S. Salvador

Publications (4)4.34 Total impact

• Article: Optimizing PET DOI Resolution With Crystal Coating and Length

  S. Salvador, J. Wurtz, D. Brasse
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  ABSTRACT: In the last few years, one of the main research programs for PET systems has been the improvement of spatial resolution using Depth Of Interaction (DOI) information. In the context of developing a new PET system dedicated to small animals with axially oriented LYSO crystals and DOI capability, we have investigated the influence of the crystal coating and its length on the DOI resolution. The proposed PET system is composed of four detection modules arranged around the animal. Each module consists in 768 LYSO crystals read at both ends by multichannel plate photodetectors. The particular geometry combined with an inner diameter of 61.2 mm, lead to high detection efficiency close to the system solid angle. The LYSO crystal is chosen for its light yield of 33 ph/keV and its attenuation length of 11.2 mm at 511 keV. To obtain a transverse spatial resolution of 1 mm, the section of the crystal was fixed to 1.5 mm. To achieve a DOI resolution close to 1 mm, measurements have been performed on different LYSO crystal coatings with a length ranging from 25 mm to 35 mm. Each crystal is positioned on an xy translation stage and read out at both ends by H3164-10 Hamamatsu PMTs. The DOI information is then derived every 0.5 mm along the crystal extent. The use of an electronic collimation leads to a ²²Na source beam size of (1.58 ± 0.04) mm reaching the crystal. The optimized coating in terms of packing fraction and DOI resolution is found to be a mixture made with 30% TiO₂ powder in a PMMA binder. With this appropriate coating, an average DOI resolution of (0.82 ± 0.13) mm can be achieved with a 25 mm crystal length using a 20% photopeak energy window. The resolution degrades to (1.39 ± 0.16) mm when a wide-open energy window is used. Those values are corrected for the source beam size. Using this experimental proposal, a matrix of LYSO crystals has been built reaching a packing fraction of 93%. In this study, we demonstrate that us- - ing a 1.5 × 1.5 × 25 mm³ LYSO crystal, a DOI resolution of less than a millimeter can be achieved while keeping a high packing fraction for a system detection efficiency close to 15%.
  IEEE Transactions on Nuclear Science 11/2010; · 1.45 Impact Factor
• Article: Evaluation of a 1024 Anodes Micro-Channel Plate PMT for Preclinical PET Imaging

  D. Brasse, J. Wurtz, S. Salvador, M. Imhoff, B. Humbert
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  ABSTRACT: A new generation of flat panel photomultiplier tube (PMT) based on micro-channel plates (MCP) offers characteristics suitable for PET imaging. We are developing a preclinical PET system composed of four detection modules arranged around the animal. Each module consists in 768 LYSO:Ce crystals read at both ends by MCP-PMT. The particular geometry combined with an inner diameter of 61.2 mm lead to a high detection efficiency with a volumetric spatial resolution of 1 μL. The purpose of this work is to characterize the 1024 anodes of the MCP-PMT (Planacon XP85023/A1, Photonis Corp.) used in our preclinical PET system. The Planacon has very compact size (58 × 58 × 13.7 mm³) with an active area of 53 × 53 mm². The anode array consists in a 32 × 32 matrix in which each individual anode is 1.4 × 1.4 mm² with a pitch of 1.6 mm. Due to the lack of backside connectors and in order to individually readout the anode current, a dedicated connection board has been developed. The dark current, the gain and the timing resolution of one anode are measured as well as the charge sharing, the gain uniformity and the intrinsic spatial resolution on the entire active field of view. With a timing resolution below 100 ps, an intrinsic spatial resolution of 400 μm, a low dark current and a high gain, the Planacon XP85023/A1 offers a promising photodetector for PET imaging.
  IEEE Transactions on Nuclear Science 11/2010; · 1.45 Impact Factor
• Article: Design of a High Performances Small Animal PET System With Axial Oriented Crystals and DOI Capability

  S. Salvador, D. Huss, D. Brasse
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  ABSTRACT: In most positron emission tomography (PET) systems dedicated to small animal imaging, the geometry of the detector module is based on a block structure where the crystal elements are coupled to a reduced number of photomultiplier tubes (PMT). In this configuration, the spatial resolution and the detection efficiency depend on the crystal dimensions and thus there is a correlation between these two figures of merit. In this paper, we present a method already used by Ter-Pogossian et al in the 1970s allowing the spatial resolution and the detection efficiency to be independent of each other. The crystals are oriented in the axial direction readout on both sides by individual photodetector channels. The spatial resolution in the transverse plane is driven by the crystal section and the spatial resolution in the axial direction is proportional to the contrast of the light collected on both sides of the crystal. The detection efficiency depends on the number of radial crystal layers and the geometry of the system. With the perfect knowledge of the interaction depth, the inner diameter of the PET system can be reduced to a minimum value leading to an increase in detection efficiency. We investigate two particular geometries dedicated to mouse and whole purpose studies and based on the same detection module. Each module consists on a matrix of 32 times24 LYSO:Ce crystals of 1.5 mm times 1.5 mm times 25 mm each read at both ends by a Photonis Corp multichannel plate photodetector. The surface treatment is optimized to reach a volumetric spatial resolution of 1 mm³. The detection efficiency of each system is evaluated using Monte Carlo simulation. The mouse and whole purpose systems are based on 4 and 6 modules with an inner diameter of 61.2 mm and 103.2 mm where the axial extent is 25 mm leading to a detection efficiency of 18% and 13%, respectively. This geometrical configuration leads to a detection efficiency close to the system solid angle with a volumetric s- - patial resolution of 1 mm³ .
  IEEE Transactions on Nuclear Science 03/2009; · 1.45 Impact Factor
• Conference Proceeding: Evaluation of a 1024 Anodes Micro-Channel Plate PMT for Preclinical PET Imaging

  D. Brasse, J. Wurtz, S. Salvador, M. Imhoff, B. Humbert
  IEEE Nuclear Science Symposium and Medical Imaging Conference; 01/2009