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Daniel Strul

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Papers by Daniel Strul

Absolute quantitation of iodine-123 epidepride kinetics using single-photon emission tomography: comparison with carbon-11 epidepride and positron emission tomography

European Journal of Nuclear Medicine and Molecular Imaging, 1999

Epidepride labelled with iodine-123 is a suitable probe for the in vivo imaging of striatal and e... more Epidepride labelled with iodine-123 is a suitable probe for the in vivo imaging of striatal and extrastriatal dopamine D 2 receptors using single-photon emission tomography (SPET). Recently, this molecule has also been labelled with carbon-11. The goal of this work was to develop a method allowing the in vivo quantification of radioactivity uptake in baboon brain using SPET and to validate it using positron emission tomography (PET). SPET studies were performed in Papio anubis baboons using 123 I-epidepride. Emission and transmission measurements were acquired on a dual-headed system with variable head angulation and low-energy ultra-high resolution (LEUHR) collimation. The imaging protocol consisted of one transmission measurement (24 min, heads at 90°), obtained with two sliding line sources of gadolinium-153 prior to injection of 0.21-0.46 GBq of 123 I-epidepride, and 12 emission measurements starting 5 min post injection. For scatter correction (SC) we used a dual-window method adapted to 123 I. Collimator blurring correction (CBC) was done by deconvolution in Fourier space and attenuation correction (AT) was applied on a preliminary (CBC) filtered back-projection reconstruction using 12 iterations of a preconditioned, regularized minimal residual algorithm. For each reconstruction, a calibration factor was derived from a uniform cylinder filled with a 123 I solution of a known radioactivity concentration. Calibration and baboon images were systematically built with the same reconstruction parameters. Uncorrected (UNC) and (AT), (SC+AT) and (SC+CBC+AT) corrected images were compared. PET acquisitions using 0.11-0.44 GBq of 11 C-epidepride were performed on the same baboons and used as a reference. The radioactive concentrations expressed in percent of the injected dose per 100 ml (%ID/100 ml) obtained after (SC+CBC+AT) in SPET are in good agreement with those obtained with PET and 11 Cepidepride. A method for the in vivo absolute quantitation of 123 I-epidepride uptake using SPET has been developed which can be directly applied to other 123 I-labelled molecules used in the study of the dopamine system. Further work will consist in using PET to model the radioligandreceptor interactions and to derive a simplified model applicable in SPET.

Correction du volume partiel en tomographie d'emission de positons : applications a l'etude des pathologies neurodegeneratives (doctorat : imagerie medicale)

Http Www Theses Fr, 2000

Use of an analytical model for optimizing the design of a small-animal PET scanner with DOI capability

2000 IEEE Nuclear Science Symposium. Conference Record (Cat. No.00CH37149), 2000

The optimization of spatial resolution is a critical issue for small-animal PET scanners, and is ... more The optimization of spatial resolution is a critical issue for small-animal PET scanners, and is often addressed by Monte-Carlo simulation. Analytical models, though less versatile are very fast and their simplicity allows a direct appreciation of the influence of different model parameters. The authors have developed an analytical model for multi-layer PET systems, which provides estimates of the radial and

Performance evaluation and MR compatibility assessment of an optical fibre based pre-clinical MR-compatible PET scanner

2008 IEEE Nuclear Science Symposium Conference Record, 2008

We have designed and constructed a small animal MR-compatible PET system for fully simultaneous M... more We have designed and constructed a small animal MR-compatible PET system for fully simultaneous MR/PET acquisitions. The scanner uses long optical fibres to distance the field sensitive PET PMTs from the high magnetic field at the centre of an MR scanner. The system has been designed to operate inside a number of different high field MRI scanners. We present a

MR-compatible shields for 511 keV gamma photons: a feasibility study

2000 IEEE Nuclear Science Symposium. Conference Record (Cat. No.00CH37149), 2000

An MR-compatible PET scanner capable of acquiring PET and MR images simultaneously will require 5... more An MR-compatible PET scanner capable of acquiring PET and MR images simultaneously will require 511 keV gamma shielding to suppress the influence of activity outside the PET field of view. Suitable materials must have a magnetic permeability close to that of water and air, high density, high Z and ideally a low conductivity. Eleven materials were selected on the basis

GATE, a Geant4-based simulation platform for PET integrating movement and time management

