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Mexico City, Mexico

Sanchez F.,CIEMAT | Moliner L.,CIEMAT | Moliner L.,University of Valencia | Correcher C.,Oncovision | And 8 more authors.
Medical Physics | Year: 2012

Purpose: The authors have developed a small animal Positron emission tomography (PET) scanner based on monolithic LYSO crystals coupled to multi-anode photomultiplier tubes (MA-PMTs). In this study, the authors report on the design, calibration procedure, and performance evaluation of a PET system that the authors have developed using this innovative nonpixelated detector design. Methods: The scanner is made up of eight compact modules forming an octagon with an axial field of view (FOV) of 40 mm and a transaxial FOV of 80 mm diameter. In order to fully determine its performance, a recently issued National Electrical Manufacturers Association (NEMA) NU-4 protocol, specifically developed for small animal PET scanners, has been followed. By measuring the width of light distribution collected in the MA-PMT the authors are able to determine depth of interaction (DOI), thus making the proper identification of lines of response (LORs) with large incidence angles possible. PET performances are compared with those obtained with currently commercially available small animal PET scanners. Results: At axial center when the point-like source is located at 5 mm from the radial center, the spatial resolution measured was 1.65, 1.80, and 1.86 mm full width at half maximum (FWHM) for radial, tangential, and axial image profiles, respectively. A system scatter fraction of 7.5 (mouse-like phantom) and 13 (rat-like phantom) was obtained, while the maximum noise equivalent count rate (NECR) was 16.9 kcps at 12.7 MBq (0.37 MBq/ml) for mouse-like phantom and 12.8 kcps at 12.4 MBq (0.042 MBq/ml) for rat-like phantom The peak absolute sensitivity in the center of the FOV is 2 for a 30 peak energy window. Several animal images are also presented. Conclusions: The overall performance of our small animal PET is comparable to that obtained with much more complex crystal pixelated PET systems. Moreover, the new proposed PET produces high-quality images suitable for studies with small animals. © 2012 American Association of Physicists in Medicine.

Moliner L.,Polytechnic University of Valencia | Gonzalez A.J.,Polytechnic University of Valencia | Correcher C.,Oncovision | Benlloch J.M.,Polytechnic University of Valencia
Journal of Instrumentation | Year: 2016

In this work, we present the online implementation of attenuation, scatter and random corrections using the LMEM algorithm for the dedicated breast PET named MAMMI. The attenuation correction is based on image segmentation, the random correction is derived from the rate estimation of single photon events and the scatter correction is determined by the dual energy window method. These three corrections are estimated and implemented in the reconstruction process without almost increasing the reconstruction time. The image quality is evaluated in terms of image uniformity and contrast using the reconstructed images of two custom-designed phantoms. When we apply the three corrections, the measured uniformity in the whole field of view is (10±1)% compared to (17±1)% without corrections. The adapted recovery contrast coefficients (normalized to 1) are approximately (0.80±0.02) in hot areas, improving the value of (0.66±0.07) obtained without corrections. The reconstruction processing time is also studied, finding an increment of around 7% when the three corrections are simultaneously included. Finally, 25 breast image datasets are also analyzed. The average acquisition time per patient is around 1200 seconds and the reconstruction times with corrections vary from 100 to 400 seconds using (1×1×1) mm3 voxel size and from 300 to 1800 seconds using (0.5×0.5×0.5) mm3 voxel size. These reconstructions are performed with a virtual pixel size of (1.6×1.6) mm2 and twelve iterations. © 2016 IOP Publishing Ltd and Sissa Medialab srl.

