Fully 3D Monte Carlo image reconstruction in SPECT using functional regions

Image reconstruction in Single Photon Emission Computed Tomography (SPECT) is affected by physical effects such as photon attenuation, Compton scatter and detector response. These effects can be compensated for by modeling the corresponding spread of photons in 3D within the system matrix used for tomographic reconstruction. The fully 3D Monte Carlo (F3DMC) reconstruction technique consists in calculating this system matrix using Monte Carlo simulations. The inverse problem of tomographic reconstruction is then solved using conventional iterative algorithms such as maximum likelihood expectation maximization (MLEM). Although F3DMC has already shown promising results, its use is currently limited by two major issues: huge size of the fully 3D system matrix and long computation time required for calculating a robust and accurate system matrix. To address these two issues, we propose to calculate the F3DMC system matrix using a spatial sampling matching the functional regions to be reconstructed. In this approach, different regions of interest can be reconstructed with different spatial sampling. For instance, a single value is reconstructed for a functional region assumed to contain uniform activity. To assess the value of this approach, Monte Carlo simulations have been performed using GATE. Results suggest that F3DMC reconstruction using functional regions improves quantitative accuracy compared to the F3DMC reconstruction method proposed so far. In addition, it considerably reduces disk space requirement and duration of the simulations needed to estimate the system matrix. The concept of functional regions might therefore make F3DMC reconstruction practically feasible.Comment: 6 pages, 3 figures, 3rd International Conference on maging Technologies in Biomedical Sciences : ITBS2005, Milos Island, Greece, 25-28 september 2005, submitted to NIM

Three-dimensional printing of mitral valve models using echocardiographic data improves the knowledge of cardiology fellow physicians in training

BackgroundHigh fidelity three-dimensional Mitral valve models (3D MVM) printed from echocardiography are currently being used in preparation for surgical repair.AimWe hypothesize that printed 3DMVM could have relevance to cardiologists in training by improving their understanding of normal anatomy and pathology.MethodsSixteen fellow physicians in pediatric and adult cardiology training were recruited. 3D echocardiography (3DE) video clips of six mitral valves (one normal and five pathological) were displayed and the fellows were asked to name the prolapsing segments in each. Following that, three still images of 3D MVMs in different projections: enface, profile and tilted corresponding to the same MVs seen in the clip were presented on a screen. Participating physicians were presented with a comprehensive questionnaire aimed at assessing whether the 3D MVM has improved their understanding of valvular anatomy. Finally, a printed 3D MVM of each of the valves was handed out, and the same questionnaire was re-administered to identify any further improvement in the participants' perception of the anatomy.ResultsThe correct diagnosis using the echocardiography video clip of the Mitral valve was attained by 45% of the study participants. Both pediatric and adult trainees, regardless of the year of training demonstrated improved understanding of the anatomy of MV after observing the corresponding model image. Significant improvement in their understanding was noted after participants had seen and physically examined the printed model.ConclusionPrinted 3D MVM has a beneficial impact on the cardiology trainees' understanding of MV anatomy and pathology compared to 3DE images

Analytical, experimental, and Monte Carlo system response matrix for pinhole SPECT reconstruction

PURPOSE: To assess the performance of two approaches to the system response matrix (SRM) calculation in pinhole single photon emission computed tomography (SPECT) reconstruction. METHODS: Evaluation was performed using experimental data from a low magnification pinhole SPECT system that consisted of a rotating flat detector with a monolithic scintillator crystal. The SRM was computed following two approaches, which were based on Monte Carlo simulations (MC-SRM) and analytical techniques in combination with an experimental characterization (AE-SRM). The spatial response of the system, obtained by using the two approaches, was compared with experimental data. The effect of the MC-SRM and AE-SRM approaches on the reconstructed image was assessed in terms of image contrast, signal-to-noise ratio, image quality, and spatial resolution. To this end, acquisitions were carried out using a hot cylinder phantom (consisting of five fillable rods with diameters of 5, 4, 3, 2, and 1 mm and a uniform cylindrical chamber) and a custom-made Derenzo phantom, with center-to-center distances between adjacent rods of 1.5, 2.0, and 3.0 mm. RESULTS: Good agreement was found for the spatial response of the system between measured data and results derived from MC-SRM and AE-SRM. Only minor differences for point sources at distances smaller than the radius of rotation and large incidence angles were found. Assessment of the effect on the reconstructed image showed a similar contrast for both approaches, with values higher than 0.9 for rod diameters greater than 1 mm and higher than 0.8 for rod diameter of 1 mm. The comparison in terms of image quality showed that all rods in the different sections of a custom-made Derenzo phantom could be distinguished. The spatial resolution (FWHM) was 0.7 mm at iteration 100 using both approaches. The SNR was lower for reconstructed images using MC-SRM than for those reconstructed using AE-SRM, indicating that AE-SRM deals better with the projection noise than MC-SRM. CONCLUSIONS: The authors' findings show that both approaches provide good solutions to the problem of calculating the SRM in pinhole SPECT reconstruction. The AE-SRM was faster to create and handle the projection noise better than MC-SRM. Nevertheless, the AE-SRM required a tedious experimental characterization of the intrinsic detector response. Creation of the MC-SRM required longer computation time and handled the projection noise worse than the AE-SRM.Nevertheless, the MC-SRM inherently incorporates extensive modeling of the system and therefore experimental characterization was not required