2002 IEEE Nuclear Science Symposium Conference Record, 2003

GATE, the Geant4 Application for Tomographic Emission, is a simulation platform developed for PET... more GATE, the Geant4 Application for Tomographic Emission, is a simulation platform developed for PET and SPECT. It combines a powerful simulation core (the Geant4 toolkit) and a large range of developments dedicated to nuclear medicine. In particular, it models the passing of time during real acquisitions, allowing to handle dynamic systems such as decaying source distributions or moving detectors. We present several series of results that illustrate the possibilities of this new platform. The simulation of decaying sources is illustrated on a dual-isotope acquisition with multiple time-frames. Count rate curves taking into account random coincidences and dead-time are shown for a dual-crystal set-up and for a small-animal PET scanner configuration. Simulated resolution curves and reconstructed images are shown for rotating PET scanners. Lastly, we present comparisons of simulated point-spread functions and spectra with experimental results obtained from a small-animal gamma camera prototype.

Monte Carlo simulation in PET and SPECT instrumentation using GATE

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2004

Monte Carlo simulation is an essential tool to assist in the design of new medical imaging device... more Monte Carlo simulation is an essential tool to assist in the design of new medical imaging devices for emission tomography. On one hand, dedicated Monte Carlo codes have been developed for PET and SPECT. However, they suffer from a variety of drawbacks and limitations in terms of validation, accuracy, and/or support. On the other hand, accurate and versatile simulation codes such as Geant3, EGS4, MCNP, and recently Geant4 have been written for high energy physics. They all include well-validated physics models, geometry modeling tools and efficient visualization utilities. Nevertheless these packages are quite complex and necessitate a steep learning curve. GATE, the Geant4 Application for Tomographic Emission, encapsulates the Geant4 libraries in order to achieve a modular, versatile, scripted simulation toolkit adapted to the field of nuclear medicine. In particular, GATE allows the users to describe time-dependent phenomena such as detector movements or source decay kinetics, thus allowing to simulate time curves under realistic acquisition conditions. At present, it is being further developed and validated within the OpenGATE Collaboration. We give a succinct overview of GATE and four examples of its validation against real data obtained with PET and SPECT cameras. r

Gamma shielding materials for MR-compatible PET

IEEE Transactions on Nuclear Science, 2003

As for standard positron emission tomography (PET) scanners, MR-compatible PET scanners will requ... more As for standard positron emission tomography (PET) scanners, MR-compatible PET scanners will require gamma shielding to suppress the influence of activity outside the PET field of view (FOV). Suitable materials must have very specific properties, including magnetic properties close to those of water, high density, high atomic number, and ideally a low conductivity. In order to identify potential suitable materials, we have selected several heavy-metal-based candidates based on the available data for magnetic and shielding properties. These materials include several nonferromagnetic metals and metal oxides, two scintillating crystals (bismuth germanate and lead tungstate) and two metal/epoxy compounds. The magnetic resonance imaging (MRI) compatibility of these materials was assessed under various conditions, both on a human and a small-animal MRI scanner. In parallel, we assessed the shielding efficiency at 661 keV of the most promising candidates. These experiments showed that there is a range of possibilities for the design of MR-compatible gamma shields. Lead has acceptable magnetic compatibility but can induce significant conductivity-related artefacts. Heavy-metal-based minerals are fully insulating and hot-pressed lead monoxide showed good MR compatibility combined with good shielding properties. Other possibilities include the use of lead based powders and heavy-metal oxide composites.

Performance Evaluation of an MRI-Compatible Pre-Clinical PET System Using Long Optical Fibers

IEEE Transactions on Nuclear Science, 2000

We have designed and constructed an MR-compatible PET system for fully simultaneous PET/MR studie... more We have designed and constructed an MR-compatible PET system for fully simultaneous PET/MR studies of small animals. The scanner uses long optical fibers to distance the magnetic field sensitive PET PMTs from the high magnetic field at the center of an MR scanner. It is a single slice system with an inner diameter of 7 cm. A full evaluation of the performance of the PET system and the results of an MR compatibility assessment in a Philips Achieva whole body 3 T MRI scanner are presented. The reconstructed resolution of the PET scanner is 1.5 mm at the center falling to 2.5 mm at the edge of the field of view; the system sensitivity is 0.95%; the count rate is linear up to an activity of 6 MBq ( 4 kcps) and the scatter fraction is 42% which can be reduced to 26% using MR-compatible gamma shields. Simultaneous PET/MR images of phantoms and a mouse have been acquired. The system is highly MR compatible, as demonstrated here, showing no degradation in performance of either the MR or PET system in the presence of the other modality. The system will be used to demonstrate novel pre-clinical applications of simultaneous PET/MR.

