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

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

International audienc

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

Intercostal Artery Laceration: Rare Complication of Thoracentesis and Role of Ultrasound in Early Detection

Hemothorax is a rare but potentially fatal postthoracentesis complication. Early clinical signs may be nonspecific resulting in diagnostic delay. A high index of suspicion is vital for early diagnosis and intervention to avoid further bleeding. Following procedure, early bedside ultrasound findings can be vital for early detection. We report a case of massive hemothorax in a 63-year-old male following therapeutic thoracentesis. Diagnosis was made following highly suggestive sonographic findings prompting thoracotomy and lacerated intercostal artery cauterization

Evaluation of an optical scintillating fiber detector for CT dosimetry

International audiencePurpose: The aim of this work is to compare the energy response of a scintillating fiber to that of standarddetectors used for dose monitoring in Computed Tomography (CT) and confirm the validity of PlasticScintillating Detectors in CT dosimetry. We also seek to model the scintillating fiber response in realistic irradiation conditions for future applications on a complete dose measurement system. For this, we have modeled anX-ray generator emission and validated the model using its measured X-rays spectrum.Materials and methods: Irradiations were performed in an X-ray generator at voltage varying from 80 to 140 kV.The Plastic Scintillating Detector (PSD) was compared with a pencil ion chamber and Thermo-LuminescentDetectors (TLD).Monte Carlo simulations of each detector response were compared to measurements in order to validate thesimulation in a simple case.Results: The Monte Carlo simulations reproduced accurately the response of each detector with less than 3% and5% of difference for the ion chamber and the TLDs respectively. When comparing the PSD with the two standarddetectors, we observed that while the plastic scintillator detector and the ion chamber responses presented lessthan 5% discrepancy, they both were very different than TLDs response on the whole investigated energy range.The Monte Carlo simulation of the PSD reproduced accurately the response of the plastic scintillating detectorwith less than 3% of difference.Conclusion: The X-ray spectrum has been accurately measured which allowed to successfully reproduce theenergy response of the PSD using Monte Carlo simulations. Although this study proved that the scintillatingfibers energy response is appropriate for CT dose measurement, further experiments must be performed inclinical conditions