Monte Carlo tomographic reconstruction in SPECT impact of bootstrapping and number of generated events

In Single Photon Emission Computed Tomography (SPECT), 3D images usually reconstructed by performing a set of bidimensional (2D) analytical or iterative reconstructions can also be reconstructed using an iterative reconstruction algorithm involving a 3D projector. Accurate Monte Carlo (MC) simulations modeling all the physical effects that affect the imaging process can be used to estimate this projector. However, the accuracy of the projector is affected by the stochastic nature of MC simulations. In this paper, we study the accuracy of the reconstructed images with respect to the number of simulated histories used to estimate the MC projector. Furthermore, we study the impact of applying the bootstrapping technique when estimating the projectorComment: 15 pages, 9 figures, 2 table

Can texture indices derived from PET images differentiate tissue types?

Congrès sous l’égide de la Société Française de Génie Biologique et Médical (SFGBM).National audienceAim: Texture indices (TI) are of growing interest for tumor characterization. Yet, whether FDG-PET images can evidence tissue-specific pattern has received little attention so far. We studied the ability of enhanced TI to determine tissue types. Materials and Methods: Forty-eight patients with non-small cell lung cancer underwent FDG-PET before treatment. Seven enhanced TI were calculated using a new resampling method. Standardized Uptake Value (SUV) and metabolic volume (MV) were also systematically computed. The ability of each index to distinguish between tumor and liver tissue and between two subtypes of cancer was investigated using ROC analyses. Results: All enhanced TI could differentiate tumor from liver tissue with an Area Under the ROC Curve (AUC) higher than 0.692. Homogeneity and Low Gray-Level Emphasis could differentiate the adenocarcinomas (n=28) and squamous cell carcinomas (n=12) with AUC better than that of SUVmax and MV (Delong’s test). Liver tissue had a more homogeneous texture than tumor tissue and adenocarcinomas exhibited a more homogeneous texture than squamous cell carcinomas. Conclusion: Enhanced TI vary as a function of the tissue type and cancer subtype, and might be used as a new tool for tumor characterization

Extension of the GATE Monte-Carlo simulation package to model bioluminescence and fluorescence imaging

International audienceThe Geant4 Application for Emission Tomography (GATE) is an advanced open-source software dedicated to Monte-Carlo (MC) simulations in medical imaging involving photon transportation (Positron emission tomography, single photon emission computed tomography, computed tomography) and in particle therapy. In this work, we extend the GATE to support simulations of optical imaging, such as bioluminescence or fluo-rescence imaging, and validate it against the MC for multilayered media standard simulation tool for biomedical optics in simple geometries. A full simulation setup for molecular optical imaging (bioluminescence and fluo-rescence) is implemented in GATE, and images of the light distribution emitted from a phantom demonstrate the relevance of using GATE for optical imaging simulations

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

Envelope Trajectory of Water Jet Issuing From a Thin Weir Obtained by Photogrammetry

Today, to have a good command of the energy dissipation of a jet issuing from a weir we need to improve our knowledge of the location of the impact. This laboratory experiment applied photogrammetry to determine the envelope trajectory of a water jet coming from a thin wall weir. The fall was about 9 meters, the weir was 1 meter wide and the flow was up to 500 l/s. The trajectory of the jet was reconstituted in the three spatial dimensions using the PhotoScan software package developed by Agisoft. The exposure time for each picture was enough to make white water. Envelope trajectory was compared to classical expressions such as those of Scimeni (1937) or De Marchi (1928

Experiments and numerical modelling of the performance and wake of a tidal converter

Water Qualit