GATE (Geant4 Application for Emission Tomography) is a Monte Carlo simulation platform developed by the OpenGATE collaboration since 2001 and first publicly released in 2004. Dedicated to the ...modelling of planar scintigraphy, single photon emission computed tomography (SPECT) and positron emission tomography (PET) acquisitions, this platform is widely used to assist PET and SPECT research. A recent extension of this platform, released by the OpenGATE collaboration as GATE V6, now also enables modelling of x-ray computed tomography and radiation therapy experiments. This paper presents an overview of the main additions and improvements implemented in GATE since the publication of the initial GATE paper (Jan et al 2004 Phys. Med. Biol. 49 4543-61). This includes new models available in GATE to simulate optical and hadronic processes, novelties in modelling tracer, organ or detector motion, new options for speeding up GATE simulations, examples illustrating the use of GATE V6 in radiotherapy applications and CT simulations, and preliminary results regarding the validation of GATE V6 for radiation therapy applications. Upon completion of extensive validation studies, GATE is expected to become a valuable tool for simulations involving both radiotherapy and imaging.
Hybrid pixel detectors, originally developed for tracking particles in high-energy physics experiments, have recently been used in material sciences and macromolecular crystallography. Their ...capability to count single photons and to apply a threshold on the photon energy suggests that they could be optimal digital x-ray detectors in low energy beams such as for small animal computed tomography (CT). To investigate this issue, we have studied the imaging performance of photon counting hybrid pixel detectors based on the XPAD3-S chip. Two detectors are considered, connected either to a Si or to a CdTe sensor, the latter being of interest for its higher efficiency. Both a standard 'International Electrotechnical Commission' (IEC) mammography beam and a beam used for mouse CT results published in the literature are employed. The detector stability, linearity and noise are investigated as a function of the dose for several imaging exposures ( approximately 0.1-400 microGy). The perfect linearity of both detectors is confirmed, but an increase in internal noise for counting statistics higher than approximately 5000 photons has been found, corresponding to exposures above approximately 110 microGy and approximately 50 microGy for the Si and CdTe sensors, respectively. The noise power spectrum (NPS), the modulation transfer function (MTF) and the detective quantum efficiency (DQE) are then measured for two energy threshold configurations (5 keV and 18 keV) and three doses ( approximately 3, 30 and 300 microGy), in order to obtain a complete estimation of the detector performances. In general, the CdTe sensor shows a clear superiority with a maximal DQE(0) of approximately 1, thanks to its high efficiency ( approximately 100%). The DQE of the Si sensor is more dependent on the radiation quality, due to the energy dependence of its efficiency its maximum is approximately 0.4 with respect to the softer radiation. Finally, we compare the XPAD3-S DQE with published curves of other digital devices in a similar radiation condition. The XPAD3-S/CdTe detector appears to be the best with the highest DQE at low frequency, although some improvements are expected to reduce the increase of noise with the counts statistics and to guarantee a better stability of the detector response.
A detailed analysis is presented of the diffractive deep-inelastic scattering process ep→eXY, where Y is a proton or a low mass proton excitation carrying a fraction 1-xIP>0.95 of the incident proton ...longitudinal momentum and the squared four-momentum transfer at the proton vertex satisfies |t|<1 GeV2. Using data taken by the H1 experiment, the cross section is measured for photon virtualities in the range 3.5≤Q2≤1600 GeV2, triple differentially in xIP, Q2 and β=x/xIP, where x is the Bjorken scaling variable. At low xIP, the data are consistent with a factorisable xIP dependence, which can be described by the exchange of an effective pomeron trajectory with intercept αIP(0)=1.118±0.008(exp.)+0.029-0.010(model). Diffractive parton distribution functions and their uncertainties are determined from a next-to-leading order DGLAP QCD analysis of the Q2 and β dependences of the cross section. The resulting gluon distribution carries an integrated fraction of around 70% of the exchanged momentum in the Q2 range studied. Total and differential cross sections are also measured for the diffractive charged current process e+p→ν̄eXY and are found to be well described by predictions based on the diffractive parton distributions. The ratio of the diffractive to the inclusive neutral current ep cross sections is studied. Over most of the kinematic range, this ratio shows no significant dependence on Q2 at fixed xIP and x or on x at fixed Q2 and β.