Monte Carlo Simulation for the ECAT EXACT HR+ system using GATE

IEEE Transactions on Nuclear Science, 2000

GATE (Geant4 Application for Tomographic Emission) is a Monte Carlo simulation platform for nucle... more GATE (Geant4 Application for Tomographic Emission) is a Monte Carlo simulation platform for nuclear medicine imaging, based on the Geant4 toolkit package. In order to improve data analysis and image quantification, a new simulator for the ECAT EXACT HR+ scanner was originally developed with GATE. In this study, we validate GATE simulations for positron emission topography (PET) imaging systems: a good agreement is obtained between simulated and actual experimental results. Additional GATE applications are also presented in the paper: an implementation of the voxelized Hoffman phantom and an example of a MRI/PET coupling system for improving image resolution.

GATE: A Geant4-Based Simulation Platform for PET and SPECT Integrating Movement and Time Management

IEEE Transactions on Nuclear Science, 2003

GATE, the Geant4 Application for Tomographic Emission, is a simulation platform developed for PET... more GATE, the Geant4 Application for Tomographic Emission, is a simulation platform developed for PET and SPECT. It combines a powerful simulation core (the Geant4 toolkit) and a large range of developments dedicated to nuclear medicine. In particular, it models the passing of time during real acquisitions, allowing to handle dynamic systems such as decaying source distributions or moving detectors. We present several series of results that illustrate the possibilities of this new platform. The simulation of decaying sources is illustrated on a dual-isotope acquisition with multiple time-frames. Count rate curves taking into account random coincidences and dead-time are shown for a dual-crystal set-up and for a small-animal PET scanner configuration. Simulated resolution curves and reconstructed images are shown for rotating PET scanners. Lastly, we present comparisons of simulated point-spread functions and spectra with experimental results obtained from a small-animal gamma camera prototype.

Quantifying cerebral PET with FDG using dynamic internal carotid arteries imaging

1998 IEEE Nuclear Science Symposium Conference Record. 1998 IEEE Nuclear Science Symposium and Medical Imaging Conference (Cat. No.98CH36255), 1998

The improvement of the PET sensitivity and resolution allows the measurement of the input functio... more

GATE: a simulation toolkit for PET and SPECT

Physics in Medicine and Biology

Monte Carlo simulation is an essential tool in emission tomography that can assist in the design ... more 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...

Optimisation of fibre-optic readout of LSO scintillation crystals with acid etching

2001 IEEE Nuclear Science Symposium Conference Record (Cat. No.01CH37310), 2002

Optimising the collection of scintillation light is essential for good PET scanner performance, a... more Optimising the collection of scintillation light is essential for good PET scanner performance, and even more so when the crystals are read out through optical fibres. Acid etching had been proposed as a cost-effective alternative to mechanical polishing, but there are discrepancies between the results published so far. The aim of this work is to gain a better understanding of

Simultaneous PET and NMR

The British journal of radiology, 2002

There is currently great interest in combining data from different imaging modalities, either by ... more There is currently great interest in combining data from different imaging modalities, either by image registration methods that are performed after the data has been acquired or using new devices that can acquire data from two modalities simultaneously, or near simultaneously. In this paper a small prototype NMR-compatible PET scanner capable of acquiring PET images simultaneously with either NMR images or NMR spectra is described. In an associated paper [1], Pamela Garlick describes some investigations of cardiac metabolism that have been made using this system. One of the main challenges in constructing an NMR-compatible PET scanner is that photomultiplier tubes, which are an essential element of nearly all current PET systems, will not function in a high magnetic field. In collaboration with Simon Cherry and the Crump Institute of Biomedical Imaging at UCLA Medical School, a small (5.4 cm diameter) NMR-compatible PET scanner that will operate within the bore of an NMR magnet has...