Optimisation et validation d'un algorithme de reconstruction 3D en tomographie d'émission monophotonique à l'aide de la plateforme de simulation GATE

Les simulations de Monte-Carlo, bien que consommatrices en temps de calcul, restent un outil puissant qui permet d'évaluer les méthodes de correction des effets physiques en imagerie médicale. Nous avons optimisé et validé une méthode de reconstruction baptisée F3DMC (Fully3D Monte CARLO) dans laquelle les effets physiques perturbant le processus de formation de l'image en tomographie d'émission monophotonique sont modélisés par des méthodes de Monte-Carlo et intégrés dans la matrice-système. Le logiciel de simulation de Monte-Carlo utilidé est GATE. Nous avons validé GATE en SPECT en modélisant la gamma-caméra (Philips AXIS) utilisé en routine clinique. Des techniques de seuillage, filtrage par analyse en composantes principales et de reconstruction ciblée (régions fonctionnelles, région hybrides) ont été testées pour améliorer la précision de la matrice-système et réduire le nombre de photons ainsi que le temps de calcul nécessaires. Les infrastructures de la grille EGEE ont été utilisées pour déployer les simulations GATE afin de réduire leur temps de calcul. Les résultats obtenus avec F3DMC sont comparés avec les méthodes de reconstruction (FBP,ML-EM,ML-EMC) pour un fantôme simulé et avec la méthode OSEM-C pour un fantôme réelCLERMONT FD-BCIU Lettr./Sci.Hum. (631132101) / SudocSTRASBOURG-Bib.Central Recherche (674822133) / SudocSudocFranceF

Optimisation et validation d'un algorithme de reconstruction 3D en tomographie d'émission monophotonique à l'aide de la plateforme de simulation GATE

Les simulations de Monte-Carlo, bien que consommatrices en temps de calcul, restent un outil puissant qui permet d'évaluer les méthodes de correction des effets physiques en imagerie médicale. Nous avons optimisé et validé une méthode de reconstruction baptisée F3DMC (Fully3D Monte CARLO) dans laquelle les effets physiques perturbant le processus de formation de l'image en tomographie d'émission monophotonique sont modélisés par des méthodes de Monte-Carlo et intégrés dans la matrice-système. Le logiciel de simulation de Monte-Carlo utilidé est GATE. Nous avons validé GATE en SPECT en modélisant la gamma-caméra (Philips AXIS) utilisé en routine clinique. Des techniques de seuillage, filtrage par analyse en composantes principales et de reconstruction ciblée (régions fonctionnelles, région hybrides) ont été testées pour améliorer la précision de la matrice-système et réduire le nombre de photons ainsi que le temps de calcul nécessaires. Les infrastructures de la grille EGEE ont été utilisées pour déployer les simulations GATE afin de réduire leur temps de calcul. Les résultats obtenus avec F3DMC sont comparés avec les méthodes de reconstruction (FBP,ML-EM,ML-EMC) pour un fantôme simulé et avec la méthode OSEM-C pour un fantôme réelCLERMONT FD-BCIU Lettr./Sci.Hum. (631132101) / SudocSTRASBOURG-Bib.Central Recherche (674822133) / SudocSudocFranceF

Acceleration of Fully 3D Monte Carlo Based System Matrix Computation for Image Reconstruction in Small Animal SPECT

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Absorbed dose to water determination for kilo-voltage X-rays using alanine/EPR dosimetry systems

International audienceAlanine's relative response to kilo-voltage X-rays, compared to 60 Co reference quality beam, was studied in this work, in order to determine correction factors to be applied to alanine's response when irradiated with low to medium energy X-rays (up to 300 keV). The relative response to kilo-voltage X-rays of Aerial's alanine dosimeters was determined by three distinct methods: experimental measurements using alanine dosimeters and a calibrated PTW Farmer 30013 ion chamber, Monte Carlo simulations using MCNPX code and finally, analytical calculations based on weighting of X-ray spectra by NIST's published mass energy absorption coefficients. Two sets of X-ray beam qualities, covering high voltages ranging from 50 kV up to 280 kV, were used to study the energy dependence of the alanine dosimeter's response. Obtained results were consistent within 2.1% (average standard deviation at k = 1)

Electron tracks simulation in water: Performance comparison between GPU CPU and the EUMED grid installation

International audiencePurposeWe explored different technologies to minimize simulation time of the Monte-Carlo method for trackgeneration following the Geant4-DNA processes for electrons in water.MethodsA GPU software tool is developed for electron track simulations. A similar CPU version is also developedusing the same collision models. CPU simulations were carried out on a single user desktop computer andon the computing grid France Grilles using 10 and 100 computing nodes. Computing time results for CPU,GPU, and grid simulations are compared with those using Geant4-DNA processes.ResultsThe CPU simulations better performs when the number of electrons is less than 104 with 100eV initialenergy, this number decreases as the energy increases. The GPU simulations gives better results whenthe number of electrons is more than 104 with initial energy of 100eV, this number decreases to 103 forelectrons with 10KeV and increases back with higher energy. The use of the grid introduces an additionalqueuing time which slows down the overall simulation performance. Thus, the Grid gives betterperformance when the number of electrons is over 105 with initial energy of 10KeV, and this numberdecreases as the energy increases.ConclusionsThe CPU is best suited for small numbers of primary incident electrons. The GPU is best suited when thenumber of primary incident particles occupies sufficient resources on GPU card in order to get animportant computing power. The grid is best suited for simulations with high number of primary incidentelectrons with high initial energy