Françoise Lefebvre

Automatic three-dimensional reconstruction and characterization of articular cartilage from high-resolution ultrasound acquisitions.

Three-dimensional (3D) high-resolution ultrasonography has proved to be useful for in vitro assessment of cartilage remodeling due to osteoarthritis. The diagnosis is performed by computation of the mean thickness of the cartilage, which reveals hypertrophy or thinning, and by 3D reconstruction of the data, which provides essential information about the size, extent, and localization of the lesion. In both cases, preliminary segmention of the cartilage is necessary. This article proposes an algorithm for automatic segmentation of the cartilage from 3D ultrasonic acquisitions of the rat patella, which includes the detection of the cartilage surface and the cartilage/bone interface. The method was designed on the assumption of regularity and smoothness of the interfaces. The use of a global threshold was sufficient to separate the patella area from the background. The cartilage/bone interface was detected by selection of regions of interest (ROIs) encompassing the interface, followed by the detection of the interface within these ROIs using the graph theory. The method was applied to 162 samples. The detection accuracy was judged to be very good or good in 99% of the cases for the cartilage surface and in 86% of the cases for the cartilage/bone interface. The mean cartilage thickness value in the central part of the patella obtained from the automatic detection method was compared to that obtained manually. The coefficient of correlation between the two measurements was 0.92. These results show that our method is reliable. Thus, fast processing of a large number of acquisitions and a more complete analysis of the cartilage surface become possible.

An Intraoperative Beta Probe Dedicated to Glioma Surgery: Design and Feasibility Study

Surgery is considered as the primary therapeutic procedure for gliomas and several recent clinical studies have shown that total tumor resection is directly associated with longer survival when compared to subtotal resection. In order to refine the resection in the boundaries of gliomas, we are developing an intraoperative probe specifically dedicated to the localization of residual tumor labeled with positron emitters. The probe is designed to be compact and electrically safe in order to be directly coupled to the excision tool leading to simultaneous detection and removal of tumor tissues. It is built with clear and plastic scintillating fibers held in a closed packed annular arrangement ensheathing the excision tool. The annihilation gamma ray background is eliminated by a real-time subtraction method. Validation of the technical choice and optimization of the probe geometry were performed by preliminary measurements and Monte Carlo simulations based on the MCNP-4C code and an anthropomorphic brain phantom. The theoretical probe sensitivity was found to be 82 cps/muCi/ml with a gamma ray rejection efficiency of 99.6%. The expected minimum radiotracer detectable concentration for tumors labeled with 18 F-FET was 0.10 muCi/ml. When compared to the 0.29 muCi/ml average concentration in the bulk of the tumor, this result demonstrate the potential ability of the probe to define more accurately the extent of brain tumor resection

Physical Performance of an Intraoperative Beta Probe Dedicated to Glioma Radioguided Surgery

The precise delineation and excision of brain tumor extent allows to improve survival outcome and quality of life of surgically treated patients. In order to refine the resection of gliomas, we are developing a novel intraoperative probe specifically dedicated to the localization of residual tumor after the bulk has been excised. The probe, built around clear and plastic scintillating fibers, was designed to detect positrons emitted from radiolabeled brain tissue in order to discriminate more specifically neoplastic from normal tissues. The probe was also built to be directly coupled to the excision tool leading to simultaneous detection and removal of tumor. We report here performances of the first radio-isotopic configuration of the intraoperative probe which consists of a detection head composed of eight detection elements held around the excision tool in a closed packed annular arrangement. This head is coupled to an optic fiber bundle that exports the scintillating light to a multi-channel photomultiplier tube. The gamma ray background generated by the annihilation of beta+ in tissues is eliminated by a real-time subtraction method. The detector exhibits a beta sensitivity of 139 cps/kBq and a gamma ray rejection efficiency of 99.5%. The ability of the probe to detect residual lesions was evaluated with a realistic brain phantom representing the surgical cavity and the boundaries of the tumor. We showed that lesions as small as 5 mm in diameter can be detected for tumor to normal tissue uptake ratios of fluorinated tracers greater than 3.5. This ratio is achieved with radiopharmaceuticals like 18F-FET or 18F-choline. These promising results suggest that the features of our system are compatible with in situ localization of residual radiolabeled tumors.