Monte Carlo simulations of a scintillation camera using GATE: validation and application modelling

Physics in Medicine and Biology, 2003

Geant4 application for tomographic emission (GATE) is a recently developed simulation platform ba... more Geant4 application for tomographic emission (GATE) is a recently developed simulation platform based on Geant4, specifically designed for PET and SPECT studies. In this paper we present validation results of GATE based on the comparison of simulations against experimental data, acquired with a standard SPECT camera. The most important components of the scintillation camera were modelled. The photoelectric effect, Compton and Rayleigh scatter are included in the gamma transport process. Special attention was paid to the processes involved in the collimator: scatter, penetration and lead fluorescence. A LEHR and a MEGP collimator were modelled as closely as possible to their shape and dimensions. In the validation study, we compared the simulated and measured energy spectra of different isotopes: 99m Tc, 22 Na, 57 Co and 67 Ga. The sensitivity was evaluated by using sources at varying distances from the detector surface. Scatter component analysis was performed in different energy windows at different distances from the detector and for different attenuation geometries. Spatial resolution was evaluated using a 99m Tc source at various distances. Overall results showed very good agreement between the acquisitions and the simulations. The clinical usefulness of GATE depends on its ability to use voxelized datasets. Therefore, a clinical extension was written so that digital patient data can be read in by the simulator as a source distribution or as an attenuating geometry. Following this validation we modelled two additional camera designs: the Beacon transmission device for attenuation correction and the Solstice scanner prototype with a rotating collimator. For the first setup a scatter analysis was performed and for the latter design, the simulated sensitivity results were compared against theoretical predictions. Both case studies demonstrated the flexibility and accuracy of GATE and exemplified its potential benefits in protocol optimization and in system design.

An improved analytical detector response function model for multilayer small-diameter PET scanners

Physics in Medicine and Biology, 2003

The optimization of spatial resolution is a critical consideration in the design of small-diamete... more The optimization of spatial resolution is a critical consideration in the design of small-diameter positron emission tomography (PET) scanners for animal imaging, and is often addressed with Monte Carlo simulations. As a faster and simpler solution, we have developed a new analytical model of the PET detector response function, and implemented the model for a small single-slice, multilayer PET scanner. The accuracy of the model has been assessed by comparison with both Monte Carlo simulations and experimental measurements published in the literature. Results from the analytical model agreed well with the Monte Carlo method, being noise free and two to three orders of magnitude faster. The only major discrepancy was a slight underestimation of the width of the point spread function by the analytical method as inter-crystal scatter is neglected. We observed good agreement between the predictions of the model and experimental measurements. For two large-diameter scanners additional discrepancies were seen due to photon acollinearity, which is not considered in the model. We have shown that the simple and fast analytical detector response function model can provide accurate estimates of spatial resolution for small-diameter PET scanners, and could be a useful tool for several applications, complementing or cross-validating other simulation methods.

Validation of the GATE Monte-Carlo simulation platform for modelling a new semi-conductor gamma-camera dedicated to nuclear cardiology

Physica Medica, 2012

9 All members are members of the OpenGATE collaboration 1 D. Lazaro et al 2 to-collimator distanc... more 9 All members are members of the OpenGATE collaboration 1 D. Lazaro et al 2 to-collimator distances was within 2%. Simulated and experimental scatter fractions in a [98-182 keV] energy window differed by less than 2% for sources located in water. Simulated and experimental energy spectra agreed very well between 40 and 180 keV. These results demonstrate the ability and flexibility of GATE for simulating original detector designs. The main weakness of GATE concerns the long computation time it requires: this issue is currently under investigation by the GEANT4 and the GATE collaborations.

Simulation of time curves in small animal PET using GATE

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2004

The ClearPET project of the Crystal Clear Collaboration (CCC) is building spin-off technology for... more The ClearPET project of the Crystal Clear Collaboration (CCC) is building spin-off technology for high resolution small animal Positron Emission Tomography (PET). Monte Carlo simulation is essential for optimizing the specifications of these systems with regards to their most important characteristics, such as spatial resolution, sensitivity, or count rate performance. GATE, the Geant4 Application for Tomographic Emission simulates the passing

Robustness of Anatomically Guided Pixel-by-Pixel Algorithms for Partial Volume Effect Correction in Positron Emission Tomography

Journal of Cerebral Blood Flow & Metabolism, 1999

Several algorithms have been proposed to improve positron emission tomography quantification by c... more Several algorithms have been proposed to improve positron emission tomography quantification by combining anatomical and functional information in a pixel-by-pixel correction scheme. The precision of these methods when applied to real data depends on the precision of the manifold correction steps, such as full-width half-maximum modeling, magnetic resonance imaging-positron emission tomography registration, tissue segmentation, or background activity estimation. A good understanding of the influence of these parameters thus is critical to the effective use of the algorithms. In the current article, the authors present a monodimensional model that allows a simple theoretical and experimental evaluation of correction imprecision. The authors then assess correction robustness in three dimensions with computer simulations, and evaluate the validity of regional SD as a correction performance criterion.

