Simultaneous SPECT/MR Imaging with a SiPM-Based Preclinical Insert

The results of a systematic and quantitative experimental characterization of simultaneous operation of a preclinical SPECT insert inside an unmodified standard MR scanner (Philips 3T Achieva) are presented. The static gantry (20 cm diameter, 15 mm field of view) is composed of 10 MRI-compatible gamma cameras based on 8-mm thick CsI(Tl) scintillator (50 mm × 50mm) coupled with arrays of SiPMs. Mutual compatibility is achieved by proper design of the SPECT system: shielding, choice of materials, design of the analog boards. The measured energy resolution is 13% at 122 keV after correction of SiPM gain variability and local crystal luminosity. The intrinsic spatial resolution, after planar image statistical reconstruction by means of maximum likelihood, is 1mm, while the extrinsic resolution is below 0.9 mm across the entire transaxial FoV, measured with capillaries of 290 pm diameter. With the custom-designed 3 × 3 multi-pinhole collimator (whose minimal perturbation of the magnetic field can be reduced below 1ppm thanks to shimming), the measured sensitivity with 99m Tc is 1100 cps/MBq. The MR image is not distorted by the operation of the SPECT, as well as SPECT performances are no degraded by MRI (T2W and gradient sequences). Simultaneous imaging of different phantoms (capillaries, Derenzo hot rods of 0.85-1.7 mm diameter) as well as a mouse brain are reported

Validation and performance assessment of a preclinical SiPM-based SPECT/MRI insert

A preclinical insert for small animal simultaneous SPECT and MR imaging, in particular for imaging mouse brains, is presented. It consists of ten static magnetic resonance imaging (MRI)-compatible gamma cameras based on tiles of silicon photomultipliers readout by a multichannel ASIC and coupled to 5 cm × 5 cm CsI(Tl) scintillators and to an MRI-compatible multipinhole collimator. Calibration and image reconstruction algorithm are illustrated. Mutual compatibility is demonstrated along with imaging performance that is comparable with other non-MR micro-SPECT systems: 0.9 mm tomographic spatial resolution across a transverse field of view of 15.6 mm, 12% energy resolution (at 140 keV), and 1105 cps/MBq sensitivity. Experimental results with phantoms (glass capillaries of 290 μm diameter and a mini Derenzo) are presented

Validation and Performance Assessment of a Preclinical SiPM-Based SPECT/MRI Insert

A preclinical insert for small animal simultaneous SPECT and MR imaging, in particular for imaging mouse brains, is presented. It consists of ten static magnetic resonance imaging (MRI)-compatible gamma cameras based on tiles of silicon photomultipliers readout by a multichannel ASIC and coupled to 5 cm x 5 cm CsI(Tl) scintillators and to an MRI-compatible multipinhole collimator. Calibration and image reconstruction algorithm are illustrated. Mutual compatibility is demonstrated along with imaging performance that is comparable with other non-MR micro-SPECT systems: 0.9 mm tomographic spatial resolution across a transverse field of view of 15.6 mm, 12% energy resolution (at 140 keV), and 1105 cps/MBq sensitivity. Experimental results with phantoms (glass capillaries of 290 mu m diameter and a mini Derenzo) are presented

Experimental Validation of a Preclinical SPECT/MR Insert

The experimental characterization of a SiPM-based 10-module SPECT gamma imager suitable for insertion and operation inside unmodified MR scanners for simultaneous (and potentially multi-tracer) preclinical imaging is presented. The design challenges, here fulfilled, such as compactness while granting proper cooling, mutual compatibility and resilience to high (3-7 T) magnetic fields inside the bore, suitable energetic (better than 14% at 140 keV) and spatial resolution (better than 1 mm) are discussed. The carefully optimized detection module, featuring a 5 imes5 cm^2 CsI(Tl) scintillator coupled to arrays of SiPM conditioned by a 36-channel ASIC, and the digital daisy chain infrastructure are the basis for the realization of a larger (20-module ring) clinical insert. Moreover, planar image reconstruction based on advanced statistical approaches such as maximum likelihood and iteratively estimated light response function is reported

Limits on the masses of supersymmetric particles at root s=189 GeV

Searches for charginos, neutralinos and sleptons at LEP2 centre-of-mass energies from 130 GeV to 189 GeV have been used to set lower limits on the mass of the Lightest Supersymmetric Particle and other supersymmetric particles within the MSSM framework. R-parity conservation has been assumed. The lightest neutralino was found to be heavier than GeV/c(2) independent of the m(0) value. The Lightest chargino, the second-to-lightest neutralino, the next-to-heaviest neutralino, the heaviest neutralino, the sneutrino and the right-handed selectron were found to be heavier than 62.4 GeV/c2, 62.4 GeV/c(2), 99.9 GeV/c(2), 116.0 GeV/c(2), 61.0 GeV/c(2), and 87.0 GeV/c(2), respectively. These limits do not depend on m(0) or M-2 and are Valid for 1 less than or equal to tan beta less than or equal to 40, in the mu region where the lightest neutralino is the LSP. If the sneutrino is heavier than the chargino the lightest neutralino has to be heavier than 32.4 GeV/c(2). The effects of mixings in the third family of sfermions on these limits are discussed. The confidence level of all limits given is 95%. (C) 2000 Published by Elsevier Science B.V

A precise measurement of the tau polarisation at LEP-1

The tau polarisation has been studied with the e(+)e(-) --> tau(+)tau(-) data collected by the DELPHI detector at LEP in 1993, 1994 and 1995 around the Z resonance firstly through the exclusive decay channels ev (v) over bar, mu v (v) over bar, pi v, rho v and a(1)v and secondly with an inclusive hadronic analysis which benefits from a higher efficiency and a better systematic precision. The results have been combined with those previously published on 1990 to 1992 DELPHI data, to produce results which reflect the full LEP-1 statistics. The fit of the tau polarisation dependence on the production angle yielded the polarisation parameters A(tau) = 0.1359 +/- 0.0096 and A(epsilon) = 0.1382 +/- 0.0116. From these results the ratio of the vector and axial-vector effective couplings (v) over bar/(a) over bar(tau) = 0.0683 +/- 0.0048 and (v) over bar/(a) over bar(e) = 0.0694 +/- 0.0058 have been derived, compatible with e-tau universality. With the assumption of lepton universality, the ratio of vector to axial-vector effective couplings for leptons (v) over bar(l)/(a) over bar(l) = 0.0687 +/- 0.0037 was obtained, implying a value of the effective weak mixing angle sin(2) theta(eff)(lept) = 0.23282 +/- 0.00092