactivity within the FOV. In this paper we discuss the physical characteristics of positron beams in air and present examples of their applications.

  • 14. Westerwoudt, Victor
    et al.
    Conti, Maurizio
    Eriksson, Lars
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Advantages of Improved Time Resolution for TOF PET at Very Low Statistics2014Ingår i: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 61, nr 1, s. 126-133Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, Monte Carlo generated data are used to simulate a time-of-flight (TOF) positron emission tomography (PET) scanner with improving time resolution, down to 200-ps time resolution. TOF and non-TOF ordered subsets expectation maximization (OSEM) reconstructions were compared in terms of contrast recovery and signal-to-noise ratio, with the purpose of characterizing the differences of TOF and non-TOF at very low counts. This study shows that there is a lower limit to the number of counts in a PET scan, in order to obtain a quantitative PET image. Below this limit, the reliability of the measurement is very poor. The use of TOF information has the beneficial effect of lowering this statistical limit, allowing for shorter reliable PET scans. Another interesting finding derives from the comparison with TOF filtered back projection (FBP) images: if time resolution can be improved, TOF FBP images become competitive with TOF MLEM and OSEM algorithms, not only in terms of contrast recovery but also in terms of reduced noise level.

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