S. Tavernier

Neural network-based position estimators for PET detectors using monolithic LSO blocks

The impinging position of a 511 keV photon onto a continuous scintillator can be obtained from the light distribution measured by a pixelated photodetector such as avalanche photodiode (APD) arrays. This information is extracted using neural networks trained for events with a particular incidence angle. Using a 20/spl times/10/spl times/10 mm block of lutetium oxyorthosilicate mounted onto a S8550 Hamamatsu APD matrix we achieved an intrinsic resolution of 1.9 mm full-width at half-maximum (FWHM) for perpendicular incident photons and 2.6 mm FWHM at a 40/spl deg/ incidence angle. A possible implementation for tomographic imaging is presented.

EXTENSIVE STUDIES ON CEF3 CRYSTALS, A GOOD CANDIDATE FOR ELECTROMAGNETIC CALORIMETRY AT FUTURE ACCELERATORS

Abstract In the framework of its search for new heavy, fast and radiation hard scintillators for calorimetry at future colliders, the Crystal Clear Collaboration performed a systematic investigation of the properties and of the scintillation and radiation damage mechanisms of CeF 3 monocrystals. Many samples of various dimensions up to 3 × 3 × 28 cm 3 were produced by industry and characterised in the laboratories by different methods such as: optical transmission, light yield and decay time measurements, excitation and emission spectra, gamma and neutron irradiations. The results of these measurements are discussed. The measured light yield is compared to the theoretical expectations. Tests in high energy electron beams on a crystal matrix were also performed. The suitability of CeF 3 for calorimetry at high rate machines is confirmed. Production and economical considerations are discussed.

LuPO4:Nd and YPO4:Nd—new promising VUV scintillation materials

Abstract LuPO 4 :Nd and YPO 4 :Nd represent new and very fast potential scintillator materials. For most types of ionizing excitation, the luminescence of these materials is dominated by an emission band whose maximum intensity occurs at ∼192xa0nm. The origin of this band is the fast 5d–4f transitions of the Nd 3+ ions. An additional emission contribution due to host-defect emission varies for different samples. These defects appear to be responsible for the limited light yield of LuPO 4 :Nd.

Cerium doped heavy metal fluoride glasses, a possible alternative for electromagnetic calorimetry

The article is an overview of the research activity performed in the framework of the Crystal Clear Collaboration to produce scintillating glasses. The manufacturing of heavy metal fluoride glasses doped with Ce3+ is discussed. The luminescence and scintillation characteristics as well as the radiation hardness properties are extensively studied in the case of Ce doped fluorohafnate , found to be the most convenient glass scintillator for high energy physics applications.

Performance study of a 3D small animal PET scanner based on BaF2 crystals and a photo sensitive wire chamber

Abstract A 3D small animal PET scanner, designed and built at the University of Brussel, has been operational since the beginning of 1996. The scanner has a transaxial field of view (FOV) of 110 mm and an axial FOV of 52 mm. The absolute sensitivity is around 35,000 coincidences s−1 MBq−1 for a point source at the center of the scanner and the time resolution is 29 ns FWHM. To measure the achievable spatial resolution, a thin 22Na source was scanned at various distances from the scanner axis. The resolution in a reconstructed image for a source close to the center is 3.0 mm FWHM. This figure can be improved at the expense of the sensitivity by lowering the voltage on the anodes in the wire chamber. Finally, to assess the overall image quality, scans were made of a cylindrical phantom with holes of varying diameter.

Study of spatial resolution and depth of interaction of APD-based PET detector modules using light sharing schemes

Using 4 /spl times/ 8 Hamamatsu S8550 APD matrices with 1.6 mm /spl times/ 1.6 mm pixels and a 2.3 mm pitch, we compared the spatial resolution of light sharing schemes using block detectors to detector modules using 1-to-1 coupling between individual 2 mm /spl times/ 2 mm /spl times/ 10 mm LSO crystals and APD pixels. In addition, depth of interaction (DOI) measurement capabilities of the block detector were studied. Using neural network methods to determine the interaction position in a 10 mm thick LSO block, we achieved an intrinsic spatial resolution of 1.5 mm FWHM compared to 2.06 mm for individual readout. The DOI resolution varied between 1.8 and 3.0 mm FWHM.

A fully 3D small PET scanner

A fully 3D small PET scanner based on a novel detection principle for gamma rays is described. It uses BaF2 scintillator and photosensitive wire chambers. Extensive tests with technical prototypes have shown that such a system will have a detection efficiency for gamma rays comparable with what can be obtained with the more traditional approach, and a spatial resolution determined by the size of the crystals. The expected performances of the scanner, based on our measurements and on simulations, are given.

Development of an Anthropomorphic Breast Phantom for Combined PET, B-Mode Ultrasound and Elastographic Imaging

Combining the advantages of different imaging modalities leads to improved clinical results. For example, ultrasound provides good real-time structural information without any radiation and PET provides sensitive functional information. For the ongoing ClearPEM-Sonic project combining ultrasound and PET for breast imaging, we developed a dual-modality PET/Ultrasound (US) phantom. The phantom reproduces the acoustic and elastic properties of human breast tissue and allows labeling the different tissues in the phantom with different concentrations of FDG. The phantom was imaged with a whole-body PET/CT and with the Supersonic Imagine Aixplorer system. This system allows both B-mode US and shear wave elastographic imaging. US elastography is a new imaging method for displaying the tissue elasticity distribution. It was shown to be useful in breast imaging. We also tested the phantom with static elastography. A 6D magnetic positioning system allows fusing the images obtained with the two modalities. ClearPEM-Sonic is a project of the Crystal Clear Collaboration and the European Centre for Research on Medical Imaging (CERIMED).

VUV scintillation of LuPO/sub 4/:Nd and YPO/sub 4/:Nd

LuPO/sub 4/:Nd and YPO/sub 4/:Nd represent new and very fast potential scintillator materials. For most types of ionizing excitation, the luminescence of these materials is dominated by an emission band whose maximum intensity occurs at about 192 nm. The origin of this band lies in the fast 5d-4f transitions of the Nd/sup 3+/ ions. An additional contribution due to host-defect emission varies for different samples. These defects appear to be responsible for the limited light yield of LuPO/sub 4/:Nd.

Study of a high resolution 3D PET scanner

Abstract Some results of a study of the properties of a low pressure multistep avalanche chamber with BaF 2 scintillators and with TMAE as the photosensitive gas for a 3D PET scanner are presented. Absolute gas amplification was carefully measured by two independent methods, giving rise to a maximum attainable total gain of the order of 10 7 . A typical electron transmission efficiency of 20–30% was obtained. The time resolution of the detector can be optimized to be ∼ 6 ns FWHM.