Latest achievements in PET techniques

Positron emission tomography (PET) has moved from a distinguished research tool in physiology, cardiology and neurology to become a major tool for clinical investigation in oncology, in cardiac applications and in neurological disorders. Much of the PET accomplishments is due to the remarkable improvements in the last 10 years both in hardware and software aspects. Nowadays a similar effort is made by many research groups towards the construction of dedicated PET apparatus in new emerging fields such as molecular medicine, gene therapy, breast cancer imaging and combined modalities. This paper reports on some recent results we have obtained in small animal imaging and positron emission mammography, based on the use of advanced technology in the field of scintillators and photodetectors, such as Position-Sensitive Detectors coupled to crystal matrices, combined use of scintillating fibers and Hybrid-Photo-Diodes readout, and Hamamatsu flat panels. New ideas and future developments are discussed

Novel high resolution detectors for Positron Emission Tomography (PET)

Abstract In this paper we present some recent results we have obtained in the development of detectors for small animal PET and for PEM, based on the use of Position Sensitive PMTS or Hybrid Photo Diodes (HPDs) coupled to crystal matrices. New ideas and future developments are discussed

Characterization of the Ferrara animal PET scanner

A dedicated small animal PET scanner, YAPPET, was designed and built at Ferrara University. Each detector consists of a 20� 20 matrix of 2� 2� 30 mm 3 YAP:Ce finger-like crystals glued together and directly coupled to a Hamamatsu position sensitive photomultiplier. The scanner is made from four detectors positioned on a rotating gantry at a distance of 7:5 cm from the center and the field of view (FOV) is 4 cm both in the transaxial direction and in the axial direction. The system operates in 3D acquisition mode. The performance parameters of YAPPET scanner such as spatial, energy and time resolution, as well as its sensitivity and counting rate have been determined. The average spatial resolution over the whole FOV is 1:8 mm at FWHM and 4:2 mm at FWTM. The sensitivity at the center is 640 cps=mCi: r 2002 Elsevier Science B.V. All rights reserved. PACS: 87.59.Wb; 87.59.Q

The PVLAS experiment for measuring the magnetic birefringence of vacuum

We describe the principle and status of the PVLAS experiment being prepared at the Department of Physics and INFN section in Ferrara, Italy. The goal of the experiment is to measure the magnetic birefringence of vacuum. This effect is directly connected to the vacuum QED structure and can be detected by measuring the ellipticity acquired by a linearly polarized laser beam traversing a strong magnetic field. Vacuum magnetic birefringence is predicted by the Euler-Heisenberg effective Lagrangian. The experimental method is also sensitive to new physics and could place new laboratory limits to hypothetical particles coupling to two photons, such as axion like particles, or millicharged particles

Detector development for a novel Positron Emission Mammography scanner based on YAP:Ce crystals

A prototype for positron emission mammography is under development within a collaboration of the Departments of Physics of Pisa and Ferrara. The device will be composed of two opposing detectors (parallel plane geometry). The active part of the detector head is constituted by a matrix of scintillators with a small pixel size (2 2m m 2 ). We have evaluated the possibility to use an array of Position Sensitive PhotoMultiplier Tube (PSPMT mod R8520-C12 from Hamamatsu) for the readout of the scintillation matrix. Two different crystal-PMT coupling techniques have been explored: the results for each method are reported in this work. The overall performance, in terms of efficiency and pixel identification of the final prototype of the detector head are also presented. For future applications the new H8500 (also called the 'flat panel' PMT) has been studied and compared to the R8520 in terms of the imaging performance and other considerations such as cost and geometry. The imaging performance of these tubes is characterized in terms of the pixel image resolution and the peak-to-valley ratio. r 2004 Elsevier B.V. All rights reserved

Probing For New Physics and Detecting non linear vacuum QED effects using gravitational wave interferometer antennas

Low energy non linear QED effects in vacuum have been predicted since 1936 and have been subject of research for many decades. Two main schemes have been proposed for such a 'first' detection: measurements of ellipticity acquired by a linearly polarized beam of light passing through a magnetic field and direct light-light scattering. The study of the propagation of light through an external field can also be used to probe for new physics such as the existence of axion-like particles and millicharged particles. Their existence in nature would cause the index of refraction of vacuum to be different from unity in the presence of an external field and dependent of the polarization direction of the light propagating. The major achievement of reaching the project sensitivities in gravitational wave interferometers such as LIGO an VIRGO has opened the possibility of using such instruments for the detection of QED corrections in electrodynamics and for probing new physics at very low energies. In this paper we discuss the difference between direct birefringence measurements and index of refraction measurements. We propose an almost parasitic implementation of an external magnetic field along the arms of the VIRGO interferometer and discuss the advantage of this choice in comparison to a previously proposed configuration based on shorter prototype interferometers which we believe is inadequate. Considering the design sensitivity in the strain, for the near future VIRGO+ interferometer, of $h<2\cdot10^{-23} \frac{1}{\sqrt{\rm Hz}}$ in the range 40 Hz $- 400$ Hz leads to a variable dipole magnet configuration at a frequency above 20 Hz such that $B^{2}D \ge 13000$ T$^{2}$m/$\sqrt{\rm Hz}$ for a `first' vacuum non linear QED detection