Sanchez F.,Polytechnic University of Valencia | Orero A.,Polytechnic University of Valencia | Soriano A.,Polytechnic University of Valencia | Correcher C.,Oncovision | And 9 more authors.
Medical Physics | Year: 2013

Purpose: The authors have developed a trimodal PETSPECTCT scanner for small animal imaging. The gamma ray subsystems are based on monolithic crystals coupled to multianode photomultiplier tubes (MA-PMTs), while computed tomography (CT) comprises a commercially available microfocus x-ray tube and a CsI scintillator 2D pixelated flat panel x-ray detector. In this study the authors will report on the design and performance evaluation of the multimodal system. Methods: X-ray transmission measurements are performed based on cone-beam geometry. Individual projections were acquired by rotating the x-ray tube and the 2D flat panel detector, thus making possible a transaxial field of view (FOV) of roughly 80 mm in diameter and an axial FOV of 65 mm for the CT system. The single photon emission computed tomography (SPECT) component has a dual head detector geometry mounted on a rotating gantry. The distance between the SPECT module detectors can be varied in order to optimize specific user requirements, including variable FOV. The positron emission tomography (PET) system is made up of eight compact modules forming an octagon with an axial FOV of 40 mm and a transaxial FOV of 80 mm in diameter. The main CT image quality parameters (spatial resolution and uniformity) have been determined. In the case of the SPECT, the tomographic spatial resolution and system sensitivity have been evaluated with a 99mTc solution using single-pinhole and multi-pinhole collimators. PET and SPECT images were reconstructed using three-dimensional (3D) maximum likelihood and ordered subset expectation maximization (MLEM and OSEM) algorithms developed by the authors, whereas the CT images were obtained using a 3D based FBP algorithm. Results: CT spatial resolution was 85 μm while a uniformity of 2.7 was obtained for a water filled phantom at 45 kV. The SPECT spatial resolution was better than 0.8 mm measured with a Derenzo-like phantom for a FOV of 20 mm using a 1-mm pinhole aperture collimator. The full width at half-maximum PET radial spatial resolution at the center of the field of view was 1.55 mm. The SPECT system sensitivity for a FOV of 20 mm and 15 energy window was 700 cpsMBq (7.8 × 10-2) using a multi-pinhole equipped with five apertures 1 mm in diameter, whereas the PET absolute sensitivity was 2 for a 350-650 keV energy window and a 5 ns timing window. Several animal images are also presented. Conclusions: The new small animal PETSPECTCT proposed here exhibits high performance, producing high-quality images suitable for studies with small animals. Monolithic design for PET and SPECT scintillator crystals reduces cost and complexity without significant performance degradation. © 2013 American Association of Physicists in Medicine.

An apparatus to detect gamma rays, comprising a scintillator, a position sensitive photo sensor and a scintillation-light-incidence-angle-constraining, SLIAC, element, the scintillator has faces and the position sensitive photo sensor detects scintillation photons exiting a scintillation photons transparent face of the scintillator, and a portion of a scintillator face is covered with an absorbing layer, which absorbs scintillation photons created by scintillation events due to the interaction of incoming gamma rays with the scintillator, and the SLIAC element is optically coupled between a scintillation photons transparent face of the scintillator and the position sensitive photo sensor and the SLIAC element guides the scintillation photons exiting the scintillator towards the position sensitive photo sensor, and the SLIAC element restricts the maximum allowed half light acceptance angle for the scintillation light hitting the position sensitive photo sensor to less than 45.

Gonzalez A.J.,Polytechnic University of Valencia | Moreno M.,CSIC - National Center of Microelectronics | Barbera J.,Oncovision | Conde P.,Polytechnic University of Valencia | And 12 more authors.
IEEE Transactions on Nuclear Science | Year: 2013

In this work we describe a procedure to reduce the number of signals detected by an array of 256 Silicon Photomultipliers (SiPMs) using a resistor network to divide the signal charge into few readout channels. Several configurations were modeled, and the pulsed signal at the readout contacts were simulated. These simulation results were experimentally tested on a specifically designed and manufactured set of printed circuit boards. Three network configurations were modeled. The modeling provided encouraging results for all three configurations. The measurements on the prototypes constructed for this study, however, provided useful position-sensitivity for only one of the network configurations. The lack of input signal amplification into the networks, the SiPM dark current, as well as the complexity of an eight layers board with parasitic capacitances, could have caused the degradation of resolving the impact photon position. This is hard to overcome with external printed circuit boards and components. © 1963-2012 IEEE.

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