Absolute quantitation of iodine-123 epidepride kinetics using single-photon emission tomography: comparison with carbon-11 epidepride and positron emission tomography

European Journal of Nuclear Medicine and Molecular Imaging, 1999

Epidepride labelled with iodine-123 is a suitable probe for the in vivo imaging of striatal and e... more Epidepride labelled with iodine-123 is a suitable probe for the in vivo imaging of striatal and extrastriatal dopamine D 2 receptors using single-photon emission tomography (SPET). Recently, this molecule has also been labelled with carbon-11. The goal of this work was to develop a method allowing the in vivo quantification of radioactivity uptake in baboon brain using SPET and to validate it using positron emission tomography (PET). SPET studies were performed in Papio anubis baboons using 123 I-epidepride. Emission and transmission measurements were acquired on a dual-headed system with variable head angulation and low-energy ultra-high resolution (LEUHR) collimation. The imaging protocol consisted of one transmission measurement (24 min, heads at 90°), obtained with two sliding line sources of gadolinium-153 prior to injection of 0.21-0.46 GBq of 123 I-epidepride, and 12 emission measurements starting 5 min post injection. For scatter correction (SC) we used a dual-window method adapted to 123 I. Collimator blurring correction (CBC) was done by deconvolution in Fourier space and attenuation correction (AT) was applied on a preliminary (CBC) filtered back-projection reconstruction using 12 iterations of a preconditioned, regularized minimal residual algorithm. For each reconstruction, a calibration factor was derived from a uniform cylinder filled with a 123 I solution of a known radioactivity concentration. Calibration and baboon images were systematically built with the same reconstruction parameters. Uncorrected (UNC) and (AT), (SC+AT) and (SC+CBC+AT) corrected images were compared. PET acquisitions using 0.11-0.44 GBq of 11 C-epidepride were performed on the same baboons and used as a reference. The radioactive concentrations expressed in percent of the injected dose per 100 ml (%ID/100 ml) obtained after (SC+CBC+AT) in SPET are in good agreement with those obtained with PET and 11 Cepidepride. A method for the in vivo absolute quantitation of 123 I-epidepride uptake using SPET has been developed which can be directly applied to other 123 I-labelled molecules used in the study of the dopamine system. Further work will consist in using PET to model the radioligandreceptor interactions and to derive a simplified model applicable in SPET.

Correction du volume partiel en tomographie d'emission de positons : applications a l'etude des pathologies neurodegeneratives (doctorat : imagerie medicale)

Http Www Theses Fr, 2000

Use of an analytical model for optimizing the design of a small-animal PET scanner with DOI capability

2000 IEEE Nuclear Science Symposium. Conference Record (Cat. No.00CH37149), 2000

The optimization of spatial resolution is a critical issue for small-animal PET scanners, and is ... more The optimization of spatial resolution is a critical issue for small-animal PET scanners, and is often addressed by Monte-Carlo simulation. Analytical models, though less versatile are very fast and their simplicity allows a direct appreciation of the influence of different model parameters. The authors have developed an analytical model for multi-layer PET systems, which provides estimates of the radial and

Performance evaluation and MR compatibility assessment of an optical fibre based pre-clinical MR-compatible PET scanner

2008 IEEE Nuclear Science Symposium Conference Record, 2008

We have designed and constructed a small animal MR-compatible PET system for fully simultaneous M... more We have designed and constructed a small animal MR-compatible PET system for fully simultaneous MR/PET acquisitions. The scanner uses long optical fibres to distance the field sensitive PET PMTs from the high magnetic field at the centre of an MR scanner. The system has been designed to operate inside a number of different high field MRI scanners. We present a

MR-compatible shields for 511 keV gamma photons: a feasibility study

2000 IEEE Nuclear Science Symposium. Conference Record (Cat. No.00CH37149), 2000

An MR-compatible PET scanner capable of acquiring PET and MR images simultaneously will require 5... more An MR-compatible PET scanner capable of acquiring PET and MR images simultaneously will require 511 keV gamma shielding to suppress the influence of activity outside the PET field of view. Suitable materials must have a magnetic permeability close to that of water and air, high density, high Z and ideally a low conductivity. Eleven materials were selected on the basis

GATE, a Geant4-based simulation platform for PET integrating movement and time management