Full text
Available for:
DOBA, FZAB, GEOZS, IJS, IMTLJ, IZUM, KILJ, KISLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The charge sharing effect in the single photon counting hybrid pixel detector XPAD3-S is studied. Several figures of merit are measured, both in the case of Si and CdTe sensors. Data are compared to ...a Monte Carlo simulation that models the main sources of charge migration.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We investigate the improvement from the use of high-Z CdTe sensors for pre-clinical K-edge imaging with the hybrid pixel detectors XPAD3. We compare XPAD3 chips bump bonded to Si or CdTe sensors in ...identical experimental conditions. Image performance for narrow energy bin acquisitions and contrast-to-noise ratios of K-edge images are presented and compared. CdTe sensors achieve signal-to-noise ratios at least three times higher than Si sensors within narrow energy bins, thanks to their much higher detection efficiency. Nevertheless Si sensors provide better contrast-to-noise ratios in K-edge imaging when working at equivalent counting statistics, due to their better estimation of the attenuation coefficient of the contrast agent. Results are compared to simulated data in the case of the XPAD3/Si detector. Good agreement is observed when including charge sharing between pixels, which have a strong impact on contrast-to-noise ratios in K-edge images.
A measurement of the inclusive deep inelastic neutral current
e
+
p
scattering cross section is reported in the region of four-momentum transfer squared, 12 GeV
2
≤
Q
2
≤150 GeV
2
, and Bjorken
x
, ...2×10
−4
≤
x
≤0.1. The results are based on data collected by the H1 Collaboration at the
ep
collider HERA at positron and proton beam energies of
E
e
=27.6 GeV and
E
p
=920 GeV, respectively. The data are combined with previously published data, taken at
E
p
=820 GeV. The accuracy of the combined measurement is typically in the range of 1.3–2%. A QCD analysis at next-to-leading order is performed to determine the parton distributions in the proton based on H1 data.
Full text
Available for:
DOBA, FZAB, GEOZS, IJS, IMTLJ, IZUM, KILJ, KISLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
PIXSCAN: Pixel detector CT-scanner for small animal imaging Delpierre, P.; Debarbieux, F.; Basolo, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2007, Volume:
571, Issue:
1
Journal Article
Peer reviewed
Open access
The PIXSCAN is a small animal CT-scanner based on hybrid pixel detectors. These detectors provide very large dynamic range of photons counting at very low detector noise. They also provide high ...counting rates with fast image readout. Detection efficiency can be optimized by selecting the sensor medium according to the working energy range. Indeed, the use of CdTe allows a detection efficiency of 100% up to 50
keV. Altogether these characteristics are expected to improve the contrast of the CT-scanner, especially for soft tissues, and to reduce both the scan duration and the absorbed dose. A proof of principle has been performed by assembling into a PIXSCAN-XPAD2 prototype the photon counting pixel detector initially built for detection of X-ray synchrotron radiations. Despite the relatively large pixel size of this detector (330×330
μm
2), we can present three-dimensional tomographic reconstruction of mice at good contrast and spatial resolution. A new photon counting chip (XPAD3) is designed in sub-micronique technology to achieve 130×130
μm
2 pixels. This improved circuit has been equipped with an energy selection circuit to act as a band-pass emission filter. Furthermore, the PIXSCAN-XPAD3 hybrid pixel detectors will be combined with the Lausanne ClearPET scanner demonstrator. CT image reconstruction in this non-conventional geometry is under study for this purpose.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We characterize the imaging performance of the micro computed tomography (micro-CT) prototype PIXSCAN equipped with an x-ray photon counting camera based on XPAD3/Si hybrid pixel detectors. The ...camera, which is composed of eight distinctive horizontal modules, permits the performance of whole-body mouse scans. Photon counting supplied by hybrid pixels guarantees acquisitions at a Poisson noise level exclusively determined by the detected photon statistics. First, we characterize the performance of the imaging system while assessing its linearity, noise, spatial resolution and low contrast detectability estimated from scans of appropriate phantoms. Then, we show CT images of mice data acquired either in vivo or post mortem, without or with an injection of iodine as a contrast agent. Although hybrid pixels guarantee a minimal noise to the images, the limited detection efficiency of Si sensors impairs detected photon statistics and therefore the improvement in contrast-to-noise ratio for standard tomographic imaging. Indeed, the most innovative potential of the PIXSCAN prototype is its capacity to perform spectral tomographic imaging and fast dynamic imaging. The first is thanks to the possibility of setting an energy threshold on the detected photons, and the second is thanks to its fast acquisition rate (till 500 images/s). We present some examples of these imaging methods applied to mice and discuss their main limiting factors.
PDF