The Tumor Resection Camera (TReCam), a multipixel imaging probe for radio-guided surgery

Using the POCI camera, we recently demonstrated the clinical impact of per-operative imaging techniques thanks to a successful clinical trial. Taking advantage of both the POCI experience and the availability of new pixelated detectors, we are developing a new hand held gamma camera TReCam (tumor resection camera). The first prototype offers a 49 × 49 mm2 field of view. It combines a 15 mm thick parallel hole collimator (with an efficiency of 5.10-4 and a spatial resolution of 7.5 mm at 50 mm), a 5 mm thick LaBr3:Ce crystal optically coupled to a Hamamatsu H9500 flat panel multianode photomultiplier tube (MAPMT). The read-out of the MAPMT is ensured thanks to a new specific integrated circuit called HARDROC2 (hadronic Rpc detector readout chip). This chip was initially designed for the digital hadronic calorimeter (DHCAL) of the linear collider. The TReCam presents an intrinsic spatial resolution of 0.65 mm (FWHM) and an energetic resolution of 17.4% at 122 keV. The new read-out by the HARDROC2 chip is currently being implemented and using this new device energetic resolution is expected to be better.

Segmentation of Quantitative Ultrasonographic Images of the Calcaneus Using Elastic Deformation of the Flexible Fourier Contour

Objective. This study investigated a new technique for automatic model‐based segmentation of broadband ultrasound attenuation (BUA) images of the calcaneus. We determined whether this technique was able to improve osteoporotic fracture discrimination. Methods. The segmentation process included 2 major steps: a model‐building stage and the automatic segmentation of new image data sets via an elastic deformation of contour models. Broadband ultrasound attenuation was then averaged within the final contour (BUAwhole). The results of the segmentation were validated on a database of 256 patients by comparison of the clinical results obtained with the automatic circular region of interest (BUAcirc) currently implemented on a commercially available ultrasonography unit. All patients were selected by the same physician, who assessed that the fractures were caused by bone fragility on the basis of the circumstances under which fractures occurred and radiologic data. Results. Short‐term reproducibility assessed in 49 women was 3.5% and 3.98% for BUAcirc and BUAwhole, respectively. Both BUAcirc (age‐adjusted T score,−3.78; P < .0005; age‐adjusted odds ratio, 1.92; 95% confidence interval, 1.34–2.75; area under the receiver operating characteristic curve, 0.70) and BUAwhole (age‐adjusted T score,−2.73; P < .01; age‐adjusted odds ratio, 1.57; 95% confidence interval, 1.12–2.21; area under the curve, 0.67) performed equally well in discriminating healthy postmenopausal patients (n = 150) from those with fractures (n = 60). Conclusions. Fully automatic segmentation by parametrically deformable elastic models for contour using Fourier descriptors can be achieved with reasonable reproducibility and fracture risk prediction. The method is similar to existing methods (automatic circular region of interest); however, the new contour‐based region of interest allows more flexible region of interest geometries and placement and potential adaptation to individual anatomy. The method could also possibly be extended to quantitative ultrasonographic imaging at different skeletal sites.

Designing the scintillation module of a pixelated mini gamma camera: The spatial spreading behaviour of light

Designing the scintillation module of a mini gamma camera requests good understanding of how the scintillation light signal spreads within the crystal and how photons are finally collected on the PMT. For a given scintillation process, the key parameters are the geometry of the crystal, its optical coating and the interface between the crystal and the PMT. In order to optimize the design of our gamma camera TReCam, we studied the shape of the spatial distribution of the scintillation light for different values and combinations of these key parameters. Our approach was to produce computer simulations, for which the optical simulation transport software DETECT2000 was used. Three major parameters were investigated: optical coatings for the crystal (aluminum, Teflon, corner cube retro-reflectors), the thickness of the crystal (ranging from 1 mm up to 5 mm) and the interfaces (air, optical grease). In addition to the FWHM of the light spot distribution, specific figures of merit were implemented to further characterize photon spreading. In order to evaluate the influence of these parameters on the imaging performances of the TReCam, the whole scintillation module (including the PMT) was also simulated with GATE v4.0.0 based on GEANT 4.9.1.p02. It appears that the best configuration is a 5 mm thick LaBr3:Ce crystal plate covered on the top with Teflon optical coating coupled optically with a PMT.