2002 IEEE Nuclear Science Symposium Conference Record, 2003

GATE, the Geant4 Application for Tomographic Emission, is a simulation platform developed for PET... more GATE, the Geant4 Application for Tomographic Emission, is a simulation platform developed for PET and SPECT. It combines a powerful simulation core (the Geant4 toolkit) and a large range of developments dedicated to nuclear medicine. In particular, it models the passing of time during real acquisitions, allowing to handle dynamic systems such as decaying source distributions or moving detectors. We present several series of results that illustrate the possibilities of this new platform. The simulation of decaying sources is illustrated on a dual-isotope acquisition with multiple time-frames. Count rate curves taking into account random coincidences and dead-time are shown for a dual-crystal set-up and for a small-animal PET scanner configuration. Simulated resolution curves and reconstructed images are shown for rotating PET scanners. Lastly, we present comparisons of simulated point-spread functions and spectra with experimental results obtained from a small-animal gamma camera prototype.

Monte Carlo simulation in PET and SPECT instrumentation using GATE

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2004

Monte Carlo simulation is an essential tool to assist in the design of new medical imaging device... more Monte Carlo simulation is an essential tool to assist in the design of new medical imaging devices for emission tomography. On one hand, dedicated Monte Carlo codes have been developed for PET and SPECT. However, they suffer from a variety of drawbacks and limitations in terms of validation, accuracy, and/or support. On the other hand, accurate and versatile simulation codes such as Geant3, EGS4, MCNP, and recently Geant4 have been written for high energy physics. They all include well-validated physics models, geometry modeling tools and efficient visualization utilities. Nevertheless these packages are quite complex and necessitate a steep learning curve. GATE, the Geant4 Application for Tomographic Emission, encapsulates the Geant4 libraries in order to achieve a modular, versatile, scripted simulation toolkit adapted to the field of nuclear medicine. In particular, GATE allows the users to describe time-dependent phenomena such as detector movements or source decay kinetics, thus allowing to simulate time curves under realistic acquisition conditions. At present, it is being further developed and validated within the OpenGATE Collaboration. We give a succinct overview of GATE and four examples of its validation against real data obtained with PET and SPECT cameras. r

Gamma shielding materials for MR-compatible PET

IEEE Transactions on Nuclear Science, 2003

As for standard positron emission tomography (PET) scanners, MR-compatible PET scanners will requ... more As for standard positron emission tomography (PET) scanners, MR-compatible PET scanners will require gamma shielding to suppress the influence of activity outside the PET field of view (FOV). Suitable materials must have very specific properties, including magnetic properties close to those of water, high density, high atomic number, and ideally a low conductivity. In order to identify potential suitable materials, we have selected several heavy-metal-based candidates based on the available data for magnetic and shielding properties. These materials include several nonferromagnetic metals and metal oxides, two scintillating crystals (bismuth germanate and lead tungstate) and two metal/epoxy compounds. The magnetic resonance imaging (MRI) compatibility of these materials was assessed under various conditions, both on a human and a small-animal MRI scanner. In parallel, we assessed the shielding efficiency at 661 keV of the most promising candidates. These experiments showed that there is a range of possibilities for the design of MR-compatible gamma shields. Lead has acceptable magnetic compatibility but can induce significant conductivity-related artefacts. Heavy-metal-based minerals are fully insulating and hot-pressed lead monoxide showed good MR compatibility combined with good shielding properties. Other possibilities include the use of lead based powders and heavy-metal oxide composites.

Performance Evaluation of an MRI-Compatible Pre-Clinical PET System Using Long Optical Fibers

IEEE Transactions on Nuclear Science, 2000

We have designed and constructed an MR-compatible PET system for fully simultaneous PET/MR studie... more We have designed and constructed an MR-compatible PET system for fully simultaneous PET/MR studies of small animals. The scanner uses long optical fibers to distance the magnetic field sensitive PET PMTs from the high magnetic field at the center of an MR scanner. It is a single slice system with an inner diameter of 7 cm. A full evaluation of the performance of the PET system and the results of an MR compatibility assessment in a Philips Achieva whole body 3 T MRI scanner are presented. The reconstructed resolution of the PET scanner is 1.5 mm at the center falling to 2.5 mm at the edge of the field of view; the system sensitivity is 0.95%; the count rate is linear up to an activity of 6 MBq ( 4 kcps) and the scatter fraction is 42% which can be reduced to 26% using MR-compatible gamma shields. Simultaneous PET/MR images of phantoms and a mouse have been acquired. The system is highly MR compatible, as demonstrated here, showing no degradation in performance of either the MR or PET system in the presence of the other modality. The system will be used to demonstrate novel pre-clinical applications of simultaneous PET/MR.