Preliminary test results on the new electronic readout of the YAP(S)PET small animal scanner

A small animal PET-SPECT scanner (YAP-(S)PET) prototype was built at the Physics Department of the University of Ferrara and is presently being used at the Nuclear Medicine Department for radiopharmaceutical studies on rats. The first YAP-(S)PET prototype shows very good performances, but needs some improvements before it can be used for intensive radiopharmaceutical research. The main problem of the actual prototype is its heavy electronics, based on NIM and CAMAC standard modules. For this reason a new, compact readout electronics was developed and tested. The results of a first series of tests made on the first prototype will be presented in this paper

Experimental perspectives in (low-energy) photon-photon scattering

The possibility of photon-photon scattering is a striking difference between classical and quantum electrodynamics. This genuinely quantum feature is made possible by the fluctuations of charged fields, and it makes quantum vacuum a nonlinear optical medium. Photon-photon scattering is thus a delicate probe into the structure of quantum electrodynamics and any departure from the expected behavior would be a powerful signal of "new physics". To date this process has never been observed – except as a radiative correction to other processes – and several experiments are trying to detect it at very low energy, in the scattering of real photons in powerful light beams off the virtual photons of intense magnetic fields. Here we briefly review the experimental state-of-the-art, with special emphasis on the PVLAS experiment, and we describe a new proposal to observe photon-photon scattering in the range 1 – 2 MeV

Optical Polarimetry for Fundamental Physics

Sensitive magneto-optical polarimetry was proposed by E. Iacopini and E. Zavattini in 1979 to detect vacuum electrodynamic non-linearity, in particular Vacuum Magnetic Birefringence (VMB). This process is predicted in QED via the fluctuation of electron–positron virtual pairs but can also be due to hypothetical Axion-Like Particles (ALPs) and/or MilliCharged Particles (MCP). Today ALPs are considered a strong candidate for Dark Matter. Starting in 1992 the PVLAS collaboration, financed by INFN, Italy, attempted to measure VMB conceptually following the original 1979 scheme based on an optical cavity permeated by a time-dependent magnetic field and heterodyne detection. Two setups followed differing basically in the magnet: the first using a rotating superconducting 5.5 T dipole magnet at the Laboratori Nazionali di Legnaro, Legnaro, Italy and the second using two rotating permanent 2.5 T dipole magnets at the INFN section of Ferrara. At present PVLAS is the experiment which has set the best limit in VMB reaching a noise floor within a factor 7 of the predicted QED signal: Delta n^{(QED)} = 2.5 x 10^{-23} @ 2.5 T. It was also shown that the noise floor was due to the optical cavity and a larger magnet is the only solution to increase the signal to noise ratio. The PVLAS experiment ended at the end of 2018. A new effort, VMB@CERN, which plans to use a spare LHC dipole magnet at CERN with a new modified optical scheme, is now being proposed. In this review, a detailed description of the PVLAS effort and the comprehension of its limits leading to a new proposal will be given

Il vuoto come cristallo birifrangente: l'esperimento PVLAS.

Il concetto di vuoto ha subìto un'evoluzione nel corso dei secoli partendo dall'idea di Aristotele che esso non potesse esistere, passando dal vuoto di Torricelli e di Maxwell fino al vuoto quantistico di oggi. Maxwell definiva il vuoto come una zona di spazio dalla quale fosse stato rimosso tutto il rimovibile. Mentre questa definizione potrebbe essere ancora valida, l'idea sottintesa che il vuoto sia un sistema statico, non lo è più. Al contrario, il vuoto è un mezzo dinamico per nulla in quiete: l'esistenza delle anti-particelle, come previsto da Dirac, e del Principio di Indeterminazione di Heisenberg prevedono che quantisticamente il vuoto fluttua. Uno dei processi possibili è che il vuoto fluttui in coppie elettrone-positrone. In presenza di un campo esterno che polarizza queste coppie, il vuoto si comporta come un cristallo uniassico. L'esperimento PVLAS, istallato a Ferrara presso la sezione INFN e il Dipartimento di Fisica e Scienze della Terra, sta cercando di osservare tale comportamento del vuoto