Caractérisation des ganglions lymphatiques péridigestifs par échoendoscopie: intérêt de l’imagerie paramétrique et analyse quantitative

RésuméObjectifsLa précision diagnostique de l’échoendoscopie dans le bilan d’extension ganglionnaire des cancers digestifs pourrait être améliorée par l’analyse paramétrique de la texture des images. Nous avons cherché à évaluer les résultats de cette méthode dans une étude prospective.MéthodesCent cinq ganglions péri-digestifs ont été analysés chez 80 malades. Le diagnostic final était obtenu par l’histologie de la pièce opératoire ou par le suivi des patients. Il s’agissait de 41 ganglions inflammatoires bénins et de 64 ganglions métastatiques. Les images étaient obtenues durant une échoendoscopie conventionnelle, numérisées puis transférées sur une station de travail pour l’analyse paramétrique. Deux régions d’intérêt (RI) étaient sélectionnées pour chaque ganglion (ganglion entier et portion périphérique). 21 paramètres étaient étudiés pour chaque RI (2 paramètres de 1er ordre et 19 de second ordre). Les paramètres étaient étudiés par analyse uni- puis multivariée pour définir les paramètres discriminant les ganglions inflammatoires des ganglions métastatiques.Principaux résultatsSept paramètres, tous de second ordre, pouvaient distinguer les ganglions inflammatoires et métastatiques de façon indépendante. La sensibilité de l’interprétation par l’endoscopiste (qui possédait les informations cliniques et morphologiques pertinentes) était de 83% et la spécificité de 90%. La sensibilité et la spécificité de l’analyse de texture étaient de 56% et 60%, respectivement.ConclusionsCes résultats suggèrent que l’analyse paramétrique de la texture des images ganglionnaires d’échoendoscopie n’améliore pas les performances de l’interprétation visuelle d’un opérateur entraîné disposant des éléments habituels du dossier clinique.SummaryBackgroundThe diagnostic accuracy of visual interpretation of peri-digestive lymph nodes (malignant vs inflammatory) by endoscopic ultrasonography (EUS) does not exceed 70–80%.AimsTo assess the ability of ultrasound image texture analysis to improve diagnostic results and to provide objective diagnostic criteria.Methods105 mediastinal, intra-abdominal and peri-rectal lymph nodes were analyzed, from 80 patients. The final diagnosis was obtained from histology of the resected specimen or from patient’s history and follow-up. There were 41 inflammatory lymph nodes and 64 malignant lymph nodes. Images were captured during EUS and computerized on a PC, then transferred on workstation for analysis. 2 regions of interest (ROI) were selected for each lymph node: one was the whole node and the other the peripheral rim of the node. 21 parameters were studied for each ROI (2 parameters of the 1st order, 14 from co-occurrence matrices, and 5 from range length matrices). Parameters were analyzed by logistic regression, then by multivariate analysis for discriminating patients in 2 groups: inflammatory vs malignant lymph nodes.Results7 parameters were able to discriminate groups by pairs. The sensitivity of the endoscopist’s visual analysis (including knowledge of patient’s history) was 83%, and specificity was 90%. After texture analysis, se was 56%, and sp was 60%.ConclusionThese results show that texture analysis of lymph node images does not improve the ability of EUS to discriminate between inflammatory and malignant lymph nodes.

In vivo precision of automatic region of measurement in ultrasound attenuation imaging

a retrospective cross-sectional assessment of bone mineral density (BMD) was performed. Measurements were made oa lumbar spine and proximal femur in a population group of children and adolescents (n=286) ranging from 9 to 19 years. Their puberaL statue was taken into account. An inquiry to evaluate the type and intensity of physical activity was used and three groups were differentiated: Group A, included 62 healthy subjects of both sexes who played recreational and sporting activities (football, gymnastics, swiping, etc.) with a dedication equal or higher to five hours a week. Group B, included 13 subjects with orthopedic alterations which conditionated a limited physical activity. Group C, taken as a control group, included 211 healthy subjects matched for age to groups A and S. Their physical activity happened only at school and their recreational activities did not take more than two hours a week.