Monte Carlo Simulation for the ECAT EXACT HR+ system using GATE

IEEE Transactions on Nuclear Science, 2000

GATE (Geant4 Application for Tomographic Emission) is a Monte Carlo simulation platform for nucle... more GATE (Geant4 Application for Tomographic Emission) is a Monte Carlo simulation platform for nuclear medicine imaging, based on the Geant4 toolkit package. In order to improve data analysis and image quantification, a new simulator for the ECAT EXACT HR+ scanner was originally developed with GATE. In this study, we validate GATE simulations for positron emission topography (PET) imaging systems: a good agreement is obtained between simulated and actual experimental results. Additional GATE applications are also presented in the paper: an implementation of the voxelized Hoffman phantom and an example of a MRI/PET coupling system for improving image resolution.

GATE: A Geant4-Based Simulation Platform for PET and SPECT Integrating Movement and Time Management

IEEE Transactions on Nuclear Science, 2003

GATE, the Geant4 Application for Tomographic Emission, is a simulation platform developed for PET... more GATE, the Geant4 Application for Tomographic Emission, is a simulation platform developed for PET and SPECT. It combines a powerful simulation core (the Geant4 toolkit) and a large range of developments dedicated to nuclear medicine. In particular, it models the passing of time during real acquisitions, allowing to handle dynamic systems such as decaying source distributions or moving detectors. We present several series of results that illustrate the possibilities of this new platform. The simulation of decaying sources is illustrated on a dual-isotope acquisition with multiple time-frames. Count rate curves taking into account random coincidences and dead-time are shown for a dual-crystal set-up and for a small-animal PET scanner configuration. Simulated resolution curves and reconstructed images are shown for rotating PET scanners. Lastly, we present comparisons of simulated point-spread functions and spectra with experimental results obtained from a small-animal gamma camera prototype.

Quantifying cerebral PET with FDG using dynamic internal carotid arteries imaging

1998 IEEE Nuclear Science Symposium Conference Record. 1998 IEEE Nuclear Science Symposium and Medical Imaging Conference (Cat. No.98CH36255), 1998

The improvement of the PET sensitivity and resolution allows the measurement of the input functio... more

GATE: a simulation toolkit for PET and SPECT

Physics in Medicine and Biology

Monte Carlo simulation is an essential tool in emission tomography that can assist in the design ... more 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...

Optimisation of fibre-optic readout of LSO scintillation crystals with acid etching

2001 IEEE Nuclear Science Symposium Conference Record (Cat. No.01CH37310), 2002

Optimising the collection of scintillation light is essential for good PET scanner performance, a... more Optimising the collection of scintillation light is essential for good PET scanner performance, and even more so when the crystals are read out through optical fibres. Acid etching had been proposed as a cost-effective alternative to mechanical polishing, but there are discrepancies between the results published so far. The aim of this work is to gain a better understanding of

Simultaneous PET and NMR

The British journal of radiology, 2002

There is currently great interest in combining data from different imaging modalities, either by ... more There is currently great interest in combining data from different imaging modalities, either by image registration methods that are performed after the data has been acquired or using new devices that can acquire data from two modalities simultaneously, or near simultaneously. In this paper a small prototype NMR-compatible PET scanner capable of acquiring PET images simultaneously with either NMR images or NMR spectra is described. In an associated paper [1], Pamela Garlick describes some investigations of cardiac metabolism that have been made using this system. One of the main challenges in constructing an NMR-compatible PET scanner is that photomultiplier tubes, which are an essential element of nearly all current PET systems, will not function in a high magnetic field. In collaboration with Simon Cherry and the Crump Institute of Biomedical Imaging at UCLA Medical School, a small (5.4 cm diameter) NMR-compatible PET scanner that will operate within the bore of an NMR magnet has...

