Monte Carlo simulation is an essential tool in emission tomography that can assist in the design of new medical imaging devices, the optimization of acquisition protocols and the development or assessment of image reconstruction algorithms and correction techniques. GATE, the Geant4 Application for Tomographic Emission, encapsulates the Geant4 libraries to achieve a modular, versatile, scripted simulation toolkit adapted to the field of nuclear medicine. In particular, GATE allows the description of time-dependent phenomena such as source or detector movement, and source decay kinetics. This feature makes it possible to simulate time curves under realistic acquisition conditions and to test dynamic reconstruction algorithms. This paper gives a detailed description of the design and development of GATE by the OpenGATE collaboration, whose continuing objective is to improve, document and validate GATE by simulating commercially available imaging systems for PET and SPECT. Large effort is also invested in the ability and the flexibility to model novel detection systems or systems still under design. A public release of GATE licensed under the GNU Lesser General Public License can be downloaded at http:/www-lphe.epfl.ch/GATE/. Two benchmarks developed for PET and SPECT to test the installation of GATE and to serve as a tutorial for the users are presented. Extensive validation of the GATE simulation platform has been started, comparing simulations and measurements on commercially available acquisition systems. References to those results are listed. The future prospects towards the gridification of GATE and its extension to other domains such as dosimetry are also discussed.

We developed positron emission tomography (PET) detectors based on monolithic scintillation crystals and position-sensitive light sensors. Intrinsic depth-of-interaction (DOI) correction is achieved by deriving the entry points of annihilation photons on the front surface of the crystal from the light sensor signals. Here we characterize the next generation of these detectors, consisting of a 20 mm thick rectangular or trapezoidal LYSO:Ce crystal read out on the front and the back (double-sided readout, DSR) by Hamamatsu S8550SPL avalanche photodiode (APD) arrays optimized for DSR. The full width at half maximum (FWHM) of the detector point-spread function (PSF) obtained with a rectangular crystal at normal incidence equals ∼1.05 mm at the detector centre, after correction for the ∼0.9 mm diameter test beam of annihilation photons. Resolution losses of several tenths of a mm occur near the crystal edges. Furthermore, trapezoidal crystals perform almost equally well as rectangular ones, while improving system sensitivity. Due to the highly accurate DOI correction of all detectors, the spatial resolution remains essentially constant for angles of incidence of up to at least 30• . Energy resolutions of ∼11% FWHM are measured, with a fraction of events of up to 75% in the full-energy peak. The coincidence timing resolution is estimated to be 2.8 ns FWHM. The good spatial, energy and timing resolutions, together with the excellent DOI correction and high detection efficiency of our detectors, are expected to facilitate high and uniform PET system resolution.

The CNR eff between tumor-suspicious and normal-appearing prostate tissue in DWI images at a b value of 1400 s/mm2 is comparable in cDWI and directly measured DWI. Computed DWI at even higher b values, calculated from measured images with b values between 0 and 800 s/mm2, yields higher CNR eff than measured DWI, which may be of clinical aid in the management of prostate cancer.

Purpose To harmonize data acquisition and post-processing of single voxel proton magnetic resonance spectroscopy (1H-MRS) at 7 Tesla (7T), and to determine metabolite concentrations, accuracy and reproducibility of metabolite levels in the adult human brain. Experimental This study was performed in compliance with local Institutional Human Ethics Committees. The same seven subjects were each examined twice using four different 7T MR-systems from two different vendors using an identical semi-LASER spectroscopy sequence. Neurochemical profiles were obtained from the posterior cingulate cortex (GM) and the corona radiata (WM). Spectra were analyzed with LCModel, and sources of variation in concentrations (‘subject’, ‘institute’ & ‘random’) were identified with a variance components analysis. Results Concentrations of 10-11 metabolites, which were corrected for T1, T2, Magnetization Transfer-effects and partial volume effects, were obtained with mean Cramér-Rao Lower Bounds below 20%. Data variances and mean concentrations in GM and WM were comparable for all institutions. The primary source of variance for glutamate, myo-inositol, scyllo-inositol, total creatine and total choline was between-subjects. Variance sources for all other metabolites were associated to within-subject and system noise, except for total N-acetylaspartate, glutamine and glutathione, which related to differences in signal-to-noise and in shimming performance between vendors. Conclusion After multi-center harmonization of acquisition and post-processing protocols, metabolite concentrations and size and sources of their variations were established for neurochemical profiles in the healthy brain at 7T, which can be used as guidance in future studies quantifying metabolite and neurotransmitter concentrations with 1H-MRS at ultra-high magnetic field.