Monte Carlo simulations of a scintillation camera using GATE: validation and application modelling

Physics in Medicine and Biology, 2003

Geant4 application for tomographic emission (GATE) is a recently developed simulation platform ba... more Geant4 application for tomographic emission (GATE) is a recently developed simulation platform based on Geant4, specifically designed for PET and SPECT studies. In this paper we present validation results of GATE based on the comparison of simulations against experimental data, acquired with a standard SPECT camera. The most important components of the scintillation camera were modelled. The photoelectric effect, Compton and Rayleigh scatter are included in the gamma transport process. Special attention was paid to the processes involved in the collimator: scatter, penetration and lead fluorescence. A LEHR and a MEGP collimator were modelled as closely as possible to their shape and dimensions. In the validation study, we compared the simulated and measured energy spectra of different isotopes: 99m Tc, 22 Na, 57 Co and 67 Ga. The sensitivity was evaluated by using sources at varying distances from the detector surface. Scatter component analysis was performed in different energy windows at different distances from the detector and for different attenuation geometries. Spatial resolution was evaluated using a 99m Tc source at various distances. Overall results showed very good agreement between the acquisitions and the simulations. The clinical usefulness of GATE depends on its ability to use voxelized datasets. Therefore, a clinical extension was written so that digital patient data can be read in by the simulator as a source distribution or as an attenuating geometry. Following this validation we modelled two additional camera designs: the Beacon transmission device for attenuation correction and the Solstice scanner prototype with a rotating collimator. For the first setup a scatter analysis was performed and for the latter design, the simulated sensitivity results were compared against theoretical predictions. Both case studies demonstrated the flexibility and accuracy of GATE and exemplified its potential benefits in protocol optimization and in system design.

An improved analytical detector response function model for multilayer small-diameter PET scanners

Physics in Medicine and Biology, 2003

The optimization of spatial resolution is a critical consideration in the design of small-diamete... more The optimization of spatial resolution is a critical consideration in the design of small-diameter positron emission tomography (PET) scanners for animal imaging, and is often addressed with Monte Carlo simulations. As a faster and simpler solution, we have developed a new analytical model of the PET detector response function, and implemented the model for a small single-slice, multilayer PET scanner. The accuracy of the model has been assessed by comparison with both Monte Carlo simulations and experimental measurements published in the literature. Results from the analytical model agreed well with the Monte Carlo method, being noise free and two to three orders of magnitude faster. The only major discrepancy was a slight underestimation of the width of the point spread function by the analytical method as inter-crystal scatter is neglected. We observed good agreement between the predictions of the model and experimental measurements. For two large-diameter scanners additional discrepancies were seen due to photon acollinearity, which is not considered in the model. We have shown that the simple and fast analytical detector response function model can provide accurate estimates of spatial resolution for small-diameter PET scanners, and could be a useful tool for several applications, complementing or cross-validating other simulation methods.

Validation of the GATE Monte-Carlo simulation platform for modelling a new semi-conductor gamma-camera dedicated to nuclear cardiology

Physica Medica, 2012

9 All members are members of the OpenGATE collaboration 1 D. Lazaro et al 2 to-collimator distanc... more 9 All members are members of the OpenGATE collaboration 1 D. Lazaro et al 2 to-collimator distances was within 2%. Simulated and experimental scatter fractions in a [98-182 keV] energy window differed by less than 2% for sources located in water. Simulated and experimental energy spectra agreed very well between 40 and 180 keV. These results demonstrate the ability and flexibility of GATE for simulating original detector designs. The main weakness of GATE concerns the long computation time it requires: this issue is currently under investigation by the GEANT4 and the GATE collaborations.

Simulation of time curves in small animal PET using GATE

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2004

The ClearPET project of the Crystal Clear Collaboration (CCC) is building spin-off technology for... more The ClearPET project of the Crystal Clear Collaboration (CCC) is building spin-off technology for high resolution small animal Positron Emission Tomography (PET). Monte Carlo simulation is essential for optimizing the specifications of these systems with regards to their most important characteristics, such as spatial resolution, sensitivity, or count rate performance. GATE, the Geant4 Application for Tomographic Emission simulates the passing

Robustness of Anatomically Guided Pixel-by-Pixel Algorithms for Partial Volume Effect Correction in Positron Emission Tomography

Journal of Cerebral Blood Flow & Metabolism, 1999

Several algorithms have been proposed to improve positron emission tomography quantification by c... more Several algorithms have been proposed to improve positron emission tomography quantification by combining anatomical and functional information in a pixel-by-pixel correction scheme. The precision of these methods when applied to real data depends on the precision of the manifold correction steps, such as full-width half-maximum modeling, magnetic resonance imaging-positron emission tomography registration, tissue segmentation, or background activity estimation. A good understanding of the influence of these parameters thus is critical to the effective use of the algorithms. In the current article, the authors present a monodimensional model that allows a simple theoretical and experimental evaluation of correction imprecision. The authors then assess correction robustness in three dimensions with computer simulations, and evaluate the validity of regional SD as a correction performance criterion.